Analysis device, method for driving laser element, and analysis method

Abstract

The present invention provides a high performance analysis device while utilizing a laser element that oscillates in a plurality of longitudinal modes. This analysis device comprises a laser element 31 that irradiates a sample with laser light L1, a drive unit 4 that drives the laser element 31, and a photodetector 5 that detects the laser light L1 that has passed through the sample. The laser element 31 oscillates in a plurality of longitudinal modes to emit the laser light L1 having a plurality of oscillation wavelengths. The drive unit 4 pulses the laser element 31 and causes the laser element 31 to sweep through the plurality of oscillation wavelengths for each pulse.

Description

Analysis device, laser element driving method, and analysis method

[0001] The present invention relates to an analyzing apparatus, a method for driving a laser element, and an analyzing method.

[0002] As shown in Patent Document 1, a conventional gas analyzer is an analyzer using a quantum cascade laser (QCL) in which a Fabry-Perot element that oscillates in multiple modes is used in the QCL. With this configuration, broader light is emitted from the first light-emitting surface of the quantum cascade laser compared to single-mode light, making it possible to analyze a variety of fluids.

[0003] Japanese Patent Application Laid-Open No. 2019-15563

[0004] As described in Patent Document 1, a Fabry-Perot element that oscillates in multiple modes emits light with a broader spectrum than a distributed feedback (DFB) element that oscillates in a single mode. However, Patent Document 1 employs a driving method that operates continuously with a constant current, and the oscillation spectrum has discrete oscillation wavelengths that correspond to the element dimensions.

[0005] Meanwhile, the inventors of the present application are developing a new analytical device that analyzes samples using a laser element that oscillates in multiple longitudinal modes. By using a laser element that oscillates in multiple longitudinal modes, the sample is irradiated with laser light having multiple oscillation wavelengths, making it possible to analyze multiple components contained in the sample. However, while there is no problem if the absorption wavelengths of multiple components and the oscillation wavelength match, it is not possible to accurately measure components with absorption wavelengths that are different from the oscillation wavelength.

[0006] Therefore, the present invention has been made to solve the above-mentioned problems, and its main object is to provide a high-performance analytical device that utilizes a laser element that oscillates in multiple longitudinal modes.

[0007] That is, the analytical device according to the present invention comprises a laser element that irradiates a sample with laser light, a drive unit that drives the laser element, a photodetector that detects the laser light that has passed through the sample, and a signal processing unit that acquires an output signal from the photodetector and analyzes the sample, wherein the laser element oscillates in a plurality of longitudinal modes and irradiates laser light having a plurality of oscillation wavelengths, and the drive unit pulse-drives the laser element and sweeps the plurality of oscillation wavelengths within each pulse.

[0008] In this analytical device, a laser element oscillating in multiple longitudinal modes is pulse-driven, and a drive current (drive voltage) is supplied to the laser element during each pulse, causing the temperature of the laser element to rise, which in turn causes a continuous change in the refractive index inside the laser element and a continuous change in multiple oscillation wavelengths. Therefore, multiple oscillation wavelengths can be swept within each pulse, and a sample can be irradiated with laser light having a broad spectrum (a spectrum of a predetermined width) when averaged over time, such as that of an LED. As a result, absorption over a wide wavelength range can be utilized, enabling accurate measurement of the components contained in the sample.

[0009] In order to generate a spectrum that is continuous over a predetermined width when viewed on a time average, it is desirable that the drive unit sweep the multiple oscillation wavelengths based on the wavelength intervals of the multiple longitudinal modes. Here, sweeping based on the wavelength intervals of the multiple longitudinal modes includes (1) sweeping the multiple oscillation wavelengths by the wavelength intervals of the longitudinal modes, (2) sweeping the multiple oscillation wavelengths at intervals narrower than the wavelength intervals of the longitudinal modes, and (3) sweeping the multiple oscillation wavelengths at intervals wider than the wavelength intervals of the longitudinal modes.

[0010] As a specific embodiment for generating a spectrum having a predetermined width when viewed on a time average, it is desirable that the driving unit pulse-drives the laser element with a driving pulse having a pulse width determined based on the wavelength intervals of the plurality of longitudinal modes.

[0011] As a specific embodiment of pulse driving, the driver may pulse-drive the laser element with a drive pulse in which the off time is set longer than the on time.

