Method, apparatus, and system for compact optical gas absorption measurement.

Abstract

An apparatus comprising a compact folded path cell for optical gas detection and / or measurement utilizing gas absorption spectroscopy. The apparatus includes an electromagnetic radiation source, a gas sample cell housing a reflector, and a detector for electromagnetic radiation. The source and detector are positioned between the reflector elements in a configuration that reflects the radiation away from the source and detector until the reflected radiation has a suitable optical path length, and then reflects the radiation towards the detector. Using spectroscopic analysis, the presence of at least one gas species in a gas sample can be determined and / or at least one parameter can be measured.

Description

[Technical Field]

[0001]

[0001] The present invention relates to gas absorption spectroscopy, and more particularly to tunable diode laser absorption spectroscopy (TDLS) and non-dispersive infrared spectroscopy. The present invention has applications in the detection and measurement of one or more species in a gas, such as those produced by artificial or natural processes, such as industrial, medical or physiological processes. [Background technology]

[0002]

[0002] An exemplary absorption measurement system consists of a combination of an electromagnetic radiation source such as a tunable laser source, e.g., 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. The radiation source emits an electromagnetic radiation beam that is focused on a detector, which may be a solid-state photovoltaic, photoconductive, photomultiplier tube, pyrometer, thermopile, or bolometer type detector. The substance to be analyzed is positioned between the electromagnetic radiation source and the detector, and as a result, the electromagnetic radiation incident on the detector can be modified (i.e., reduced by absorption) by its path through the substance. The modification of the electromagnetic radiation allows a signal processing system coupled to the detector to determine various parameters of the gas being measured. Such measurements can be performed over an in-situ gas sample measurement volume such as a process stack, or within a measurement gas sample cell, which is the subject of this specification. Figure 1 illustrates a basic extractive absorption analyzer, where 101 is an electromagnetic radiation source, 102 is a sample cell having transmission windows and gas inlets 103 and outlets 104 at each end, and 105 is a detector. A signal processing system 106 is used to process the detector signal and generate the concentration of the substance to be measured based on a calibrated algorithm. In some cases, the substance to be analyzed is a gas produced by industrial, medical, or natural processes, and the substance to be measured may be a parameter of one or more chemical species present in this gas. References to “substance to be measured gas” or “substance to be measured species” in this patent specification are intended to refer to a gas or gas species in which one or more parameters are measured or detected. “Substance to be measured” is the presence of a gas species or a measurable parameter of a gas species. Examples of substance to be measured species include, but are not limited to, gaseous water, O2, NO, NO2, CO, CO2, and hydrocarbons such as methane or ethane. These measurements are often used to optimize process efficiency, monitor and / or minimize the generation of pollutants and greenhouse gases, and monitor and / or optimize physiological well-being.The presence and / or fraction (concentration) of one or more of these target substances can be determined by absorption spectroscopy measurements using one or more TDLs. However, translating observed changes in electromagnetic radiation intensity into useful physical parameters such as concentration and temperature requires a series of assumptions about the target substance and measuring apparatus. 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, though not exclusively. The examples in this patent are given for the infrared region of the electromagnetic spectrum to obtain absorption spectroscopy measurements corresponding to specific molecular vibrational energy transitions, but the same principles may apply to other relevant wavelength regions and should not be considered limited to this spectral region. For ease of expression, throughout this patent specification, the terms electromagnetic radiation or light may be used interchangeably and should be interpreted as equally applicable to the ultraviolet, visible, infrared, or other relevant regions of the electromagnetic spectrum.

[0003]

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

[0004] In the operation of an exemplary broadband gas analyzer system, the radiation source emits over a relatively wide wavelength range (encompassing at least one relevant absorption line), even if limited by the use of a light passband filter or diffraction grating, and the throughput intensity is modified by absorption occurring simultaneously over one or more absorption lines of the gas species being measured. The combined effect of the spectral absorption line(s) can be detected by measuring the change in the light beam passing through the substance being analyzed due to the presence of the substance being measured.

[0005]

[0004] Absorption lines have characteristic "shapes" in wavelength space that depend on the intrinsic physical properties of the gas species (bond angle, bond length, electron number), as well as extrinsic physical properties (velocity, temperature) and environmental properties (pressure, ambient composition, etc.). The following paragraphs provide a brief overview of the mechanisms by which these shapes are generated and attempt to offer some insights into the current practical limitations on the recovery of useful properties such as concentration and temperature, where other perturbation factors are not clearly defined or cannot be defined.

[0006]

[0005] In the above context, an absorption "line" is an observable change in light transmission that coincides with a frequency (wavelength) interval that a photon can induce a gas molecule to transition from one quantum state to another. The probability that a photon with a particular wavelength and polarization will induce a quantum state transition is given by the absorption cross-section of the transition. The transition-dependent cross-section can be estimated from first principles, but in practice, it is usually measured experimentally with high precision.

[0007]

[0006] Since the interaction between light and matter is inherently quantum, the extent to which a gas species of measurement with a certain chemical identity absorbs light of a given frequency is determined not only by its number density in the measurement path but also by its precise quantum mechanical state. For any given gas species, there are numerous quantum states with spectroscopically different absorption characteristics.

[0008]

[0007] According to Heisenberg's uncertainty principle, it is not possible to precisely define the energy of a quantum state. This uncertainty causes blurring of the photon energy required to induce a transition between two states, preventing the spectral lines from becoming infinitely narrow. The statistical effects of various broadening mechanisms can be summarized in a frequency-dependent term called "spectral line shape."

[0009]

[0008] As mentioned above, the energy of a molecule's quantum state can be perturbed by its physical environment. For example, outside of a perfect vacuum, molecules collide with other particles. These collisions can induce changes in the molecule's quantum state, such as photons, that shorten the natural lifetime of the original state. In gaseous states, the effect of this collision spreading is largely similar to natural spreading, and therefore its effect is generally treated as a modification of Lorentz's full width at half maximum (FWHM) height. However, in contrast to natural line spreading, the pressure contribution has a more complex relationship with the absorption line shape. Pressure spreading, applicable only to gases for a given set of conditions, can be estimated by physically measuring the line shape and carefully subtracting other known spreading mechanisms. This is often impractical, and collision spreading is often cataloged only at "room temperature and atmospheric pressure" (NTP) in the absence of other gases. The obtained values ​​can then be fed into mathematical models, thereby extrapolating line widths corresponding to different conditions.

[0010]

[0009] Due to the thermal motion of the gas being measured, its constituent molecules 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 compared to heavier molecules. Thus, the spread of heat has a positive relationship with temperature and an inverse relationship with molecular weight.

[0011]

[0010] From the above paragraph, in the most practical spectroscopic applications where temperature and pressure have a significant effect, the resulting transition profile will not have a shape that is entirely Lorentzian or Gaussian. For this reason, it is known to use the "Voigt" profile, which is a convolution of Lorentzian and Gaussian linear shapes.

[0012]

[0011] If the perturbation factors listed above are stable and there are no fluctuations in incident light intensity and measurement path length, it is possible to accurately determine, for example, changes in the volume density of the gas being measured in a simple manner. Such fluctuations can occur, for example, during thermal bending and mechanical vibration of the measurement chamber. Fluctuations in incident light intensity can be caused by many factors other than changes in the density of absorbing molecules. For example, fluctuations can be caused by inherent fluctuations in laser power, changes in ambient light intensity levels, and / or obscuration in the process sample stream which can be caused by any combination of dust, tar, corrosion, or mismatch of the light beam. In extraction or laboratory settings, such environmental factors can be limited, for example, by chemical and / or physical filtration to eliminate the presence of dust and / or other physical contaminants as well as undesirable chemical species such as water, or can be mitigated, for example, by compensating for or controlling ambient temperature and / or pressure. Even in this situation, compensation for light intensity fluctuations may still be desirable due to instability or drift of the light source (for example, as described in U.S. Patent No. 9546902). The inventors of this invention have provided a solution that is particularly well suited to inline extraction environments such as laboratories or equivalent environments, but it can also be used for field measurements of pipes or stacks.

[0013]

[0012] Due to spatial averaging, further sources of measurement uncertainty may exist. This type of uncertainty arises from the fact that the spectroscopic measurement described above reduces the state of a three-dimensional system to a one-dimensional transmittance value. This means that any variation over the path length is averaged out so that all spatial information is completely lost. Assuming that these parameters are not constant along the measurement path length, this can present significant challenges in recovering a useful signal, especially in field gas measurements.

[0014]

[0013] Direct and indirect cross-interference can also occur. This interference arises from the influence of the partial pressure of foreign gases on the measurement, either through the "direct" overlap of absorption lines within the wavelength range being measured, or through the "indirect" influence of foreign gases that collide with the target gas and alter the target gas absorption lines. The composition of the measurement stream is not precisely known, and if it is, the requirements of the measurement become invalid, and therefore, if the partial pressure of the gases spreading the foreign matter is unknown, the line shape produced by a certain amount of target gas can change unpredictably. Direct cross-interference, when caused by foreign gases, always results in some additional indirect cross-interference. Depending on the spectroscopic technique used, this can have a significant impact on the transition intensity being measured. For example, when wavelength-modulated spectroscopy (WMS) is used, the recovered line intensity depends on the ratio of the applied amplitude modulation to the transition linewidth. Therefore, indirect cross-interference requires a measurement technique used in this situation where the line shape is always measured and the variation in transition intensity is normalized. For example, any uncertainty in the linearity arising from electronic noise can be coupled to the measurement signal, impairing its accuracy and precision. Alternatively, measurements from secondary sensors can be used as the reference input, but uncertainty is still coupled to the measurement, and multiple sensors may be required to achieve complete coverage of the interference.

[0015]

[0014] Another potential cause of photodetector signal fluctuations not attributable to direct fluctuations in ambient light or laser output signal is the occurrence of constructive and destructive optical interference (etalons) that cause oscillations in the detector signal as the laser is scanned across the measurement wavelength range. Optical interference is present to some extent even in incoherent broadband light sources due to random effects, but the use of coherent laser light means that any reflection at any optical surface or interface along the optical path from the laser output to the detector surface (e.g., from surfaces / interfaces such as windows, lenses and reflective interfaces, but not limited to these) leads to the generation of reflected light with a phase difference compared to the incident light, and thus leads to optical interference in which the rays interact. This phase relationship between the reflected and incident light can change over time due to factors such as temperature, vibration and pressure fluctuations, as these factors can cause changes in physical dimensions, density or refractive index.

[0016]

[0015] The detector integrates this optical interference when generating the intensity signal. Because the phase difference varies with wavelength along the measurement path, the symptom of this optical interference (or etalon) is typically the generation of oscillations on the signal baseline as the laser output is scanned across the wavelength measurement range. These, combined with other distortions, cause measurement inaccuracies. The signal “baseline” is the signal that would be seen even if no absorption signal were present, in other words, the “zero absorption” signal. This baseline signal is superimposed on the actual absorption signal, if present. In an ideal world, the baseline is a straight line (a flat line centered at 0 in perfect conditions), but this is not achieved in practice. The baseline may not be perfectly flat across the scanning range and may have fluctuations and other distortions (or “noise”), which can be random or systematic in nature and may include the oscillations described above. These oscillations are sometimes called “striped” signals in the case of optical interference. Whatever the cause, the effects of these various distortions lead to increased uncertainty in the determination of one or more absorption signals, and therefore to increased uncertainty in the derived molecular density or concentration of the gas being measured. When the presence of indirect cross-interference necessitates measuring the linear shape in addition to the transition intensity, uncertainty is exacerbated because periodic etalon fringes can broaden or narrow the recovered signal.

