Photoacoustic measurement system and photoacoustic measurement method

Abstract

The present invention provides a photoacoustic measurement system and a photoacoustic measurement method. The photoacoustic measurement system includes a light source, a beam splitter, a power monitoring unit, a first detector and a controller. The first detector receives the reflected light of the detection light on the surface of the sample. The power monitoring unit is added in the optical path of the photoacoustic measurement system to receive the split beam of the laser beam, or the split beam of the excitation light and / or the split beam of the detection light. The controller obtains the parameter to be measured of the sample based on the output signal of the first detector and the output signal of the power monitoring unit. The present invention adds a power monitoring unit in the optical path, measures the parameter to be measured of the sample based on the output signal of the first detector and the output signal of the power monitoring unit, eliminates the system error caused by adverse factors such as the airflow effect and laser fluctuation in the measurement cavity of the photoacoustic measurement system, and ensures the signal quality of the detection light, thereby improving the signal-to-noise ratio of the photoacoustic measurement system and the stability of the excitation signal.

Description

Technical Field

[0001] The present invention relates to the field of photoelectric detection, and more specifically, to a photoacoustic measurement system and a photoacoustic measurement method. Background Art

[0002] The photoacoustic measurement system is used to detect the film thickness of metal films, dielectric films and other test samples. The photoacoustic signal generation mechanism is as follows: Figure 1 As shown, see Figure 1 The signal generation mechanism of the photoacoustic measurement system is as follows: short pulse laser is used as excitation light to irradiate the sample surface, the sample absorbs photons to generate thermal stress, the thermal elastic deformation generates photoacoustic signals that propagate on the solid surface and inside, and the longitudinal sound wave propagates to the sample interface (the interface between the substrate or the membrane) to generate the first echo signal. The first echo signal reaches the upper surface, causing the material reflectivity to change; the echo signal rebounds after hitting the upper surface, and generates a second echo signal after rebounding and hitting the interface; the second echo signal reaches the upper surface, causing the material reflectivity to change.

[0003] The measurement principle of the photoacoustic measurement system can be found in Figure 2 ,like Figure 2 As shown, the detection light is projected onto the excitation light spot. Since the reflectivity changes when the echo is transmitted back, the light detector obtains the change in the detection light power caused by the excitation light, so the time interval between the two echoes can be obtained, and the film thickness value can be obtained through the film thickness calculation formula, which can be seen in Figure 3 The film thickness calculation formula is: Δd = Δt × v / 2.

[0004] The existing structure of photoacoustic measurement system is as follows Figure 4 , mainly including laser, beam splitter, chopper, reflector, optical delay line, beam combiner, condenser and photoelectric detector. Its detection method is as follows: the selected laser is expanded and collimated by the beam expander group, and the expanded and collimated laser is then divided into two beams by the beam splitter, one for detection light and the other for excitation light; the excitation light needs to pass through optical devices such as polarizers and choppers, and the detection light path needs to pass through optical devices such as reflectors and optical delay lines, and finally the excitation light and the detection light are combined and emitted by the beam combiner. The detection light and the excitation light are converged to the sample surface through the condenser to ensure that the excitation light spot and the detection light spot coincide, and perform photoacoustic action and detection.

[0005] The existing detection methods have certain technical problems:

[0006] The power fluctuation of the laser itself is usually less than 1%, and in abnormal cases the power fluctuation can be as high as 5-10%, which will introduce random noise into the system; optoelectronic devices such as modulators and choppers will introduce noise caused by light intensity fluctuations; since there are heat-generating bodies such as power supplies in the measurement cavity, the air flow in the cavity is in an uncontrollable state, and the air density and particle density on the optical path are constantly changing, which will introduce noise into the final measurement signal, and beams with larger beam diameters are more susceptible to the influence of air density and particle density; the optical path before the photodetector does not eliminate noise, and all external noise and system noise will enter the photodetector, resulting in a decrease in the signal-to-noise ratio of the photoacoustic measurement system. Summary of the invention

[0007] The present invention aims at the technical problem that the existing detection method has noise measurement error, and provides a photoacoustic measurement system and a photoacoustic measurement method.

