A photothermal deflection spectrum testing device with wide wavelength coverage

Abstract

The invention discloses a photothermal deflection spectrum test device with wide wavelength coverage, comprising a pump light source, a monochromator, an optical chopper and a beam splitter arranged in sequence along the optical path; a photodetector is arranged on the reflected optical path of the beam splitter, and an absorption cell is arranged on the transmitted optical path of the beam splitter; the signal output end of the photodetector is connected to a computer; the absorption cell is respectively provided with a detection light source and a position-sensitive detector on two sides perpendicular to the transmitted optical path of the beam splitter; the signal output end of the position-sensitive detector is connected to a phase-locked amplifier and a computer in sequence; the absorption cell is used to accommodate a heat-conducting medium, and a sample stage is fixed at the bottom, and the sample stage is used to fix the film to be tested; a focusing lens is provided between the absorption cell and the beam splitter, and the pump light transmitted through the beam splitter enters the absorption cell through the focusing lens; the pump light source adopts a laser-driven broadband light source, which is used to emit a pump light of 170nm to 2100nm. By using the present invention, the testing requirements from narrow bandgap materials to wide bandgap materials can be met at the same time.

Description

Technical Field

[0001] The present invention belongs to the technical field of spectrum detection, and in particular relates to a photothermal deflection spectrum testing device with wide wavelength coverage. Background Art

[0002] Thin films are the basis of optoelectronic devices and directly determine their performance. Existing general thin film characterization methods are often limited in their applicability and low in sensitivity. Therefore, it is necessary to develop a thin film characterization method with a wide range of applications and high sensitivity to guide the development and application of optoelectronic devices.

[0003] At present, there are many thin film characterization methods based on light absorption. For example, Chinese patent document with publication number CN106546536A discloses a high-precision thin film weak absorption test device and method, and Chinese patent document with publication number CN105021627A discloses a highly sensitive and rapid online detection method for laser damage on the surface of optical thin films and components.

[0004] After the film absorbs light, it can release light energy or heat energy. The phenomenon that the material absorbs light energy and converts it into heat energy is called the photothermal effect. A beam of pump light is irradiated on the film, and the film absorbs light and generates heat. In the medium area near the film, a temperature gradient is generated due to thermal diffusion. The refractive index of the medium is related to the temperature, thus forming a refractive index gradient. The probe light passes through the area above the film with a significant refractive index gradient, and the direction of travel is deflected. There is a quantitative relationship between the deflection amount of the probe light and the absorbance of the film. The above characterization method based on the photothermal effect is called photothermal deflection spectroscopy technology.

[0005] Limited by the low power output of common pump light sources (such as xenon lamps) in the ultraviolet and near-infrared regions and the structure of the entire test device, the reported photothermal deflection spectroscopy test devices cannot meet the high-sensitivity testing requirements of narrow-bandgap materials and wide-bandgap materials. Summary of the invention

[0006] In order to solve the deficiencies in the prior art, the present invention provides a photothermal deflection spectrum testing device with wide wavelength coverage, which can simultaneously meet the testing requirements from narrow bandgap materials to wide bandgap materials.

[0007] The technical solution of the present invention is as follows:

[0008] A photothermal deflection spectrum testing device with wide wavelength coverage, comprising a pump light source, a monochromator, an optical chopper and a beam splitter arranged in sequence along an optical path; a photodetector is arranged on the reflected light path of the beam splitter, and an absorption cell is arranged on the transmitted light path of the beam splitter; a signal output end of the photodetector is connected to a computer;

[0009] The absorption cell is provided with a detection light source and a position-sensitive detector on two sides perpendicular to the beam splitter transmission light path; the signal output end of the position-sensitive detector is connected to a phase-locked amplifier and a computer in sequence;

[0010] The absorption cell is used to contain a heat-conducting medium, and a sample stage is fixed on the inner bottom surface of the absorption cell, and the sample stage is used to fix the film to be tested; a focusing lens is provided between the absorption cell and the beam splitter, and the pump light transmitted through the beam splitter enters the absorption cell through the focusing lens;

[0011] The pump light source adopts a laser-driven broadband light source, which is used to emit pump light of 170nm to 2100nm.