[0017]

[0016] Methods to reduce such optical interference include reducing reflective or partially reflective surfaces in the optical path from the light source to the detector that may form an etalon, such as by minimizing the number of optical components, using wedge windows instead of parallel-plane windows, or using anti-reflective coatings optimized for the desired wavelength range. However, in practice, it is impossible to completely eliminate the effects of this interference by reducing reflective surfaces. When a multipath cell is used, interference is unavoidable because the beam path within the multipath cell always produces some amount of optical interference, which is usually important when the cell is used for trace-level measurements.

[0018]

[0017] Another method to reduce the effect of optical interference on the baseline is to measure and record a reference baseline when the object gas is not present. This reference baseline can then be subtracted from the live signal to generate a cleaner signal to process. While this may provide an immediate improvement in the uncertainty of object determination, it does not address oscillations on the baseline under changes in ambient conditions (especially temperature), and therefore the effectiveness of this technique is limited.

[0019]

[0018] Another method involves using a piezoelectric element or similar means to vibrate an active optical element such as a lens or mirror in the optical path. This continuously changes the optical path length and therefore has the effect of phase variation and the resulting optical interference. As a result, the periodic vibrations on the baseline are blurred or smoothed through the time-dependent integration of the formed interference fringes, and thus the overall effect is reduced. However, this adds complexity and cost and suffers from several problems inherent in the use of moving elements, such as shortened component lifespan and mechanical failure, and does not actually completely eliminate the problem. Furthermore, most piezoelectric elements require a sufficiently high voltage supply, which makes them unsuitable for operation in flammable hazardous areas.

[0020]

[0019] Another method takes advantage of the differences between the aforementioned distinct transition line shapes and the periodic intensity fluctuations resulting from optical self-interference. This can be done, for example, by least-squares fitting the recovered spectrum to a suitable basis vector that would be similar to the spectrum expected in the absence of interference. This method has the advantage that further basis vectors similar to the individual spectra of other cross-interfering gases in the measurement can be used. Alternatively, a similar procedure may be performed in the frequency domain using convolution with a suitable kernel function, such as described in U.S. Patent No. 10234378. However, these methods are limited in that they require assumptions about the transition line shapes. Deviations from expected values ​​will result in inaccurate measurements. For example, if direct cross-interference is present in the measurement stream that is not considered in the corrected basis set or frequency domain kernel, such techniques may negatively affect measurement accuracy. Furthermore, the effectiveness of such techniques is reduced if factors influencing the generation of optical noise differ significantly from expected values, such as the free spectral range of the resulting etalon fringes.

[0021]

[0020] A recent novel method (described in UK Patent Application Publication No. 2113699.9) involves applying electric and / or magnetic fields to modify the absorption line characteristics resulting from the Zeeman effect and / or Stark effect without altering the effects of optical interference. In this way, the baseline effect of optical interference can be estimated and / or reduced or eliminated.

[0022]

[0021] Under constant ambient conditions of pressure, temperature, and background gas composition, the specific intensity of electromagnetic absorption by a gas depends on the gas concentration, the fundamental properties of the gas (wavelength-dependent extinction coefficient), and the path length. The mathematical relationships between these properties are described by the Lambert-Beer law. When it is desirable to determine low gas concentrations, sensitivity to a particular gas can be increased by selecting strong absorption lines and / or long path lengths. However, if the absorption of light is too strong, such as in the case of high concentrations of the target gas and / or long path lengths, nonlinearity and / or absorption saturation may occur, and sensitivity will decrease with increasing concentration. Therefore, the required sensitivity (determining the wavelength and path length to be selected) depends on the required measurement range. The wavelength selected for excitation also has practical considerations such as the availability and cost of the excitation source and detector. For example, long-wavelength infrared lasers that may have stronger absorption (such as interband lasers or quantum cascade lasers) can be considerably more expensive than near-infrared lasers that operate using weaker harmonic absorption bands (such as vertical-cavity surface-emitting lasers (VCSELs) or dispersion feedback (DFB) lasers). Also, when longer wavelengths are selected for broadband measurements, infrared LEDs typically become more expensive and have lower output intensity. Once the excitation wavelength or wavelength range is selected, the path length is determined by the required measurement range. Long path lengths can be achieved simply by using longer sample cells, but this is (physically) impractical and can result in slower time responses due to the large cell volume, especially when the required path length is several meters or more. Many of these problems can be mitigated by using multipath or folded path cells such as heliot cells (Figure 2a), white cells (Figure 2b), or tuned optical cavities, which can significantly reduce the overall cell size. In Figure 2a, the electromagnetic radiation source 201 is collimated by a lens 202 and directed to the folded optical geometry 203 of the heliot cell. Inside this cell are two concave mirrors 204 for angling the beam by multiple folds to increase its path length. A detector 205 measures the transmitted radiation intensity.The gas exchange port 206 allows a sample or calibration gas mixture to enter and exit the cell. In FIG. 2b, the electromagnetic radiation source 207 is collimated by the lens 208 and directed towards the optical geometry 209 of the white cell. Inside this cell, a set of planar mirrors 210 is used to fold and steer the beam multiple times to increase the optical path length. The detector 211 measures the intensity of the transmitted radiation. The gas exchange port 212 allows a sample or calibration gas mixture to enter and exit the cell. In any of the above cases, the optical processing and / or focusing of the excitation beam is typically required for optimal functionality, requires custom optical design elements such as refractive and / or reflective elements, and precise alignment adjustments as part of the manufacturing process. High-performance, long-path-length multipass or folded-path cells require the use of low-temperature expansion coefficient materials and precise temperature control for the best performance. In addition, multipass cells and optical cavities can be very sensitive to vibration and contamination.

[0023]

[0022] Thus, even when using a multipass or folded-path absorption spectroscopy cell for the detection or measurement of gas species, several problems remain to be addressed. There may be a desire for an intermediate-length folded absorption path length in a more compact form to obtain some additional absorption benefit without the optical complexity and environmental sensitivity of a very long-path-length multipass cell. Conventional methods still typically require beam shaping and / or focusing optics with an individual optical adjustment (alignment or beam shaping) process for such a form.

Summary of the Invention

[0024]

[0023] The inventors of the present invention have determined that it is possible to provide a compact, folded-path, easily assembled device for measuring gas measurement objects that does not require individual optical adjustments and is resistant to vibration and contamination. A first device for use in gas detection and / or measurement using absorption spectroscopy is A gas cell having at least one gas exchange port, At least one electromagnetic radiation source arranged to transmit a divergent beam of electromagnetic radiation in a direction passing through the gas cell, At least one detector for detecting electromagnetic radiation incident on the detector, At least a first mirror and a second mirror arranged in the gas cell in a facing relationship, wherein at least the first mirror is a curved mirror, and the opposing mirror is arranged to reflect a beam transmitted through a folded optical path passing through the gas cell between at least one source and at least one detector, at least the first mirror and the second mirror; Comprising, The transmitted electromagnetic radiation is incident on the first surface region of the first mirror at a non-zero angle with respect to the direction perpendicular to the first surface region, and the transmitted electromagnetic radiation incident on the first mirror is reflected from the source towards the second mirror. Thus, at least one source is positioned at a position offset from the central optical axis passing through the center of curvature of the first mirror, and the second mirror is arranged to reflect the electromagnetic radiation towards the second surface region of the first mirror.

[0025]

[0024] At least one light source can be positioned between opposing mirrors. Positioning the light source between mirrors and arranging the components so that the folded path avoids the incidence of reflected light on the light source makes it possible to provide a compact optical device with a suitable path length for absorption spectroscopy. The use of curved mirrors and suitable positioning of the components can provide automatic focusing of the transmitted divergent beam toward the detector, enabling the use of low-cost light sources and low-cost manufacturing without the need for focusing lenses. This specification describes various examples of apparatus and systems for spectral absorption measurements. The inventors have determined that the apparatus can be implemented as a robust, potentially high optical throughput, lensless, compact, extended path length, autofocus, low-noise, and easy-to-assemble folded path optical cell for gas spectral absorption measurements. The inventors have determined that by selecting reflective surfaces and positioning them relative to the light source and detector, it is possible to use divergent or collimated light sources without expensive focusing lenses.

[0026]

[0025] An example of this is shown in Figure 3, and a second apparatus is provided for compact optical gas detection and / or measurement in an absorption spectroscopy system. The apparatus is A gas cell for containing a gas sample or calibration gas, comprising at least one gas exchange port and at least one optical element for enabling the transmission of electromagnetic radiation of a desired wavelength range into and out of the gas cell, A gas cell containing a gas sample and transmitting electromagnetic radiation to at least one divergent or collimated electromagnetic radiation source, Two or more mirrors arranged in a relationship opposite to each other, including at least one curved mirror positioned to reflect transmitted electromagnetic radiation toward a second mirror, the second mirror positioned to reflect electromagnetic radiation toward at least one curved mirror, and the two or more mirrors are positioned to reflect electromagnetic radiation toward at least one detector in a folded path through a gas sample such that transmitted divergent or collimated electromagnetic radiation converges toward at least one detector, A system comprising at least one detector that monitors the absorption of electromagnetic radiation at at least one absorption wavelength or wavelength range associated with at least one gas species by detecting transmitted electromagnetic radiation that is not absorbed, At least one analyzer for analyzing the output signal from at least one detector to determine the presence of at least one gas species in a gas sample and / or measure parameters, It is equipped with.

[0027]

[0026] In one example, at least one curved mirror includes at least one spherical or substantially spherical mirror, and the device is arranged to focus transmitted electromagnetic divergent or collimated electromagnetic radiation toward a detector. At least one curved mirror is arranged opposite to a second mirror to define the folded path trajectory of electromagnetic radiation transmitted through a gas sample contained in a gas cell. At least one spherical mirror (or curved mirror) may be provided as one or more separate mirror sections, each corresponding to a section of the same sphere but potentially separated from one another. A pair of separate sections of mirror is sufficient, as it is not necessary for the curved mirror to be a continuous mirror surface if the transmitted and reflected beams are incident on only a portion of the surface.

[0028]

[0027] If at least one electromagnetic radiation source is positioned at a distance from the spherical mirror that is approximately equal to half the radius of curvature of the spherical mirror, the divergent beam of electromagnetic radiation from the source incident on the spherical mirror is reflected as a substantially parallel beam. This can be reflected from a second planar mirror such that the reflected parallel beam is then incident on the spherical mirror a second time and then reflected toward the detector as a convergent beam. The detector can be positioned at a distance from the spherical mirror that is approximately half the radius of curvature of the spherical mirror. The second planar mirror can also be positioned at a distance from the spherical mirror that is approximately half the radius of curvature.

[0029]

[0028] In one example, the electromagnetic radiation trajectory follows a return path, and the return path is A step of directing the output from a divergent or collimated electromagnetic source to at least one spherical or substantially spherical mirror, The steps include reflecting electromagnetic radiation from a spherical or substantially spherical mirror onto a second mirror, which may be substantially flat or a cylindrical concave mirror, The steps include: reflecting electromagnetic radiation from a substantially flat or cylindrical concave mirror onto a spherical or substantially spherical mirror; The steps include reflecting electromagnetic radiation from a spherical or nearly spherical mirror to at least one photodetector, Provided by [company name].

[0030]

[0029] In the example of the first apparatus described above, as shown in Figure 16, the second opposing mirror may be a second spherical mirror having the same radius of curvature as the first spherical mirror and positioned at a distance from the first spherical mirror corresponding to their radii of curvature. In such an embodiment, a divergent beam of electromagnetic radiation from a source positioned at half the radius of curvature of the first mirror is reflected as a substantially parallel beam, and then the parallel beam of electromagnetic radiation is incident on the second mirror and reflected back as a focused beam focused at half the radius of curvature, which then diverges again before being incident on the first spherical mirror a second time. The first spherical mirror reflects this back as a parallel beam incident on the second spherical mirror, and the second spherical mirror reflects the radiation again so that it converges toward a focal point at half the radius of curvature from each mirror. This has the advantage of extending the optical path compared to the exemplary embodiment described above in Figure 3, but still allows a divergent beam of electromagnetic radiation from an inexpensive source to be automatically focused onto the detector by two opposing mirrors. This is shown in Figure 16, where the source 1601 and detector 1602 are positioned "back to back" so that the electromagnetic radiation is emitted toward the first mirror 1604 and the detected radiation is reflected toward the detector from the second mirror 1605.

