Photoacoustic detection device

Abstract

The embodiment of the invention provides a photoacoustic detection device, which is used for realizing switching between a reflection detection mode and a differential detection mode in the same detection device through a mode switching device, namely realizing two measurement modes in the same detection device. The photoacoustic detection device in the embodiment of the invention comprises a reflection mode detection device used for receiving a reflection light beam of a detection light beam on a to-be-detected object and measuring the light intensity of the reflection light beam; the differential mode detection device is used for receiving a reflected light beam which is generated after the detection light beam is reflected by the to-be-detected object and has a deviated direction, and measuring the luminous flux of the reflected light beam with the deviated direction; and the mode switching device is used for switching between the reflection mode detection device and the differential mode detection device, so that the photoacoustic detection device is in a reflection mode or a differential mode.

Description

Technical Field

[0001] The present invention relates to the technical field of photoacoustic detection, and in particular to a photoacoustic detection device. Background Art

[0002] Photoacoustic detection technology is a technical means used to measure the thickness of thin films or wafers and the physical properties of internal materials. The basic principle of this detection technology is as follows: use ultrashort pulse laser as pump light to irradiate the sample surface. After absorbing the laser energy, the sample surface produces thermal deformation, thereby generating sound waves inside and on the surface of the solid. When the sound waves propagate in the sample, two effects can be produced: one, the reflectivity of the sample surface changes; two, the sample surface is deformed.

[0003] When a beam of probe light is used to illuminate the sample surface, the reflection direction of the probe light is deflected or the wavefront changes due to the change in the reflectivity of the sample surface or the deformation of the sample surface. The detector measures the intensity change of the probe light caused by the change in reflectivity or the reflection deflection of the light beam, and the film thickness and internal physical properties of the sample can be obtained.

[0004] For different materials and structures, the changes in reflectivity and surface deformation caused by the acoustic waves generated by pump light excitation have different effects, and the measured signals are also different. How to realize two measurement modes in the same detection device is an urgent problem that needs to be solved. Summary of the invention

[0005] The embodiment of the present invention provides a photoacoustic detection device, which is used to switch between a reflection detection mode and a differential detection mode in the same detection device through a mode switching device, that is, to realize two measurement modes in the same detection device.

[0006] A first aspect of an embodiment of the present application provides a photoacoustic detection device, comprising:

[0007] A reflection mode detection device, used for receiving a reflected light beam of the detection light beam at the object to be detected, and measuring the light intensity of the reflected light beam;

[0008] A differential mode detection device, used for receiving a reflected light beam after the detection light beam is reflected by the object to be detected and after the reflected light beam has been shifted in direction, and measuring the luminous flux of the reflected light beam after the reflected light beam has been shifted in direction;

[0009] The mode switching device is used to switch between the reflection mode detection device and the differential mode detection device, so that the photoacoustic detection device is in the reflection mode or the differential mode.

[0010] Preferably, the mode switching device comprises: a beam splitter and a beam splitter position control device, the reflection mode detection device comprises: a first photodetector, and the differential mode detection device comprises: the first photodetector and a second photodetector;

[0011] The beam splitter position control device is used to control the beam splitter to deviate from the optical path where the reflected beam of the detection beam is located in the reflection mode, so that the reflected beam of the detection beam is incident on the first photodetector, or to control the beam splitter to move to the optical path where the reflected beam of the detection beam is located in the differential mode, so that the beam splitter splits the reflected beam of the detection beam into the first beam and the second beam;

[0012] The beam splitter is used to split the reflected beam of the detection beam into a first beam and a second beam in the differential mode, so that the first beam is incident on the first photodetector and the second beam is incident on the second photodetector.

[0013] Preferably, the beam splitter comprises a fiber beam splitter or a knife-edge prism, and the beam splitter position control device comprises a piezoelectric displacement stage.

[0014] Preferably, a first optical path where the first detector and the beam splitter are located is perpendicular to a second optical path where the second detector and the beam splitter are located;

[0015] An optical path of the first light beam between the beam splitter and the first photodetector is the same as an optical path of the second light beam between the beam splitter and the second photodetector.

