Electromagnetic control of absorption and suppression of spectral artifacts

Abstract

To provide a method for gas detection and / or measurement and an instrument for use in gas detection and / or measurement, in a novel absorption spectroscopy system.SOLUTION: A method and system for suppression and / or modulation of absorption spectrum artifacts for the purpose of gas detection and concentration measurement using at least one magnetic, electric or electromagnetic field. A field applied selectively to at least one section of the system modulates absorption by influencing quantum energy state transitions of gas species.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001]

[0001] This invention generally relates to absorption spectroscopy, and more particularly to tuneable diode laser absorption spectroscopy (TDLS) and non-dispersive infrared spectroscopy. The present invention has applications in detecting and measuring one or more species in gases produced by artificial or natural processes, such as industrial, medical, or physiological processes. [Background technology]

[0002]

[0002] An exemplary absorption measurement system comprises an electromagnetic radiation source, such as a tunable laser light source, for example a tunable diode laser (TDL), or a broadband light source such as an incandescent light source or a light-emitting diode (LED), combined with a wavelength range selection element such as a light passband filter or grating. The light source emits a beam of electromagnetic radiation that is focused onto a detector, which may be a solid photovoltaic or photoconductive detector, a radiation thermometer, a thermopile, or a microthermometer. The substance to be analyzed is placed between the electromagnetic radiation source and the detector such that the electromagnetic radiation incident on the detector is modified by the path it takes through the substance. By modifying the electromagnetic radiation, various parameters of the gas to be measured can be determined using a signal processing system coupled to the detector. In some cases, the substance to be analyzed is a gas produced by an industrial process, and the parameters to be measured are parameters of one or more chemical species present in this process gas. In this specification, references to “gas to be measured” or “species to be measured” are intended to refer to the gas or gas species for which one or more parameters are measured or detected. A "measured object" is the presence of a gas species or a measurable parameter of a gas species. Examples of measured objects include, but are not limited to, gaseous water, O2, NO, NO2, CO, CO2, and hydrocarbons such as methane. These measurements are often used to optimize process efficiency and to monitor and / or minimize the generation of pollutants and greenhouse gases. The presence and / or amount fraction (concentration) of one or more of these measured objects can be determined by absorption spectroscopy measurements using one or more TDLs. However, converting observed changes in the intensity of electromagnetic radiation into useful physical parameters such as concentration and temperature requires a series of assumptions about the measured object and measuring instrument. The term electromagnetic radiation covers a very broad wavelength range, and absorption spectroscopy measurements are often performed in the ultraviolet, visible, and infrared regions of the electromagnetic spectrum, but are not limited to these.The figures within this patent are presented for the infrared region of the electromagnetic spectrum to obtain absorption spectroscopic measurements corresponding to specific molecular vibrational energy transitions. However, the same principle may be applicable to other related wavelength regions and should not be construed as limited to this spectral region. For the sake of simplicity, the terms electromagnetic radiation or light can be used interchangeably throughout this patent specification and are to be construed as equally applicable to ultraviolet, visible, infrared, or other related regions of the electromagnetic spectrum.

[0003]

[0003] In the operation of an exemplary laser gas analyzer system, the wavelength of the beam emitted from the TDL is scanned over a wavelength range that includes one or more absorption lines of the gas species to be measured. Light is absorbed by the gas to be measured at specific wavelengths within the scanned wavelength region, and by measuring the change in the light beam passing through the substance to be analyzed, this spectral absorption line can be detected.

[0004]

[0004] Absorption lines have characteristic "shapes" in wavelength space that vary depending on the intrinsic physical properties (bond angles, bond lengths, number of electrons) of the gas species, as well as external physical properties (velocity, temperature) and environmental properties (pressure, surrounding composition, etc.). In the following paragraphs, an overview of the mechanisms by which these shapes are generated is presented, along with some insight into current practical limitations regarding the recovery of useful properties such as concentration and temperature. Other factors that add perturbations are not clearly defined or cannot be clearly defined.

[0005]

[0005] In the above context, an absorption "line" is an observable change in light transmittance that coincides with a frequency (wavelength) interval at which photons can induce a gas molecule to transition from one quantum state to another. The probability that a photon with a specific wavelength and polarization causes a transition between quantum states is given by the absorption cross-section σ ν (cm 2 / molecule). The cross-section corresponding to a transition can be roughly estimated from first principles but can also be measured experimentally with high precision. The measured and calculated absorption cross-sections are HITRAN 1and HITEMP 2 are catalogued in a freely available spectral database such as...

[0006]

[0006] Since the interaction between light and matter is inherently quantum, the degree to which a given chemically identical measurement target gas species absorbs light of a given frequency is determined not only by the number density of quanta in the measurement path, but also by the exact quantum mechanical state of the quanta. This is further defined by a "quantum label" consisting of quantum numbers corresponding to the eigenvalues that replace the molecular Hamiltonian. For any given gas species, there will be a number of quantum states with spectrally distinct absorption characteristics.

[0007]

[0007] From the Heisenberg uncertainty principle, it follows that the energy of a quantum state cannot be precisely defined. This uncertainty obscures the photon energy required to cause a transition between two states and prevents the spectral line from becoming infinitely narrow. The statistical effects of various broadening mechanisms can be grouped into a frequency-dependent term called the "spectral line shape" (g ν ). The absorption cross-section of a given transition can be divided into two parts: the strength (S) of the transition, which depends on the nature of the quantum states that the molecule can occupy, and the spectral line shape g ν which depends directly on the lifetime of the transition state. σ ν = Sg ν (1)

[0008]

[0008] Regarding the strength of the transition or "spectral line strength", assuming that the molecular ensemble is in a thermal equilibrium state, this can be calculated as shown in Equation (2).

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[0009]

[0009] Here, E’’ represents the energy of the state (lower state) that the molecule occupies before the transition, and A ijrepresents the Einstein coefficient of natural radiation, and c² is the "second radiation constant" hc / k. The partition function Q is calculated as shown in equation (3). It should be noted that equation (3) only specifies the temperature dependence of the line in thermal equilibrium, and the intrinsic line intensity is given by A ij It will be encoded as follows.

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[0010]

[0010] Normally, Einstein's A 21 Given that the spontaneous decay rate of the excited state, known as a coefficient, is known, the effect of the lifetime on the shape of the spectral line can be predicted. In such a case, if no other broadening mechanism exists, Γ, which represents the full-width half max (FWHM) of the transition, is equal to the spontaneous decay rate (τ) of γ given by equation (4).

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[0011]

[0011] Assuming that Γ is known, the spectral line shape g ν This can be calculated using equation (5), and the line will adopt a Lorentz profile. The natural linewidth represents the fundamental limit of the measurement resolution.

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[0012]

[0012] As mentioned above, the energy of a molecule's quantum state can be perturbed by the molecule's physical environment. For example, outside of a perfect vacuum, molecules collide with other particles. Such collisions, like those of photons, can induce changes in the molecule's quantum state, shortening the natural lifetime of the original state. In gaseous states, the broadening effect due to these collisions is quite similar to natural broadening, and the broadening effect is generally treated as a modification of Lorentz's FWHM. However, in contrast to the broadening of natural lines, the contribution of pressure to Γ has a complex relationship with the pressure, temperature, and chemical properties of the colliding antagonists. Pressure broadening, applicable only to gases, can be estimated by physically measuring the shape of the line under a given set of conditions and carefully subtracting other known broadening mechanisms. This is often impractical, and broadening due to collisions is often registered only at "normal temperature and pressure" (NTP) in air where no other gases are present. The obtained values ​​can then be input into a model like the one shown in equation (6) so that line widths corresponding to other conditions can be extrapolated.

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[0013]

[0013] The restriction of formula (6) arises because the following assumptions are made. The effect of air pressure on broadening is linear. The effect of pressure can be estimated exponentially. This index applies not only to air but also to the types of gases being measured. In mixtures containing various gases, effective Γ s The values ​​need to be calculated separately. In this simple model, Γ coll ga Γ life It is added to and entered into equation (5), g ν This is the result obtained. However, this result does not take into account the thermal contribution to broadening, so it is only applicable to low temperatures.

[0014]

[0014] Due to the thermal motion of the gas being measured, the constituent molecules of the gas have a range of velocities relative to the light source. If we consider these molecules as "observers" of the incident photons, these photons appear to be shifted to red or blue. At any given temperature, in order to conserve energy and momentum, lighter molecules move faster on average than heavier molecules. Therefore, thermal broadening has a positive relationship with temperature and an inverse relationship with molecular weight. The full width at half maximum (FWHM) of the resulting Gaussian velocity distribution is shown in equation (7).

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[0015]

[0015] From the above paragraph, in most practical spectroscopic applications where temperature and pressure have a considerable influence, the resulting transition profile is neither entirely Lorentzian nor Gaussian in shape. For this reason, it is common to use a "Voigt" profile, which is a convolution of a Lorentzian linear shape and a Gaussian linear shape (8), where x and y are dimensionless, as follows:

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[0016]

[0016] Voigt profiles can reasonably describe spectral line shapes and are sufficient for most purposes, but they are insufficient for high-resolution measurements, and numerous alternatives have been proposed. 3~5However, the Voigt profile represents the standard for measuring the shape of a line. In gas detection, a standard measurable quantity with conventional spectrometers is the change in intensity after light of a given wavelength interacts with the target gas in a sample volume. In this figure, the probability that a photon is absorbed depends on the absorption cross-section given by equation (1) and the volume density of the target gas (9) integrated over the intersection portion l of the optical path and the target gas, commonly called the path length or measurement path. Assuming that the volume density [X] remains constant throughout the measurement path, this holds on average when the target gas is in thermal equilibrium with its surroundings, and u = [X]l. u=∫ l [X]dl (9)

[0017]

[0017] To calculate the proportion of light absorbed by the gas to be measured in the sample volume, it is necessary to combine the spectral overlaps (i) of all possible transitions occurring at the measurement frequency, as well as all possible lines (j) resulting from any other chemical species present. The transmittance is the fraction of light that does not interact with the gas to be measured across the measurement path, and in this case, it can be calculated as shown in equation (10).

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[0018]

[0018] The inventors of the present invention have determined that, provided that the perturbing factors listed above are stable and there are no fluctuations in the incident light intensity and measurement path length, it is possible to determine the change in the volume density of the gas to be measured using a simple method, for example, from equation (10). Such fluctuations may occur, for example, during thermal bending and mechanical vibration of the measurement chamber. Fluctuations in the incident light intensity can be caused by many factors other than absorbing changes in molecular density. For example, fluctuations may be caused by inherent fluctuations in laser output, changes in ambient light intensity levels, and / or obscuration of the process sample stream, and may be caused by any combination of dust, tar, corrosion, or misalignment of the light beam. Obscuration and changes in ambient light intensity are expected inside the furnace. If fluctuations in incident light are not corrected, measurement uncertainty (error) will be introduced into the concentration of the processed sample to be measured. Various methods for compensating for these fluctuations are described in the references. 6 It is summarized here.

[0019]

[0019] From equations (9) and (10), we can derive a further cause of measurement uncertainty, which we will henceforth refer to as "mutual interference". This type of interference arises, at least in part, from the fact that the spectroscopic measurement described above reduces the state of the three-dimensional system to a one-dimensional value (T(ν)). This is due to u over the path length j or σ ν i,j Any fluctuations are averaged out, meaning all spatial information is completely lost. As is often the case with field gas measurements, assuming these parameters are not constant along the measurement path length presents a significant challenge to useful signal reconstruction. Specifically, it means that the reconstructed spectrum is a linear combination of a series of distinct linear shapes resulting from one or more gases whose precise distributions are not defined. When this occurs, assumptions about pressure, temperature, and concentration along the measurement path length must be made, for example.