[0008] According to a first aspect of the present invention, there is provided a photoacoustic measurement system, the system comprising: a light source, a beam splitter, a power monitoring unit, a first detector and a controller;

[0009] The light source emits a laser beam, which is divided into an excitation light and a detection light by the beam splitter, the excitation light is transmitted to the sample along the excitation light path, the detection light is transmitted to the sample along the detection light path, and the reflection light of the detection light on the surface of the sample is received by the first detector;

[0010] The power monitoring unit includes a spectrometer and at least one detector;

[0011] The spectrometer is arranged at any position in the optical path of the photoacoustic measurement system to obtain the split beam of the laser beam and enable the at least one detector to receive the split beam of the laser beam, or to obtain the split beam of the excitation light and / or the split beam of the detection light and enable the at least one detector to receive the split beam of the excitation light and / or the split beam of the detection light;

[0012] The controller obtains the parameter to be measured of the sample based on the output signal of the first detector and the output signal of the power monitoring unit.

[0013] Based on the above technical solution, the present invention can also make the following improvements.

[0014] Optionally, a measurement signal of the photoacoustic measurement system is obtained, wherein the measurement signal is an output signal of the first detector divided by an output signal of the power monitoring unit;

[0015] The curve of the measurement signal is analyzed to obtain the parameters to be measured of the sample.

[0016] Optionally, the at least one detector includes a second detector and a third detector, the second detector and the third detector respectively receive the split beam of the excitation light and the split beam of the detection light, and the output signal of the power monitoring unit is the product of the output signal of the second detector and the output signal of the third detector.

[0017] Optionally, the spectrometer is disposed in a position close to the sample in the optical path of the photoacoustic measurement system.

[0018] Optionally, the at least one detector includes a fourth detector, which receives the split beam of the laser beam or the split beam of the excitation light or the split beam of the detection light, and the output signal of the power monitoring unit is the output signal of the fourth detector.

[0019] Optionally, the beam splitter is disposed between the light source and the beam splitter, and the fourth detector is used to receive the split beam of the laser beam;

[0020] Alternatively, the spectrometer is disposed at any position of the excitation light path, and the fourth detector is used to receive the spectroscopic beam of the excitation light;

[0021] Alternatively, the spectrometer is disposed at any position of the detection light path, and the fourth detector is used to receive the spectroscopic light beam of the detection light.

[0022] Optionally, the photoacoustic measurement system further includes a data acquisition card and a lock-in amplifier;

[0023] The input end of the data acquisition card is connected to the at least one detector, the output end of the data acquisition card is connected to the controller, the input end of the lock-in amplifier is connected to the first detector, and the output end of the lock-in amplifier is connected to the controller;

[0024] The controller obtains the output signal of the first detector through the phase-locked amplifier, and the controller obtains the output signal of the at least one detector through the data acquisition card, and makes the frequency of the output signal of the at least one detector consistent with the frequency of the output signal of the first detector.

[0025] Optionally, the controller obtains the first frequency of the phase-locked amplifier output signal and the second frequency of the data acquisition card output signal, respectively, and averages the data acquisition card output signal based on the first frequency and the second frequency to obtain the output signal of the at least one detector.

[0026] Optionally, the photoacoustic measurement system further comprises a lock-in amplifier;

[0027] The input end of the phase-locked amplifier is connected to the first detector and the at least one detector, and the output end of the phase-locked amplifier is connected to the controller. The controller obtains the output signal of the first detector and the output signal of the at least one detector through the phase-locked amplifier.

[0028] Optionally, the beam splitter includes at least one beam splitter plate, or the beam splitter includes at least one beam splitter plate and at least one reflector.

