CN216771491U - Polarization resolution second harmonic testing device - Google Patents
Polarization resolution second harmonic testing device Download PDFInfo
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- CN216771491U CN216771491U CN202123417412.XU CN202123417412U CN216771491U CN 216771491 U CN216771491 U CN 216771491U CN 202123417412 U CN202123417412 U CN 202123417412U CN 216771491 U CN216771491 U CN 216771491U
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Abstract
The utility model discloses a polarization resolution second harmonic testing device which comprises a laser, a first polarizing film, a quarter glass, a light splitting lens, a second polarizing film, a microscope objective and a sample, wherein the laser, the first polarizing film, the quarter glass, the light splitting lens, the second polarizing film, the microscope objective and the sample are sequentially arranged, a filter, a focusing lens and a signal acquisition device are sequentially arranged, the optical axis of the first polarizing film and the optical axis of the quarter glass form an angle of 45 degrees, the light splitting lens is used for transmitting circularly polarized light output from the quarter glass and then sequentially focusing the circularly polarized light on the sample through the second polarizing film and the microscope objective, and a second harmonic signal emitted by the sample sequentially passes through the microscope objective and the second polarizing film and then is reflected by the microscope objective and then enters a collection light path. The microscopic imaging method is simpler, the measurement result is more accurate, the application range is wider, and the adopted optical components are common optical components, so that the cost is low, the microscopic imaging method can be widely used for crystal axis detection of two-dimensional materials, and is suitable for popularization.
Description
Technical Field
The utility model relates to the technical field of nonlinear micro-area spectral measurement, in particular to a polarization resolution second harmonic testing device.
Background
In recent years, two-dimensional materials represented by graphene and transition metal sulfides have attracted much attention due to their excellent electrical, optical, and mechanical properties. Accurate determination of the crystal axis orientation of such materials is important for studying their properties and for producing two-dimensional material heterojunctions with precise twist angles. Common crystal axis determination methods include transmission electron microscopy and second harmonic optical methods. The transmission electron microscope method utilizes a scattering pattern of collision of electron beams and atoms in a material to determine information such as crystal lattices, density and the like, but the method can cause great damage to a sample, and the sample preparation is troublesome, the equipment is expensive, and the fine operation of special personnel is required. For a crystal material with a non-centrosymmetric structure, frequency-doubled output, i.e. second harmonic, can be generated under the excitation of higher optical power. The second harmonic effect is directly related to the symmetry of the crystal structure, the intensity of the second harmonic effect is very sensitive to the crystal structure, and the corresponding crystal structure can be analyzed and the crystal axis orientation can be determined by detecting the angular distribution diagram of the second harmonic which is co-polarized with the exciting light. The method has the characteristics of nondestructive testing, simplicity, rapidness and the like, and is widely used for measuring the crystal axis orientation of the two-dimensional material. In the measurement of the crystal structure by using a second harmonic optical method, the angular distribution of second harmonics which have the same polarization with exciting light needs to be measured, and at present, two methods are mainly used for realizing the measurement of the angular distribution of the second harmonics; one is to place the sample on a rotating table, obtained by rotating the sample 360 °, as described in documents [ y.li, et al; as shown in Nano lett.13, 3329-3333 (2013), the method requires that the position to be measured of the sample must be located at the center of the rotating platform, the positioning accuracy is high, and the method is not suitable for measuring some samples which cannot be placed on the rotating platform, such as some samples which are placed in a low-temperature chamber (the low-temperature chamber is generally heavy and cannot rotate due to external components). Another approach is to place an 1/2 slide in the excitation light path to change the polarization state of the excitation light and a polarizer in the second harmonic collection path to detect its polarization state, as described in the literature [ s.klimmer, et al; nat. photonics,15, 837-842 (2021) ], this method requires precise alignment of 1/2 slide and polarizer, ensuring that they always maintain the polarization in the same direction during rotation, is cumbersome to operate and requires two rotation stages. Therefore, a simple and flexible polarization-resolved second harmonic device and method for measuring the optical axis of a two-dimensional material are in need of development.
SUMMERY OF THE UTILITY MODEL
The utility model aims to provide a polarization-resolved second harmonic testing device to overcome the defects in the prior art.
In order to achieve the purpose, the technical scheme adopted by the utility model is as follows:
a polarization resolution second harmonic testing device comprises a laser, a first polaroid, a quarter glass, a beam splitter lens, a second polaroid, a microscope objective, a sample, a filter, a focusing lens and a signal acquisition device, the optical axis of the first polaroid and the optical axis of the quarter glass sheet form an angle of 45 degrees, the spectroscope is used for transmitting circularly polarized light output from the quarter glass sheet and then sequentially focusing the circularly polarized light on a sample through the second polaroid and the microscope objective lens, the second harmonic signal emitted by the sample passes through the microscope objective lens and the second polaroid in sequence, is reflected by the spectroscope plate to enter the collection light path, passes through the filter plate and the focusing lens on the collection light path in sequence and is collected by the signal collecting device, the polaroid is fixed on the electric rotating platform, and the signal acquisition device and the electric rotating platform are both connected with the control computer.