[0020]

[0020] Let's consider oxygen monitoring for the entire furnace. Since the furnace temperature is usually sufficiently high, a cooling purge gas is used near the light source and detector to prevent the light source and detector from being damaged by heat. The purge gas also has a secondary function, for example, to prevent damage from particulate matter in the gas stream. Compressed air can be used as a “purge gas” and is readily available and economically viable compared to oxygen-free purge gases such as nitrogen, but the use of compressed air presents several technical challenges. The air being purged must be cooler than the gas in the furnace, which is the target volume to be measured. According to the law of ideal gases, the density of the purge gas is significantly higher than that of the gas in the furnace, as are its transition intensity and linear profile. Any volume of air purged, both inside and outside the furnace, which contributes to the overall absorption path of the instrument, will affect the measured oxygen reading. Without precise knowledge of the effective purge gas absorption path length, which can vary significantly over time depending on the temperature distribution along the measurement path, the composition of the purge gas, and the source of the compressed gas, it is impossible to calculate the O2 concentration in the furnace. This task is extremely difficult, and even numerical approximations are insufficient in most applications. Often, measures are taken to circumvent this problem, and the absorption intensities of one or more lines are carefully measured. For example, because the ground state "E''" value of the purge gas is high. 7In some cases, a "hot" line may be measured where "S" is close to zero at the purge gas temperature, meaning the effect of purge gas absorption is minimized (see equation (2)). However, such lines are always weaker than lines with lower E'' at normal furnace operating temperatures, and measurement performance is significantly reduced, so this choice incurs a cost for measurement sensitivity. Furthermore, since these lines can only be measured at high temperatures, significant challenges are imposed regarding the calibration and / or "startup" process or low-temperature furnace conditions. Finally, the usefulness of such compensation techniques is limited because they depend on the concentration, pressure, and temperature of the purge gas, which are known constants or continuously measured. A simpler solution is to purge with a non-absorbent gas such as nitrogen or argon, which can directly eliminate mutual interference, but this method, while providing the best measurement performance and improved accuracy, is not only significantly more expensive and energy-inefficient but also ecologically undesirable. An energy-efficient and cost-effective solution to the challenge of purge gas absorption affecting spectroscopic measurements is still needed.

[0021]

[0021] The type of interference in question will henceforth be called “indirect mutual interference,” which is readily apparent from equation (6). This interference is due to the influence of the partial pressures of dissimilar gases on the linear shape of the transition of the gas being measured. The composition of the measurement stream is rarely known precisely. If it is, the requirements for measurement become invalid, and therefore the linear shape generated by a fixed amount of the gas being measured can vary unpredictably when the partial pressures of the dissimilar broadening gases are unknown. Direct mutual interference caused by dissimilar gases always leads to some degree of further indirect mutual interference. This can have a significant impact on the intensity of the transition being measured, depending on the spectroscopic technique used. For example, when using wavelength modulation spectroscopy (WMS), the intensity of the reconstructed line varies depending on the ratio of the applied amplitude modulation to the transition linewidth. Indirect mutual interference in this state necessitates a measurement technique that constantly measures the linear shape and uses it to normalize the variation in the transition intensity. For example, any uncertainty in the linearity caused by electronic noise is coupled to the measured signal, impairing its accuracy and precision. Alternatively, measurements from a secondary sensor can be used as a reference input, but uncertainty is still coupled to the measurement, and multiple sensors may be required to completely cover interference.

[0022]

[0022] However, there is another possible cause of fluctuations in the photodetector signal, which is not due to direct fluctuations in ambient light or laser output signal, but rather due to constructive and destructive optical interference that occurs as the laser is scanned across the entire measurement wavelength range, causing oscillations in the detector signal. The use of coherent laser light means any reflection at any optical surface or interface along the optical path from the laser output to the detector surface (for example, but not limited to, reflections from surfaces / interfaces such as windows, lenses, and reflective interfaces), which results in the generation of reflected light with a phase difference compared to the incident light, and thus causes optical interference in which the light rays interact. This phase relationship between the reflected light and the incident light can change over time due to factors such as temperature, vibration, and pressure fluctuations, because these factors can cause changes in physical dimensions, density, or refractive index.

[0023]

[0023] The detector integrates this optical interference to generate an intensity signal. Because the phase difference changes with wavelength along the measurement path, a symptom of this optical interference (or etalon) is typically the generation of oscillations in the signal baseline as the laser output is scanned across the entire wavelength measurement range. Oscillations, combined with other distortions, can cause measurement inaccuracies. The signal “baseline” is a signal that is present even when no absorption signal is present, in other words, a “zero absorption” signal. This baseline signal is superimposed on the actual absorption signal, if present. Ideally, the baseline would be a straight line (a flat line centered at zero in perfect conditions), but this is not actually achieved. The baseline may not be perfectly flat across the entire scanning range and may have fluctuations and other distortions (or “noise”) that are random or ordered in nature and may include the oscillations described above. Such oscillations are sometimes called “interference fringe” signals in the case of optical interference. Whatever the cause, the effects of these various distortions increase uncertainty in determining one or more absorption signals, and consequently, in deriving the molecular density or concentration of the gas being measured. Periodic etalon interference fringes can broaden or narrow the reconstructed signal, so the presence of indirect interference, in addition to the strength of the transition, increases the degree of uncertainty when linear shape measurements are required.

[0024]

[0028] Therefore, there is still a need for absorption spectroscopy gas analysis systems that minimize the influence of perturbing factors that can affect gas measurements, so that readings are meaningful and the assumptions required to obtain those readings are minimized. [Overview of the project]

[0025]

[0029] This patent specification describes methods, apparatus, and systems for reducing uncertainty in spectroscopically derived parameters of a gas to be measured, such as concentration, which may be affected by one or more of the following: Light noise Direct and indirect mutual interference Path length variation Pressure / temperature non-uniformity

[0026]

[0030] The first instrument used for detecting and / or measuring gases is: At least one electromagnetic radiation source that transmits electromagnetic radiation through a gas sample toward at least one detector, A detector for monitoring the absorption of electromagnetic radiation for at least one absorption wavelength or absorption wavelength range associated with a gas species by detecting electromagnetic radiation that is transmitted without being absorbed, At least one field generator is arranged to apply at least one of an electric field, a magnetic field, or an electromagnetic field to at least one section of the transmission path of electromagnetic radiation to be transmitted between at least one source and at least one detector, A signal processor analyzes the output signal from at least one detector to determine the presence of a gas species and / or to measure gas species parameters, such as the concentration of a specific gas species, or the isotopologue or isotopomer of a gas species. It is equipped with.

[0027]

[0031] A first method used for gas detection and / or measurement in an absorption spectroscopy system is: To transmit electromagnetic radiation from at least one electromagnetic radiation source through a gas sample toward at least one detector, Applying at least one of an electric field, a magnetic field, or an electromagnetic field to at least one section of the transmission path of electromagnetic radiation to be transmitted between at least one source and at least one detector, By using at least one detector to detect electromagnetic radiation that is transmitted without being absorbed, the absorption of electromagnetic radiation is monitored for at least one absorption wavelength or absorption wavelength range associated with the gas species, and Analyze the output signals from at least one detector to determine the presence of a gas species and / or measure the parameters of the gas species. Includes.

[0028]

[0032] An exemplary method involves applying at least one of an electric field, a magnetic field, or an electromagnetic field to at least one section of an absorption spectroscopy system, wherein this section is separated from the gas sample but is within the transmission path of electromagnetic radiation transmitted between at least one source and at least one detector, thereby suppressing or modulating spectral artifacts resulting from absorption by at least one gas species within the section. Apparatus, systems, and methods according to the present invention can improve detection and / or measurement in an absorption spectroscopy system by changing the absorption wavelength of one or more gas species by altering the transitions between the quantum energy states of the gas species using one or more applied electric fields, magnetic fields, and / or electromagnetic fields. The applied field can be used to influence the absorption by interfering material and / or the gas species under measurement. Thus, for the purpose of improving gas detection and / or measurement, the applied field can be used to suppress or modulate at least one absorption spectral artifact.

[0029]

[0033] For example, an applied magnetic field, electric field, or electromagnetic field can alter the quantum energy state transitions of one or more interfering materials located in a separate section of the absorption spectroscopy system, separated from the measurement chamber. This allows the field to be applied only to a portion of the transmission path of electromagnetic radiation within the absorption spectroscopy system, thereby assisting in the detection and / or measurement of parameters of one or more gases within the measurement chamber. For instance, changing the absorption wavelength of oxygen outside the measurement chamber, within a section of the absorption spectroscopy system, can separate this oxygen absorption line from the oxygen absorption line inside the measurement chamber. By thus reducing the effects of interference from oxygen or other interfering materials that may occur outside the measurement chamber of the absorption spectroscopy system, using air as a purge gas for cleaning such sections of the system becomes far more practical.

[0030]

[0034] In this example of air purging, both the gas species being measured and the interfering substance are oxygen, but the absorption spectrum is affected separately by applying different electromagnetic fields to different parts of the system (e.g., the measurement chamber and the volume purged with separate air), which can produce different absorption characteristics for the same gas species in different parts of the system. In other examples, the gas species being measured and the interfering substance may be two different constituent gas species within the measurement chamber (e.g., the sample chamber or furnace or exhaust flue) or elsewhere in the transmission path of electromagnetic radiation. Note that the effect of the applied magnetic field on the spectral absorption characteristics is dominant over any attractive or repulsive force on the gas species due to the paramagnetic or diamagnetic properties of the gas species.

[0031]

[0035] The inventors determined that it might not be necessary to actually measure the absorption by interfering substances present in the purge gas after shifting the quantum energy transitions of the interfering substances to enable separation of the absorption wavelength of the target gas species in the measurement chamber from the effects of interference. The function of shifting and / or modulating the absorption by interfering substances in the purge gas can significantly reduce costs by allowing the use of inexpensive gas mixtures such as air as the purge gas in the absorption spectroscopy system, even if one of the targets for measurement is the concentration of oxygen.

[0032]

[0036] The application of magnetic, electric, and / or electromagnetic fields, which influence known quantum energy state transitions of atoms and molecules represented by the absorption profiles of gas species, represents a significant departure from previously available absorption spectroscopy systems. Some previous solutions relied on registered temperature-dependent absorption wavelengths and absorption profiles (held in databases such as the HITRAN and HITEMP spectral databases) to identify the constituent gases, while others relied on estimating the influence of the purge gas by measuring the composition of the purge gas, the temperature distribution along the measurement path, and the actual absorption path length of the purge gas.

[0033]

[0037] Various novel systems and methods using magnetic fields, electric fields, and electromagnetic fields to improve or simplify gas detection and / or measurement in absorption spectroscopy systems by mitigating interference and noise-related issues are described below. Throughout this document, references to applied fields or electromagnetic fields are intended to encompass one or more electric fields, magnetic fields, and / or electromagnetic fields unless a more specific meaning is specified. The various embodiments described use applied fields to influence the quantum energy state transitions of gas molecules and thus influence the absorption wavelength. Other features, advantages, and embodiments of the invention will become apparent from this specification, including the drawings.

[0034]

[0038] While some of the following detailed descriptions and systems illustrate the use of the present invention in relation to second harmonic (2f) wavelength modulation spectroscopy (WMS) for detection and measurement, it should be noted that the novel techniques described in this patent specification are applicable to any harmonic absorption measurement, i.e., from the first harmonic (direct absorption) to the second harmonic and above.

[0035]

[0039] The spectral interference described above arises from processes other than absorption by the target gas species and contributes to changes in the intensity of light at the detector. In this invention, electric, magnetic, and / or electromagnetic fields are intentionally used to change the energy of quantum states belonging to one or more of the target gas species, interfering substances, or both at specific locations along the measurement path. These fields can alter the absorption cross-section of the target gas or interfering substances at a given wavelength without affecting other sources of optical noise or baseline noise, and their relative contributions can be isolated. The nature and magnitude of the changes depend on the system. Furthermore, since the magnitude and gradient of the applied field are appropriately defined in three-dimensional space, selective application of the field along the measurement path can enable the collection of two-dimensional spectral data. With appropriate processing, this data can be used to calculate σ, which is a function of the path length (l). ν and S ν This allows for the extraction of certain parameters, and as a result, measurement uncertainties related to pressure and temperature non-uniformity are effectively eliminated.