[0031]

[0030] One or more spherical or substantially spherical mirrors may each include a segment of a sphere or multiple segments of the same sphere.

[0032]

[0031] In exemplary embodiments, at least one light source and at least one detector are mounted adjacent to a second mirror which is substantially flat or cylindrical concave. For example, the light source and the detector are substantially coplanar with each other and parallel to the plane of the substantially flat second mirror. An exemplary mounting is shown in Figure 3.

[0033]

[0032] In another exemplary embodiment that can be combined with the features of the above example, the optical path to be followed exhibits substantially central reflection and / or rotational symmetry between at least one light source and at least one detector, and substantially identical optical paths can be obtained by swapping the positions of at least one light source and at least one detector.

[0034]

[0033] This interchangeability of at least one light source and detector offers significant advantages in the design, assembly, and testing of the sensor. Examples of these advantages include a reduction in the number of unique parts, simplification of the stamping or molding process, easier assembly, and error-prevention assembly, especially in production environments.

[0035]

[0034] The inventors also envision that at least two folded path geometryes can be combined, as described in this patent specification. In some examples, two or more additional mirrors can be positioned in the optical path between the light source and the detector. In such combined systems, the focused light from the folded path geometry described above is presented as a divergent source that is supplied to another folded optical path geometry instead of reaching at least one detector. This extends the path length. Several different folded path geometryes and different orientations of the planes of the folded path cells relative to each other are possible, making it possible to achieve the entire required path length. Alternatively, a more compact version can be achieved by replacing the detector with a mirror to reflect the light to at least one additional optical system and positioning the detector to receive the light after it has been reflected by at least one additional optical system.

[0036]

[0035] Other features and functions may also be integrated into and around the cell to improve its optical performance, environmental stability and signal processing. These optional features and functions may include optical elements such as windows, lenses, mirrors, attenuators, optical bandpass filters, or reference cells for line locking and / or verification. Additionally, physical and spectroscopic features can be used to minimize stray light reflection, such as by using surface roughening and / or blackening, or to control and / or compensate for environmental factors, including gas flow, temperature and pressure. In some examples, flow and / or diffusion features (such as gas ports for flow-through and / or gas ports having diffusion exchange films, collectively referred to in this specification as “gas exchange ports”) as well as volume reduction features are used to reduce response time. In some examples, the application of electric and / or magnetic fields to the measurement cell and / or other regions, and / or path modulation are used to reduce the etalon effect.

[0037]

[0036] Another enhancement is to introduce a gel or other suitable material into the gas detection / measurement device, such that the refractive index of this gel substantially matches that of the optical element separating the light source from the measurement cell. The reason for adding this gel or other suitable material is to minimize dead space within the device, reduce the need to chemically scrub areas, and potentially provide a secondary barrier against gas intrusion in case the seal of the sample cell fails. This is particularly relevant to flammable and / or toxic gas mixtures, but also helps to address spectral interference and reflection losses / etalons that otherwise occur between the light source, detector and at least one optical element. Signal processing, including frequency domain, filtering, and averaging techniques, may also be suitably used.

[0038]

[0037] In the example of Figure 3, the radiation source (301) and detector (302) can be mounted on a common, coplanar surface (303), which may be a printed circuit board. Although the radiation source 301 in Figure 3 is schematically shown inside a container, the radiation source and detector may preferably be supplied in chip-on-board (COB) form and positioned near the inlet / outlet window 304 of the sample cell 307. Radiation from the collimated or divergent radiation source (301) passes through a first optical element (304), which may be at least one of a flat window, a wedge window, an attenuation window, or a bandpass filter. The radiation passes through the sample gas in the sample cell body (307) as it is reflected between a curved or spherical mirror (306) and a second mirror (305) in the cell, and then passes through a second optical element (304), which may be at least one of a flat window, a wedge window, an attenuation window, or a bandpass filter, to reach the detector (302). The sample gas enters and exits the main cell body through the inlet and outlet (308).

[0039]

[0038] In some exemplary embodiments, the detector (302) may be at the focal point of the optical geometry, but in other examples, it may be selected to be at an out-of-focus position. An out-of-focus position may be preferred to reduce optical saturation in the detector and to reduce tolerance requirements for positioning the detector (302).

[0040]

[0039] In the example in Figure 4, radiation from the source (401) enters the sample cell (405), is reflected by the first curved or spherical mirror (403) to the second mirror (407), returns to the first mirror (403), which then focuses the light as it exits the first cell (at the convergence point 408), and this then becomes the input to the second cell (409). Similarly, the light is reflected by the mirrors (404) and (407) in the cell (409) and focuses on the detector (402). The sample gas can pass through the cell via the inlet and outlet ports (406).

[0041]

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

[0042] [Figure 1] This shows the configuration of a conventional spectroscopic absorption gas analysis system for measuring extracted sample gases. [Figure 2a] This shows the configuration of a conventional spectroscopic gas analysis system with a folded path length achieved by using multiple reflections from a collimated light beam. [Figure 2b] This shows the configuration of a conventional spectroscopic gas analysis system with a folded path length achieved by using multiple reflections from a collimated light beam. [Figure 3] An exemplary spectroscopic gas analysis system using the present invention is shown. [Figure 4] An example of a spectroscopic gas analysis system using the present invention is shown, which increases the total absorption path length by using a combination of two or more folded path cells. [Figure 5a] The design considerations for spherical mirror geometric cell shapes are illustrated. [Figure 5b] The design considerations for spherical mirror geometric cell shapes are illustrated. [Figure 6a] This shows a reduced volume cell for faster time response without inserts. [Figure 6b] This shows a reduced volume cell for faster time response with an insert. [Figure 7a] The diffusion and flow-through design regimes of the sample cells are illustrated. [Figure 7b] The diffusion and flow-through design regimes of the sample cells are illustrated. [Figure 7c] The diffusion and flow-through design regimes of the sample cells are illustrated. [Figure 7d] The diffusion and flow-through design regimes of the sample cells are illustrated. [Figure 7e] The diffusion and flow-through design regimes of the sample cells are illustrated. [Figure 7f]The diffusion and flow-through design regimes of the sample cells are illustrated. [Figure 8] An exemplary embodiment of a spectroscopic gas analysis system having two radiation sources and two detectors is shown. [Figure 9a] The optical geometric shape of a single measurement is illustrated. [Figure 9b] Three independent measurements in a circular geometric shape are illustrated. [Figure 10a] The chip-on-board design is illustrated. [Figure 10b] The chip-on-board design is illustrated. [Figure 11a] A comparison between diffraction patterns generated by rectangular and circular apertures is illustrated. [Figure 11b] A comparison between diffraction patterns generated by rectangular and circular apertures is illustrated. [Figure 12] This shows a comparison between the normalized amplitudes of light fringes generated by circular and rectangular apertures. [Figure 13] This demonstrates the inclusion of wavelength-locked cells in the device. [Figure 14a] An example of a spectroscopic gas analysis system using the present invention is shown, in which a sample gas, purge gas, or reference gas is flowed through a dead space, or a scrubber or gel is applied to the dead space region of the source and / or detector. [Figure 14b] An example of a spectroscopic gas analysis system using the present invention is shown, in which a sample gas, purge gas, or reference gas is flowed through a dead space, or a scrubber or gel is applied to the dead space region of the source and / or detector. [Figure 14c] An example of a spectroscopic gas analysis system using the present invention is shown, in which a sample gas, purge gas, or reference gas is flowed through a dead space, or a scrubber or gel is applied to the dead space region of the source and / or detector. [Figure 14d]An example of a spectroscopic gas analysis system using the present invention is shown, in which a sample gas, purge gas, or reference gas is flowed through a dead space, or a scrubber or gel is applied to the dead space region of the source and / or detector. [Figure 15a] An example of a spectroscopic gas analysis system using the present invention is shown, in which an electric field and / or a magnetic field is applied to one or more regions. [Figure 15b] An example of a spectroscopic gas analysis system using the present invention is shown, in which an electric field and / or a magnetic field is applied to one or more regions. [Figure 16] An alternative embodiment of the optical geometry, in which the path length per cell length is longer, is illustrated. [Figure 17] Figure 16 illustrates the folded optical path of the transmitted divergent light beam when reflected within the gas cell, showing the light that converges to the detector. [Figure 18] The main physical structure of the exemplary apparatus is shown in Figures 16 and 17. [Modes for carrying out the invention]

[0043]

[0041] As described above, absorption spectroscopy is known for its use in gas analysis, including determining the presence of at least one specific gas species in a measurement volume and measuring parameters including the concentrations of individual gas species in a gas sample.

[0044]

[0042] As described in this patent specification, various physical design parameters can be used to assist in the design of optical cells for use in absorption spectroscopy. Non-zero path length (P) using spherical mirrors L An example of this is shown in Figures 5a and 5b. The total path length is shown by the dashed line. In this example, a roughly spherical mirror (M R The radius of curvature of ) corresponds to approximately half of the desired path length. The parameters used to describe the exemplary optical layout are given by the following equation for angles A from 0 to 90°, and are illustrated in Figure 5a.

number

number

number

number

[0045]

[0043] In the case of a spherical mirror with a narrow cross-section (high aperture) or low beam divergence, this may also be approximated by a cylindrical concave mirror or other curved mirror surface. Using a cylindrical concave mirror instead of a spherical mirror reduces manufacturing complexity and cost. Alternatively, a parabolic mirror surface may also be used.

[0046] Note that FIG. 5b is a central cross-section perpendicular to the plane of FIG. 5a. This indicates that the second mirror M2 should ideally be a curved mirror for focusing the reflected beam, such as a cylindrical concave mirror of radius (C R ).

Number

[0047] As described above, in certain examples, this cylindrical concave mirror may be approximated by using a plane mirror instead.

[0048]

[0045] The use of reflective optics is preferable to refractive optics for several reasons, including having higher optical throughput (higher transmittance) and being wavelength-independent (chromatic aberration), which is particularly important for modular systems for detecting many different gas species at different wavelengths. In principle, a cylindrical concave mirror should be used as the second (lower) reflective surface in Figures 5a and 5b to focus on the detector or an approximate spot near it, although a useful configuration can still be obtained by using a substantially flat second mirror instead, which is easier to manufacture and less expensive, as the light is still focused in one plane, especially when only small cross-sectional slice depths are used. The depth of the cross-sectional slice used (e.g., different options in Figure 6) is influenced by the required sample cell volume, the optical throughput efficiency, and mechanical considerations such as the available space and any multi-cell stacking requirements. Lower depths can reduce the cell flash time and improve the volume exchange time under the same conditions, either by flow, diffusion, or a combination, but depending on the output angle of the light source, the reduced solid angle of light output may be collected by the detector. Sometimes, counterintuitively, it may be desirable to use less efficient optical throughput, which requires amplified slight signal changes due to increased path length, but the unattenuated signal from, for example, a laser diode, LED, or incandescent light source may be too strong and saturate the detector signal, or the laser intensity may be too high to be used with a flammable gas mixture. Reducing the cell depth can be achieved by inherent physical design and / or, in some embodiments, by using an element inserted to reduce the cell volume. Figure 6 illustrates these concepts, with Figure 6a showing a cell of greater depth (603) where a light source (601) radiates a divergent light beam into a sample cell (606) through an optical element (602), and the beam is opened by the cell depth (603) before being reflected by a substantially spherical mirror (605). This has a relatively wide cross-sectional area (604) of the beam compared to Figure 6b (612).In Figure 6b, divergent light from the light source (607) passes through the optical element (608) and enters the sample cell (609), where it is opened to a smaller depth (610).