[0029] According to a second aspect of the present invention, there is provided a photoacoustic measurement method, which is applied to a photoacoustic measurement system, comprising:

[0030] Acquiring an output signal of the power monitoring unit;

[0031] Acquiring an output signal of the first detector;

[0032] Obtain the measurement signal S of the photoacoustic measurement system optimize :

[0033] S optimize =V / V';

[0034] Analyze the measurement signal S optimize The curve of the sample is obtained by measuring the parameters of the sample;

[0035] Among them, S optimize is the measurement signal of the photoacoustic measurement system, V is the output signal of the first detector, and V' is the output signal of the power monitoring unit.

[0036] The present invention provides a photoacoustic measurement system and a photoacoustic measurement method. A power monitoring unit is added to an optical path. A first detector receives reflected light of a detection light on a sample surface. The power monitoring unit receives a split beam of a laser beam, or receives a split beam of an excitation light and / or a split beam of a detection light. The power monitoring unit is used to improve the signal-to-noise ratio of the photoacoustic measurement system. Based on the output signal of the first detector and the output signal of the power monitoring unit, a parameter to be measured of the sample is measured, thereby eliminating system errors caused by adverse factors such as airflow influence and laser fluctuation in a measurement cavity of the photoacoustic measurement system, and ensuring the signal quality of the detection light, thereby improving the signal-to-noise ratio of the photoacoustic measurement system and the stability of the excitation signal. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 The schematic diagram of the photoacoustic signal generation mechanism of the existing photoacoustic measurement system;

[0038] Figure 2 It is a schematic diagram of the measurement principle of the existing photoacoustic measurement system;

[0039] Figure 3It is a schematic diagram of the film thickness measurement principle of the existing sample to be tested;

[0040] Figure 4 It is a structural schematic diagram of an existing photoacoustic measurement system;

[0041] Figure 5 A schematic diagram of the structure of a photoacoustic measurement system according to an embodiment of the present invention;

[0042] Figure 6 A schematic diagram of the structure of a photoacoustic measurement system according to another embodiment of the present invention;

[0043] Figure 7 A schematic diagram of the output signal processing principle of a photoacoustic measurement system according to an embodiment;

[0044] Figure 8 A schematic diagram of the output signal processing principle of a photoacoustic measurement system according to another embodiment;

[0045] Fig. 9 A schematic flow chart of a photoacoustic measurement method provided by the present invention. DETAILED DESCRIPTION

[0046] The specific implementation of the present invention is further described in detail below in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0047] In order to solve the noise errors caused by various factors in the prior art, the present invention provides a photoacoustic measurement system, which mainly includes a light source, a beam splitter, a power monitoring unit, a first detector and a controller.

[0048] Wherein, the light source emits a laser beam, and the laser beam is divided into an excitation light and a detection light by the beam splitter, the excitation light is transmitted to the sample along the excitation light path, the detection light is transmitted to the sample along the detection light path, and the reflection light of the detection light on the surface of the sample is received by the first detector. The power monitoring unit includes a spectrometer and at least one detector; the spectrometer is arranged at any position in the optical path of the photoacoustic measurement system to obtain the split beam of the laser beam and enable the at least one detector to receive the split beam of the laser beam, or to obtain the split beam of the excitation light and / or the split beam of the detection light and enable the at least one detector to receive the split beam of the excitation light and / or the split beam of the detection light. The controller obtains the parameter to be measured of the sample based on the output signal of the first detector and the output signal of the power monitoring unit.