[0016] Preferably, the reflection mode detection device further comprises: a first aperture arranged on the optical path between the object to be detected and the first photodetector;

[0017] The differential mode detection device further includes: the first aperture, and a second aperture disposed on the optical path between the object to be detected and the second photodetector.

[0018] Preferably, the reflection mode detection device further comprises: a first polarizer and / or a first filter arranged on the optical path between the object to be measured and the first aperture;

[0019] The differential mode detection device further includes: the first polarizer and / or the first filter, and a second polarizer and / or the second filter arranged on the light path between the object to be measured and the second aperture.

[0020] Preferably, the device further comprises:

[0021] An amplifying device is arranged on the optical path between the object to be measured and the differential mode detection device, and is used to receive a reflected light beam formed after the detection light beam is reflected from the object to be measured.

[0022] Preferably, the magnifying device comprises a concave lens, a beam expander or a reflector group.

[0023] Preferably, the amplification device and the mode switching device are arranged on the same position control platform;

[0024] The same position control platform is used to control the amplifying device and the mode switching device to simultaneously deviate from the optical path where the reflected light beam of the detection light beam is located, so that the reflection mode detection device is in a working state, or to control the amplifying device and the mode switching device to simultaneously move to the optical path where the reflected light beam after the direction deviation is located, so that the differential mode detection device is in a working state.

[0025] Preferably, the device further comprises:

[0026] A pump light emitting device, used for emitting a pump light beam to the object to be measured, so as to generate a deformation zone on the surface of the object to be measured;

[0027] The detection light emitting device is used to emit a detection light beam to the deformation area of ​​the object to be measured.

[0028] Preferably, the device further comprises:

[0029] An incident beam direction adjustment device, used to adjust the incident direction of the pump beam and / or the detection beam when the reflection mode detection device is in working state, so that the pump beam and the detection beam are focused to the same position of the object to be measured, or;

[0030] When the differential mode detection device is in a working state, the incident direction of the pump light beam and / or the detection light beam is adjusted so that the detection light beam is focused on the deformation area of ​​the object to be detected.

[0031] Preferably, the incident light beam direction adjustment device comprises a piezoelectric deflection device.

[0032] Preferably, the deformation zone includes an area at a first distance d from a first position, the first position being a focusing point of the pump light on the object to be measured, and the first distance d is greater than zero and less than one quarter of the diameter of the pump light spot.

[0033] Preferably, the polarization direction of the detection light beam is different from the polarization direction of the pump light;

[0034] and / or,

[0035] The wavelength of the probe light beam is different from the wavelength of the pump light.

[0036] It can be seen from the above technical solutions that the embodiments of the present invention have the following advantages:

[0037] The photoacoustic detection device in the embodiment of the present application includes: a reflection mode detection device, which is used to receive a reflected light beam of the detection light beam from the object to be detected and measure the light intensity of the reflected light beam;

[0038] A differential mode detection device is used to receive a reflected light beam after the detection light beam is reflected by the object to be measured, and measure the luminous flux of the reflected light beam after the direction is shifted; a mode switching device is used to switch between the reflection mode detection device and the differential mode detection device, so that the photoacoustic detection device is in reflection mode or differential mode.

[0039] Because the photoacoustic detection device in the embodiment of the present application includes a reflection mode detection device and a differential mode detection device, as well as a mode switching device, the photoacoustic detection device includes two detection modes and convenient switching between the two detection modes. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 A schematic diagram of an embodiment of a photoacoustic detection device in an embodiment of the present application;

[0041] Figure 2A This is a schematic diagram of the optical path of the reflection mode in the embodiment of the present application;

[0042] Figure 2B Schematic diagram of the optical path of the differential mode in the embodiment of the present application;

[0043] Figure 3 This is another schematic diagram of a photoacoustic detection device in an embodiment of the present application;

[0044] Figure 4 This is another schematic diagram of a photoacoustic detection device in an embodiment of the present application;

[0045] Figure 5 This is another schematic diagram of a photoacoustic detection device in an embodiment of the present application;

[0046] Figure 6 This is another schematic diagram of a photoacoustic detection device in an embodiment of the present application;

[0047] Figure 7 Schematic diagram of another embodiment of the photoacoustic detection device in the embodiment of the present application. DETAILED DESCRIPTION

[0048] The embodiment of the present invention provides a photoacoustic detection device, which is used to switch between a reflection detection mode and a differential detection mode in the same detection device through a mode switching device, that is, to realize two measurement modes in the same detection device.