[0049]

[0046] The flash time of a sample cell is determined by the sample cell volume and the flow rate and / or diffusion rate of the sample gas, among other factors, but other factors such as surface shape, composition and roughness, and the flash path taken by the gas are also important. For flow regimes, faster flash times can be achieved if the entire volume is accessible to the flow and turbulence is also present. There are many possible flow regimes, including gas inlets and outlets from the same side or opposite sides, from the top or bottom, and / or combined sides, and Figures 7b to 7f illustrate some possible configurations. The size, shape and surface finish of the gas inlets and outlets can be optimized for a particular application. For example, if back pressure is required, the cross-section of the outlet may be selected to be smaller than that of the inlet. Conversely, if a small pressure drop across the cell is desired, a larger cross-section of the outlet can be selected. In the case of diffusion, for example, for a rectangular cross-sectional design where the cell length is longer than the depth, top and / or bottom diffusion designs provide a faster response because the diffusion rate is proportional to the cross-sectional area and inversely proportional to the diffusion depth, and possible configurations are illustrated in Figure 7a. In addition to the required flow / diffusion regime, the influence of the inlet / outlet size, position, and surface finish on the optical properties of the sample cell regarding its absorption and reflection properties should also be considered.

[0050]

[0047] Multi-gas measurements can also be performed using two or more lasers and / or detectors. In a preferred embodiment (Figure 8), at least two light sources (801) and two detectors (802) are mounted in the same plane and axis. Although the light sources 801 and detectors 802 are shown in a relatively large container, these components can be provided in a chip-on-board configuration with closer proximity via an access window 806. In this case, a divergent beam from the light source (801) passes through an optical element (806), is reflected by a spherical mirror (804) and a second mirror (803), passes through the second optical element (806), and is then focused on the detector (802). The wavelength of the light source is selected to correspond to the desired absorption wavelengths of two different objects to be measured. Similarly, the detectors are selected to be responsive at the desired wavelengths of the objects to be measured. Due to the optical properties of the cells, each light source focuses on its corresponding detector, as can be seen from the arrows in Figure 8 indicating the central beam trajectory. In some applications, depending on the size of the object being measured and the components and optics used, more than two matched pairs of light sources and detectors can be used. As shown in Figure 9, multiple light sources and detectors can also be used in a circular mirror configuration. This may be a preferred embodiment where many objects need to be measured simultaneously and / or sequentially in a compact configuration, and this also allows the use of a standard circular mirror optics rather than a rectangular mirror optics. To illustrate this principle, a single measurement is first considered, as illustrated in Figure 9a. A diverging beam from a light source (901) is reflected by a spherical mirror (904) and a second mirror (903) and focused onto a detector (902). The wavelength of the light source is selected to correspond to the desired absorption wavelength range of the object being measured. Similarly, the detector is selected to be responsive at the desired wavelength of the object being measured. The spherical mirror (904) consists of a cross-sectional slice of a substantially spherical mirror (905). The dimensions of this cross-sectional slice (904) can be selected according to the beam divergence, path length, and aperture required for the application, and can also be selected to be rectangular.For multiple measurements, the first spherical mirror cross-sectional slice (907) and the second spherical mirror (906) may be selected to have a circular geometric shape. This allows for multiple measurements to be performed using multiple light sources (901) and detectors (902), with each coincident pair on the same plane and axis behaving as the coincident pair in Figure 9a.

[0051]

[0048] In some preferred embodiments, signal processing can be performed using analog and / or digital electronic equipment, including the use of a multiplexed ADC and / or processor.

[0052]

[0049] The mirror is made of machined and / or molded metal, glass or polymer, and may be polished as needed, and may have a reflective coating and / or protective coating such as gold. Constructive and destructive interference effects (etalons) can occur when the light from the light source is less than the total solid angle reflected by the substantially spherical mirror, so it may be important to suppress stray light reflections from being collected by the detector, especially with coherent light sources such as lasers. Suppression of these stray light reflections can take the form of random surface roughening and / or associated surface blackening (optically absorbing coating) to break down specular reflection. Any such applied optically absorbing coating or material should ideally be chemically compatible with the gas sample it is in contact with and be substantially a perfect light absorber in the optical wavelength range used. Alternatively, in some preferred embodiments, for example, in the case of a broadband light source (e.g., a non-coherent LED or incandescent lamp), stray light reflections reaching the detector may actually be useful in increasing the overall optical throughput and improving signal-to-noise ratio, and therefore reflection suppression is not necessary, and / or these stray light reflections may even be enhanced by applying a reflective layer to at least one surface in the sample cell, such as a gold layer.

[0053]

[0050] Any interaction with at least one optical element or reflective feature, such as an attenuator, passband filter, window, lens, polarizer (for use when not all laser output is inherently polarized), or reflective surface, can cause etalon formation. Generally, to minimize etalon formation, the number of optical elements should be kept to a minimum, although there are always some elements or features, such as a light source and / or detector and a window for light entering and leaving the sample cell. In some applications where stray light reflection needs to be minimized, as discussed in the previous section, the formation of such etalons can be minimized by the use of anti-reflective coatings and / or angled and / or wedge windows. In addition, dimensional changes can cause etalon shifts and thus affect the signal. This can be reduced by the use of materials with a low coefficient of thermal expansion, such as Invar, and / or by using a temperature-controlled cell. Using a temperature-controlled cell and / or pre-equilibrium for the sample gas brings the inflowing gas into equilibrium with the cell temperature, improving signal stability.

[0054]

[0051] The size and temperature variations of the etalon can be reduced by using at least one path length modulator. At least one modulator may be used at different locations in the system, depending on the location of the etalon-generating feature and the overall optics-mechanical arrangement, among other considerations. The modulator may be a solid-state device such as a piezoelectric device, whose dimensions can be changed by the application of a voltage, although the magnitude of the voltage should be considered for potentially flammable mixtures. Alternatively, the modulator may be an electromechanical device, such as a voice coil configuration combined with a permanent magnet, in a design similar to a speaker or electromechanical vibrating element. A mechanical bend, such as a spring or elastic polymer or foam, may be used to act as a director and damping element. If a foam is used, a sealed cell format may be preferably used to modify the physical properties of the bend, such as density and / or elastic properties, without entraining the sample gas. In some embodiments, path length modulation may be preferably applied to a substantially spherical mirror slice cross section (306) because it has less impact on the focus position in the detector than when a substantially flat or concave mirror (305) is modulated. The frequency of any such modulation should take into account the functional scanning speed in the case of diode laser measurements, or the pulse rate in the case of LED or pulsed incandescent light sources, and the expected response time, so as not to adversely affect the measurement. The amplitude of the modulation should ideally be greater than the wavelength of the light used, but the frequency and amplitude may be selected theoretically and / or empirically to give the desired performance and / or lifetime of the modulation element.

[0055]

[0052] The novel optical design described in this patent does not require a lens mounted near a light source such as a laser diode. For example, in most conventional laser optics, the lens is generally designed to be mounted together with the laser diode metal can package, or in close proximity to the laser diode can window. The novel design described in this patent eliminates the need for any special metal package for the laser diode, although standard metal sealed diode packages with flat, angled and / or wedge windows can still be suitably used in this device. However, this is a significant advantage that allows the use of a bare laser device within its inherent divergent cone in the optical chip format. Using a chip-on-board (COB) format for laser devices has several advantages, including cost reduction, less packaging material, lower etalon, higher light transmission, and significantly reduced heating and / or cooling power required to maintain the laser chip at precise setpoint temperatures and tighter temperature control, due to lower thermal mass and higher heat transfer efficiency. Chip-on-board (COB) technology describes the mounting of a bare VCSEL or laser chip in direct contact with the (copper) surface of a substrate or PCB (Figure 10). Among the advantages of COB are compactness, the provision of the best thermal coupling of the laser (1001) to a thermoelectric cooler (TEC) (1005), and the elimination of any light fringes formed inside the conventional metal can window enclosure of the laser diode. The COB process consists of three main manufacturing processes. The first is die mounting or “die attach” (1003), which consists of applying a special conductive adhesive to fix the chip directly to the PCB substrate (1004). The second is the “wire bonding” (1002) process, which makes an electrical connection between the laser chip and the PCB pads. In some embodiments, the third process is “encapsulation” (1009), which consists of supplying a very thin layer of clear epoxy or gel over the die and wire bond. Ideally, the encapsulating material has a refractive index that matches the optical element (1008), which may be one or more of a window, an attenuator, or a bandpass filter.The heat generated by TEC(1005) is dissipated by a suitable heat sink(1006). Due to the small size of the laser chip and its direct thermal contact with the PCB copper area, a significant reduction in the amount of TEC power required to maintain the laser chip at the desired setpoint temperature is achieved. In addition, the remarkably low thermal capacity of the bare chip allows for very rapid and precise thermal adjustment of the laser temperature and its wavelength.

[0056]

[0053] The above section described the advantages and embodiments of chip-on-board for laser diode light sources, but similar preferred embodiments can use chip-on-board diode lasers, LED light sources, and / or solid-state detectors.

[0057]

[0054] When designing the optomechanics of the sample cell and associated optical system, there are two important considerations to take into account. 1-Optomechanics should ideally provide increased path length while having a small sample flash volume for fast response times. 2-Optomechanics, when used with diverging coherent light sources such as laser diodes, should produce low levels of light fringes.

[0058]

[0055] Previously, a geometry of an optical cell has been disclosed that still provides an increase in path length while eliminating the need to use a lens to collimate the laser light source. Due to the absence of a lens, the diverging light cone of the laser light source can intersect well with the gas cell wall. This aperture of the light cone of the coherent light source results in the formation of light fringes. The mathematical analysis described in this section shows that when the coherent light source is apertured, a rectangular geometry of the gas cell plane may be preferable to a conventional tubular shape due to a significant reduction in the resulting light fringes.

[0059]

[0056] Conventional tubular gas cells with optical windows and gas ports at both ends are commonly used in many spectroscopic applications. However, the geometric shape of a planar rectangular gas cell has significant practical advantages when interfaced with a diverging coherent light source such as a laser diode. When the diverging optical cone of a laser light source intersects with the wall of the gas cell, an aperture is formed. Here, we discuss the optical properties of circular apertures versus rectangular apertures, particularly in relation to light fringes.

[0060]

[0057] Using Fourier transform theory, the Fraunhofer diffraction pattern (far-field diffraction) from a rectangular aperture and the relationship between the size of the diffraction pattern and the size of the aperture can be calculated.

[0061]

[0058] From Figure 11a, if the object is a rectangular slit with width a in the x direction and width b in the y direction, and this aperture is irradiated by a plane wave with perpendicular incidence and the amplitude is within the plane of the aperture, the rectangular aperture transmission function t(x,y) is given by the following.

number

[0062] Since the aperture is two-dimensional, a two-dimensional Fourier transform is used, and the amplitude transmission function is separable in x and y. The diffraction amplitude distribution from a rectangular aperture is simply a one-dimensional transform performed separately for the x and y dimensions, where λ is the wavelength of light. The diffraction amplitude at distance z under the Fraunhofer approximation is as follows:

number

[0063] Therefore, the diffraction pattern from a rectangular aperture is described by the sinc function. The intensity distribution of Fraunhofer diffraction produced by a rectangular aperture is as follows:

number

[0064]

[0059] In the case of a circular aperture (an example of which is shown in Figure 11b): Using the transmission function and its Fourier transform of a circular aperture of diameter D, the equation for the diffraction amplitude can be derived at distance z under the Fraunhofer approximation of the circular aperture. The diffraction pattern from the circular aperture is described by a Bessel function, which describes the well-known Airy rings at the observation surface.

number

[0065]

[0060] To perform a comparison between rectangular and circular apertures, plots of normalized intensity of diffraction amplitude can be used from equations 13 and 14 (Figure 12). As can be seen from Figure 12, when the a / b ratio is at its optimal value, the fringes from the rectangular aperture are significantly lower than those from the circular aperture with a similar overall cross-sectional area. The actual dimensions selected for a given embodiment depend on this plus many other factors, but this analysis can provide a useful guide to optimal cell design.