[0012] When the present invention is tested, the output light of the pump light source is introduced into a monochromator controlled by a computer, and monochromatic light of a specific band is derived; the monochromatic light is modulated in light intensity by an optical chopper arranged after the monochromator, and the modulation frequency is introduced into a phase-locked amplifier as a reference signal; the beam splitter divides the light into two beams, and the photoelectric detector monitors the light intensity of one of the beams, and the signal is transmitted to a computer, and the other beam is introduced into an absorption cell; the film to be tested and the substrate are fixed in the sample stage, the position of the film in the optical path is fixed, and the absorption cell is filled with a heat-conducting medium; the pump light is irradiated on the film, and the detection light emitted by the detection light source passes over the top of the film; the position-sensitive detector is arranged on the output light path of the absorption cell, and the detection signal is transmitted to the phase-locked amplifier for demodulation; the signal demodulated by the phase-locked amplifier is transmitted to the computer.

[0013] The pump light source adopts a laser-driven broadband light source. The pump light has a strong power distribution from the ultraviolet region (~170nm) to the infrared region (~2100nm), which meets the testing requirements from narrow bandgap materials such as (lead selenide, lead telluride, etc.) to wide bandgap materials (such as zinc oxide, nickel oxide, etc.), greatly expanding the application scope of photothermal deflection spectroscopy technology.

[0014] The heat-conducting medium filled in the absorption cell needs to be a fluid that has no absorption of pump light and detection light, has low thermal conductivity, small refractive index, and large refractive index change with temperature, so as to form a larger refractive index gradient, increase the deflection amount of detection light, and improve test sensitivity. Preferably, the heat-conducting medium is a perfluoroalkane.

[0015] Preferably, the sample stage is provided with two groups of steps symmetrically arranged in the vertical direction, the two groups of steps constitute a concave structure, the sample stage is provided with a light-transmitting hole at the bottom of the concave structure, and the two groups of steps are provided with a fixing portion for fixing a substrate, and the substrate is used to place the film to be tested.

[0016] Optionally, the fixing portion includes two groups of mounting holes symmetrically arranged on the two groups of steps and a clamping piece arranged on the mounting holes for clamping the base.

[0017] In order to facilitate the fixing and disassembly of the sample stage in the absorption cell, the inner bottom surface of the absorption cell is provided with a groove which is embedded and matched with the lower end of the sample stage.

[0018] Preferably, the detection light emitted by the detection light source passes in front of the outer surface of the film to be tested, and is less than 50 μm away from the outer surface of the film to be tested, so that the detection light passes through a region with a larger refractive index gradient, resulting in a larger deflection, thereby improving the test sensitivity.

[0019] Preferably, the spot diameter of the pump light emitted by the pump light source irradiating the film to be tested is greater than 3 μm, and the spot diameter can be adjusted by the front and rear positions of the focusing lens, so that the detection light passes through a sufficiently long area with a refractive index gradient, resulting in a larger deflection and improving the signal-to-noise ratio.

[0020] Preferably, the photothermal deflection spectrum testing device is built on a seismic isolation platform to reduce the disturbance of ground vibration to the optical path, reduce the intensity of interference signals, and improve the signal-to-noise ratio.

[0021] Preferably, the optical chopper is connected to a lock-in amplifier, and a signal of the optical chopper is input to a reference signal terminal of the lock-in amplifier.

[0022] Furthermore, during testing, the entire optical path system is covered with an opaque cover to reduce the intensity of interference signals caused by external stray light and air disturbances, thereby increasing the signal-to-noise ratio.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1. The present invention adopts a laser-driven broadband light source as a pump light source, and the spectral detection range covers part of the far ultraviolet region to most of the near infrared region, while meeting the high-sensitivity detection requirements from narrow-bandgap materials (such as lead selenide, lead telluride, etc.) to wide-bandgap materials (such as zinc oxide, nickel oxide, etc.).

[0025] 2. The device of the present invention has a simple structure, is easy to install and operate, and has a high detection sensitivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 A schematic diagram of the optical path of a photothermal deflection spectrum testing device with wide wavelength coverage according to the present invention;

[0027] Figure 2 Schematic diagram of a top view of an absorption tank in an embodiment of the present invention;

[0028] Figure 3 It is a schematic diagram of the structure of the sample stage in the present embodiment;

[0029] Figure 4 It is the emission spectrum of the deuterium lamp in the prior art;

[0030] Figure 5 The emission spectrum of the laser-driven broadband light source EQ-99X in the embodiment of the present invention;

[0031] Figure 6 1 is the UV-visible absorption spectrum of the wide bandgap material in the embodiment of the present invention, wherein (a) is the UV-visible absorption spectrum of zinc oxide nanocrystals; (b) is the UV-visible absorption spectrum of nickel oxide nanocrystals.