[0049] It can be understood that the photoacoustic measurement system is used to measure the parameters to be measured of the sample. The traditional photoacoustic measurement system is easily affected by the noise errors in the optical devices and the optical path transmission. Therefore, the present invention provides a photoacoustic measurement system, which at least includes a light source, a beam splitter, a power monitoring unit, a first detector and a controller. Among them, the light source emits a laser beam, and the beam splitter divides the laser beam into an excitation light and a detection light. The excitation light is transmitted to the sample through the excitation light path. Similarly, the detection light is transmitted to the sample through the detection light path, and the reflected light of the detection light on the sample surface is received by the first detector. The power monitoring unit includes a spectrometer and at least one detector. The power monitoring unit can be set at any position on the optical path of the photoacoustic measurement system. According to the number of detectors included in the power monitoring unit, the detector can receive the split beam of the laser beam, the split beam of the excitation light and / or the split beam of the detection light. The power monitoring unit is used to improve the signal-to-noise ratio of the photoacoustic measurement system. Finally, the controller obtains the parameters to be measured of the sample according to the output signal of the first detector and the output signal of the power monitoring unit.

[0050] The present invention adds a power monitoring unit in the optical path, wherein the first detector receives the reflected light of the detection light on the sample surface, and the power monitoring unit receives the split light beam of the laser beam, or receives the split light beam of the excitation light and / or the split light beam of the detection light; based on the output signal of the first detector and the output signal of the power monitoring unit, the parameter to be measured of the sample is measured, the system error caused by unfavorable factors such as the airflow influence in the measurement cavity of the photoacoustic measurement system and the laser fluctuation is eliminated, the signal quality of the detection light is guaranteed, and thus the signal-to-noise ratio of the photoacoustic measurement system and the stability of the excitation signal are improved.

[0051] As an embodiment, a measurement signal of the photoacoustic measurement system is obtained, where the measurement signal is the output signal of the first detector divided by the output signal of the power monitoring unit; and a curve of the measurement signal is analyzed to obtain a parameter to be measured of the sample.

[0052] It is understandable that the measured parameters of the sample are calculated and analyzed based on the curve of the measurement signal of the photoacoustic measurement system, so it is necessary to calculate the measurement signal of the photoacoustic measurement system. In the present invention, the measurement signal of the photoacoustic measurement system is obtained by dividing the output signal of the first detector by the output signal of the power monitoring unit, and the measurement signal of the photoacoustic measurement system is obtained by dividing the two output signals, thereby eliminating the system error and improving the signal-to-noise ratio of the photoacoustic measurement system.

[0053] As an embodiment, the at least one detector includes a second detector and a third detector, the second detector and the third detector respectively receive the split beam of the excitation light and the split beam of the detection light, and the output signal of the power monitoring unit is the product of the output signal of the second detector and the output signal of the third detector.

[0054] It is understandable that the power monitoring unit may include one detector or two detectors. The following describes the case where the power monitoring unit includes two detectors. Figure 5 The power monitoring unit includes a spectrometer and two detectors (called a second detector and a third detector), wherein the second detector receives the split beam of excitation light, and the third detector receives the split beam of detection light. At this time, the output signal of the power monitoring unit is the product of the output signal of the second detector and the output signal of the third detector.

[0055] In this case, the spectrometer is placed in the optical path of the photoacoustic measurement system close to the sample, e.g. Figure 5 The beam splitter can be set between the beam combiner and the sample and biased towards the sample. The closer the beam splitter is to the sample, the more obvious the effect of eliminating jitter / system noise is, and the better the effect of improving the signal-to-noise ratio of the photoacoustic measurement system is.

[0056] For example, Figure 5 In the embodiment, the spectrometer includes a beam sampling plate and a reflector. The beam sampling plate is a beam splitting plate that performs a beam splitting function. The two reflective surfaces of the reflector respectively reflect the excitation light and the detection light to the corresponding detectors. Optionally, the power monitoring unit can also be respectively arranged in the excitation light path and the detection light path. A beam sampling plate is arranged in the excitation light path. The beam sampling plate directly reflects the excitation light split beam to the corresponding detector. Similarly, a beam sampling plate is arranged in the detection light path. The beam sampling plate directly reflects the detection light split beam to the corresponding detector. In addition, according to the configuration requirements of the system light path, a reflector can be arranged on the optical path where the excitation light split beam and / or the detection light split beam is transmitted to the corresponding detector.