[0066]

[0061] In a preferred embodiment of the TDLS measurement system, the laser diode temperature is controlled by a thermoelectric cooler (TEC), and temperature feedback is provided by a temperature sensor such as a thermistor, resistance thermometer (RTD), or thermocouple. Both the laser temperature and current are electronically controlled to enable scanning across the desired gas absorption line. The unique optical system described in this patent focuses the laser beam, traversed through the gas cell, onto a detector through an optical element. The detector output, incorporating a photodetector and amplifier, is used with real-time signal processing software that determines the true gas concentration by utilizing a second harmonic signal, as well as its unique absorption shape characteristics such as height and width. As described in U.S. Patent No. 10,234,378, the measured signal can be correlated or convolved with a kernel function selective for the effects of predicted signal distortion to mitigate the effects of variations and other distortions on the absorption signal baseline, thereby reducing uncertainty in the determination of the object(s) being measured.

[0067]

[0062] The stability of the scanning current and the characteristics of the laser diode are of paramount importance to the wavelength stability of TDLS measurements. In the case of electronic equipment or laser diode drift over time, it is important that the measurement not only remains "locked" to the desired absorption line, but also that it is possible to generate a diagnostic report on the degree of this drift as a measure of preventive maintenance. A simple technique is to enable an algorithm that detects the position of the gas absorption second harmonic peak by continuously fine-tuning the setpoint temperature of the laser diode and actively maintains this position in a feedback loop. However, this technique assumes that the process gas flowing through the cell always contains some desired gas, which generates a measurable second harmonic peak. In reality, such an assumption cannot be made. Real processes can be very variable and, over long periods of time, may not contain the desired gas, or worse, may contain a gas with adjacent interfering absorption lines. For this reason, the equipment is ideally fitted with an onboard "wavelength reference" device, which in a preferred embodiment constantly monitors the actual spectral second harmonic signal from a known reference gas that is always present regardless of process variations. Ideally, this reference gas may be the primary gas of interest or another surrogate gas having an absorption line nearby. Due to practical cost and size constraints, this reference device should be as compact and low-cost as possible. For example, in this figure (Figure 13) of a preferred embodiment of a TDLS instrument, a divergent beam from a light source (1301) passes through an optical element (1304), is then reflected by a first mirror (1310) and a second mirror (1303), passes through a second optical element (1304), and is then focused on a detector (1302). This detector (1302) is used for detecting the primary object to be measured. In a preferred embodiment, a small percentage of the light incident on the optical element (1304) in front of the detector (1302) is reflected onto a secondary detector (1308) mounted on a printed circuit board (1309) through a low-volume sealed gas capsule (cuvette) (1306) filled with a reference gas (1307) at a maximum concentration of 100%, which has a transmitting optical element (1305) up to the relevant wavelength range, in order to maintain line lock.To generate a detectable second harmonic signal, it is crucial that the reference gas in the reference cell has sufficient optical absorbance. This is achieved by a combination of sufficient path length and gas filling pressure. The dead space lies between at least one light source (1409) and / or at least one detector (1410) and at least one optical element (1406) on the sample cell (Figure 14). Where appropriate, the dead space may be filled with a surrogate gas or alternative gas having an absorption line located near at least one that is within the scanning range of the diode laser and ideally outside the absorption line of the gas of interest, and this method can be used to optionally implement wavelength locking.

[0068]

[0063] The dead space may, alternatively or additionally, contain high levels of interfering gas such that the absorption is in the nonlinear region of the Lambert-Beer absorption curve and the presence of the interfering gas in the sample reduces its effect on the measured signal. In some embodiments, strong magnetic and / or electric fields can be used to split the absorption lines of the gas of interest (Zeeman effect and Stark effect), thus obtaining wavelength lock with reduced cross-interference.

[0069]

[0064] A dead space (Figure 14) between at least one light source (1409) and / or at least one detector (1410) and at least one optical element (1406) on the sample cell can cause measurement uncertainty due to the presence of a target gas species or optical interferant. This interfering gas species may be present from the time of manufacture or due to diffusion from the surrounding environment and may be variable. This can be mitigated by several means, such as removing the optical element 1406 and allowing the sample gas to fill the dead space (Figure 14a), flushing the dead space with a non-optically absorbing gas such as nitrogen (Figure 14b), and / or chemical scrubbing of a specific gas or a number of specific gases (Figure 14c) (Figure 14). However, in certain cases, this dead space can also be suitably used to accommodate a lock gas, as described in the previous section. If a target gas is used, the signal offset caused by the presence of this reference gas can be subtracted from the measured signal. Refer to Figure 14 for a more detailed explanation of the above options. In Figure 14a, the optical element 1406 is removed to allow the sample gas to fill the dead space. This has the advantages of simplicity, reduced cost, longer path length, higher transmission, and reduced etalon, but it has the disadvantage of exposing the light source (1409), detector (1410), and other elements of the design to potentially harmful (e.g., corrosive and / or flammable) gases. However, in Figure 14b, the dead space is sealed by the optical element 1406 and purged with a gas that does not interfere optically. This has the advantage of eliminating measurement uncertainty, but it has the disadvantage of requiring a continuous supply of purge gas, which increases complexity and cost. In Figure 14c, a scrubber 1407 is used to remove interfering gases in the dead space. This has the advantage of not requiring a continuous supply of purge gas, but the scrubber may become saturated over time and require replacement, and the scrubber material should be selected according to the application, which increases complexity and cost.

[0070]

[0065] Alternatively, as shown in Figure 14d, the dead space may be filled with a gas-impermeable gel or other suitable material 1408, which is ideally substantially transparent to the desired wavelength range and has a refractive index that substantially matches the optical element materials of the light source 1409 and detector 1410, as well as the optical element 1406 of the cell. In addition, the properties of 1408 must be substantially insulating and substantially thermal insulating. The refractive index match minimizes stray light reflection and transmission loss and reduces etalon formation. The gel or other suitable material can also act as a secondary physical barrier against gas intrusion in the event of a failure of the sample cell optical seal. This may be particularly relevant for flammable and / or toxic gas samples. In a preferred embodiment, the gel or other suitable material 1408 can be injected / poured or placed into the dead space by suitable means to completely fill the gap between the optical element of the light source, the detector, and the gas sample optical element 1406. In preferred embodiments, when a gel or other suitable material is injected into a dead space, its viscosity should be selected to allow for complete flow access to avoid the formation of any bubbles or voids. This viscosity can be controlled by composition and / or temperature. Additionally, minimizing (bubble) formation can be enhanced by the use of vacuum during gel preparation and / or injection and / or gel setting. Flexibility within the gel structure reduces the likelihood of crack formation due to aging or temperature cycling. The presence of bubbles in the gel can degrade performance due to scattering, absorption, and etalon formation.

[0071]

[0066] As described above, a magnetic field and / or an electric field may be applied to the dead space (see Figure 15a) and / or the sample volume (see Figure 15b). In Figure 15a, a divergent beam from the light source (1501) passes through the optical element (1504) into the sample cell (1506), where it is reflected by the first (1505) mirror and the second mirror (1503), and then focused onto the detector (1502) through the second optical element (1504). If the sample gas is present in the dead space (1508) when the beam passes through the dead space between the light source (1501) and the optical element (1504) and between the second optical element (1504) and the detector (1502), beam absorption may occur, potentially leading to measurement uncertainty. The presence of a magnetic and / or electric field within this dead space 1508 can induce the splitting of these absorption lines by the Zeeman effect and / or Stark effect, thereby reducing measurement uncertainty as the gas in the sample cell does not undergo similar splitting of lines. This reduction in measurement uncertainty can be achieved using a constant magnetic and / or electric field, or, in some embodiments, a modulated magnetic and / or electric field.

[0072]

[0067] In the case of Figure 15b, this uses the Zeeman effect and / or the Stark effect to induce absorption line splitting, but in this case the sample cell gas is subject to these effects.

[0073]

[0068] In the case of a modulated field, comparing the signals with and without the field applied may improve the detection of the object being measured because the etalon effect in any of the cells is reduced.

[0074]

[0069] In some embodiments, the features of 15a and 15b can be combined into a single device.

[0075]

[0070] The inventors anticipate that there are potentially many different embodiments using the optical design principles described in this patent to form a compact folded-path spectroscopic cell. For example, Figure 16 illustrates an embodiment in which the path length per cell length is longer. This embodiment achieves improved path length by simplifying the design and construction compared to a modular system comprising two of the aforementioned structures (in the embodiment of Figure 4). A divergent beam from the light source (1601) passes through the first optical element (1603) and enters the sample cell (1606). Inside the sample cell, multiple reflections occur between the first mirror (1604) and the second mirror (1605), as shown in Figure 16. In such a simplified embodiment, the light source and detector can be positioned back-to-back within a common housing 1609 (see Figure 18), and the mirrors (1604) and (1605) are identical cross-sectional slices of a spherical section. The exit beam passes through a second optical element (1603') and is incident on a detector (1602). Optionally, a wavelength-locking cell (1610 in Figures 17 and 18) may be included, preferably positioned at a location (1607) where a local focal point is formed, as described in the previous section, and the optical elements may be used to redirect a small portion of the beam through the optionally positioned wavelength-locking cell. All the foregoing descriptions relating to the potential features and benefits of alternative embodiments apply equally to this embodiment or similar embodiments.

[0076]

[0071] Figure 17 illustrates the folded path of the transmitted divergent light beam as it is reflected within the gas cell of Figure 16, showing the light that converges to the detector. The housing, shown as turret 1610, can accommodate a wavelength-locked cell and / or optical filter. This folded path shows how the reflected divergent beam passes through the cell in a symmetrical path such that all the light has substantially equal path lengths.

[0077]

[0072] Figure 18 shows the main physical structure of the exemplary apparatus according to Figures 16 and 17, including housings 1609 and 1610, light source 1601 and detector 1602, and mirrors 1604 and 1605.

[0078]

[0073] In some embodiments, the light source and / or detector are mounted separately, and electromagnetic radiation is conducted to and from the device using at least one optical fiber cable. This may have advantages when temperature and / or electromagnetic interference may make direct coupling impractical.

[0079]

[0074] The following are examples of apparatus for optical gas detection and / or measurement. Features of these various examples can be combined.

[0080]

[0075] A first compact device for optical gas detection and / or measurement in an absorption spectroscopy system is provided. A gas cell 307 for containing a gas sample or calibration gas, comprising at least one gas exchange port 308 and at least one optical element 304 for enabling the transmission of electromagnetic radiation of a desired wavelength range into and out of the gas cell, At least one divergent or collimated electromagnetic radiation source 301 for transmitting electromagnetic radiation through a gas sample contained in a gas cell 307) toward at least one detector 302, Two or more mirrors 305, 306 arranged in a relationship opposite to each other, including at least one curved mirror 306 arranged to reflect transmitted electromagnetic radiation toward a second mirror 305, the second mirror 305 being arranged to reflect electromagnetic radiation toward at least one curved mirror, and the two or more mirrors 305, 306 are arranged to reflect electromagnetic radiation toward at least one detector 302 in a folded optical path through a gas sample, such that transmitted divergent or collimated electromagnetic radiation is reflected toward at least one detector 302, A detector 302 monitors the absorption of electromagnetic radiation at at least one absorption wavelength or wavelength range associated with at least one gas species by detecting transmitted electromagnetic radiation that is not absorbed, At least one analyzer for analyzing the output signal from at least one detector to determine the presence of at least one gas species in a gas sample and / or measure parameters, It is equipped with.