[0036]

[0040] Several exemplary systems and methods are described below with reference to the attached drawings. [Brief explanation of the drawing]

[0037] [Figure 1A] Figures 1A and 1B show the effect of applying a magnetic field on an exemplary oxygen absorption spectrum, including a pair of absorption lines in the quantum energy state. Figure 1A shows the spectrum obtained using 2f WMS in the absence of a magnetic field. [Figure 1B] Figures 1A and 1C show the effect of an applied magnetic field on the absorption spectrum of an example oxygen molecule, including a pair of absorption lines in its quantum energy state, while Figure 1B is a schematic diagram of the effect of the applied field on the energy of the quantum state of an O2 molecule. [Figure 1C] Figures 1B and 1C show the effect of an applied magnetic field on an exemplary oxygen absorption spectrum, including a pair of absorption lines in the quantum energy state. Figure 1C shows the spectrum obtained using a 2f WMS in the presence of a magnetic field. [Figure 2] This figure shows how spectral noise is removed using the applied field. [Figure 3] This figure shows the configuration of a spectroscopic gas analysis system for on-site measurements, along with exemplary absorption spectra obtained using three different laser polarizations applied to the field. [Figure 4] This figure shows a spectroscopic gas analysis system in which the central section is exposed to an adjustable field, and an exemplary absorption spectrum. [Figure 5-1] This figure shows a spectroscopic gas analysis system in which multiple sections are exposed to various applied field modulations to enable simultaneous measurement of gas concentrations in different sections. [Figure 5-2] This figure shows a spectroscopic gas analysis system in which multiple sections are exposed to various applied field modulations to enable simultaneous measurement of gas concentrations in different sections. [Figure 5-3] This figure shows a spectroscopic gas analysis system in which multiple sections are exposed to various applied field modulations to enable simultaneous measurement of gas concentrations in different sections. [Figure 6] This is a schematic diagram of a known gas filter correlation system. [Figure 7] This figure shows the arrangement configuration of a spectroscopic gas analysis system that implements the present invention. [Figure 8] This figure shows an exemplary oxygen absorption spectrum illustrating the use of a magnetic field to identify the effects of optical interference (etalons). [Figure 9] This figure shows the direct absorption spectrum and difference spectrum of exemplary oxygen, including etalone, obtained across the measurement pathway. [Figure 10] This figure shows an exemplary absorption spectrum obtained using the system shown in Figure 4. [Figure 11] This figure shows an exemplary oxygen spectrum obtained using a WMS with varying numbers of magnets near the laser. [Figure 12] This figure shows the splitting of several representative water absorption lines as a function of the applied electric field. [Figure 13] This figure shows the applied field (top), the intensity of light received by the detector as a function of time, the H2O concentration in the sample cell (center), and the mean-centered (MC) signal at H2O sample concentrations of 20 ppm and 40 ppm after subtracting the 0 ppm MC signal (bottom). [Figure 14] This figure shows the difference in transmittance as a function of the H2O concentration of the sample, under conditions of zero field and 10 MV / m field. [Figure 15] Figure 13 shows the frequency spectrum generated by applying FFT to the trace shown. [Figure 16] Figure 15 shows the dependence of the 2F and 6F frequency components on the H2O concentration of the sample. [Modes for carrying out the invention]

[0038]

[0041] Absorption spectroscopy is known for its use in gas analysis, as described above, including determining the presence of specific gas species within a measurement volume and measuring parameters including the concentrations of individual gas species in a gas sample. In this context, the gas sample being investigated is not necessarily an extracted “sample,” but could be the contents of any measurement volume or chamber, and a detector is used to detect the absorption effect by the gas species within that volume. The measurement volume may be, for example, an industrial process chamber such as a furnace, or a fluid flow duct such as an exhaust flue from an industrial process chamber, or an extraction volume for holding an extracted sample. In an exemplary absorption measurement system, an electromagnetic radiation source emits a beam of radiation toward a detector, which may be, for example, a solid photovoltaic or photoconductive detector, a radiation thermometer, a thermopile, or a microthermometer. The electromagnetic radiation source may be a combination of a tunable laser source, such as a tunable diode laser (TDL) or a broadband source such as an incandescent light source or a light-emitting diode (LED), and a wavelength range selecting element such as an optical passband filter or a grating.

[0039]

[0042] Examples of instruments, methods, and absorption spectroscopy systems that use a field applied to a specific section of the transmission path of electromagnetic radiation by an absorption spectroscopy system to improve or simplify detection and / or measurement are described below.

[0040]

[0043] The influence of external electromagnetic fields on the energy levels of polyatomic molecules is complex and will not be explained in detail here. For illustrative purposes, the influence of external fields on atoms will be described here. This is because the process is simpler and the general concepts can be applied to more industrially relevant species such as O2 and CO2.

[0041]

[0044] A collection of molecules can be interpreted as charged particles, which can be converted into each other using methods that clearly quantize them. These charged particles interact with an external electric field using conventional methods; for example, a positively charged particle is repelled by a positive electric field, and vice versa. Similarly, the motion of charged particles represents an electric current that generates magnetic flux through induction. Electrons, depending on their electronic structure, may occupy orbitals, and therefore the final motion of an electron has some orbital angular momentum.

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[0042]

[0045] The existence of spin, an intrinsic form of angular momentum carried by particles such as protons, neutrons, electrons, and photons, makes the classical diagram somewhat more complex. For example, electrons

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[0043]

[0046] The application of an external electromagnetic field has the effect of shifting the energy of quantum states that would otherwise overlap, and these are generally called degenerate energy levels. For example, consider an electron orbiting an atom in the x / y plane. In the absence of an external field, the total energy of the resulting states should be approximately equal, so clockwise and counterclockwise rotations are interpreted as degenerate. However, if an external field is applied, Z When applied in the Z direction such that >0, the clockwise state should have lower energy than the counterclockwise state (left-hand rule). The effect of a magnetic field is called the "Zeeman effect," and the effect of an electric field is called the "Stark effect." For historical reasons, the Zeeman effect can be divided into three different states: the "normal Zeeman effect," the "anomalous Zeeman effect," and the "Paschen-Bach effect."

[0044]

[0047] In a normal Zeeman effect, electron spin is zero, and the only contributing factor to the resulting magnetic moment is from orbital angular momentum. In such a case, the energy shift caused by the field is M L The projection of orbital angular momentum onto the magnetic field axis, encoded by (13)(B), and dependent on the gyromagnetic ratio.Z and

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[0045]

[0048] The anomalous Zeeman effect represents the effect of a magnetic field on a system where S≠0. In such cases, the spin and orbital angular momentum are coupled to obtain the "total angular momentum" (J), and the orbital and spin...

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[0046]

[0049] The Stark effect can be interpreted as an electrical analogue of the Zeeman effect, in that an electric field, rather than a magnetic field, shifts the energy associated with a given quantum state. One very important consideration for both the Zeeman and Stark effects is that when an electromagnetic field is applied, the absorption cross-section changes with respect to the polarization of the incident light. To avoid ambiguity, the absorption spectrum of a sample in an applied field changes depending on the polarization of the light source relative to the applied field. The effects of the Zeeman and Stark effects on molecular energy are considerably more complex due to the potential coupling of vibrational and rotational energies in addition to orbital and spin angular momentum, but a complete explanation of this coupling is not necessary for understanding or implementing this patent specification. Some illustrative details are found in the following references. 10~12 It can be observed and used to help predict the expected absorption spectrum of a molecule for various polarizations of light under a given set of physical conditions. "PGopher" 13 Several available computer programs that enable the simulation of molecular spectra can also be used. However, it should be noted that various systems and methods for carrying out the present invention utilize the application of a magnetic field, electric field, or electromagnetic field to a section of the path of electromagnetic radiation to separate the absorption spectrum of the gas under measurement without the need to predict or measure the effects of the electromagnetic field. To shift and separate the absorption lines of interfering gas species from the absorption lines of the gas under measurement, for example, the energy transition shift of molecules of the interfering gas species can be used in the spectroscopic system, and purging with air can be used without compromising the usual complexity and required measurement accuracy. Furthermore, by determining which features of the output signal have not been shifted by the application of the electromagnetic field, optical noise and other baseline noise can be separated and then removed by monitoring and using the energy transition shift.

[0047]

[0050] The schematic diagram in Figure 3 shows the configuration of a spectroscopic gas analyzer for on-site measurements in an industrial process. On-site measurements are desirable for high-speed, real-time measurements, while extractive measurements have phase delays, costs, and complexities. In one example, light from a tunable diode laser (31) that emits light within the wavelength range absorbed by oxygen is supplied to a gas sample path (32) containing a process gas whose oxygen concentration needs to be determined. After passing through this sample gas, the light is focused by a detector (33). The decrease in the intensity of the detected light is observed at the wavelengths in which the emitted light is absorbed by oxygen molecules present in the sample gas. Although this example concerns oxygen, the same general principle can be applied to many suitable gas species. The decrease in the intensity of the detected light depends on the wavelength, path length, and gas species and is expressed by the Lambert-Beer law in equation (10).

[0048]

[0051] Optical elements (34 and 35) such as windows, lenses, mirrors, passband filters, and attenuators may be present, and the optical elements include windows between sealed zones that separate the purge gas from the sample gas, and elements that shape, focus, or diffuse the light beam or transmit a desired wavelength range. There are purged regions (36 and 37) where the purge gas is used, as described above, to keep the radiation and detection optics and / or electronic circuits undamaged and cooled. Additional sealed sections may be present that are not exposed to the active purge flow and can be filled with an optically non-absorbent gas or air. Such a system is described in a previous publication. 14及び7 As described therein, one or more individual oxygen absorption lines can be selected for measurement, and a tunable laser diode is scanned across the absorption line(s). The absorbed light can be measured from the detector signal as direct absorption, by using second and / or higher harmonic processing, or a combination thereof.

[0049]

[0052] In Figure 3, sections 36 and 37 of the spectroscopic system are 35 cm purge regions containing air at room temperature and pressure (NTP), while the central region 32 is 105 cm long and contains a mixture of 5% O2 in N2 at 1300 K. The upper, middle, and lower slices of the detected spectrum are shown above the schematic diagram of the apparatus, representing the O2 spectrum in WMS(2f) for various regions, where the laser polarization relative to the field in the purge section is one of random, perpendicular, or parallel, respectively. The right side of Figure 3 shows the spectra obtained by passing light through each region, first with a magnetic field applied to the purge gas (results shown using dashed lines), and then without a magnetic field (shown using solid lines). Note that the location of spectral absorption in the perturbed field spectrum differs significantly from that shown in Figure 1. This is due to the greater field intensity applied in this example. Furthermore, the shape of the spectrum obtained from the purge section varies depending on whether the applied magnetic field is parallel or perpendicular to the polarization of the laser, and the random orientation represents the average of the parallel and perpendicular spectral components. The magnitude of the absorption lines in the purge section is significantly larger than in the central region due to the higher concentration and density of O2 in this region (lower temperature). Regardless of the orientation of the field used, the spectral overlap in the purge section is reduced compared to the central region of interest. The nature of the residual spectral overlap can be subtly altered by adjusting the intensity of the field applied to the purge section or by adjusting the orientation of the applied field relative to the laser polarization. The use of this technique can help decompose the final spectrum into components related to various sections.

[0050]

[0053] The one or more magnetic fields applied may be one or more preferred directions determined theoretically and / or empirically, such as two orthogonal directions, for example, perpendicular and parallel to the light source and / or the polarization of the light source, because the resulting spectrum differs slightly depending on the orientation (Figure 10). If the light source is not polarized, it can be polarized, for example, by using a polarizer optical element or other suitable means, in order to benefit from the spectral differences.

[0051]

[0054] Polarization can be achieved by aligning a window or other optical element at an angle, such as the Brewster angle, to selectively transmit and reflect light, thereby achieving a specific preferential polarization of light in response to an applied electric, magnetic, or electromagnetic field. Even in the case of polarized light sources, the use of aligned optical elements helps avoid back reflections that can cause etalons. The orientation of optical elements can be changed as needed, for example, when replacing a laser diode with another laser diode having slightly different polarization characteristics, or when changing the polarization purity and / or intensity of the main beam. Since a portion of the light reflected from the optical element can be redirected by a secondary optical system to pass through the same optical path as the transmitted portion of the light, two portions can be detected simultaneously by a single detector or by multiple detectors.

[0052]

[0055] In an exemplary embodiment, incident light is modified by a polarizer or other means so that two or more distinct polarizations (e.g., left-handed polarized light (LH) and right-handed polarized light (RH), or parallel and perpendicular) pass through the gas sample in the presence of an applied field and are detected by one or more detectors.

[0053]

[0056] In another example, one or more detectors distinguish light passing through a field via one or more paths so that the intensity of light of a specific polarization relative to the applied field and light source can be reconstructed.

[0054]

[0057] In another example, the intensity of light of various polarizations reaching the detector can be modulated, for example, by rotating a linear polarizer in the optical path or by using a stack of liquid crystal panels.

[0055]

[0058] In an exemplary embodiment, polarized light of various polarizations is received by a single detector, the transmittable polarization is modulated, the detector's output signal is processed, and as a result, a time profile of the phase angle is reconstructed, which can then be used to infer a Faraday spectrum and measure concentration and / or other useful properties. This can also be done using multiple detectors.