[0057] As an embodiment, the at least one detector includes a fourth detector, which receives the split beam of the laser beam or the split beam of the excitation light or the split beam of the detection light, and the output signal of the power monitoring unit is the output signal of the fourth detector.

[0058] It is understandable that the power monitoring unit may also include only one detector (called the fourth detector). In this case, the fourth detector may be arranged at any position of the photoacoustic measurement system. For example, the spectrometer is arranged between the light source and the beam splitter. Figure 6, in this case, the fourth detector is used to receive the split beam of the laser beam. The spectrometer can also be set at any position of the excitation light path, in which case, the fourth detector is used to receive the split beam of the excitation light; or, the spectrometer is set at any position of the detection light path, in which case, the fourth detector is used to receive the split beam of the detection light. When the power monitoring unit includes only one detector (the fourth detector), the output signal of the power monitoring unit is the output signal of the fourth detector.

[0059] As an embodiment, the photoacoustic measurement system also includes a data acquisition card and a phase-locked amplifier; the input end of the data acquisition card is connected to the at least one detector, the output end of the data acquisition card is connected to the controller, the input end of the phase-locked amplifier is connected to the first detector, and the output end of the phase-locked amplifier is connected to the controller; the controller obtains the output signal of the first detector through the phase-locked amplifier, and the controller obtains the output signal of the at least one detector through the data acquisition card, and makes the frequency of the output signal of the at least one detector consistent with the frequency of the output signal of the first detector.

[0060] It can be understood that the measurement signal of the photoacoustic measurement system is calculated based on the output signal of the first detector divided by the output signal of the power monitoring unit. Therefore, when specifically calculating the measurement signal of the photoacoustic measurement system, it is necessary to collect the output signal of the first detector and the output signal of the detector of the power monitoring unit, and then transmit the collected output signal of the first detector and the collected output signal of the power monitoring unit to the controller, and the controller calculates the measurement signal of the photoacoustic measurement system based on the output signal of the first detector divided by the output signal of the power monitoring unit.

[0061] Among them, when the output signals of each detector are collected, the output signal of the first detector is collected by a phase-locked amplifier, and the output signal of the detector in the power monitoring unit is collected by a data acquisition card. Since the acquisition frequency of the phase-locked amplifier is different from the acquisition frequency of the data acquisition card, when the controller calculates the measurement signal of the photoacoustic measurement system based on the output signal of the first detector and the output signal of the detector of the power monitoring unit, it is required that the frequency of the output signal of the first detector is the same as the frequency of the output signal of the detector in the power monitoring unit. Therefore, it is necessary to process the output signal of the first detector and the output signal of the power monitoring unit.

[0062] As an embodiment, the controller obtains the first frequency of the phase-locked amplifier output signal and the second frequency of the data acquisition card output signal respectively, and based on the first frequency and the second frequency, averages the data acquisition card output signal to obtain the output signal of at least one detector.

[0063] Here, the power monitoring unit includes two detectors (the second detector and the third detector) as an example for explanation. The output signal of the second detector and the output signal of the third detector are collected based on the data acquisition card, and the output signal of the first detector is collected by the phase-locked amplifier. Figure 7 The analog signals output by the second and third detectors are converted to a frequency of F after entering the data acquisition card. card The analog signal output by the first detector enters the phase-locked amplifier and the output frequency is F LIA The first digital signal data. Wherein, F card >F LIA , so the two signals cannot be directly operated.

[0064] Therefore, for frequency F card The second digital signal data and the third digital signal data are processed so that the frequencies of the processed second digital signal data, the third digital signal data and the first digital signal data are equal.

[0065] Specifically, for each N = F card / F LIA The second digital signal data and every N third digital signal data are averaged, and the average value is used to replace every N second digital signal data or N third digital signal data, so that the frequency of all digital signal data is F LIA .