[0081]

[0076] In an exemplary apparatus, the folded optical path through the gas sample is substantially symmetrical with respect to the central optical axis or the center point between the opposing mirrors, and the folded optical path has substantially equal path lengths with respect to electromagnetic radiation transmitted between the source and the detector and reflected by the mirrors.

[0082]

[0077] An exemplary apparatus for gas detection and / or measurement using absorption spectroscopy is: A gas cell 1606 having at least one gas exchange port 1608, At least one electromagnetic radiation source 1601 is positioned to transmit a divergent beam of electromagnetic radiation in the direction of passing through the gas cell 1606, At least one detector 1602 for detecting electromagnetic radiation incident on the detector, At least a first mirror 1604 and a second mirror 1605 are arranged substantially symmetrically within the gas cell in a relationship of facing each other, wherein at least the first mirror is a curved mirror, and the opposing mirrors are arranged to reflect a divergent beam transmitted through a folded optical path through the gas cell between at least one source and at least one detector such that the reflected beam passes through the gas cell in a substantially symmetric path, the reflected beam has substantially equal path lengths, and is focused toward at least one detector, Equipped with, An apparatus in which transmitted electromagnetic radiation is incident on a first surface region of the first mirror 1604 at a non-zero angle with respect to a direction perpendicular to the first surface region, and at least one source is positioned offset from the central optical axis passing through the center of curvature of the first mirror such that transmitted electromagnetic radiation incident on the first mirror is reflected from the source toward the second mirror.

[0083]

[0078] The offset source may be located between the first mirror and the second mirror (as shown for example in Figures 16, 17 and 18).

[0084]

[0079] Substantially equal optical paths of electromagnetic radiation in a reflected beam can be achieved by a device having reflection symmetry, as shown in the examples in Figures 3, 7-8 and 13-16. The first and second mirrors can have a common central optical axis passing through the center of curvature of the first mirror (see Figures 3, 7-8 and 13-16), and the transmitted beam follows a folded optical path that is substantially symmetric about this central optical axis. In Figure 16, the light source 1601 and detector 1602 are shown larger than typically required and are positioned within a larger housing. In an optimally compact absorption device, the light source is provided as a chip-on-board (COB) implementation, with the light source positioned opposite the beam convergence point (shown as the dotted circle 1607). In that arrangement, the light source 1601 and convergence point 1607 can each be positioned at a distance from the two mirrors corresponding to half the radius of curvature of the mirrors. As a result, the diverging beam follows a symmetric folded path, collimated by the first mirror 1604, then reflected by the second mirror 1605 to converge toward point 1607, then diverging again and being reflected again by the second surface region of the first mirror 1604 to be collimated again. Finally, the beam is reflected by the second reflection region of the second mirror and converges toward detector 1602.

[0085]

[0080] As an alternative to the above example, the folded optical path may include a system having substantially two or more devices as described above to provide a longer optical path length. Such an arrangement is schematically shown in Figure 4. Each of the two devices is substantially symmetrical about its respective central axis, and the combined system has substantially rotational symmetry about the beam convergence point shown in the dotted circle 408. In Figure 4, the light source 401 is shown in a container or support structure, which is larger in the figure than is typical. In an optimally compact absorption device, the light source may be provided as a chip-on-board (COB) implementation with the light source closer to the inlet window to the gas measurement cell than schematically shown in Figure 4. In a symmetrical arrangement, the light source and the two convergence points (shown in the dotted circle 408 and closer to the detector) are at the same distance from their respective curved mirrors, which is also a feature of the optimal COB implementation of the device in Figure 16.

[0086]

[0081] In a second example of the apparatus, at least one curved mirror 306 includes at least one spherical or substantially spherical mirror, and the apparatus is arranged to focus transmitted electromagnetic divergence or collimated electromagnetic radiation toward the detector 302.

[0087]

[0082] In a third example of the apparatus, at least one electromagnetic radiation source 301 is positioned at a distance from the spherical mirror 306 that is approximately equal to half the radius of curvature of the spherical mirror, such that the divergent beam of electromagnetic radiation from the source incident on the spherical mirror 306 is reflected as substantially parallel beams.

[0088]

[0083] A fourth example corresponding to the third apparatus described above further comprises a second planar or concave mirror 305 positioned opposite the spherical mirror such that a parallel beam is reflected from the second mirror, incident a second time on the spherical mirror 306, and then reflected toward the detector 302 as a converged beam, the detector 302 being positioned at a distance from the spherical mirror 306 that is about half the radius of curvature of the spherical mirror 306.

[0089]

[0084] In the fifth example corresponding to the fourth apparatus described above, the second mirror 305 is also positioned at a distance of about half the radius of curvature of the spherical mirror from the spherical mirror 306.

[0090]

[0085] In the sixth exemplary apparatus, the electromagnetic radiation trajectory follows a return path, and the return path is The steps include directing the output from the divergent or collimated electromagnetic source 301 to at least one spherical or substantially spherical mirror 306, The steps include reflecting electromagnetic radiation from a spherical or substantially spherical mirror 306 onto a second mirror 305, which may be substantially flat or concave; The steps include reflecting electromagnetic radiation from the second mirror 305 onto a spherical or substantially spherical mirror 306, The steps include reflecting electromagnetic radiation from a spherical or substantially spherical mirror to at least one photodetector 302, Provided by [company name].

[0091]

[0086] In the exemplary apparatus, the spherical or substantially spherical mirror 306 includes a segment of the same sphere or multiple segments of the same sphere.

[0092]

[0087] In the exemplary apparatus, at least one radiation source 301 and at least one detector 302 are mounted on a mount 303 which is substantially coplanar with each other and parallel to the plane of a substantially planar mirror, or perpendicular to a plane perpendicular to the center of a concave second mirror 305.

[0093]

[0088] The exemplary apparatus has substantially central reflection and / or rotational symmetry between at least one radiation source 301 and at least one detector 302.

[0094]

[0089] An exemplary system for absorption spectroscopy comprises the apparatus according to the above example, combined with two or more additional mirrors positioned in the optical path between the source and the detector.

[0095]

[0090] In the exemplary apparatus, at least one optical element has a window, which constitutes both an inlet window and an outlet window.

[0096]

[0091] In an exemplary apparatus, at least one optical element comprises at least one inlet window and at least one outlet window, the inlet window being separate from the outlet window.

[0097]

[0092] In an exemplary device, the window is a wedge window and / or an attenuation window and / or a bandpass filter.

[0098]

[0093] In the exemplary apparatus, one or more windows are mounted at a non-zero angle to a substantially flat mirror or a cylindrical concave mirror.

[0099]

[0094] In the exemplary apparatus, one or more windows are mounted at the Brewster (polarization) angle.

[0100]

[0095] In the exemplary apparatus, at least one electromagnetic radiation source is a laser.

[0101]

[0096] In the exemplary apparatus, the laser is a tunable diode laser (TDL), and current and / or temperature are used to adjust the wavelength of the laser.

[0102]

[0097] In the exemplary apparatus, direct absorption spectroscopy is used to determine at least one parameter of at least one gas.

[0103]

[0098] In another example, wavelength modulation spectroscopy is used to measure at least one parameter of at least one gas.

[0104]

[0099] In another exemplary apparatus, at least one electromagnetic radiation source is a broadband source. In one example, the broadband source is either an incandescent light source or a light-emitting diode (LED).

[0105]

[0100] In the exemplary apparatus, at least one detector is a solid-state photoconductive, photovoltaic, photomultiplier tube, bolometer, or pyroelectric detector.

[0106]

[0101] In an exemplary apparatus, the inner surface of the sample cell is roughened and / or coated with an electromagnetic radiation absorbing layer to absorb electromagnetic radiation that may interfere with the signal.

[0107]

[0102] In the exemplary apparatus, at least one radiation source and at least one detector are mounted on the same printed circuit board (PCB). In one example, the PCB is mounted parallel to the second mirror.

[0108]

[0103] In one example, a gas contained in the space between the optical element and at least one electromagnetic radiation source and / or the space between the at least one optical element and at least one detector of electromagnetic radiation is used to provide a lock line and / or verification and / or calibration line for the gas to be measured.

[0109]

[0104] In an exemplary device, at least one bandpass filter is provided to limit the transmission bandwidth of electromagnetic radiation.

[0110]

[0105] In the exemplary apparatus, a magnetic field source is positioned across the sample cell and / or across the space between the optical element and at least one electromagnetic radiation source and / or across the space between at least one optical element and at least one detector to apply a permanent magnetic field and / or a transient magnetic field, and / or an electric field source is positioned to apply a permanent electric field and / or a transient electric field. In one example, the magnetic field source is at least one permanent magnet. In another example, the magnetic field source is at least one electromagnet. In one example, the magnetic field source is a combination of at least one permanent magnet and at least one electromagnet. In one example, the electric field is supplied by applying an electric field gradient between at least two electrodes.

[0111]

[0106] In the exemplary apparatus, the space between the electromagnetic radiation source and at least one optical element, and / or the space between the electromagnetic radiation detector and at least one optical element are sealed, flushed with a purge gas, and / or scrubbed with an arbitrary spectrally absorbing gas at the desired wavelength.

[0112]

[0107] In an exemplary apparatus, a spectroscopic measurement signal at twice the modulated excitation frequency is used to determine at least one parameter of at least one gas. In an exemplary apparatus for use in an absorption spectroscopy system, the spectroscopic measurement signal is processed in the frequency domain.

[0113]

[0108] In one example, the signal is convolved with a kernel function selected to minimize the effects of baseline noise.

[0114]

[0109] In an exemplary apparatus, at least one optical element may constitute one or more of a window, a refractive element, a reflecting element, a diffracting element, or an electromagnetic radiation passband filter.

[0115]

[0110] An exemplary apparatus for optical gas detection and / or measurement in an absorption spectroscopy system is: A gas cell (307) for containing a gas sample or calibration gas, comprising at least one gas exchange port (308) and at least one optical element (304) for enabling the transmission of electromagnetic radiation of a desired wavelength range into and out of the gas cell, A gas cell (307) contains a gas sample through which a divergent beam of electromagnetic radiation is transmitted, and at least one divergent electromagnetic radiation source (301) is transmitted. Two or more mirrors (305, 306) arranged in a relationship opposite to each other, including at least one curved mirror (306) arranged to reflect transmitted electromagnetic radiation toward a second mirror (305), the second mirror (305) being arranged to reflect electromagnetic radiation toward at least one curved mirror, and the two or more mirrors (305, 306) being arranged to reflect electromagnetic radiation toward at least one detector (302) in a folded optical path through a gas sample such that the divergent beam of transmitted electromagnetic radiation is focused toward at least one detector (302), A minimum one detector (302) monitors the absorption of electromagnetic radiation at at least one absorption wavelength or wavelength range associated with at least one gas species by the steps of detecting transmitted electromagnetic radiation that is not absorbed and incident on at least one detector, and generating an output signal indicating the absorption of electromagnetic radiation, At least one processor for analyzing the output signal from at least one detector to determine the presence of at least one gas species in the gas sample and / or measure parameters, It is equipped with.