[0056]

[0059] In another exemplary embodiment, a method for detecting and / or measuring a gas includes comparing the polarization of light before it passes through a gas sample with the polarization after it passes through the gas sample (in the presence of an applied field) to estimate the proportion of light scattered by dust or some other medium. Since the polarization and phase are randomized when light is scattered by dust, the purity of the polarization decreases with increasing scattering. By performing the polarization comparison in combination with Faraday spectral measurements, the dust load can be measured independently of light transmission and sample absorption. This information can then be used to correct absorption measurements.

[0057]

[0060] Another exemplary method involves spatially and temporally modulating the optical path of a light source, for example, by using a rotating mirror or a digital light processing (DLP) array to change the optical path of the light source in time and space. In this example, the optical path may be obstructed by a scattering medium such as a wall or pipe, resulting in scattering of light. The light can be focused by one or more detectors, each equipped with either a fixed or variable polarizer. In an exemplary embodiment, information from the detectors is combined with the temporal and spatial modulation patterns to construct an image of polarization intensity. Information from this image can be used to measure gas concentration in two-dimensional space, for example, to help detect leaks. In one exemplary embodiment, a magnetic field gradient or pulsed magnetic field may be applied to a region of interest in the optical path, and / or an electric field gradient and / or pulsed electric field may be used.

[0058]

[0061] In one exemplary embodiment, a three-dimensional image of the properties of the gas being measured is inferred from spectral measurements, and further types of measurements can then be performed from this three-dimensional image. For example, if high-pressure air leaks from a pipe into the atmosphere, the exact location can be inferred by measuring the density and temperature profile of O2 in three-dimensional space. Another example is measuring the Doppler shift of the O2 line in the leak region and extracting the velocity vector to determine the direction of the leak. If the properties of the gas in the medium are uniform (e.g., air), the reconstructed three-dimensional absorption image can be used to reconstruct information about the applied field. This can be used to calibrate instruments used to infer a three-dimensional image of the properties of the gas being measured. Alternatively, this can be used to assist in the manufacture and maintenance of certain instruments that use large volumes of gas and large field gradients, such as nuclear magnetic resonance (NMR) or magnetic resonance imaging (MRI) devices.

[0059]

[0062] Figure 10 shows the expected spectra of the central section shown in Figure 4, with and without gas (dotted line) in the upper, middle, and lower left sections of the figure, where the laser polarization is random (A, B), perpendicular (C, D), or parallel (D, E) relative to the 0.6T field applied to the purge section. The right side shows the corresponding difference spectra. These difference spectra are identical to each other, but the spectra corresponding to the purge section with different polarization states are not identical. For example, when the field is parallel to the polarization of the light, certain transitions are more pronounced compared to when it is perpendicular. By carefully selecting the orientation of the field, it is possible to distinguish gas signals arising from different regions of the measurement path. Furthermore, a specific orientation facilitates simple spectral subtraction. For example, when there is no gas in the central region shown in Figure 4, the central peak of spectrum D is flat.

[0060]

[0063] While optically non-absorbent purge gases such as nitrogen may be used as the purge gas, this is costly and energy-inefficient. Instead, cheaper and more abundant air can be used as purge by either using cooler air in combination with the use of the sample's "high temperature" oxygen absorption line to counteract absorption from the purge section, or by using calibration and / or calculations to compensate for the measured absorption and determine the sample gas concentration, taking into account the oxygen present in the purge section. The air being purged is ideally clean and free of interfering gases other than oxygen. When using air for purging, accuracy is still reduced because sensitivity decreases when using the "high temperature" absorption line, as opposed to the stronger absorption line that is present even at lower temperatures. Furthermore, even when absorption is compensated for in signal processing to account for the oxygen present in the purge section, the uncertainty of the measurement still increases due to variations in purge entry due to flow and / or pressure fluctuations, as well as the temperature difference between the purge section and the sample section.

[0061]

[0064] In exemplary system embodiments, improved oxygen measurements can be obtained by using a static magnetic field and / or a fluctuating magnetic field (electromagnetic field, permanent magnetic field, or combination) to surround the optical paths of purge sections 36 and 37 and / or any sealed sections. As shown in Figure 11, the effect of the field applied along the spectral path is additive, and therefore, signals of any length can be affected simply by extending the field domain as needed. The upper left spectrum in Figure 11 is an example of a spectrum obtained in a WMS when there are 0 (A), 1 (B), 2 (C), and 3 (D) magnets near a laser measuring a pair of oxygen transitions. As the number of magnets increases, the intensity of one of the oxygen transitions decreases. The differences between spectra are shown in the lower left plot, and the magnitude of the differences is plotted as a function of the number of magnets in the scattering diagram on the right. As the number of magnets increases, the proportion of the measurement path surrounded by the magnetic field increases. The neutralization of the oxygen signal is linear with respect to the proportion of the measurement path where the applied field exceeds a certain critical threshold, which varies depending on the application. The behavior described herein suggests that all signals originating from the purge section can be neutralized by applying a critical field along the entire length of the purge section.

[0062]

[0065] Similarly, if the path length over which a variable field is applied is known, the total path length can be calculated using the ratio of the restored signals with and without the field, provided that a suitable object to be measured is known to have uniform physical properties and density throughout the entire path length. This is advantageous in terms of measurement accuracy when the distance between the detector and transmitter is known to change unpredictably, for example, due to thermal expansion and / or contraction of the support structure. In addition, this method has advantages over established length-measuring techniques such as LIDAR (light detection and ranging) in that it uses the actual measurement path, not a substitute for the measurement path used by the measuring instrument. This can be beneficial when light undergoes a series of reflections that cannot be emulated using a spatially offset secondary light source. Thus, the path length of an optical system can be determined by measuring the effect of the applied field within an absorption spectrometer, by measuring the ratio of the signals that a portion of the light has passed through inside and outside an electric, magnetic, or electromagnetic field, or by facilitating accurate scaling of absorption when measuring an object by spatially and / or temporally varying the field.

[0063]

[0066] As mentioned above, for gas species such as oxygen, there may be degenerate or overlapping energy states, resulting in a single absorption line at a specific wavelength in the absence of a magnetic field. In the presence of a magnetic field, this single absorption line splits into multiple lines on both sides of the original peak absorption wavelength. This is shown in Figures 1A, 1B, and 1C. The degree of splitting and separation varies depending on the species, the specific absorption line, and the magnetic field strength. The potential utility of this method is as follows:

[0064] Within a sealed section surrounded by a purge gas and / or magnetic field, the intensity of selected oxygen absorption lines decreases or becomes invisible relative to the measurement, thus allowing for the benefit of using air purging without the negative side effects described above.

[0065] When the laser wavelength drifts, one or more of the split lines can be used as the laser line lock (wavelength reference), eliminating the inconvenience of having the line of the absorbing purge gas present in the measurement, and eliminating the need for a reference such as an oxygen cuvette (as in the case of purging with nitrogen) or oxygen present in the sample gas.

[0066] When a fluctuating magnetic field is used by mechanical, electromagnetic, or combined means, the oxygen absorption line of the purge gas can be brought into or outside the measurement by adjusting the magnetic field strength of the wavelength-referenced lock of the main oxygen absorption line, even when little or no oxygen is present in the sample gas.

[0067] When a fluctuating magnetic field is used by mechanical or electromagnetic means, the line of absorbed oxygen can be brought in or out by adjusting the magnetic field strength for calibration checks and / or recalibration. Any change in the oxygen concentration of the sample can be checked / recalibrated by measuring the signal with and without the magnetic field, provided that it is relatively slow compared to the required calibration time and / or the frequency of the fluctuating magnetic field. Subtracting the signal with the magnetic field present from the signal without the magnetic field results in a signal that is almost entirely due to absorption by oxygen within the purge section, regardless of the oxygen concentration of the sample gas. If the length, temperature, pressure, and oxygen concentration in the air of the purge section are known and / or can be calculated, then, provided that there is a known relationship between the ambient conditions of the purge and the sample environment, the oxygen calibration can be checked / recalibrated, and consequently, the concentration of the sample gas can also be confirmed.

[0068] When using permanent magnets, a high field intensity can be obtained at a relatively low cost and with low power consumption.

[0069] If a fluctuating magnetic field is required, at least one oscillating or moving permanent magnet and / or motorized solenoid can be used. The solenoid consists of a coil of wires densely packed in a helical structure, which can be wound around a core of a high-permeability material to increase the magnetic field strength. When current flows through the coil, it functions as a magnet, and the magnetic field strength is determined by the design used, the number of turns, and the driving current, or a combination of these factors.

[0070]

[0067] According to one practical embodiment of the present invention, the physical design and electrical and magnetic properties of the materials used are taken into consideration with respect to the applied electric, magnetic, and electromagnetic fields. This may require the use of electrically insulating materials in the case of a strong electric field, and in the case of a magnetic field, it may be necessary to use materials that direct or localize the field. In the case of a magnetic field, the design of the pole pieces can be optimized using selected physical designs and materials (such as those with high permeability) to localize and concentrate the magnetic field and / or limit the extent to which the magnetic field penetrates into the surrounding area. The magnetic field strength and profile of both permanent magnets and electromagnets can be optimized using the design and materials of the pole pieces. When creating a magnetic field using permanent magnets, a strong magnetic field can be obtained by selecting a specific composition of the magnet, such as a rare-earth magnet, and in the case of high-temperature operation, it is necessary to use a magnet with a high Curie temperature and / or to locally cool the magnet to maintain the magnetic field strength. To create a magnetic field using permanent magnets, a single permanent magnet may be used, or multiple magnets may be used in pairs or other combinations facing opposite directions to create a localized or extended magnetic field. When using at least one electromagnet (solenoid), the material used for the coil should ideally have low electrical resistance to minimize self-heating. Large currents may be required to create the necessary magnetic field strength, and external cooling may be necessary. Very high magnetic field strengths can be obtained by using superconducting electromagnets cooled to cryogenic temperatures. This is particularly useful when measurements are taken near nuclear magnetic resonance (NMR) or magnetic resonance imaging (MRI) machines, where this type of magnet is essential for the proper functioning of NMR or MRI machines. An electric field can be created by using two or more electrodes maintained at different voltages to create an electrical field between the electrodes. The shape and strength of the electric field are determined by factors including the shape and material of the electrodes, as well as any materials the electrodes are in contact with, the voltage difference between the electrodes, and the isolation gap. As the isolation gap increases, the voltage required to maintain the same electric field strength also increases. Beyond a certain electric field strength, a discharge of the gas mixture occurs.

[0071]

[0068] A simplified form of an extracted version of the system described above is shown in Figure 4. Since a purge section is no longer required, electromagnetic radiation output from the tunable diode laser source 41 is supplied directly to the sample chamber 42. There is at least one gas inlet and one gas outlet to allow the passage of the sample or calibration gas into and out of the sample chamber 42. The sample chamber may include a path length extension design, such as a multipath cell (e.g., a Heliot or White design) or a resonant cavity. The transmitted light is focused by a detector 43 and the signal is analyzed to produce a gas concentration measurement. Optical elements 44 and 45 may be present and may include windows, lenses, mirrors, passband filters, and attenuators. In this form, no extra uncertainty is introduced by the purge gas section, but there are still advantages to applying one or more fluctuating magnetic fields across the sample gas section. One or more fluctuating fields can be generated by moving one or more permanent magnets, or by controlling one or more electromagnets 46, or by a combination thereof. As mentioned earlier, optical interference can exist in the form of constructive and destructive interference (etalons) and is susceptible to vibration and temperature. This can cause the actual signals to overlap, limiting the accuracy achievable by the system. When a tunable diode laser is scanned across a wavelength range containing one or more oxygen absorption lines, the optical interference remains the same with or without a magnetic field, although the oxygen absorption lines may split in the presence of a magnetic field. This is illustrated by example in Figures 1A, 1B, and 1C.

[0072]

[0069] Figure 1A shows a 2f-modulated spectrum obtained from an oxygen-containing gas using WMS in the absence of a magnetic field. A pair of O2 absorption lines can be seen. Figure 1C shows the same transitions under a static magnetic field of 0.3 T, where one of the transitions appears to be significantly broadened and reduced. Figure 1B shows the effect of the applied field on the energy of the quantum state, resulting in the modification of the absorption spectrum described above. The length of the arrow in Figure 1B is proportional to the energy of the transition.

[0073]

[0070] In the example in Figure 4, the purge gas regions 41 and 43 have the same path length and gas conditions, but the central region 42 is maintained at 296 K and 1.5 atmospheres and exposed to an adjustable applied magnetic field. The spectrum shown in the upper right of Figure 4 shows the (2f) spectrum obtained by changing the oxygen concentration in the central region from 0 to 21% without applying a magnetic field. The lower right of Figure 4 shows the spectrum obtained by subtracting the spectrum obtained in the absence of a field from the spectrum obtained at each concentration in the presence of a 0.6 T field. In the latter case, a linear response is obtained regardless of the surrounding conditions of the purge region.