[0049] For ease of understanding, the photoacoustic detection device in the embodiment of the present application is described below. Figure 1 , an embodiment of the photoacoustic detection device in the embodiment of the present application includes:

[0050] A reflection mode detection device, used for receiving a reflected light beam of the detection light beam at the object to be detected, and measuring the light intensity of the reflected light beam;

[0051] A differential mode detection device, used for receiving a reflected light beam after the detection light beam is reflected by the object to be detected and after the reflected light beam has been shifted in direction, and measuring the luminous flux of the reflected light beam after the reflected light beam has been shifted in direction;

[0052] The mode switching device is used to switch between the reflection mode detection device and the differential mode detection device, so that the photoacoustic detection device is in the reflection mode or the differential mode.

[0053] Specifically, the reflection mode detection device in the embodiment of the present application includes a first photodetector 101, the differential detection device includes a first photodetector 101 and a second photodetector 102, and the mode switching device includes a beam splitter 103 and a beam splitter position control device 104, wherein the beam splitter position control device 104 is used to control the beam splitter 103 to deviate from the optical path where the reflected optical path of the detection beam is located when the photoacoustic detection device is in the reflection mode, so that the reflected optical path of the detection beam is incident on the first photodetector 101, and when the photoacoustic detection device is in the differential mode, control the beam splitter 103 to move to the optical path where the reflected optical path of the detection beam is located, so that the beam splitter 103 divides the reflected optical path of the detection beam into a first optical beam and a second optical beam, wherein the first optical beam is incident on the first photodetector 101, and the second optical beam is incident on the second photodetector 102.

[0054] As an optional embodiment, the beam splitter 103 in the embodiment of the present application includes a fiber beam splitter or a knife-edge prism, and the beam splitter position control device includes a piezoelectric displacement stage, wherein the piezoelectric displacement stage can drive the beam splitter to move in a direction perpendicular to the light beam to control the beam splitter to deviate from or move to the optical path where the reflected light beam of the detection light beam is located, wherein the present application Figure 1 The beam splitter 103 in the embodiment is a knife-edge prism.

[0055] As an optional embodiment, in order to reduce the loss of light energy in the optical path, the embodiment of the present application sets the optical path of the first light beam between the beam splitter and the first photodetector to be the same as the optical path of the second light beam between the beam splitter and the second photodetector.

[0056] based on Figure 1 For the convenience of understanding, the working principles of the reflection mode and differential mode of the photoacoustic detection device are described below:

[0057] Reflection mode such as Figure 2A As shown in the figure, when the pump light is irradiated to the sample surface, due to the photothermal effect, the sample expands due to the heat and deforms to generate sound waves. When the sound waves encounter the film interface, a reflected echo is generated. When the echo reaches the surface, the material surface will produce corresponding deformation, causing the surface reflectivity to change. In the reflection mode, the probe light and the pump light are irradiated to the same point of the sample. When the sound waves generated by the pump light in the sample return to the sample surface, the reflectivity of the sample film layer will change significantly, so the reflected light intensity of the probe light on the sample surface will also change significantly. We can measure the time t when the reflected light intensity of the probe light changes, and according to T=2*V*t, we can obtain the thickness of the sample film layer, where T is the thickness of the sample film layer, v is the propagation speed of the sound wave in the sample material, and t is the time when the reflected light intensity of the probe light changes.

[0058] Differential mode such as Figure 2B As shown, since the sound waves generated by the pump light in the sample will cause deformation on the sample surface, when the detection light is irradiated to the deformation position, the angle of the reflected light of the detection light will be deflected. Since the angle of the reflected light of the detection light is deflected, the luminous flux of the offset reflected light detected by the detector changes. Therefore, the time t when the reflected light flux of the detection light changes can be obtained, and according to T=2*V*t, the thickness of the sample film layer can be obtained, wherein T is the thickness of the sample film layer, v is the propagation speed of the sound wave in the sample material, and t is the time when the luminous flux of the reflected light of the detection light changes.