[0012] Here, it is desirable that the off-time of the drive pulse is a time set to return the temperature of the laser element to the temperature immediately before the on-time of the drive pulse. With this configuration, it is possible to emit laser light of the same oscillation wavelength for each pulse.

[0013] As a specific embodiment of pulse driving, the driving unit may pulse-drive the laser element with a pulse width of 10 μsec or less, a repetition frequency of 0.1 to 10 MHz, and a duty ratio of 5% or more but less than 50%.

[0014] As a specific embodiment of the method of driving a laser element by a driving unit, the driving unit may repeat a pulse driving period in which the laser element is pulse-driven and a stop period in which the pulse driving of the laser element is stopped.

[0015] By using the NDIR method, which is highly sensitive because it is an autocorrelation detection method even with a relatively short optical path, and a laser element that is easy to control the wavelength or duty, it is possible to configure an analytical device that is simple in configuration and highly sensitive, that is, an analytical device that combines the advantages of the NDIR method and laser spectroscopy. Therefore, the analytical device according to the present invention may have a sample cell that contains a gas that is the sample, and a reference cell that contains a reference gas, the laser element irradiating the sample cell and the reference cell with laser light, and the photodetector may be a pneumatic detector that detects the laser light that has passed through the sample cell and the reference cell.

[0016] Furthermore, a method for driving a laser element according to the present invention is a method for driving a laser element that irradiates a sample with laser light, wherein the laser element oscillates in a plurality of longitudinal modes and irradiates laser light having a plurality of oscillation wavelengths, and the laser element is pulse-driven and the plurality of oscillation wavelengths are swept within each pulse.

[0017] Furthermore, an analytical method according to the present invention comprises a laser element that irradiates a sample with laser light, a drive unit that drives the laser element, a photodetector that detects the laser light that has passed through the sample, and a signal processing unit that acquires an output signal from the photodetector and analyzes the sample, wherein the laser element oscillates in a plurality of longitudinal modes and irradiates laser light having a plurality of oscillation wavelengths, and the drive unit pulse-drives the laser element and sweeps the plurality of oscillation wavelengths within each pulse.

[0018] Furthermore, the analysis program of the present invention is an analysis program used in an analytical device comprising a laser element that irradiates a sample with laser light, a driving unit that drives the laser element, a photodetector that detects the laser light that has passed through the sample, and a signal processing unit that acquires an output signal from the photodetector and analyzes the sample, wherein the laser element oscillates in multiple longitudinal modes and irradiates laser light having multiple oscillation wavelengths, and is characterized in that the analysis program causes the driving unit to pulse-drive the laser element and perform the function of sweeping the multiple oscillation wavelengths within each pulse.

[0019] According to the present invention configured in this manner, it is possible to provide a high-performance analytical device using a laser element that oscillates in a plurality of longitudinal modes.

[0020] Fig. 1 is a schematic diagram showing an analysis device according to one embodiment of the present invention; Fig. 2 is a schematic diagram showing the oscillation wavelengths of a plurality of longitudinal modes of the laser element of the same embodiment; Fig. 3 is a schematic diagram showing the driving mode of the laser element of the same embodiment and the spectrum averaged over time; Fig. 4 is a schematic diagram showing the sweep of the oscillation wavelength within each pulse of the same embodiment and the spectrum averaged over time; Fig. 5 is a schematic diagram showing an analysis device according to a modified embodiment.

[0021] An embodiment of an analytical device according to the present invention will be described below with reference to the drawings. Note that, for ease of understanding, all of the drawings shown below are drawn in a schematic manner with appropriate omissions or exaggerations. Identical components are designated by the same reference numerals, and their description will be omitted where appropriate.

[0022] The analytical device 100 according to this embodiment measures the concentration of a measurement component contained in a gas sample (hereinafter referred to as sample gas) by infrared absorption.

[0023] Specifically, as shown in FIG. 1, the analytical device 100 includes a sample cell 21 that contains a sample gas, a reference cell 22 that contains a reference gas, a laser light source 3 having a laser element 31 that irradiates infrared laser light L1 onto the sample cell 51 and the reference cell 52, a drive unit 4 that drives the laser element 31, a photodetector 5 that detects the laser light L1 that has passed through the sample cell 51 and the reference cell 52, and a signal processing unit 6 that acquires a light intensity signal from the photodetector 5 and calculates the concentration of the component to be measured.