[0074]

[0071] The potential usefulness of the methods and systems described above is as follows: By subtracting the signal scanned with a magnetic field from the signal without a magnetic field, the resulting signal shows a scanned signal with oxygen absorption but no optical interference, thereby improving the overall accuracy of the measurement and reducing the effects of temperature and vibration (Figure 2). The experimental results obtained using this method are shown in Figure 8 for the WMS spectrum and in Figure 9 for the direct absorption spectrum.

[0075]

[0072] Figure 2 uses the same pair of transitions shown in the spectrum of Figure 1 to illustrate how an applied magnetic field can remove spectral noise even when noise is dominant in the spectrum. A, C, E, and G are spectra of 100% O2 focused in the absence of a field, and B, D, F, and H are spectra of 100% O2 focused with a magnetic field of 0.3 T. The etalon in the top spectrum is FSR or approximately 0.07 cm -1 The etalon below is 0.25cm -1It has the following characteristics. The etalon in the right-hand spectrum is out of phase with the etalon on the left-hand spectrum. For each pair of spectra, dividing the signal obtained in the presence of the applied field by the spectrum without the field yields the same signal, the magnitude of which is proportional to the concentration of O2 in the region of the applied magnetic field. The signal is simply proportional to the difference in the O2 signal under different field states (see Figures 1A and 1C).

[0076]

[0073] In the example in Figure 8, the upper left trace shows a pair of oxygen spectra obtained when an etalon is present in the optical measurement path. One spectrum was focused over a small path (1.5 cm) and exposed to a magnetic field of approximately 0.1 T perpendicular to the polarization of the laser. The lower left spectrum shows the difference between these two spectra, with the oxygen transition, whose strength is most affected by the magnetic field, being dominant, and the etalon signal being significantly reduced. The small residual noise signal arises from a slight shift to the location of the etalon interference fringes that occurred during the interval (approximately 10 seconds) between focusing the two spectra. The two spectra in the upper right were focused under identical conditions, except that the etalon was not in the measurement path. The corresponding difference signal (lower right) is of the same magnitude (same scale) as that obtained when the etalon was present.

[0077]

[0074] In Figure 9, the two direct absorption spectra (shown above) represent the spectral signals of raw O2 obtained over the measurement path, including the etalon, with one measurement acquired in the presence of a 0.1 T field applied over a 1.5 cm area. Due to the additional 1 / f noise, the measurement noise is higher compared to the WMS spectra shown in the rest of the figure. The lower spectrum is the ratio of the upper "with field" spectrum to the "without field" spectrum and corresponds to the transmission spectrum of the oxygen line reduced by the magnetic field. This difference spectrum demonstrates the usefulness of the difference field method for obtaining "clean" spectroscopic measurements that are unaffected by optical interference.

[0078]

[0075] Hybrids of the above examples, as shown in Figures 5-1 to 5-3, can also be used, where the porous or semi-open probe 51 extends partially or completely across the sample width, and the fluctuating magnetic field means 52 is used to vary the magnetic field strength across one or more sections of the sample width.

[0079]

[0076] In the example in Figure 5-2, the measurement path consists of five zones, A, B, C, D, and E. Sections A and E are 35 cm purge sections containing air in the NTP. Sections B, C, and D are the measurement areas of interest, containing 5% O2 in N2. Sections B, C, and D do not have to be of equal length and temperature; for example, B and D are 20 cm long and held at 773 K, while section C is 65 cm long and held at 1273 K. The temperature and concentration of the sections are shown at the top of Figure 5-1 (labeled 1). Sections A and E, C and D, and E yield different spectra due to the different physical conditions of the sections. Typically, distinguishing these three components requires applying complex deconvolution to the final spectra and making numerous assumptions about the temperature profiles. Furthermore, it becomes impossible to distinguish sections with the same physical concentration (such as A and E and B and D). However, by applying different field modulation schemes to different sections, it becomes possible to simultaneously measure the gas concentration in each section and use the resulting spectra to infer the respective concentrations and physical states. This example shows the effect of modulating sections B, C, and D at frequencies of 45, 50, and 55 kHz, respectively, using a 1T sinusoidal magnetic field, while leaving sections A and E unmodulated. The resulting direct absorption spectra from the different sections are shown in the second row of the graph in Figure 5-1 (labeled 2). Sections A and E have the largest DAS signals because the oxygen concentration and density are excessively high in these regions. The frequency spectra associated with the DAS signals from the different regions are labeled (3) in Figure 5-1 and shown in the third row of the graph. Sections B, C, and D have significant components at intervals twice the field modulation frequency compared to sections A and E. This is because the splitting of the absorption lines changes depending on the magnitude of the applied field, and the field is sinusoidal in shape, resulting in two maximums over a single modulation cycle (in this example).In Figure 5-3, the rows of graphs labeled 4, 5, and 6 show the spectra obtained by filtering the DAS signals from sections A to E with third-order Butterworth notch filters centered at 90, 100, and 110 kHz. In the above example, the signal from the section is maximized when the demodulation frequency is twice the frequency of the applied field, while signals from other sections are suppressed. In Figure 5-2, labeled 7, the spectra obtained by demodulating the spectra of sections 4, 5, and 6 with sinusoidal waveforms at frequencies of 90, 100, and 110 kHz and then filtering them with a low-pass filter are shown. In all cases, the spectral components from sections B (dotted line), C (solid line), and D (dashed line) in Figure 5-3 are shown. Spectra from sections with fields modulated at frequencies different from the notch filter and demodulated signals are suppressed. By using the selectively demodulated signal obtained as a result and appropriately analyzing the shape of the lines in the resulting spectrum, the concentration, temperature, and pressure of the corresponding sections can be estimated separately.

[0080]

[0077] The potential usefulness of this method is as follows: For example, if we subtract the signal scanned when the magnetic field is present across both the air purge and the sample section from the signal when the magnetic field is only present in the air purge section, the resulting signal will be very similar to the signal due to oxygen absorption in the sample gas, which is unaffected by air purging or optical interference.

[0081]

[0078] When one or more sample sections are exposed to a magnetic field separately, the local oxygen absorption of the sample can be examined and measured, and the height, width, and shape of the local line may have information about the local sample concentration, pressure, and temperature. This may make it possible to determine the sample measurement width, which can be useful in certain industrial processes, such as when the sample width is the cross section of a duct or chimney and the industrial process is a combustion process in a power plant or chemical manufacturing facility.

[0082]

[0079] The above example concerned oxygen in the presence of a magnetic field, but it should be noted that, advantageously, other gases, particularly paramagnetic gases such as nitric oxide and nitrogen dioxide, can be measured in the same manner. An electric field is advantageous as it can also be used for suitable gases such as ammonia and water. Preferred embodiments vary depending on the type of gas and whether a high voltage field is permissible for a particular system.

[0083]

[0080] The above example was for a scanning laser diode application using a very narrow bandwidth (sub-single absorption line bandwidth), but broadband applications spanning multiple absorption lines are also possible, and advantageous measurements can be made by applying a magnetic and / or electric field. Consider a known measurement method for gas filter correlation (GFC). An example of GFC is shown in Figure 6. Parallel light from a broadband light source 601, such as an incandescent light source or a broadband light-emitting diode (LED), passes through an optical element 602 and then through an optical passband filter 603 to narrow the wavelength bandwidth and reduce ambient optical noise. The light then passes through a rotating chopper wheel 604 that houses two sealed cuvettes. One of the cuvettes 605 is called the “measurement” cuvette and contains an optically non-absorbent gas such as nitrogen, and the other cuvette 606 is called the “reference” cuvette and contains the gas of interest, such as nitric oxide or nitrogen dioxide. Each cuvette consists of an identical thin cylinder or other suitable form, sealed at both ends by a window that is transparent to the wavelength range of interest. The partial pressure of the gas of interest and the length of the cuvette are selected so as to have at least one absorption peak within the passband range of an optical filter, which has sufficient optical density to be within the nonlinear absorption range as defined by the Lambert-Beer equation. Light exiting the cuvette is transmitted through an optical element such as a lens or window to a sealed sample cell 607 that can contain a sample gas or calibration gas containing the gas of interest. The sample cell is sealed on the opposite side by an optical element such as a lens or window that is transparent to the wavelength range of interest, and has a gas inlet 609 and a gas outlet 610. Light exiting the cell is focused by a concentrator 611 and measured by a detector 612. The detector 612 may be a pyroelectric detector, but may be another suitable detector such as a microthermometer, thermoelectric pile, solid photoconductive or photovoltaic optical detector, or photon multiplier device. Measurements are often performed in the infrared range, corresponding to absorption from molecular vibrational transitions. Because the wheel rotates, the detector detects transmitted light from the measurement cuvette and sample cell. mThe corresponding signal, as well as light from the reference cuvette and sample cell. r The corresponding signals will be examined alternately. The reference signal is the electronically or digitally applied gain G o It can have, and the gain value is the amplified signal G when calibrated using nitrogen in the sample cell. o l r However, in the case of nitrogen in a cell, l m It is set to be equal to l. r is always l m It should be smaller than (that is, G o >1). The reason is, m The signal path is l r This is because, unless the measurement cuvette is modified and throughput is reduced due to alternating transmission between the measurement cuvettes, some of the light is pre-absorbed by the gas of interest within the reference cuvette. When the gas of interest is in the sample cell, the measurement signal decreases by an amount related to the concentration in the sample cell, but the reference signal does not decrease as much because some absorption has already occurred in the gas of interest within the cuvette, corresponding to the nonlinear absorption region of the Lambert-Beer behavior (i.e., it is approaching saturation). The signal S can be defined as follows:

number

[0084]

[0081] For suitable gases, performance can be improved by applying a magnetic field and / or electric field. Consider the exemplary system shown in Figure 7 for the applied magnetic field, which may be suitable for gases such as nitric oxide and / or nitrogen dioxide (NO and NO2). Similar to the GFC, there is a broadband light source 701 (such as an incandescent light source, LED, or flashlight). The output from the light source passes through one or more optical elements 702, which may include a window, a light passband filter, a reflective optical system, and a refractive optical system. This output then passes through at least one cuvette 703 containing at least one gas of interest, which may be nitric oxide and / or nitrogen dioxide and / or other suitable gas species. The gas of interest may be an interfering substance to be characterized and used to compensate for any uncertainty caused in the determination of the target gas and / or the main target(s) whose concentration needs to be determined. The gas of interest may be at least one isotopomer or isotopologue of a gas species. When it is necessary to determine the concentration of one or more specific isotopomers or isotopologues of the same gas species, they can be measured separately, as different isotopomers or isotopologues of the same gas species may have different absorption characteristics with and without a magnetic field. When multiple gases of interest are being measured simultaneously, two or more gases of interest can be filled into a cuvette at the same time, provided that the gases do not chemically react with each other. Alternatively, two or more cuvettes may be used in series or in parallel. At least one cuvette may consist of a narrow cylinder sealed at both ends by an optical element, which may be a window or refractive optical system that is transparent to the wavelength range of interest. For convenience, the cuvette containing the mixture of the relevant reference gases can be completely sealed, but alternative configurations are also possible, such as continuously flowing the mixture of known reference gases through the cuvette. The partial pressure of at least one gas of interest and the length of the cuvette are selected such that there is at least one absorption peak within the passband range of the optical filter, which has sufficient optical density to be within the nonlinear absorption range, as defined by the Lambert-Beer equation.To improve performance, the temperature of at least one cuvette can be known and / or controlled. Light emanating from at least one cuvette is transmitted through an optical element 704 sealing one side of a sample cell 705 capable of containing a sample gas or calibration gas containing at least one gas of interest. The other side of the sample cell is sealed by another optical element 706 and has a gas inlet 707 and a gas outlet 708. Both optical elements on either side of the cell are transparent to the wavelength range of interest and may include windows, reflective and refractive optics. Light emanating from the cell is focused by a concentrator 709, which may include optical elements such as windows, lenses, optical passband filters, reflective and refractive optics, and then measured by at least one suitable detector 710, which may be a pyroelectric body, thermoelectric pile, microthermometer, solid photovoltaic or photoconductive detector. Note that the location of the at least one optical passband filter and / or at least one cuvette shown in the example still has the same function even if it is located at the detector end rather than the light source end. Wavelength range selection can also be performed using alternative appropriate methods, such as diffraction gratings. When analyzing two or more gases of interest, at least two separate detectors with at least two separate wavelength selection means can be used, or a single detector can be used by manually or automatically selecting the wavelength range alternately, such as by using a piezoelectric device or a rotating wheel. In this case, compared to a GFC, there is only one optical path and no moving parts when analyzing one gas of interest or when using multiple detectors. For simplicity, the following example will only describe one gas of interest. Now, consider the effect of applying a fluctuating magnetic field to the cuvette 711 and / or sample cell 712. The magnetic field can be moved by mechanical means such as a motor or a piezoelectric device, or it can be formed electromagnetically by the use of a solenoid and / or a permanent magnet. Because this technique involves alternating repetitions of the signal, sensitivity can be increased by using frequency domain analysis such as synchronization detection, (fast) Fourier transform, harmonic analysis, and amplitude modulation analysis.