[0059] The working principle of the photoacoustic detection device is described below:

[0060] based on Figure 1 In the photoacoustic detection device, when the beam splitter position control device 104 controls the beam splitter 103 to deviate from the optical path where the reflected light beam of the detection light beam is located, the photoacoustic detection device in the present application is in the reflection mode (that is, the detection light and the pump light are irradiated to the same position on the sample surface), and the reflected light beam of the detection light beam is directly incident on the first photodetector 101 to measure the light intensity of the reflected light beam of the detection light beam to obtain the time t when the light intensity of the reflected light beam of the detection light beam changes.

[0061] When the beam splitter position control device 104 controls the beam splitter 103 to be located in the optical path where the reflected beam of the detection beam is located, the photoacoustic detection device in the present application is in differential mode, and the beam splitter 103 divides the reflected beam of the detection beam on the sample surface into a first beam and a second beam, wherein the first beam is incident on the first photodetector 101, and the second beam is incident on the second photodetector 102, and then the light flux detected by the first photodetector is subtracted from the light flux detected by the second photodetector, so as to amplify the change value of the light flux of the reflected beam of the detection beam, thereby making it easier to observe the time t when the light flux of the reflected beam of the detection light changes.

[0062] In the above embodiments, the reflection detection mode and differential detection mode in the photoacoustic detection device, as well as the working principle of the mode switching device are described in detail, thereby realizing that the same photoacoustic detection device includes two detection modes at the same time, as well as convenient switching between the reflection mode and the differential detection mode.

[0063] based on Figure 1 The optical path schematic diagram, in order to eliminate stray light in the environment, the embodiment of the present application, as an optional embodiment, can also be provided before the light receiving surface of the first photodetector and before the light receiving surface of the second photodetector, a first aperture adjustable diaphragm 105 and a second aperture adjustable diaphragm 106, for ease of understanding, Figure 3 Another schematic diagram of the photoacoustic detection device is given.

[0064] As another optional embodiment, when the pump light and the detection light are lasers of different wavelengths, in order to prevent the first photodetector and the second photodetector from receiving the pump light, the embodiment of the present application may further provide a first filter 107 before the light receiving surface of the first photodetector, and a second filter 108 before the light receiving surface of the second photodetector, wherein: Figure 4 Another schematic diagram of the photoacoustic detection device is given.

[0065] As another optional embodiment, when the pump light and the detection light are lasers of the same wavelength band, in order to prevent the first photodetector and the second photodetector from receiving the pump light, the polarization direction of the pump light is generally set to be different from the polarization direction of the detection light. Therefore, in the embodiment of the present application, a first polarizer 109 may be arranged before the light receiving surface of the first photodetector, and a second polarizer 110 may be arranged before the light receiving surface of the second photodetector, wherein: Figure 5 Another schematic diagram of the photoacoustic detection device is given.

[0066] based on Figure 1The optical path schematic diagram, when the photoacoustic detection device is in the differential mode, the deviation angle of the reflected light of the detection light can also be amplified to better measure the luminous flux of the reflected light after the reflection angle is offset. Therefore, the embodiment of the present application can also include an amplifying device 111 on the optical path between the object to be measured (sample) and the differential mode detection device. The amplifying device is used to receive the reflected light beam of the detection light beam at the object to be measured to increase the deviation angle of the reflection direction of the detection light beam. For ease of understanding, Figure 6 A schematic diagram of a photoacoustic detection device with an amplifier is given.

[0067] Specifically, the amplifying device in the embodiment of the present application can be a concave lens, a beam expander or a reflector group. When the amplifying device is a concave lens or a beam expander, the reflected light beam of the detection light can be expanded to increase the deflection angle of the reflected light beam of the detection light. When the amplifying device is a reflector group, the reflected light beam of the detection light passing through the deformation zone of the sample can be received and reflected by the first reflector, and the reflected light beam of the detection light can be incident and reflected at a preset incident angle by setting the second reflector, thereby increasing the offset angle of the reflected light beam of the detection light relative to the original reflected light beam (the original reflected light beam is the reflected light beam of the detection light before the sample is deformed).