[0066] As an embodiment, the photoacoustic measurement system also includes a phase-locked amplifier, which is a multi-channel phase-locked amplifier; the input end of the phase-locked amplifier is connected to the first detector and the at least one detector, and the output end of the phase-locked amplifier is connected to the controller, and the controller obtains the output signal of the first detector and the output signal of the at least one detector through the phase-locked amplifier.

[0067] It is understandable that, in practice, the output signal of the first detector is usually collected by a phase-locked amplifier, and the output signal of the detector in the power monitoring unit can be collected by a data acquisition card or a phase-locked amplifier. Still taking the example that the power monitoring unit includes two detectors (the second detector and the third detector), a three-channel phase-locked amplifier can be used to collect the output signals of the first detector, the second detector and the third detector, as shown in FIG. Figure 8 , the frequencies of the output signals of the first detector, the second detector and the third detector are equal. At this time, the output signals of the three detectors do not need to be processed.

[0068] As an embodiment, the beam splitter includes at least one beam splitter plate, or the beam splitter includes at least one beam splitter plate and at least one reflector.

[0069] It is understandable that in the present invention, the main function of the beam splitter is to reflect a part of the light beam and transmit a part of the light beam. On the basis of the beam splitter realizing this function, the beam splitter may include at least one beam splitter plate, which is arranged after the light source, or may be arranged separately on the excitation light path, or may be arranged separately on the detection light path. The beam splitter may also be a combination of at least one beam splitter plate and at least one reflector. In the present invention, the beam splitter can realize the functions of reflection and transmission, and the specific structure is not limited.

[0070] See also Fig. 9 , provides a photoacoustic measurement method, which can be applied to the above-mentioned photoacoustic measurement system, and the photoacoustic measurement method mainly includes the following steps:

[0071] S1, obtaining an output signal of the power monitoring unit;

[0072] S2, obtaining an output signal of the first detector;

[0073] S3, obtaining the measurement signal S of the photoacoustic measurement system optimize :

[0074] S optimize =V / V';

[0075] S4, analyzing the measurement signal S optimize The curve of the sample is obtained by measuring the parameters of the sample;

[0076] Among them, S optimize is the measurement signal of the photoacoustic measurement system, V is the output signal of the first detector, and V' is the output signal of the power monitoring unit.

[0077] It can be understood that the technical features of obtaining the output signal of the power monitoring unit in step S1 and obtaining the output signal of the first detector in step S2 can refer to the corresponding technical features in the aforementioned photoacoustic measurement system, and will not be repeated here.

[0078] After the output signal of the first detector and the output signal of the power monitoring unit are obtained respectively, the measurement signal S of the photoacoustic measurement system can be calculated. optimize :

[0079] S optimize =V / V'.

[0080] Analyze the measurement signal S optimize The curve of the sample is obtained by measuring the parameters of the sample;

[0081] Among them, S optimize is the measurement signal of the photoacoustic measurement system, V is the output signal of the first detector, and V' is the output signal of the power monitoring unit.

[0082] The principle of using this photoacoustic measurement method to calculate the measurement signal of the photoacoustic measurement system and eliminate the noise fluctuation error is described as follows:

[0083] The power monitoring unit including the second detector and the third detector is used as an example for explanation, that is, Figure 5 As an example, according to the measurement principle and actual optical path of the photoacoustic measurement system, the intensity fluctuation of the detection light is ΔI probe , the excitation light intensity fluctuation is ΔI pump , the ideal light intensity I after the detection light is reflected on the surface of the sample to be tested r The relationship between the actual light intensity I received by the first photodetector is I = I r ×(1+ΔI probe )×(1+ΔI pump ).

[0084] The reflectivity of the beam splitter to the detection light and the excitation light are r1 and r2 respectively, then the light intensity entering the third photodetector after passing through the beam splitter is I probe ′=r1×I probe ×(1+ΔI probe ), the intensity of the excitation light entering the second photodetector after passing through the beam splitter is I pump ′=r2×I pump ×(1+ΔI pump ), where I probe is the ideal intensity of the detection light between the beam combiner and the beam splitter, I pump is the ideal intensity of the excitation light between the beam combiner and the beam splitter.