[0116]

[0111] In one example, the opposing mirrors include two or more mirrors 305, 306 arranged in a relationship of opposing each other, and include at least one first spherical or substantially spherical mirror 306 having a first surface region located in the optical path of the transmitted divergent beam, the first mirror being located at a distance from the source that is shorter than the radius of curvature of the first mirror, and the first mirror being oriented such that the divergent beam is incident on the first surface region at a non-zero angle with respect to the radial direction of the first mirror. In one example, the first mirror is arranged to reflect the transmitted electromagnetic radiation toward a second mirror 305, the second mirror 305 is arranged to reflect the electromagnetic radiation toward a second surface region of the first curved mirror 306, and the two or more mirrors 305, 306 are arranged to reflect the electromagnetic radiation toward at least one detector 302 in a folded optical path through the gas sample such that the divergent beam of the transmitted electromagnetic radiation converges toward at least one detector 302.

[0117]

[0112] In an exemplary apparatus or system, the gas inlet is attached to a gas conduit and is arranged such that a sample gas flows in through at least one gas inlet and flows out through at least one gas outlet.

[0118]

[0113] In the exemplary apparatus or system, at least one gas inlet and at least one gas outlet consist of at least one diffusion element.

[0119]

[0114] In the exemplary apparatus or system, the same diffusion element is used to provide at least one gas inlet and at least one gas outlet.

[0120]

[0115] In an exemplary apparatus or system, a combination of direct flow and diffusion is used to pass the sample gas through at least one gas inlet and discharge it through at least one gas outlet.

[0121]

[0116] Another exemplary apparatus or system comprises two or more sources and / or detectors.

[0122]

[0117] Another exemplary apparatus or system comprises at least one auxiliary photodetector, wherein reflected light not on the principal light measurement path passes through at least one auxiliary optical element to at least one auxiliary photodetector for the purpose of obtaining line-lock and / or verification readings. In one example, the reflected light is light reflected from an inner or outer window or reflective element of the sample cell. In one example, the at least one auxiliary optical element is a cuvette containing the gas of interest and / or an optical filter.

[0123]

[0118] In one example, the sample cell is maintained at a controlled temperature and / or pressure.

[0124]

[0119] In the exemplary apparatus, at least one volume outside the gas cell is sealed and scrubbed to remove impurities, and / or purged with a non-optical absorption purge gas.

[0125]

[0120] In an exemplary device, the light source and / or detector are mounted separately, and electromagnetic radiation is conducted to and from the device using at least one light guide or fiber optic cable.

[0126]

[0121] In the exemplary apparatus, at least one space outside the gas cell is filled with an coherent optically absorbing gas.

[0127]

[0122] In the exemplary apparatus, at least one space outside the gas cell is filled with gel. In the exemplary apparatus, the gel has a refractive index that matches that of at least one optical element it is in contact with. In one example, the chemical and physical properties of the gel, as well as / or the application of reduced pressure, are used to minimize the presence of voids within the gel structure.

[0128]

[0123] In the exemplary apparatus, at least one light source is a bare chip mounted directly on the PCB. In one example, the chip is a diode laser or an LED.

[0129]

[0124] In the exemplary apparatus, stray light reflection from surfaces other than the first and second mirrors is used, reflection suppression is not used, and / or stray light reflection is enhanced, in order to increase the overall optical throughput and improve signal-to-noise ratio. In one example, stray light reflection enhancement consists of applying a reflective layer to at least one surface in the sample cell.

[0130]

[0125] In another example, an apparatus for optical gas detection and / or measurement for use in an absorption spectroscopy system, A gas cell (307) for containing a gas sample or calibration gas, comprising at least one gas exchange port (308) and at least one optical element (304) for enabling the transmission of electromagnetic radiation of a desired wavelength range into and out of the gas cell, A gas cell (307) contains a gas sample through which a divergent beam of electromagnetic radiation is transmitted, and at least one divergent electromagnetic radiation source (301) is transmitted. Two or more mirrors (305, 306) arranged in a relationship opposite to each other, including at least a first spherical or substantially spherical mirror (306) having a first surface region located in the optical path of a transmitted divergent beam, the first mirror being located at a distance from the source shorter than the radius of curvature of the first mirror, the first mirror being oriented such that the divergent beam is incident on the first surface region at a non-zero angle with respect to the radial direction of the first mirror, and the first mirror reflecting the transmitted electromagnetic radiation to the second mirror (306). 5) The second mirror (305) is positioned to reflect the electromagnetic radiation toward the second surface region of the first mirror (306), and the two or more mirrors (305, 306) are positioned to reflect the electromagnetic radiation toward at least one detector (302) in a folded optical path through the gas sample, such that the divergent beam of transmitted electromagnetic radiation is focused toward at least one detector (302), A minimum one detector (302) monitors the absorption of electromagnetic radiation at at least one absorption wavelength or wavelength range associated with at least one gas species by the steps of detecting transmitted electromagnetic radiation that is not absorbed and incident on at least one detector, and generating an output signal indicating the absorption of electromagnetic radiation, At least one analyzer for analyzing the output signal from at least one detector to determine the presence of at least one gas species in a gas sample and / or measure parameters, It is equipped with.

Claims

1. Apparatus for gas detection and / or measurement using absorption spectroscopy, A gas cell having at least one gas exchange port, At least one electromagnetic radiation source is arranged to transmit a divergent beam of electromagnetic radiation in the direction passing through the gas cell, At least one detector, for detecting electromagnetic radiation incident on the detector, At least a first mirror and a second mirror arranged in the gas cell in a relationship of facing each other, wherein at least the first mirror is a curved mirror, and the opposing mirrors are arranged to reflect the transmitted beam in a folded optical path through the gas cell between the at least one source and the at least one detector such that the reflected beam passes through the gas cell with substantially equal path lengths and is reflected toward the at least one detector, Equipped with, An apparatus in which at least one radiation source is positioned offset from the central optical axis passing through the center of curvature of the first mirror such that transmitted electromagnetic radiation is incident on a first surface region of the first mirror at a non-zero angle with respect to a direction perpendicular to the first surface region, and the transmitted electromagnetic radiation incident on the first mirror is reflected from the source toward the second mirror, and the second mirror is positioned to reflect the electromagnetic radiation toward the second surface region of the first mirror.

2. The apparatus according to claim 1, wherein the first and second mirrors of the curved surface are arranged to reflect the transmitted beam such that the reflected beam converges toward the detector.

3. The apparatus according to claim 1, wherein the offset position of the radiation source is located between the first mirror and the second mirror.

4. The apparatus according to any one of claims 1 to 3, wherein the first mirror and the second mirror are arranged so as to have a common axis of symmetry passing through the center of curvature of the first mirror, and the axis of symmetry is parallel to the central optical axis of the transmitted beam such that the transmitted beam is reflected in a folded optical path that is substantially symmetric about the common axis of symmetry.

5. The apparatus according to any one of claims 1 to 4, wherein the first mirror is positioned at a distance from the radiation source that is shorter than the radius of curvature of the first mirror.

6. The apparatus according to claim 5, wherein the at least one electromagnetic radiation source is positioned at a distance from the first mirror that is approximately equal to half the radius of curvature of the first mirror, such that the divergent beam of electromagnetic radiation from the source incident on the first mirror is reflected as substantially parallel beams.

7. The apparatus according to claim 6, wherein the second mirror is a planar or curved second mirror (305) positioned opposite the first spherical mirror such that the substantially parallel beam is reflected from the second mirror, incident a second time on the first spherical mirror (306), and then reflected toward the detector (302) as a converged beam, and the detector (302) is positioned at a distance from the first spherical mirror (306) that is about half the radius of curvature of the first spherical mirror (306).

8. The apparatus according to claim 7, wherein the second mirror is positioned at a distance from the spherical mirror that is approximately half the radius of curvature of the spherical mirror.

9. The apparatus according to any one of claims 1 to 8, wherein the first mirror comprises a plurality of separate surface regions of the same spherical surface.

10. The apparatus according to any one of claims 1 to 9, wherein the at least one radiation source (301) and the at least one detector (302) are mounted on a common substrate or submount (303) and are arranged substantially on the same plane as each other in a plane parallel to the plane of a substantially planar second mirror or perpendicular to a plane perpendicular to the center of a concave second mirror (305).

11. The apparatus according to any one of claims 1 to 10, wherein the transmitted beam has substantially central reflection and / or rotational symmetry such that the transmitted beam follows substantially equal optical path lengths between the at least one source (301) and the at least one detector (302).

12. The apparatus according to any one of claims 1 to 11, combined with two or more additional mirrors positioned in the optical path between the radiation source and the detector.

13. The apparatus according to any one of claims 1 to 12, further comprising at least one optical element having an inlet window and an outlet window for electromagnetic radiation to enter and exit the gas cell.

14. The apparatus according to claim 13, wherein the at least one optical element comprises at least one inlet window and at least one outlet window, and the inlet window is separate from the outlet window.

15. The apparatus according to claim 13 or 14, wherein the window is a wedge window and / or an attenuation window and / or a bandpass filter.

16. The apparatus according to any one of claims 13 to 15, wherein one or more windows are mounted to a substantially planar second mirror, or to a direction perpendicular to a plane perpendicular to the center of a cylindrical concave second mirror, at a non-zero inclination angle.

17. The apparatus according to claim 16, wherein one or more of the windows are mounted at a Brewster (polarization) angle.

18. The apparatus according to any one of claims 1 to 17, wherein the at least one electromagnetic radiation source is a laser.

19. The apparatus according to claim 18, wherein the laser is a tunable diode laser (TDL), and current and / or temperature are used to adjust the wavelength.

20. The apparatus according to claim 19, wherein direct absorption spectroscopy is used to determine at least one parameter of at least one gas.

21. The apparatus according to claim 19, wherein wavelength modulation spectroscopy is used to measure at least one parameter of at least one gas.

22. The apparatus according to any one of claims 1 to 21, wherein the at least one electromagnetic radiation source is a broadband source.

23. The apparatus according to claim 22, wherein the broadband source is either an incandescent light source or a light-emitting diode (LED).

24. The apparatus according to any one of claims 1 to 23, wherein the at least one detector is a solid-state photoconductive, photovoltaic, photomultiplier tube, bolometer, or pyroelectric detector.

25. The apparatus according to any one of claims 1 to 24, wherein the inner surface of the sample cell is roughened to absorb electromagnetic radiation and / or coated with an electromagnetic radiation absorbing layer to mitigate potential interference with the signal.

26. The apparatus according to any one of claims 1 to 25, wherein the at least one radiation source and the at least one detector are mounted on the same printed circuit board (PCB).

27. The apparatus according to claim 26, wherein the PCB is mounted parallel to the second mirror.

28. The apparatus according to any one of claims 1 to 27, wherein a gas contained in the space between the optical element and the at least one electromagnetic radiation source and / or the space between the at least one optical element and the at least one detector of electromagnetic radiation is used to provide a lock line and / or verification and / or calibration line for the gas to be measured.

29. The apparatus according to any one of claims 1 to 28, wherein at least one bandpass filter is provided to limit the transmission bandwidth of the electromagnetic radiation.

30. The apparatus according to any one of claims 1 to 29, wherein a magnetic field source is arranged to apply a permanent magnetic field and / or a transient magnetic field across the sample cell and / or across the space between the optical element and the at least one electromagnetic radiation source and / or across the space between the at least one optical element and the at least one detector, and / or an electric field source is arranged to apply a permanent electric field and / or a transient electric field.

31. The apparatus according to claim 30, wherein the magnetic field source is at least one permanent magnet.

32. The apparatus according to claim 30, wherein the magnetic field source is at least one electromagnet.

33. The apparatus according to claim 30, wherein the magnetic field source is a combination of at least one permanent magnet and at least one electromagnet.

34. The apparatus according to claim 30, wherein the electric field is supplied by applying an electric field gradient between at least two electrodes.