[0085]

[0082] First, we consider the situation when a magnetic field is applied to the cuvette. When the magnetic field is switched off and on, the detector detects the transmitted light from the cuvette and sample cell of the “gas of interest” in the absence of a magnetic field. r The signal corresponding to the magnetic field, and the light from the "measurement" cuvette in a magnetic field state, where one or more lines of gas of interest are split by the magnetic field and sample cell. m The two will be examined alternately. Therefore, the measurement and the reference are optically identical optical paths, except for the splitting of absorption lines due to the presence of a magnetic field. For convenience, the reference signal is given an electronically or digitally applied gain G o It can have, and the gain value is the amplified signal G when calibrated using nitrogen in the sample cell. o l r However, when the inside of the cell is nitrogen, l m It is set to be equal to G. o It should be noted that the value differs from conventional GFC measurements because absorption still occurs in the split absorption line. When the gas of interest is in the sample cell, the measured signal decreases by an amount related to the concentration in the sample cell, but the reference signal does not decrease as much because the cuvette causes some absorption in the gas of interest corresponding to the nonlinear absorption region of the Lambert-Beer behavior (i.e., it approaches saturation). The signal S can be defined as follows:

number

[0086]

[0083] Using such a system, highly accurate measurements with improved drift characteristics can be obtained. Since there are no moving parts, the lifespan and reliability should also be improved.

[0087]

[0084] Differential gain G o If cross-interference is caused by splitting lines resulting from the presence of a magnetic field that overlaps with the absorption line(s) of a background cross-interferor, this can be compensated for by modulating the range of the resulting splitting using two or more magnetic field strengths. The occurrence of cross-interference can then be detected and corrected using a system of equations or other appropriate method, with the detected strengths of the lines corresponding to the strengths of these two or more different fields.

[0088]

[0085] This can be explained by considering the following.

number

number

number

number

number

[0089]

[0086] When there are two or more sources of mutual interference, a greater magnetic field strength can be applied to define the compensation algorithm.

[0090]

[0087] Alternatively, the effects of mutual interference can be neutralized by adding the mutual interference source(s) as background gas(s) to the cuvette of the gas of interest, or as packing material to a second cuvette in the optical path, in order to minimize the effects of the presence of the mutual interference source(s) in the sample gas, and absorbing the radiation corresponding to the wavelength of the mutual interference source(s).

[0091]

[0088] Similar detection and / or correction methods can be used for temperature and / or line broadening (pressure or collision). This is because the effect of detection and / or correction methods on absorption lines may differ depending on whether or not a magnetic field is present. For example, if temperature and pressure are determined and corrected separately, the presence of broadening due to collisions caused by background gas can also be corrected.

[0092]

[0089] Note that another version of the above is possible, in which the sample cell is switched on or off with a magnetic field instead of a cuvette of the gas of interest. In this case, the detector signal looks the same even when there is no gas of interest in the sample cell. That is, ideally G o = 1. When the gas of interest is present in the sample cell and the magnetic field is off, the absorption in the cuvette is so strong that there is almost no change in the detector signal. However, when the gas of interest is present in the sample cell in the presence of a magnetic field, the splitting line of the sample gas is different from the splitting line in the cuvette, resulting in extra absorption. This has the same advantages as having no moving parts and excellent common-phase rejection.

[0093]

[0090] A hybrid version is also possible in which the magnetic field can be applied separately to both the sample cell and the cuvette, and the concentrations measured using the above method are compared to each other in order to detect and correct for in-phase effects such as mutual interference.

[0094]

[0091] While the above examples in this patent specification describe gases using a magnetic field, it should be noted that any suitable one or more gases, and an electric field instead of a magnetic field (for example, using ammonia or water), or a combination of electric and magnetic fields, can also be used. The term “suitable gas” here refers to a gas in which at least one spectral absorption line within the wavelength range of interest is freed from absorption degeneracy in the presence of a magnetic and / or electric field, resulting in the splitting of the absorption line(s), which can help analyze absorption features that are not visible in the absence of a magnetic and / or electric field.

[0095]

[0092] Another exemplary method for use in an absorption spectroscopy system allows for the measurement of changes in transmittance at one or more wavelengths as a function of the intensity of the applied field, or as a function of the polarization of the electromagnetic radiation source relative to the applied field, and for determining specific isotopologue or isotopomer properties of the species being measured, such as determining pressure, temperature, or concentration.

[0096]

[0093] The target gas species may consist of a set of elements with different isotopic masses such that the spectrum resulting from a single chemical species is composed of multiple distinct spectra from different isotopologues and / or isotopomers. In some specialized applications, detecting isotopic composition is useful to determine, for example, whether the target species originates from a biosource or from a particular geographical location or historical period. The differences in spectra resulting from different isotopologues depend on the differences in the masses of the isotopes involved in the associated vibrational modes. Similarly, the profiles of energy level splitting that occur with respect to the applied field differ slightly between different isotopologues and / or isotopomers. 15 When spectral transitions arising from isotopologes and / or isotopomers overlap and cannot be uniquely identified due to the absence of a field, the relative contributions of different species can be elucidated by monitoring the splitting of line(s) with respect to the applied field at one or more wavelengths.

[0097]

[0094] Now, considering the effect of the electric field applied to the sample cell (712) or cuvette (711), the effect is different from that of the magnetic field because it perturbs the electric dipole of the molecule. This further changes the electric dipole moment, which is the cause of virtually all infrared transitions. Changing the electric field around the molecule not only changes the final dominance of the light-absorbing molecule, but also splits the individual energy levels of the molecule. Modulation can take many forms, such as a square wave, a sinusoidal wave, or any other arbitrary form including a modulated and possibly a steady-state component. In Figure 12, the splitting of several water absorption lines is shown as a function of the applied electric field. Some lines are split over a larger range due to the specifics of the quantum states involved. The spectral overlap between the sample spectrum (at zero field) and the spectrum obtained at high potentials has a complex, nonlinear, and non-monotonic dependence on the intensity of the applied field.

[0098]

[0095] This complex behavior is also shown in Figure 13, which illustrates the effect of applying an electric field, which is sinusoidally modulated between -10 and 10 MV / m at 50 kHz, to a 1 cm long cuvette containing 1% water at 0.1 atmospheres and 296 K. Light passes through this cuvette (711), then through a 1 m sample cell (712) without a field, and reaches an infrared detector (710).

[0099]

[0096] The Stark effect depends on the magnitude, not the sign, of the applied field, regardless of the presence of gas in the sample region (712). Therefore, the total transmission through such a system is primarily modulated at 100 kHz, i.e., twice the excitation frequency (2f). While the signal can be interpreted in the time domain or the frequency domain, the modulation of the desired signal at twice the excitation frequency means that frequency-based detection means, such as synchronous detection or Fourier transform techniques, have the advantage of separating the desired signal from the signal associated with the first excitation frequency, thereby improving the signal-to-noise ratio. Adding 20 ppm and 40 ppm of water to the sample cell results in the 2f (and other harmonic) modulation remaining, but further absorption of light by the gas being measured reduces the overall transmission of light to the detector (710). Subtracting the average centered signal obtained with 0 ppm of water in 712 from the average centered signals obtained with 20 ppm and 40 ppm of water reveals that the difference between these modulated signals is proportional to the concentration of water in the sample. The difference between the (average-centered) signals obtained at 0 MV / m and 10 MV / m is plotted as a function of H2O concentration in Figure 14, demonstrating that the water concentration in 712 can be easily determined by this method.

[0100]

[0097] It is worth emphasizing that the resulting signal is normalized by the DC offset required to average-center the trace, thereby minimizing the effects of the aforementioned variations in the light source and detector. As an alternative to the above normalization, the beam leaving the cuvette can be split and the signal passed to another detector. Thus, the signal received at 710 can be normalized without relying solely on the DC offset at the detector. The drawback of this method is that without a DC offset signal, it becomes more difficult to normalize changes in intensity passing through the sample cell, for example, due to alignment shifts. On the other hand, splitting the beam in this way allows for separate determination of the gas concentrations in the cuvette and provides warnings about problematic system changes to the optical arrangement configuration that may affect the measurement, whether due to leakage or otherwise.

[0101]

[0098] In particular, when the absorption of the sample gas is being considered, the effect of the oscillating electric field on the cell's transmittance is nonlinear and complex, as shown in Figures 12 and 13. Perturbations to the resulting waveform resulting from the change in the overall overlap between the absorption lines of the sample and the cuvette can be easily extracted continuously by recording the frequency spectrum of the resulting detector signal. In a live measurement system, it is possible to perform a "rolling FFT" on a portion of the detector's output stream that has been tapered, cosine (Tukey) time-windowed, and mean-centered to enable streaming measurements. The results of applying the method shown in the trace in Figure 13 are shown in Figure 15. As the concentration of H2O in the sample cell increases from 0 to 100 ppm, the magnitudes of various frequency components increase and decrease (see Figure 16). The magnitude of the 100kHz (2f) frequency peak generated by this method increases by approximately 20% for every 100ppm of water added to a 1m sample cell (STP) compared to a 0ppm H2O measurement, while it decreases by approximately 10% for a 300kHz signal (6f).

[0102]

[0099] Note that the sum of the integrated absorptions, i.e., the transmitted signal, can be affected by the presence of an electric and / or magnetic field, so if the field is modulated with respect to time, a modulated signal may be observed even without the presence of a cuvette. This could mean, for example, that a very simple spectrometer consists of a steady-state light source that transmits light across the entire defined wavelength range (e.g., through the presence of an optical band-pass filter) into a sample cell where the electric and / or magnetic field is modulated throughout, and the light transmitted through the sample cell is detected by an optical detector. As discussed above, the electric field can have a significant effect on the electric dipole and thus the integrated absorption cross-section, but even a magnetic field can have a significant effect on the modulation, as the Lambert-Beer nonlinearity is not the same in the degenerate state (no field) and the non-degenerate state (when a field is applied). This type of configuration can, in some cases, achieve advantages over lasers, and can create low-cost sensors using very strong fundamental absorption wavelengths, otherwise requiring expensive lasers. Such configurations can also achieve advantages over current broadband sensors. The reason is that current broadband sensors typically use dual-wavelength detection to minimize the effects of variations in light source output, using either two separate detectors or a rotating wheel housing two separate passband filters. In this case, for example, the sensor may be solid or use a rotating permanent magnet, but it may be outside the optical path. Variations in light source intensity can be compensated for, for example, by normalizing the magnitude of the output from a steady-state signal or by a secondary detector, and by examining small changes between the two signals to indicate the concentration of the substance being measured.

[0103]

[0100] As already described herein, the technologies described herein can be implemented in a variety of ways. The foregoing disclosure is intended to include, but is not limited to, the systems, methods, and combinations thereof, as well as subcombinations thereof, as described below in exemplary implementations. Features of these various examples can be combined.

[0104]

[0101] A first exemplary method for gas detection and / or measurement in an absorption spectroscopy system includes transmitting electromagnetic radiation from at least one electromagnetic radiation source through a gas sample toward at least one detector; applying at least one of an electric field, a magnetic field, or an electromagnetic field to at least one section of the transmission path of the electromagnetic radiation transmitted between the at least one source and the at least one detector; monitoring the absorption of the electromagnetic radiation for at least one absorption wavelength or absorption wavelength range associated with at least one gas species by detecting the electromagnetic radiation transmitted without being absorbed using at least one detector; and analyzing the output signals from at least one detector to determine the presence of at least one gas species in the gas sample and / or measuring the parameters of at least one gas species. One or more electric fields or magnetic fields can be applied to a section of the absorption spectroscopy system that is separated from the gas sample but is in the transmission path of the electromagnetic radiation to modulate or suppress the absorption effect by the gas species in that section. Furthermore, or by alternative means, one or more electric or magnetic fields may be applied to the gas sample chamber by changing the modulation of the field over time, thereby modulating the transmission of electromagnetic radiation from either a tunable laser light source or a broadband light source (for example, using an optical band filter or diffraction grating).