[0032] In the figure: 1-pump light source; 2-monochromator; 3-optical chopper; 4-beam splitter; 5-photodetector; 6-detection light source; 7-absorption cell; 71-film to be tested; 72-substrate; 73-heat-conducting medium; 74-sample stage; 741-concave structure; 742-light-transmitting hole; 743-mounting hole; 8-position-sensitive detector; 9-phase-locked amplifier; 10-computer; 11-focusing lens. DETAILED DESCRIPTION

[0033] The present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be pointed out that the embodiments described below are intended to facilitate the understanding of the present invention and do not have any limiting effect on the present invention.

[0034] like Figure 1 As shown, a photothermal deflection spectrum test device with wide wavelength coverage includes a pump light source 1, a monochromator 2, an optical chopper 3, a beam splitter 4, a detection light source 6, an absorption cell 7, a position-sensitive detector 8, a photodetector 5, a lock-in amplifier 9, and a computer 10. The entire photothermal deflection spectrum test device is built on a seismic isolation platform.

[0035] Among them, a pump light source 1, a monochromator 2, an optical chopper 3 and a beam splitter 4 are arranged in sequence along the optical path; a photodetector 5 is arranged on the reflected light path of the beam splitter 4, and an absorption pool 7 is arranged on the transmitted light path of the beam splitter 4; and a signal output end of the photodetector 5 is connected to a computer 10.

[0036] The absorption cell 7 is provided with a detection light source 6 and a position-sensitive detector 8 on two sides perpendicular to the transmission light path of the beam splitter 4; the signal output end of the position-sensitive detector 8 is connected to a phase-locked amplifier 9 and a computer 10 in sequence.

[0037] The pump light source 1 emits pump light PP which is introduced into the monochromator 2 controlled by the computer 10 through the optical fiber, and the pump light PP of a specific wavelength band is derived. In order to meet the requirements of universality and high sensitivity of the test, the device of the present invention uses a laser-driven broadband light source, such as EQ-99X (emission spectrum see Figure 5 ) as the pump light source 1. Meanwhile, the spectroscopic range of the monochromator 2 matches the pump light source 1.

[0038] Compared with the ordinary deuterium lamp emission spectrum (see Figure 4As shown in the figure, the spectral detection range of the laser-driven broadband light source adopted in the present invention covers part of the far ultraviolet region to most of the near infrared region, and at the same time meets the high-sensitivity detection requirements from narrow-bandgap materials (such as lead selenide, lead telluride, etc.) to wide-bandgap materials (such as zinc oxide, nickel oxide, etc.).

[0039] The pump light PP passes through the optical chopper 3 placed after the monochromator 2 , and the intensity of the pump light PP is modulated; the signal of the optical chopper 3 is input to the reference signal terminal of the lock-in amplifier 9 .

[0040] The beam splitter 4 splits the pump light PP into two beams, one of which is a reflected light beam received by the photodetector 5 to eliminate the test error caused by the power change of the pump light source 1. The signal of the photodetector 5 is processed and input into the computer 10. The other transmitted light beam is injected into the absorption cell 7.

[0041] like Figure 2 As shown, the absorption cell 7 is filled with a heat-conducting medium 73, a sample stage 74 is fixed at the bottom, and a base 72 for fixing the film 71 to be tested is provided on the sample stage 74. A focusing lens 11 is also provided between the absorption cell 7 and the beam splitter 4, and the pump light transmitted through the beam splitter 4 enters the absorption cell 7 through the focusing lens 11.

[0042] After the transposition and installation is completed, the film 71 to be tested and the substrate 72 are fixed in the sample stage 74, the sample stage 74 is fixed in the absorption cell 7, and the position of the absorption cell 7 is fixed, thereby the position of the film 71 to be tested in the optical path is fixed.

[0043] like Figure 3 As shown, the sample stage 74 is provided with two groups of steps symmetrically arranged in the vertical direction, the two groups of steps constitute a concave structure 741, the sample stage 74 is provided with a light-transmitting hole 742 at the bottom of the concave structure 741, and two groups of mounting holes 743 are symmetrically arranged on the two groups of steps, and the number of mounting holes (743) in each group is three, and the mounting holes 743 are provided with clips (not shown in the figure) for clamping the base 72.

[0044] In order to facilitate the fixing and removal of the sample stage 74 in the absorption cell 7 , the inner bottom surface of the absorption cell 7 is provided with a groove which is embedded and matched with the lower end of the sample stage 74 .

[0045] In this embodiment, the absorption pool 7 is filled with a heat-conducting medium - perfluoroalkane, which has low thermal conductivity, small refractive index, large refractive index change with temperature, and no absorption of pump light PP and detection light PB. After the pump light PP is focused, it is irradiated on the film to be tested 71 to form a light spot with a diameter greater than 3 mm; the film to be tested 71 absorbs light to generate heat; in the area of ​​the heat-conducting medium 73 near the film to be tested 71, due to heat diffusion, a temperature gradient is generated, and the temperature is higher as it is closer to the film surface. The higher the temperature of the heat-conducting medium 73, the smaller the refractive index, thereby forming a refractive index gradient, and the refractive index is smaller as it is closer to the film surface.