35. The apparatus according to any one of claims 1 to 34, wherein the space between the electromagnetic radiation source and the at least one optical element, and / or the space between the electromagnetic radiation detector and the at least one optical element, is sealed, flushed with a purge gas, and / or scrubbed with an arbitrary spectrally absorbing gas at a desired wavelength.

36. The apparatus according to any one of claims 1 to 35, for use in an absorption spectroscopy system, wherein a spectroscopic measurement signal at twice the modulated excitation frequency is used to determine at least one parameter of at least one gas.

37. The apparatus according to any one of claims 1 to 36, for use in an absorption spectroscopy system in which a spectroscopic measurement signal is processed in the frequency domain.

38. The apparatus according to claim 37, wherein the spectroscopic measurement signal is convolved with a kernel function selected to minimize the influence of baseline noise.

39. The apparatus according to claim 13, wherein the at least one optical element includes one or more of a window, a refractive element, a reflecting element, a diffracting element, or an electromagnetic radiation passband filter.

40. The apparatus according to any one of claims 1 to 39, wherein the at least one gas exchange port of the gas cell includes one or more gas inlets and one or more gas outlets, the gas inlet being attached to a gas conduit, and the sample gas being arranged to flow in through the at least one gas inlet and flow out through the at least one gas outlet.

41. The apparatus according to any one of claims 1 to 40, wherein the at least one gas exchange port of the gas cell includes at least one gas inlet and at least one gas outlet, and the at least one gas inlet and the at least one gas outlet consist of at least one diffusion element.

42. The apparatus according to claim 41, wherein the same diffusion element is used to realize the at least one gas inlet and the at least one gas outlet.

43. The apparatus according to any one of claims 1 to 42, wherein the sample gas is passed through the at least one gas inlet of the gas cell and discharged through the at least one gas outlet of the gas cell using a combination of direct flow and diffusion.

44. The apparatus according to any one of claims 1 to 43, comprising two or more radiation sources and / or detectors.

45. The apparatus according to any one of claims 1 to 44, comprising at least one auxiliary photodetector, wherein reflected light not on the principal light measurement path passes through at least one auxiliary optical element to at least one auxiliary photodetector for the purpose of obtaining line-lock and / or verification readings.

46. The apparatus according to claim 45, wherein the reflected light not on the principal light measurement path is light reflected from an inner or outer window or reflective element of the sample cell.

47. The apparatus according to claim 45 or 46, wherein the at least one auxiliary optical element is a cuvette for housing the gas and / or optical filter of interest.

48. The apparatus according to any one of claims 1 to 47, wherein the gas cell is maintained at a controlled temperature and / or pressure.

49. The apparatus according to any one of claims 1 to 48, wherein at least one volume located within the optical path of the transmitted electromagnetic radiation and outside the gas cell is sealed and scrubbed and / or purged with a non-optical absorption purge gas to remove impurities.

50. The apparatus according to any one of claims 1 to 49, wherein the radiation source and / or detector are mounted separately, and the electromagnetic radiation is conducted to and / or from the device using at least one light guide or fiber optic cable.

51. The apparatus according to any one of claims 1 to 50, wherein at least one volume in the apparatus, located within the optical path of the transmitted electromagnetic radiation but outside the gas cell, is filled with an coherent optical absorbing gas.

52. The apparatus according to any one of claims 1 to 51, wherein at least one volume in the apparatus, located within the optical path of the transmitted electromagnetic radiation but outside the gas cell, is filled with an optically transparent filler material.

53. The apparatus according to claim 52, wherein the optically transparent filler material has a refractive index that matches that of at least one optical element in contact with the optically transparent filler material.

54. The apparatus according to claim 52 or 53, wherein the chemical and physical properties of the optically transparent filler material and / or the application of reduced pressure are used to minimize the presence of voids within the structure of the filler material.

55. The apparatus according to any one of claims 1 to 54, wherein the at least one radiation source and / or the at least one detector is a bare chip directly mounted on a PCB in a chip-on-board (COB) configuration.

56. The apparatus according to claim 55, wherein the at least one radiation source is a diode laser or an LED, and / or the at least one detector is a photodiode.

57. The apparatus according to any one of claims 1 to 56, wherein stray light reflection is used to increase overall optical throughput and improve signal-to-noise ratio, reflection suppression is not used, and / or stray light reflection enhancement is performed.

58. The apparatus or system according to claim 57, wherein the enhancement of stray light reflection comprises applying a reflective layer to at least one surface within the sample cell.

59. Apparatus for gas detection and / or measurement using absorption spectroscopy, A gas cell having at least one gas exchange port, At least one electromagnetic radiation source is arranged to transmit a beam of electromagnetic radiation in the direction passing through the gas cell, At least one detector, for detecting electromagnetic radiation incident on the detector, At least a first mirror and a second mirror are arranged in the gas cell in a manner that faces each other, wherein at least the first mirror is a curved mirror, and the opposing mirrors are arranged to create a reflected light path through the gas cell between the at least one radiation source and the at least one detector, Equipped with, An apparatus in which at least one radiation source is positioned between the opposing mirrors at a position offset from the center of curvature of the first mirror, such that transmitted electromagnetic radiation incident on the first mirror is reflected from the source toward the second mirror.

60. The apparatus according to claim 59, further comprising a spectrometer for analyzing output signals from at least one detector to detect the presence of one or more gas species in the gas cell and / or to measure the parameters of the one or more gas species in the gas cell.

61. The apparatus according to claim 59 or 60, wherein the first mirror and the second mirror are curved mirrors, and the at least one detector is positioned between the opposing mirrors at a position offset from the centers of curvature of the first mirror and the second mirror.

62. The apparatus according to claim 61, wherein the first mirror is a spherical mirror.

63. The apparatus according to claim 62, wherein the second mirror is a spherical mirror.

64. The apparatus according to any one of claims 59 to 63, wherein the at least one radiation source transmits a divergent beam toward the first mirror, and the mirror is arranged to automatically focus the divergent beam toward the at least one detector.

65. The apparatus according to claim 64, wherein the divergent beam of electromagnetic radiation is incident on the first surface region of the first mirror at a non-zero angle with respect to a direction perpendicular to the first surface region.

66. The apparatus according to claim 65, wherein electromagnetic radiation reflected from the first surface region of the first mirror is incident on the first surface region of the second mirror at a non-zero angle with respect to a direction perpendicular to the first surface region of the second mirror, then reflected by the second surface region of the first mirror toward the second surface region of the second mirror, then incident on the second mirror and reflected by the second mirror toward the at least one detector, thereby forming a reflected light path through the gas cell with automatic focusing of the transmitted divergent beam toward the at least one detector.

67. The apparatus according to any one of claims 59 to 66, wherein the at least one radiation source and the at least one detector are positioned together between the opposing mirrors within the housing.

68. The apparatus according to claim 67, wherein the housing comprises at least a first optical element and a second optical element on both sides thereof, the first optical element being optically aligned with the source to allow electromagnetic radiation to pass from the source into the gas cell, and the second optical element being optically aligned with the detector to allow reflected electromagnetic radiation to pass from the gas cell toward the detector.

69. The apparatus according to claim 68, wherein the radiation source is arranged to transmit electromagnetic radiation in a transmission direction into the gas cell toward the first mirror through the first optical element, and the detector is arranged on the opposite side of the radiation source from the transmission direction to detect electromagnetic radiation reflected from the second mirror toward the detector toward the detector toward the second optical element from the opposite direction of the transmission.

70. The apparatus according to claim 69, wherein the first optical element is a window positioned at a non-zero inclination angle with respect to the transmission direction, and the second optical element is a window positioned at a non-zero inclination angle with respect to the direction of electromagnetic radiation reflected toward the detector.

71. The apparatus according to claim 70, wherein the window is mounted at a Brewster polarization angle with respect to the direction of electromagnetic radiation incident on the window.

72. The apparatus according to any one of claims 59 to 71, wherein the at least one radiation source is positioned at a distance from the first mirror that is shorter than the first radius of curvature of the first mirror.

73. The apparatus according to claim 72, wherein the first mirror is positioned within the gas cell at a distance from the at least one radiation source of about half the first radius of curvature of the first mirror.

74. The apparatus according to any one of claims 59 to 73, wherein substantially all radiation incident on the detector has an equal path length within the gas cell.

75. The apparatus according to any one of claims 59 to 74, wherein the at least one electromagnetic radiation source is a laser.

76. The apparatus according to claim 75, wherein the laser is a tunable diode laser (TDL), and current and / or temperature are used to adjust the wavelength.

77. The apparatus according to claim 60, wherein the spectrometer is adapted to determine at least one parameter of at least one gas by direct absorption spectroscopy.

78. The apparatus according to claim 60, wherein the spectrometer is adapted to determine at least one parameter of at least one gas by wavelength-modulated spectroscopy.

79. The apparatus according to any one of claims 59 to 74, wherein the at least one electromagnetic radiation source is a broadband source.

80. The apparatus according to claim 79, wherein the broadband source is either an incandescent light source or a light-emitting diode (LED).

81. The apparatus according to any one of claims 59 to 80, wherein the at least one detector is a solid-state photoconductive, photovoltaic, photomultiplier tube, bolometer, or pyroelectric detector.

82. The apparatus according to any one of claims 59 to 81, wherein the inner surface of the gas cell other than the mirror is roughened and / or coated with an electromagnetic radiation absorbing layer to absorb electromagnetic radiation.

83. The apparatus according to any one of claims 59 to 82, wherein the at least one radiation source and the at least one detector are mounted on both sides of the same printed circuit board (PCB).

84. The apparatus according to any one of claims 59 to 83, wherein at least one bandpass filter is provided to limit the transmission bandwidth of the electromagnetic radiation.

85. The apparatus according to claim 84, wherein the at least one bandpass filter is provided in a housing located within the gas cell at the convergence point of the reflected radiation.

86. The apparatus according to any one of claims 59 to 85, wherein a magnetic field source is arranged across the gas cell to apply a permanent magnetic field and / or a transient magnetic field, and / or an electric field source is arranged to apply a permanent electric field and / or a transient electric field.

87. The apparatus according to any one of claims 59 to 86, wherein a magnetic field source is positioned to apply a permanent magnetic field and / or a transient magnetic field across the space between the source and an optically aligned first optical element, and / or across the space between the detector and an optically aligned second optical element, and / or an electric field source is positioned to apply a permanent electric field and / or a transient electric field.

88. The apparatus according to claim 86 or 87, comprising at least one permanent magnet as a magnetic field source.

89. The apparatus according to claim 86 or 87, comprising at least one electromagnet as a magnetic field source.

90. The apparatus according to claim 86 or 87, comprising a magnetic field source combining at least one permanent magnet and at least one electromagnet.

91. The apparatus according to claim 86 or 87, wherein the electric field is supplied by applying an electric field gradient between at least two electrodes.

92. The apparatus according to claim 68, wherein the space between the electromagnetic radiation source and the optically aligned first optical element, and / or the space between the electromagnetic radiation detector and the optically aligned second optical element, is sealed, flushed with a purge gas, and / or scrubbed with an interference gas.

93. The apparatus according to any one of claims 59 to 92, for use in an absorption spectroscopy system, wherein a spectroscopic measurement signal at twice the modulated excitation frequency is used to determine at least one parameter of at least one gas.

94. The apparatus according to any one of claims 59 to 93, for use in an absorption spectroscopy system in which a spectroscopic measurement signal is processed in the frequency domain.

95. The apparatus according to claim 93 or 94, wherein the signal is convolved with a kernel function selected to minimize the influence of baseline noise.

96. The apparatus according to claim 68 or 69, wherein the at least one optical element is a refractive element, a reflective element, a diffracting element, or an electromagnetic radiation passband filter.

97. The apparatus according to any one of claims 59 to 96, comprising two or more radiation sources and / or detectors.

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