[0024] The sample cell 21 is a single-pass cell having a storage space for storing sample gas, and has an inlet port P1 for introducing the sample gas into the storage space and an outlet port P2 for discharging the sample gas from the storage space. The sample cell 21 also has an entrance window W11 through which laser light L1 enters the cell 21, and an exit window W12 through which the laser light L1 that has passed through the sample gas in the cell 21 exits the cell 21. The entrance window W11 and the exit window W12 are arranged opposite each other and are made of a material that is transparent to infrared rays.

[0025] The reference cell 22 is a single-pass cell having a storage space for storing a reference gas, and is provided with an entrance window W21 through which the laser light L1 enters the cell 22, and an exit window W22 through which the laser light L1 that has passed through the reference gas in the cell 22 is emitted to the outside of the cell 22. The entrance window W21 and the exit window W22 are arranged opposite each other and are made of a material that is transparent to infrared rays. The reference cell 22 is filled with a reference gas. Here, the reference gas is a gas that does not absorb infrared rays, such as nitrogen (N ２ ) and other inert gases.

[0026] The laser light source 3 of this embodiment is provided corresponding to each of the sample cell 21 and the reference cell 22, and each laser light source 3 has a laser element 31 that emits infrared laser light L1 and a shaping optical system 32 such as a lens or a concave mirror that shapes the laser light L1 from the laser element 31. Note that the laser light source 3 may not have the shaping optical system 32.

[0027] The laser element 31 is a semiconductor laser that emits infrared laser light L1, and in this embodiment is a quantum cascade laser. Specifically, the laser element 31 is a double-cleaved Fabry-Perot quantum cascade laser. This laser element 31 is supplied with a driving current or driving voltage by the driver 4, and oscillates in multiple longitudinal modes to emit laser light L1 having multiple oscillation wavelengths. While FIG. 2 shows an example in which the laser element 31 oscillates in nine longitudinal modes to produce nine oscillation wavelengths, the number of longitudinal modes can be changed depending on the driving current or driving voltage. The method of driving the laser element 31 by the driver 4 will be described later.

[0028] The photodetector 5 is an infrared detector that detects the laser light L1 that has passed through the sample cell 21 and the reference cell 22. The photodetector 5 of this embodiment is a pneumatic detector that outputs a detection signal according to the difference in intensity between the laser light L1 that has passed through the sample cell 21 and the laser light L1 that has passed through the reference cell 22. Note that an optical filter such as a bandpass filter may be provided between the photodetector 5 and the sample cell 21 and the reference cell 22.

[0029] This pneumatic detector 5 uses a condenser microphone, and two chambers separated by a diaphragm of the condenser microphone are filled with a measurement component gas or a component gas with the same or similar optical absorption characteristics as the measurement component gas. Laser light L1 passing through a sample cell 21 is incident on one chamber, and laser light L1 passing through a reference cell 22 is incident on the other chamber. When laser light L1 is incident on each chamber of the pneumatic detector 5, the laser light L1 is absorbed, causing the gas in each chamber to expand, creating a pressure difference, which deforms the diaphragm and changes the capacitance. The pneumatic detector 5 outputs a detection signal corresponding to this change in capacitance.

[0030] The signal processing unit 6 calculates the concentration of the measurement component contained in the sample gas using the light intensity signal output from the photodetector 5. This signal processing unit 6 has an amplifier 61 that amplifies the light intensity signal from the photodetector 5, and a concentration conversion unit 62 that converts the amplified light intensity signal into a concentration. The concentration converted by the concentration conversion unit 62 can be displayed on a display unit 7 such as a monitor.

[0031] <Method of Driving Laser Element 31 by Driver 4> As shown in FIG. 3 , the driver 4 alternates between a pulse drive period T1 during which the laser element 31 is pulse-driven and a stop period T2 during which the pulse drive of the laser element 31 is stopped. The pulse drive period T1 and the stop period T2 are intended to cause the laser element 31 to perform the function of a mechanical chopper used in conventional NDIR methods. The stop period T2 is a period required to generate a pressure change inside the pneumatic detector 5 and extract a detection signal. The pulse drive period T1 and the stop period T2 are determined based on the operating speed of the photodetector 5, and each period T1 and T2 is, for example, approximately 0.1 to 10 seconds. In this embodiment, a driver 4 is provided for each of the two laser elements 31, and drives the two laser elements 31 in synchronization with each other.

[0032] During the pulse driving period T1, the driving section 4 pulse-drives the laser element 31 and sweeps a plurality of oscillation wavelengths within each pulse.