[0068] Furthermore, in order to improve the convenience of switching between the reflection mode and the differential mode, the embodiment of the present application can also set the amplifying device and the mode switching device on the same position control platform, wherein the same position control platform is used to control the amplifying device and the mode switching device to simultaneously deviate from the optical path where the reflected light beam of the detection light beam is located (reflection mode), or control the amplifying device and the mode switching device to simultaneously move to the optical path where the reflected light beam of the detection light beam is located (differential mode), that is, the photoacoustic detection device is switched between the reflection mode and the differential mode through the same position control platform.

[0069] Of course, the amplifying device and the mode switching device in the embodiment of the present application can also be set on different position control platforms, so that the amplifying device and the mode switching device can be controlled respectively by different position control platforms to improve the convenience of controlling the amplifying device and the mode switching device.

[0070] Further, based on Figure 1 In the described embodiment, the photoacoustic detection device in the embodiment of the present application may also include a pump light emitting device 112 and a detection light emitting device 113, wherein the pump light emitting device 112 is used to emit a pump light beam to the object to be measured (sample surface) to generate a deformation zone on the surface of the object to be measured, and the detection light emitting device 113 is used to emit a detection light beam to the deformation zone of the object to be measured.

[0071] As an optional embodiment, in order to avoid the influence of the pump light on the detection light measurement, the polarization directions of the pump light and the detection light in the embodiment of the present application can be different from each other, such as the polarization direction of the pump light is horizontal, and the polarization direction of the detection light is vertical; or, the wavelength of the pump light is set to be different from the wavelength of the detection light, such as the wavelength of the pump light is λ1, and the wavelength of the detection light is λ2.

[0072] Furthermore, when the photoacoustic detection device is in the reflection mode, the time t when the light intensity changes is obtained by measuring the light intensity of the detection light. Therefore, in order to better measure the light intensity of the detection light, in the embodiment of the present application, the pump light and the detection light are set to irradiate the same position of the object to be measured, and when the photoacoustic detection device is in the differential mode, the time t when the light flux changes is obtained by measuring the light flux of the reflected light of the detection light after the direction is shifted. Therefore, in order to obtain a reflected light beam with a larger offset angle, the detection light should be incident on the deformation zone of the object to be measured. Therefore, the embodiment of the present application may also include an incident light beam direction adjustment device 114, which is used to adjust the incident direction of the pump light beam and / or the detection light beam, so that in the reflection mode, the pump light and the detection light are irradiated to the same position of the object to be measured, and in the differential mode, the detection light is incident on the deformation zone of the object to be measured.

[0073] As an optional embodiment, the incident light beam direction adjustment device in the embodiment of the present application is a piezoelectric deflection device.

[0074] As an optional embodiment, in the embodiment of the present application, in the differential mode, the deformation zone where the detection light is incident on the object to be measured includes an area at a first distance d from the first position, wherein the first position is the focusing point of the pump light on the object to be measured, and the first distance d is greater than zero and less than one quarter of the spot diameter of the pump light. For ease of understanding, Figure 7 A schematic diagram of a photoacoustic detection device incorporating a pump light emitting device 112 , a detection light emitting device 113 , and an incident light beam direction adjusting device 114 is given.

[0075] As described above, the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features thereof may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A photoacoustic detection device, characterized in that: include: A reflection mode detection device, used for receiving a reflected light beam of the detection light beam at the object to be detected, and measuring the light intensity of the reflected light beam; A differential mode detection device, used for receiving a reflected light beam after the detection light beam is reflected by the object to be detected and after the reflected light beam has been shifted in direction, and measuring the luminous flux of the reflected light beam after the reflected light beam has been shifted in direction; The mode switching device is used to switch between the reflection mode detection device and the differential mode detection device, so that the photoacoustic detection device is in the reflection mode or the differential mode.