[0046] The detection light PB emitted by the detection light source 6 enters the absorption cell 7 and passes through the high refractive index gradient area less than 50μm from the film surface; affected by the refractive index gradient, the detection light PB is deflected away from the film. The position-sensitive detector 9 is placed on the outgoing light path of the absorption cell 7, and the detection signal is transmitted to the phase-locked amplifier 9 for demodulation; the demodulated signal of the phase-locked amplifier 9 is transmitted to the computer 10 for data analysis.

[0047] like Figure 6 The figure shows the UV-visible absorption spectra of the wide bandgap materials in this embodiment, where (a) is the UV-visible absorption spectrum of zinc oxide nanocrystals; (b) is the UV-visible absorption spectrum of nickel oxide nanocrystals. It can be seen that the absorption peaks of the two wide bandgap oxide nanocrystals are both in the ultraviolet band below 350nm. The radiation spectrum of ordinary xenon lamps cannot cover this band, while the laser-driven broadband light source used in the present invention has a strong distribution in this band, which can be used for high-sensitivity and accurate testing.

[0048] The embodiments described above provide a detailed description of the technical solutions and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, supplements and equivalent substitutions made within the scope of the principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A photothermal deflection spectrum testing device with wide wavelength coverage, characterized in that: It comprises a pump light source (1), a monochromator (2), an optical chopper (3) and a beam splitter (4) arranged in sequence along an optical path; a photodetector (5) is arranged on the reflected light path of the beam splitter (4), and an absorption cell (7) is arranged on the transmitted light path of the beam splitter (4); a signal output end of the photodetector (5) is connected to a computer (10); The absorption cell (7) is provided with a detection light source (6) and a position-sensitive detector (8) on two side surfaces perpendicular to the transmission light path of the beam splitter (4); the signal output end of the position-sensitive detector (8) is connected to a phase-locked amplifier (9) and a computer (10) in sequence; The absorption cell (7) is used to contain a heat-conducting medium (73), wherein the heat-conducting medium (73) is a perfluoroalkane. A sample stage (74) is fixed to the inner bottom surface of the absorption cell (7), wherein the sample stage (74) is used to fix the film to be tested (71). A focusing lens (11) is provided between the absorption cell (7) and the beam splitter (4), and the pump light transmitted through the beam splitter (4) enters the absorption cell (7) through the focusing lens (11). The detection light emitted by the detection light source (6) passes through the front of the outer surface of the film to be tested (71), and the distance from the outer surface of the film to be tested (71) is less than 50 μm. The pump light source (1) adopts a laser-driven broadband light source for emitting pump light of 170nm-2100nm; the pump light emitted by the pump light source (1) irradiates the film (71) to be tested with a spot diameter greater than 3mm, and the spot diameter is adjusted by the front and rear positions of the focusing lens (11), so that the detection light passes through a sufficiently long area with a refractive index gradient, resulting in a larger deflection, thereby improving the signal-to-noise ratio.

2. The photothermal deflection spectrum testing device with wide wavelength coverage according to claim 1, characterized in that: The sample stage (74) is provided with two groups of steps symmetrically arranged in the vertical direction, the two groups of steps forming a concave structure (741), the sample stage (74) is provided with a light-transmitting hole (742) at the bottom of the concave structure (741), and the two groups of steps are provided with fixing parts for fixing a substrate (72), and the substrate (72) is used to place a film (71) to be tested.

3. The photothermal deflection spectrum testing device with wide wavelength coverage according to claim 2, characterized in that: The fixing portion comprises two groups of mounting holes (743) symmetrically arranged on the two groups of steps and a clamping piece arranged on the mounting holes (743) for clamping the base (72).

4. The wide wavelength coverage photothermal deflection spectrum testing device according to claim 1, characterized in that: The inner bottom surface of the absorption pool (7) is provided with a groove which fits into the lower end of the sample stage (74).

5. The photothermal deflection spectrum testing device with wide wavelength coverage according to claim 1, characterized in that: The photothermal deflection spectrum testing device is built on a seismic isolation platform.

6. The photothermal deflection spectrum testing device with wide wavelength coverage according to claim 1, characterized in that: The optical chopper (3) is connected to a lock-in amplifier (9), and a signal from the optical chopper (3) is input to a reference signal terminal of the lock-in amplifier (9).

Images