[0033] Specifically, the driver 4 pulse-drives the laser element 31 with a drive pulse DP having a pulse width determined based on the wavelength interval (Δλ) of a plurality of longitudinal modes. Here, the on-time of the drive pulse DP is t １ , off time t ２ In addition, the driving unit 4 is turned on for a period t １ Off time t ２ The driving pulse DP (t １ <t ２ ) to pulse-drive the laser element 31. For example, the driver 4 pulse-drives the laser element 31 with a pulse width of 10 μsec or less, a repetition frequency of 0.1 to 10 MHz, and a duty ratio of 5% or more and less than 50%.

[0034] Here, the on time t of the drive pulse DP １ The pulse width (Δλ) is set so as to sweep the multiple oscillation wavelengths by the wavelength interval (Δλ) between multiple longitudinal modes. That is, in one pulse from the driver 4, the multiple oscillation wavelengths are swept to the next adjacent oscillation wavelength in the direction of increasing wavelength.

[0035] Off time t in the drive pulse DP ２ is the on-time t of the drive pulse DP １ This is the time set to return the temperature of the laser element 31 to the previous temperature. ２ is the on time t １ This is the time it takes for the temperature change that occurs in the

[0036] For example, between adjacent oscillation wavelengths, the shorter oscillation wavelength is designated as λ １ , the longer wavelength is λ ２ (=λ １ +Δλ), as shown in FIG. 4, the first pulse (first ON time t １ ) at the oscillation wavelength λ １ is swept by Δλ, and the oscillation wavelength λ ２ (FIG. 4(a)→(b)→(c)). That is, the oscillation wavelength λ before the sweep Ｎ is swept by Δλ to obtain the oscillation wavelength λ Ｎ＋１ In addition, immediately after that, the off time t２ In this state, the laser element 31 is cooled and the on-time t １ Then, in the second pulse (second ON time t1), the oscillation wavelength λ １ is swept by Δλ, and the oscillation wavelength λ ２ (FIG. 4(a)→(b)→(c)). That is, the oscillation wavelength λ before the sweep Ｎ is swept again by Δλ to obtain the oscillation wavelength λ Ｎ＋１ In this way, a plurality of oscillation wavelengths are swept in each pulse, and when viewed on a time average, the wavelength range (wavelength width) changes to λ 1 as shown in FIGS. １ ~λ ９ Laser light having a continuous spectrum of +Δλ is emitted.

[0037] <Effects of the Present Embodiment> According to the analytical device 100 of the present embodiment configured as described above, the laser element 31 oscillating in multiple longitudinal modes is pulse-driven. Therefore, a drive current (drive voltage) is supplied to the laser element 31 in each pulse, causing the temperature of the laser element 31 to rise. This causes the refractive index inside the laser element 31 to continuously change, resulting in continuous changes in the multiple oscillation wavelengths. Therefore, multiple oscillation wavelengths can be swept within each pulse, and the sample can be irradiated with laser light L1 having a broad spectrum (a spectrum with a predetermined width) similar to that of an LED, when viewed on a time average. As a result, absorption over a wide wavelength range can be utilized, enabling accurate measurement of the components contained in the sample.

[0038] <Other Embodiments> For example, in the above embodiment, the configuration includes the sample cell 21 and the reference cell 22, but the configuration may not include the reference cell 22. In this case, a cross-flow method may be used in which the sample gas and the reference gas are alternately supplied to the sample cell 21 to perform the analysis.

[0039] The sample cell 21 in which the sample is accommodated may be a multi-pass cell (a White or Herriot type multi-reflection cell) in addition to a single-pass cell.

[0040] In the above embodiment, the sample cell 21 and the reference cell 22 are each provided with a laser light source 3, but as shown in Fig. 5, the laser light source 3 may be common to the sample cell 21 and the reference cell 22. In this case, the laser light emitted from the common laser light source 3 may be branched using a branching optical system 33, and the branched laser light may be irradiated onto the sample cell 21 and the reference cell 22.

[0041] Furthermore, the photodetector 5 is not limited to a pneumatic detector, and may be, for example, a thermal type such as a relatively inexpensive thermopile, or a quantum photoelectric element such as HgCdTe, InGaAs, InAsSb, or PbSe, which has good responsiveness.