2. The photoacoustic detection device according to claim 1, characterized in that: The mode switching device includes: a beam splitter and a beam splitter position control device, the reflection mode detection device includes: a first photodetector, and the differential mode detection device includes: the first photodetector and a second photodetector; The beam splitter position control device is used to control the beam splitter to deviate from the optical path where the reflected beam of the detection beam is located in the reflection mode, so that the reflected beam of the detection beam is incident on the first photodetector, or to control the beam splitter to move to the optical path where the reflected beam of the detection beam is located in the differential mode, so that the beam splitter splits the reflected beam of the detection beam into the first beam and the second beam; The beam splitter is used to split the reflected beam of the detection beam into a first beam and a second beam in the differential mode, so that the first beam is incident on the first photodetector and the second beam is incident on the second photodetector.

3. The photoacoustic detection device according to claim 2, characterized in that: The beam splitter comprises a fiber beam splitter or a knife-edge prism, and the beam splitter position control device comprises a piezoelectric displacement stage.

4. The photoacoustic detection device according to claim 3, characterized in that: A first optical path where the first detector and the beam splitter are located is perpendicular to a second optical path where the second detector and the beam splitter are located; An optical path of the first light beam between the beam splitter and the first photodetector is the same as an optical path of the second light beam between the beam splitter and the second photodetector.

5. The photoacoustic detection device according to claim 2, characterized in that: The reflection mode detection device further comprises: a first aperture disposed on the optical path between the object to be detected and the first photodetector; The differential mode detection device further includes: the first aperture, and a second aperture disposed on the optical path between the object to be detected and the second photodetector.

6. The photoacoustic detection device according to claim 5, characterized in that: The reflection mode detection device further comprises: a first polarizer and / or a first filter arranged on the optical path between the object to be measured and the first aperture; The differential mode detection device further includes: the first polarizer and / or the first filter, and a second polarizer and / or the second filter arranged on the optical path between the object to be measured and the second aperture.

7. The photoacoustic detection device according to claim 1, characterized in that: The device also includes: An amplifying device is arranged on the optical path between the object to be measured and the differential mode detection device, and is used to receive a reflected light beam formed after the detection light beam is reflected by the object to be measured.

8. The photoacoustic detection device according to claim 7, characterized in that: The amplifying device comprises a concave lens, a beam expander or a reflector group.

9. The photoacoustic detection device according to claim 7, characterized in that: The amplifying device and the mode switching device are arranged on the same position control platform; The same position control platform is used to control the amplifying device and the mode switching device to simultaneously deviate from the optical path where the reflected light beam of the detection light beam is located, so that the reflection mode detection device is in a working state, or to control the amplifying device and the mode switching device to simultaneously move to the optical path where the reflected light beam after the direction deviation is located, so that the differential mode detection device is in a working state.

10. The photoacoustic detection device according to claim 1, characterized in that: The device also includes: A pump light emitting device, used for emitting a pump light beam to the object to be measured, so as to generate a deformation zone on the surface of the object to be measured; The detection light emitting device is used to emit a detection light beam to the deformation area of ​​the object to be measured.

11. The photoacoustic detection device according to claim 10, characterized in that: The device also includes: An incident beam direction adjustment device, used to adjust the incident direction of the pump beam and / or the detection beam when the reflection mode detection device is in a working state, so that the pump beam and the detection beam are focused to the same position of the object to be measured, or; When the differential mode detection device is in a working state, the incident direction of the pump light beam and / or the detection light beam is adjusted so that the detection light beam is focused on the deformation area of ​​the object to be detected.

12. The photoacoustic detection device according to claim 11, characterized in that: The incident light beam direction adjustment device comprises a piezoelectric deflection device.

13. The photoacoustic detection device according to claim 11, characterized in that: The deformation zone includes an area at a first distance d from a first position, the first position being a focusing point of the pump light on the object to be measured, and the first distance d is greater than zero and less than one quarter of the diameter of the pump light spot.

14. The photoacoustic detection device according to claim 10, characterized in that: The polarization direction of the detection light beam is different from the polarization direction of the pump light; and / or, The wavelength of the probe light beam is different from the wavelength of the pump light.

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