[0105]

[0102] In the first example, the method may include applying different field modulations to multiple different sections of the transmission path of electromagnetic radiation. In the first example, at least one electric field, magnetic field, and / or electromagnetic field may be invariant with respect to time. Alternatively, at least one electric field, magnetic field, and / or electromagnetic field may change with respect to time. For example, at least one electric field, magnetic field, and / or electromagnetic field may be modulated at a fixed frequency, or at least one electric field, magnetic field, and / or electromagnetic field may be modulated at a variable frequency. In the exemplary method, a combination of invariant and changing fields is applied.

[0106]

[0103] In the first example, the method may include analyzing the effects of changing fields with respect to the output signal from at least one detector in order to identify and separate spectral artifacts from the absorption spectrum of at least one gas species. In one example, the spectral artifact to be identified is the result of absorption by an interfering substance or noise, and the method includes suppressing artifacts in the absorption spectrum for improved detection and / or measurement.

[0107]

[0104] In the first example, the method may include analyzing the output signals from the detector when an applied field is present and when an applied field is not present, and calculating the difference between the two output signals.

[0108]

[0105] In an exemplary method, at least a first electric field, magnetic field, or electromagnetic field is applied to a first section of the transmission path of electromagnetic radiation to modulate the spectral absorption by at least one gas species in the first section by shifting the quantum energy state transition of at least one gas species in the first section, and at least a second electric field, magnetic field, or electromagnetic field is applied to a second section of the transmission path of electromagnetic radiation, wherein the first and second fields are different from each other in order to separately modulate the spectral absorption by at least one gas species in the first and second sections.

[0109]

[0106] In the exemplary method, the parameter to be measured is the concentration of at least one gas species.

[0110]

[0107] In one example, this method includes supplying a purge gas to a section of an absorption spectroscopy system before applying an electric, magnetic, or electromagnetic field, and suppressing or modulating spectral artifacts caused by absorption by at least one gas species in the purge gas by controlling the quantum energy state transitions of at least one gas species in the purge gas by applying at least one electric, magnetic, or electromagnetic field to the section of the transmission path of electromagnetic radiation that is to be purged. In one example, the purge gas is air, and the at least one gas species to be detected and / or measured is oxygen.

[0111]

[0108] In one example, this method includes selecting at least one wavelength of electromagnetic radiation or a range of wavelengths of transmitted electromagnetic radiation by adjusting the solid-state laser by controlling the laser temperature and / or drive current, or by using one or both of the following: a bandpass filter, a diffraction grating, or a spectrometer.

[0112]

[0109] In one example, at least one electric field is generated by a voltage gradient between at least two electrodes. In another example, at least one magnetic field is generated by one or more permanent magnets. In yet another example, at least one magnetic field is generated by the movement of charge carriers, such as electrons, within a solenoid.

[0113]

[0110] In one example, at least one polarizer is used to polarize or filter electromagnetic radiation in a particular plane. An exemplary method includes applying a field with a plurality of different orientations of applied fields with respect to polarization to at least one section of the transmission path of electromagnetic radiation. An exemplary method includes applying fields having different orientations with respect to polarization to a plurality of different sections of the transmission path of electromagnetic radiation. An exemplary method includes using at least one polarizer to divide electromagnetic radiation into a plurality of separately polarized portions and oriented the plurality of separately polarized portions of electromagnetic radiation through a gas sample for detection by one or more detectors in the presence of at least one applied field. In an exemplary method, at least one polarizer comprises an optical element having an adjustable orientation for selectively polarizing incident electromagnetic radiation with respect to an applied electric, magnetic, or electromagnetic field. In one example, polarization involves partial reflection by an optical element, where a first portion of the electromagnetic radiation is transmitted along a first optical path, and a second portion of the electromagnetic radiation is reflected from the optical element and redirected to pass through a second optical path, and both portions of the electromagnetic radiation are detected simultaneously by a single or multiple detectors.

[0114]

[0111] In an exemplary method, the gas sample is housed in a sample chamber having at least one gas inlet and at least one gas outlet, and one or more optical elements on the wall of the sample chamber allow the wavelength of the relevant electromagnetic radiation to pass through to and from the sample chamber.

[0115]

[0112] In an exemplary method, the laser lock line is verified and / or calibrated using the application of at least one magnetic field, electric field, or electromagnetic field.

[0116]

[0113] An exemplary method includes determining the path length of an absorption spectroscopy system by measuring the ratio of a first detector output signal to a second detector output signal, wherein the first signal is obtained by the transmission of electromagnetic radiation through a gas sample in an electric, magnetic, or electromagnetic field, and the second signal is obtained by the transmission of electromagnetic radiation through a gas sample in the absence of an electric, magnetic, or electromagnetic field, or after the field has changed spatially and / or temporally, thereby facilitating accurate scaling of absorption when measuring the object being measured.

[0117]

[0114] An exemplary apparatus used for detecting and / or measuring a gas comprises: at least one electromagnetic radiation source for transmitting electromagnetic radiation through a gas sample toward at least one detector; at least one detector for monitoring the absorption of electromagnetic radiation for at least one absorption wavelength or absorption wavelength range associated with a gas species by detecting electromagnetic radiation transmitted without being absorbed; at least one field generator arranged to apply at least one of an electric field, a magnetic field, or an electromagnetic field to at least one section of the transmission path of electromagnetic radiation transmitted between the at least one source and the at least one detector; and a signal processor for analyzing the output signals from the at least one detector to determine the presence of at least one gas species in the gas sample or to measure the parameters of at least one gas species.

[0118]

[0115] An exemplary apparatus comprises a sample chamber for housing a gas sample, the sample chamber having at least one gas inlet and at least one gas outlet, and one or more optical elements on the wall of the sample chamber, the optical elements allowing the transmission of the wavelength of relevant electromagnetic radiation in and out of the sample chamber.

[0119]

[0116] In the exemplary apparatus, one or more optical elements include one or more windows, lenses, or passband filters.

[0120]

[0117] In the exemplary apparatus, at least one field generator is arranged to apply at least one magnetic field, electric field, and / or electromagnetic field across the sample chamber.

[0121]

[0118] The exemplary apparatus includes at least one gas-purged section of the apparatus in the transmission path of electromagnetic radiation, and a field generator is arranged to apply at least one magnetic field, electric field, and / or electromagnetic field across the gas-purged section of the apparatus.

[0122]

[0119] An exemplary apparatus comprises a sample chamber and a reference cuvette, the reference cuvette containing one or more known gas species, at least one of which is a gas species to be analyzed, the sample chamber is arranged to receive a gas sample to be analyzed, and at least one field generator is arranged to apply at least one magnetic field, electric field, and / or electromagnetic field across the cuvette and / or sample chamber.

[0123]

[0120] In the exemplary apparatus, the reference cuvette contains at least one isotopomer or isotopologue of a gas species.

[0124]

[0121] In an exemplary apparatus, at least one detector is arranged to detect electromagnetic radiation transmitted through the sample chamber and at least one reference cuvette, at least one magnetic field, electric field, or electromagnetic field is applied to the cuvette and / or sample cell, and a signal processor is arranged to analyze the output signals from at least one detector to compare the absorption by one or more gas species and / or one or more gas species isotopomers or isotopologues.

[0125]

[0122] In the exemplary apparatus, at least one field generator is configured to apply at least two different magnetic field strengths and / or electric field strengths to at least one section of the transmission path, and a signal processor is configured to generate a comparison signal using output signals from at least one detector obtained using the at least two field strengths.

[0126]

[0123] In an exemplary apparatus, the electromagnetic radiation source is a solid diode laser, the output wavelength of the electromagnetic radiation source is adjustable by controlling the temperature and / or current of the electromagnetic radiation source, and the detector is a solid photodiode.

[0127]

[0124] In the exemplary device, the signal processor is configured to compensate for the effects of optical interference by analyzing a first signal when a magnetic field, electric field, or electromagnetic field is applied, and a second signal when no such field is applied.

[0128]

[0125] In the exemplary apparatus, at least one electromagnetic radiation source is one of a laser, a light-emitting diode, an incandescent element, or a flashlight.

[0129]

[0126] In the exemplary apparatus, at least one detector is one of a solid photodiode, a photomultiplier tube, a mercury cadmium telluride (MCT) detector, a microthermometer, a radiation thermometer, or a thermoelectric pile.

[0130]

[0127] In one example, an absorption spectroscopy system used for detecting and / or measuring a gas comprises a sample chamber for housing a gas sample, the sample chamber having at least one gas inlet and at least one gas outlet, and one or two optical elements on the wall of the sample chamber, the optical elements enabling the transmission of electromagnetic radiation in and out of the sample chamber; at least one electromagnetic radiation source arranged to transmit electromagnetic radiation through the gas sample toward at least one detector; at least one detector for monitoring the absorption of electromagnetic radiation for at least one absorption wavelength or absorption wavelength range associated with a gas species by detecting electromagnetic radiation that has been transmitted without being absorbed; at least one field generator arranged to apply at least one electric field, magnetic field, or electromagnetic field to at least one section of the transmission path of electromagnetic radiation transmitted between the at least one source and the at least one detector; and a signal processor for analyzing at least one output signal from the at least one detector to determine the presence of at least one gas species in the gas sample or to measure the parameters of at least one gas species.

[0131]

[0128] An exemplary absorption spectroscopy system comprises means for measuring changes in the transmittance of electromagnetic radiation through a gas sample at one or more wavelengths, as a function of the intensity of the applied field or as a function of the polarization of the electromagnetic radiation source relative to the applied field, and for determining the properties of a specific gas species and / or the isotopologue or isotopomer of the species being measured, such as determining pressure, temperature, or concentration.

[0132]

[0129] An exemplary method used in an absorption spectroscopy system includes determining the properties of a specific gas species and / or a specific isotopologue or isotopomer of a particular gas species and / or species under test, such as by measuring the change in transmittance of electromagnetic radiation through a gas sample at one or more wavelengths as a function of the intensity of the applied field or as a function of the polarization of the electromagnetic radiation source relative to the applied field, and determining pressure, temperature, or concentration.

[0133]

[0131] 1. Gordon, I. E. et al. The HITRAN2016 molecularspectroscopic database. J Quantitative Spectrosc Radiat Transf 203, 3-69(2017). 2. Rothman, L. S. et al. HITEMP, the high-temperature molecularspectroscopic database. J Quantitative Spectrosc Radiat Transf 111, 2139-2150 (2010). 3. Ngo, N. H., Lisak, D., Tran, H. & Hartmann, J.-M. An isolatedline-shape model to go beyond the Voigt profile in spectroscopic databases andradiative transfer codes. J Quantitative Spectrosc Radiat Transf 129, 89-100 (2013). 4. Rautian, S. G. & Sobel’man, I. I. The effect of collisions on theDoppler broadening of spectral lines. Uspekhi Fizicheskih Nauk 90, 209-236 (1966). 5. Galatry, L. Simultaneous Effect of Doppler and Foreign Gas Broadeningon Spectral Lines. Phys Rev 122, 1218-1223 (1961). 6. European Patent Application Publication No. 2955495, Kovacich, R.P.,Alizadeh, B, Gaskin, I., Hobby, J. & Lopez, M. ‘Method and system forcorrecting incident light fluctuations in absorption spectroscopy’. 7. US Patent Application Publication No. US 2008 / 0204720 A1, Howell, J.‘Two line gas spectroscopy calibration’. 8. European Patent Application Publication No. 3171159, Alizadeh,B.,Hobby, J., Lopez, M. & Gaskin, I. ‘Method and system for reduction ofinfluence of baseline distortion in absorption spectroscopy measurements’. 9. Ishak, B. Spectra of atoms and molecules (3rd edition), by Peter F.Bernath. Contemp Phys 58, 1-1 (2017). 10. Ramos, A. A. & Bueno, J. T. Theory and Modeling of the Zeeman andPaschen‐Back Effects in Molecular Lines. Astrophysical J 636, 548-563 (2006). 11. Quack, M. Angular Momentum: Understanding Spatial Aspects in chemistryand Physics. Von R. N. Zare. Wiley, New York 1988. XI, 349 S., geb.. - ISBN 0‐471‐85892‐7. Angew Chem-ger Edit 101, 959-959 (1989). 12. Brown, J. M. & Carrington, A. Rotational Spectroscopy of DiatomicMolecules. 177-301 (2003)doi:10.1017 / cbo9780511814808.007. 13. Western, C. M. PGOPHER: A program for simulating rotational,vibrational and electronic spectra. J Quantitative Spectrosc Radiat Transf186, 221-242 (2017). 14. European Patent Application Publication No. 2927668, Kasuitsich, V.& Lopez, M. Attachment and alignment device for optical sources, detectorsand analysers, and modular analysis system. 15. Batz, L., Ganz, S.,Hermann, G., Scharmann, A. & Wirz, P. The measurement of stable isotopedistribution using Zeeman atomic absorption spectroscopy. Spectrochimica ActaPart B Atomic Spectrosc 39, 993-1003(1984).