[0085] Then, the measurement signal of the photoacoustic measurement system is:

[0086]

[0087] It can be seen from the above formula that adding a power monitoring unit to the traditional photoacoustic measurement system includes two detectors to detect the spectroscopic signal of the detection light and the spectroscopic signal of the excitation light respectively. Finally, the measurement signal of the photoacoustic measurement system and the intensity fluctuation of the detection light are ΔI probe and the excitation light intensity fluctuation ΔI pump This means that the improved photoacoustic measurement system eliminates the noise fluctuation error of the system caused by the fluctuation of the detection light intensity and the excitation light intensity. The measurement signal is related to the parameter to be measured of the sample. Therefore, the parameter to be measured of the sample based on the improved photoacoustic measurement system of the present invention will not be affected by the fluctuation of the detection light intensity of ΔI. probe and the excitation light intensity fluctuation ΔI pump impact.

[0088] In the actual process, each detector outputs an analog voltage signal. According to the principle of the detector, the output signal V is directly proportional to the input light intensity I: V = a × I, a is the gain amplification factor. probe ′ is I probe 'The voltage signal obtained by the third detector, V pump ′ is I pump ' is the voltage signal obtained after passing through the second detector, and V is the voltage signal after the input light intensity I passes through the first detector.

[0089] Therefore, V probe ′ and V pump ′ Perform the following operation to obtain the measurement signal of the photoacoustic measurement system That is, when the power monitoring unit includes the second detector and the third detector, the output signal of the power monitoring unit is the product of the output signal of the second detector and the output signal of the third detector. The measurement signal of the photoacoustic measurement system is represented by the output signal of the first detector and the output signal of the power monitoring unit, which can be expressed as follows: S optimize =V / V', where V is the output signal of the first detector, V' is the output signal of the power monitoring unit, and when the power monitoring unit includes a second detector and a third detector, V'=V' probe ×V' pump .

[0090] The present invention provides a photoacoustic measurement system and a photoacoustic measurement method, which are used to improve the signal-to-noise ratio of the photoacoustic measurement system by adding a power monitoring unit in an optical path. A first detector receives reflected light of the detection light on the surface of a sample, and the power monitoring unit receives a split beam of a laser beam, or receives a split beam of an excitation light and / or a split beam of the detection light. Based on the output signal of the first detector and the output signal of the power monitoring unit, a parameter to be measured of the sample is measured, and the system error caused by adverse factors such as the influence of airflow in the measurement cavity of the photoacoustic measurement system and laser fluctuations, and jitter of the optical path of the measurement system is eliminated, and the signal quality of the detection light is guaranteed, thereby improving the signal-to-noise ratio of the photoacoustic measurement system and the stability of the excitation signal.

[0091] In addition, the sampling frequency of the data acquisition card does not match the frequency of the phase-locked amplifier. Through interpolation and averaging, the sampled data is compressed to match the signals obtained by the data acquisition card and the phase-locked amplifier.

[0092] Furthermore, by sampling the excitation light and the detection light into the photodetector, the photoacoustic measurement system can be provided with the power fluctuation at the current moment according to the power change, and the real-time power of the detection light and the excitation light can be monitored in real time.