[0042] Furthermore, if the spectrum can be acquired by the photodetector 5, the signal processing unit 6 may calculate the concentration of the component to be measured by performing multivariate analysis of the spectrum.

[0043] Furthermore, in the above embodiment, the laser light is irradiated onto the sample cell 21 containing the sample, but the laser light may be irradiated onto a sample that is not contained in a sample cell.

[0044] In addition, the laser element is not limited to a double-cleaved Fabry-Perot quantum cascade laser, but may be any other laser element as long as it oscillates in multiple longitudinal modes and emits laser light having multiple oscillation wavelengths.

[0045] In addition, various modifications and combinations of the embodiments may be made as long as they do not go against the spirit of the present invention.

[0046] According to the present invention, a high-performance analytical device can be provided while utilizing a laser element that oscillates in a plurality of longitudinal modes.

[0047] REFERENCE SIGNS LIST 100: Analytical device 21: Measurement cell P1: Inlet port P2: Outlet port W11: Incident window W12: Exit window 22: Reference cell W21: Incident window W22: Exit window L1: Laser light 3: Laser light source 31: Laser element 32: Shaping optical system 4: Driving unit T1: Pulse driving period T2: Stop period DP: Driving pulse t １ ...On time of drive pulse t ２ ...Off time of driving pulse 5 ...Photodetector 6 ...Signal processing unit 7 ...Display unit

Claims

1. a laser element that irradiates a sample with laser light; a drive unit that drives the laser element; a photodetector that detects the laser light that has passed through the sample; a signal processing unit that acquires an output signal from the photodetector and analyzes the sample, and comprising: the laser element oscillates in a plurality of longitudinal modes and irradiates the sample with laser light having a plurality of oscillation wavelengths; the drive unit pulse-drives the laser element and sweeps the plurality of oscillation wavelengths within each pulse, an analyzer.

2. The analyzer according to claim 1, wherein the drive unit sweeps the plurality of oscillation wavelengths based on the wavelength intervals between the plurality of longitudinal modes.

3. The analyzer according to claim 1 or 2, wherein the drive unit pulse-drives the laser element with a drive pulse having a pulse width determined based on the wavelength intervals between the plurality of longitudinal modes.

4. The analyzer according to claim 1 or 2, wherein the drive unit pulse-drives the laser element with a drive pulse having an off-time longer than an on-time.

5. The analyzer according to claim 4, wherein the off-time in the drive pulse is a time set to return the temperature of the laser element immediately before the on-time in the drive pulse.

6. The analyzer according to claim 1 or 2, wherein the drive unit pulse-drives the laser element with a pulse width of 10 μsec or less, a repetition frequency of 0.1 to 10 MHz, and a duty ratio of 5% or more and less than 50%.

7. The analyzer according to claim 1 or 2, wherein the drive unit repeats a pulse drive period for pulse-driving the laser element and a stop period for stopping the pulse drive of the laser element.

8. a sample cell that contains the gas as the sample; a reference cell that contains a reference gas, and the laser element irradiates the sample cell and the reference cell with laser light; the photodetector is a pneumatic detector that detects the laser light that has passed through the sample cell and the reference cell, the analyzer according to claim 1 or 2.

9. A method for driving a laser element that irradiates a sample with laser light, wherein the laser element oscillates in a plurality of longitudinal modes and irradiates the sample with laser light having a plurality of oscillation wavelengths. A method for driving a laser element, which pulse-drives the laser element and sweeps a plurality of oscillation wavelengths within each pulse.

10. A laser element that irradiates a sample with laser light, A drive unit that drives the laser element, A photodetector that detects the laser light that has passed through the sample, A signal processing unit that acquires an output signal from the photodetector and analyzes the sample, comprising: The laser element oscillates in a plurality of longitudinal modes and irradiates the sample with laser light having a plurality of oscillation wavelengths, The drive unit pulse-drives the laser element and sweeps a plurality of oscillation wavelengths within each pulse, an analysis method.

11. An analysis program used in an analysis apparatus including a laser element that irradiates a sample with laser light, a drive unit that drives the laser element, a photodetector that detects the laser light that has passed through the sample, and a signal processing unit that acquires an output signal from the photodetector and analyzes the sample, wherein the laser element oscillates in a plurality of longitudinal modes and irradiates the sample with laser light having a plurality of oscillation wavelengths, An analysis program that causes the drive unit to pulse-drive the laser element and to exhibit a function of sweeping a plurality of oscillation wavelengths within each pulse.