Claims

1. 1. A method of gas detection and / or measurement in an absorption spectroscopy system, comprising: transmitting electromagnetic radiation from at least one electromagnetic radiation source along a transmission path within a measurement volume of the absorption spectroscopy system, through the gas sample, and towards at least one detector; applying at least one of an electric field, a magnetic field, or an electromagnetic field to at least one section of the absorption spectroscopy system, the section being separated from the gas sample but within the transmission path of the electromagnetic radiation transmitted between the at least one source and at least one detector, thereby modulating absorption by at least one gas species in the at least one section; monitoring absorption of electromagnetic radiation by the gas sample in the measurement volume for at least one absorption wavelength or range of absorption wavelengths associated with a quantum energy state transition of at least one gas species by detecting unabsorbed transmitted electromagnetic radiation using the at least one detector; analyzing an output signal from the at least one detector to determine the presence of at least one gas species in the gas sample and / or measure a parameter of the at least one gas species; A method comprising:

2. 10. The method of claim 1, comprising applying different respective fields to a plurality of different sections of the absorption spectroscopy system along the transmission path of the electromagnetic radiation to modulate absorption separately in the different sections.

3. The method of claim 2, further comprising the step of applying at least one of an electric field, a magnetic field, or an electromagnetic field to the measurement volume.

4. The method of claim 1 , wherein at least one electric field, magnetic field, and / or electromagnetic field is time invariant.

5. The method of claim 1 , wherein at least one of the electric, magnetic, and / or electromagnetic fields is time-varying.

6. The method of claim 5 , wherein at least one of the electric, magnetic and / or electromagnetic fields is modulated at a fixed frequency.

7. The method of claim 6 , wherein at least one of the electric, magnetic and / or electromagnetic fields is modulated at a variable frequency.

8. The method of claim 5 wherein a combination of constant and varying fields is applied.

9. 6. The method of claim 5, further comprising analyzing the effects of varying fields on the output signal from the at least one detector to identify and separate spectral artifacts from the absorption spectrum of the at least one gas species.

10. 10. The method of claim 9, wherein the identified spectral artifacts are the result of absorption by interfering substances or noise, and the method comprises suppressing the absorption spectral artifacts for improved detection and / or measurement.

11. 6. The method of claim 5, comprising analyzing output signals from a detector in the presence of an applied field and in the absence of the applied field, and calculating a difference between the two output signals.

12. applying at least a first electric, magnetic, or electromagnetic field to a first section of the transmission path of the electromagnetic radiation to shift a quantum energy state transition of at least one gas species in the first section, thereby modulating spectroscopic absorption by at least one gas species in the first section; applying at least a second electric, magnetic, or electromagnetic field to a second section of the transmission path of the electromagnetic radiation, the first and second fields being different from one another to separately modulate spectral absorption by at least one gas species in the first and second sections. The method of claim 1.

13. The method of claim 1 , wherein the parameter measured is the concentration of at least one gas species.

14. supplying a purge gas to a section of the absorption spectroscopy system, the gas purged section being separated from the gas sample in the measurement volume but within the transmission path of the transmitted electromagnetic radiation transmitted from the at least one source towards the at least one detector; suppressing or modulating absorption by at least one gas species in the purge gas by controlling quantum energy state transitions of the at least one gas species in the purge gas by applying at least one electric field, magnetic field, or electromagnetic field to a gas-purged section of the transmission path of the electromagnetic radiation; The method according to any one of claims 1 to 13, comprising:

15. 15. The method of claim 14, wherein the purge gas is air and the at least one gas species to be detected and / or measured is oxygen.

16. 10. The method of claim 1, comprising selecting at least one wavelength of electromagnetic radiation or range of wavelengths of electromagnetic radiation to be transmitted by one or both of tuning a solid state laser by controlling a temperature and / or a drive current of the laser, or using an optical bandpass filter, a diffraction grating, or a spectrometer.

17. The method of claim 1 , wherein the at least one electric field is generated by a voltage gradient between at least two electrodes.

18. The method of claim 1 , wherein the at least one magnetic field is generated by one or more permanent magnets.

19. The method of claim 1 , wherein the at least one magnetic field is generated by the movement of charge carriers, such as electrons, in a solenoid.

20. The method of claim 1 , wherein at least one polarizer is used to polarize or filter electromagnetic radiation in a particular plane.

21. 21. The method of claim 20, comprising applying a field to at least one section of the transmission path of the electromagnetic radiation, each of a plurality of different applied field orientations relative to the polarization.

22. 21. The method of claim 20, comprising applying fields having different orientations relative to the polarization to different sections of the transmission path of the electromagnetic radiation.

23. 21. The method of claim 20, comprising: splitting the electromagnetic radiation into a plurality of differently polarized portions using at least one polarizer; and directing the plurality of differently polarized portions of the electromagnetic radiation through the gas sample in the presence of the applied at least one field for detection with one or more detectors.

24. 21. The method of claim 20, wherein the at least one polarizer comprises an optical element having an adjustable orientation to selectively polarize incident electromagnetic radiation with respect to an applied electric, magnetic, or electromagnetic field.

25. 25. The method of claim 24, wherein the polarization comprises partial reflection by the optical element, a first portion of the electromagnetic radiation is transmitted along a first optical path, and a second portion of the electromagnetic radiation is reflected from the optical element and redirected to pass through a second optical path, and the two portions of electromagnetic radiation are detected simultaneously by a single detector or multiple detectors.

26. 10. The method of claim 1, wherein the gas sample is contained within a sample chamber having at least one gas inlet and at least one gas outlet, and wherein one or more optical elements in a wall of the sample chamber allow transmission of relevant wavelengths of electromagnetic radiation into and out of the sample chamber.

27. The method of claim 1 , wherein the application of at least one magnetic, electric, or electromagnetic field is used for verification and / or calibration of a laser lock line.

28. 2. The method of claim 1, comprising determining a path length of an absorption spectroscopy system by measuring a ratio of a first detector output signal to a second detector output signal, wherein the first signal is obtained by transmission of electromagnetic radiation through a gas sample in an electric, magnetic, or electromagnetic field, and the second signal is obtained by transmission of electromagnetic radiation through the gas sample in the absence of the electric, magnetic, or electromagnetic field or after the field has been spatially and / or temporally varied, facilitating accurate scaling of absorption when making measurements of interest.

29. An apparatus for use in detecting and / or measuring gases in an absorption spectroscopy system, comprising: at least one electromagnetic radiation source for transmitting electromagnetic radiation along a transmission path through a gas sample in a measurement volume of the absorption spectroscopy system toward at least one detector; at least one detector for monitoring absorption of electromagnetic radiation by the gas sample in the measurement volume for at least one absorption wavelength or range of absorption wavelengths associated with a quantum energy state transition of a gas species by detecting unabsorbed transmitted electromagnetic radiation; at least one field generator positioned to apply at least one of an electric field, a magnetic field, or an electromagnetic field to at least one section of the absorption spectroscopy system separated from the gas sample but within the transmission path of the transmitted electromagnetic radiation between the at least one source and at least one detector; a signal processor that analyzes an output signal from the at least one detector to determine the presence of at least one gas species in the gas sample or measure a parameter of the at least one gas species; An apparatus comprising:

30. 30. The apparatus of claim 29, comprising a sample chamber containing the gas sample, the sample chamber having at least one gas inlet and at least one gas outlet, and one or more optical elements in a wall of the sample chamber, the optical elements allowing transmission of relevant wavelengths of electromagnetic radiation into and out of the sample chamber.

31. 31. The apparatus of claim 30, wherein the one or more optical elements comprise one or more of a window, a lens, or a passband filter.

32. 30. The apparatus of claim 29, wherein at least one field generator is arranged to apply at least one magnetic, electric and / or electromagnetic field across the sample chamber.

33. An instrument as described in any one of claims 29 to 32, comprising at least one gas purged section of the instrument, the gas purged section being separated from the gas sample in the measurement volume but within the transmission path of the transmitted electromagnetic radiation, and a field generator arranged to apply at least one magnetic, electric and / or electromagnetic field across the gas purged section of the instrument.

34. 30. The apparatus of claim 29, comprising a sample chamber and a reference cuvette, the reference cuvette containing one or more known gas species, at least one of the gas species being a gas species to be analyzed, the sample chamber being arranged to receive a gas sample to be analyzed, and at least one field generator being arranged to apply at least one magnetic, electric, and / or electromagnetic field across the cuvette and / or sample chamber.

35. 35. The apparatus of claim 34, wherein the reference cuvette contains at least one isotopomer or isotopologue of a gas species.

36. 35. The apparatus of claim 34, wherein at least one detector is arranged to detect electromagnetic radiation transmitted through the sample chamber and at least one reference cuvette, and wherein at least one magnetic, electric, or electromagnetic field is applied to the reference cuvette and / or sample cell, and wherein the signal processor is arranged to analyze output signals from the at least one detector to compare absorption by one or more gas species and / or isotopomers or isotopologues of one or more gas species.

37. 30. The apparatus of claim 29, wherein the at least one field generator is configured to apply at least two different magnetic and / or electric field strengths to at least one section of the transmission pathway, and the signal processor is configured to generate a comparison signal using output signals from the at least one detector obtained using the at least two field strengths.

38. 30. The apparatus of claim 29, wherein the electromagnetic radiation source is a solid state diode laser, the output wavelength of the electromagnetic radiation source is tunable by controlling the temperature and / or current of the electromagnetic radiation source, and the detector is a solid state photodiode.

39. 30. The apparatus of claim 29, wherein the signal processor is configured to correct for effects of optical interference by analyzing a first signal with an applied magnetic, electric, or electromagnetic field and a second signal without the applied magnetic, electric, or electromagnetic field.

40. 30. The apparatus of claim 29, wherein the at least one electromagnetic radiation source is one of a laser, a light emitting diode, an incandescent element, or a flash lamp.

41. 30. The instrument of claim 29, wherein the at least one detector is one of a solid state photodiode, a photomultiplier tube, a mercury cadmium telluride (MCT) detector, a microcalormeter, a radiation thermometer, or a thermopile.

42. The absorption spectroscopy system for use in gas detection and / or measurement, comprising: a sample chamber containing a gas sample, the sample chamber having at least one gas inlet and at least one gas outlet, and one or more optical elements in a wall of the sample chamber, the optical elements allowing transmission of electromagnetic radiation into and out of the sample chamber; at least one electromagnetic radiation source positioned to transmit electromagnetic radiation through the gas sample in the sample chamber toward at least one detector; at least one detector for monitoring absorption by the gas sample in the sample chamber of at least one absorption wavelength or range of absorption wavelengths associated with a quantum energy state transition of a gas species by detecting unabsorbed transmitted electromagnetic radiation; a plurality of field generators positioned to apply at least one of an electric field, a magnetic field, or an electromagnetic field to each of a plurality of sections of the absorption spectroscopy system along a transmission path of the transmitted electromagnetic radiation between the at least one source and at least one detector; a signal processor for analyzing at least one output signal from the at least one detector to determine the presence of at least one gas species in the gas sample or to measure a parameter of the at least one gas species; 30. The apparatus of claim 29, comprising:

43. 1. An absorption spectroscopy system comprising means for measuring the change in transmission of electromagnetic radiation at one or more wavelengths through a gas sample as a function of the strength of an applied field or as a function of the polarization of an electromagnetic radiation source relative to said applied field, to determine characteristics of a particular gas species and / or isotopologues or isotopomers of a measured species, such as determining pressure, temperature, or concentration.

44. 1. A method for use in an absorption spectroscopy system, comprising measuring the change in transmission of electromagnetic radiation at one or more wavelengths through a gas sample as a function of the strength of an applied field or as a function of the polarization of an electromagnetic radiation source relative to said applied field, to determine characteristics of a particular gas species and / or particular isotopologue or isotopomer of the species being measured, such as determining pressure, temperature, or concentration.

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