[0093] It should be noted that in the above embodiments, the description of each embodiment has its own emphasis, and for parts that are not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0094] Although the preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0095] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A photoacoustic measurement system, characterized in that: The system includes: a light source, a beam splitter, a power monitoring unit, a first detector and a controller; The light source emits a laser beam, which is divided into an excitation light and a detection light by the beam splitter, the excitation light is transmitted to the sample along the excitation light path, the detection light is transmitted to the sample along the detection light path, and the reflection light of the detection light on the surface of the sample is received by the first detector; The power monitoring unit includes a spectrometer and at least one detector; The spectrometer is arranged at any position in the optical path of the photoacoustic measurement system to obtain the split beam of the laser beam and enable the at least one detector to receive the split beam of the laser beam, or to obtain the split beam of the excitation light and / or the split beam of the detection light and enable the at least one detector to receive the split beam of the excitation light and / or the split beam of the detection light; A controller, which acquires a parameter to be measured of the sample based on an output signal of the first detector and an output signal of the power monitoring unit; Acquire a measurement signal of the photoacoustic measurement system, wherein the measurement signal is an output signal of the first detector divided by an output signal of the power monitoring unit; The curve of the measurement signal is analyzed to obtain the parameters to be measured of the sample.

2. A photoacoustic measurement system according to claim 1, characterized in that: The at least one detector includes a second detector and a third detector, the second detector and the third detector respectively receive the split beam of the excitation light and the split beam of the detection light, and the output signal of the power monitoring unit is the product of the output signal of the second detector and the output signal of the third detector.

3. A photoacoustic measurement system according to claim 2, characterized in that: The spectrometer is arranged in a position close to the sample in the optical path of the photoacoustic measurement system.

4. The photoacoustic measurement system according to claim 1, characterized in that: The at least one detector includes a fourth detector, which receives the split beam of the laser beam or the split beam of the excitation light or the split beam of the detection light, and the output signal of the power monitoring unit is the output signal of the fourth detector.

5. The photoacoustic measurement system according to claim 4, characterized in that: The beam splitter is disposed between the light source and the beam splitter, and the fourth detector is used to receive the split beam of the laser beam; Alternatively, the spectrometer is disposed at any position of the excitation light path, and the fourth detector is used to receive the spectroscopic beam of the excitation light; Alternatively, the spectrometer is disposed at any position of the detection light path, and the fourth detector is used to receive the spectroscopic light beam of the detection light.

6. The photoacoustic measurement system according to any one of claims 1 to 5, characterized in that: The photoacoustic measurement system also includes a data acquisition card and a lock-in amplifier; The input end of the data acquisition card is connected to the at least one detector, the output end of the data acquisition card is connected to the controller, the input end of the lock-in amplifier is connected to the first detector, and the output end of the lock-in amplifier is connected to the controller; The controller obtains the output signal of the first detector through the phase-locked amplifier, and the controller obtains the output signal of the at least one detector through the data acquisition card, and makes the frequency of the output signal of the at least one detector consistent with the frequency of the output signal of the first detector.

7. The photoacoustic measurement system according to claim 6, characterized in that: The controller obtains the first frequency of the output signal of the phase-locked amplifier and the second frequency of the output signal of the data acquisition card respectively, and performs average processing on the output signal of the data acquisition card based on the first frequency and the second frequency to obtain the output signal of the at least one detector.

8. The photoacoustic measurement system according to any one of claims 1 to 5, characterized in that: The photoacoustic measurement system also includes a lock-in amplifier; The input end of the phase-locked amplifier is connected to the first detector and the at least one detector, and the output end of the phase-locked amplifier is connected to the controller. The controller obtains the output signal of the first detector and the output signal of the at least one detector through the phase-locked amplifier.

9. The photoacoustic measurement system according to claim 1, characterized in that: The beam splitter includes at least one beam splitter plate, or the beam splitter includes at least one beam splitter plate and at least one reflector.

10. A photoacoustic measurement method, characterized in that: A photoacoustic measurement system as claimed in any one of claims 1 to 9, comprising: Acquiring an output signal of the power monitoring unit; Acquiring an output signal of the first detector; Obtain the measurement signal S of the photoacoustic measurement system optimize : S optimize =V / V′; Analyze the measurement signal S optimize The curve of the sample is obtained by measuring the parameters of the sample; in, optimize is the measurement signal of the photoacoustic measurement system, V is the output signal of the first detector, and V' is the output signal of the power monitoring unit.

Images