Further, the light splitting lens is a dichroic mirror or a semi-reflecting and semi-permeable lens.
Further, the signal acquisition device is a spectrometer or a photodetector.
Further, the light path of the light splitting lens and the light collecting path form an angle of 90 degrees.
Compared with the prior art, the utility model has the advantages that: the microscopic imaging method is simpler, the measurement result is more accurate, the application range is wider, and the adopted optical components are common optical components, so that the cost is low, the microscopic imaging method can be widely used for crystal axis detection of two-dimensional materials, and is suitable for popularization.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
FIG. 1 is a schematic diagram of an optical path of a polarization-resolved second harmonic testing apparatus according to the present invention.
FIG. 2 is a graph of the intensity profile at the finger where the second harmonic peak is collected as a function of the angular distribution in the present invention.
In the figure: the device comprises a laser 1, a first polaroid 2, a quarter glass 3, a beam splitting lens 4, a filter 5, a focusing lens 6, a signal acquisition device 7, a second polaroid 8, a microscope objective 9, a sample 10 and a control computer 11.
Detailed Description
The preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings so that the advantages and features of the present invention can be more easily understood by those skilled in the art, and the scope of the present invention will be more clearly and clearly defined.
Referring to fig. 1, the embodiment discloses a polarization-resolved second harmonic testing device, which comprises a laser 1, a first polarizer 2, a quarter glass 3, a splitting lens 4, a second polarizer 8, a microscope objective 9, a sample 10, a filter 5, a focusing lens 6, and a signal collecting device 7, wherein the filter 5, the focusing lens 6, and the signal collecting device 7 are sequentially arranged, an angle between an optical axis of the first polarizer 2 and an optical axis of the quarter glass 3 is 45 degrees, the splitting lens 4 is used for transmitting circularly polarized light output from the quarter glass 3 and then sequentially focusing the circularly polarized light on the sample 10 through the second polarizer 8 and the microscope objective 9, a second harmonic signal emitted by the sample 10 sequentially passes through the microscope objective 9 and the second polarizer 8 and then is reflected by the splitting lens 4 to enter a collecting light path, and then sequentially passes through the filter 5 and the focusing lens 6 on the collecting light path to be collected by the signal collecting device 7, the polaroid 8 is fixed on the electric rotating platform, and the signal acquisition device 7 and the electric rotating platform are both connected with the control computer 11.
In this embodiment, the laser 1 is used as an excitation source for emitting excitation laser; the first polarizing plate 2 is used for converting laser light into linearly polarized light; the quarter glass 3 is used for converting the excitation laser into circularly polarized light; the beam splitting lens 4 is used for transmitting the excitation light and reflecting the signal light; the filter 5 is used for filtering stray light except the second harmonic signal; the focusing lens 6 is used for focusing the second harmonic signal on the spectrograph; the signal acquisition device 7 is used for acquiring a second harmonic spectrum signal; the second polarizer 8 is used for accurately rotating the polarization angle of the incident laser; the microscope objective 9 is used for focusing the excitation laser on a sample to be detected; taking the sample 10 as a sample to be detected; the control computer 11 is used for controlling the electric rotating platform and collecting second harmonic signal data.
In this embodiment, the dichroic mirror or the semi-reflective and semi-transparent mirror can be selected by the light splitting lens 4 according to different excitation and collection wavelengths.
In this embodiment, the signal collection device 7 can select a spectrometer or a photodetector according to the test requirement.
In this embodiment, the two paths of light output by the spectroscopic lens 4 form an angle of 90 °.
In this embodiment, the signal acquisition in the computer 11 may be performed by using a tool such as Labview to couple the electric turntable and the signal acquisition device 7.
As a group of preferred embodiments, the laser 1 has a center wavelength of 1550nm, a pulse width of 100fs, and a repetition frequency of 80 MHz; the first polaroid 2 and the quarter glass 3 are wide spectrum glass, and the working wavelength of the wide spectrum glass covers the emergent wavelength of the laser; the light splitting lens 4 is a semi-reflecting and semi-transparent lens, transmits the wavelength of more than 800nm and reflects the wavelength of less than 800 nm; the filter 5 is a short-pass filter with a cut-off wavelength of 950 nm; the focusing lens 6 is a convex lens; the signal acquisition device 7 is a spectrometer; the second polarizing film 8 is a wide-spectrum polarizing film, and the working wavelength of the second polarizing film covers the excitation laser and the two-dimensional harmonic wavelength of the excitation laser; the microscope objective 9 is a 50x wide-spectrum objective; sample 10 was a single layer MoS2A sample; the control computer 11 is a computer equipped with control and data acquisition software.
Specifically, the first polarizer 2 and the quarter-glass 3 convert the excitation laser into circularly polarized light, and the excitation light passes through the beam splitting lens and another second polarizer fixed on the electric rotating tableThe two polarizing plates 8 are focused on a sample through a microscope objective 9; the second harmonic signal emitted by the sample is reflected back to the microscope objective 9, passes through a second polaroid fixed on the electric rotating platform, and then is reflected by the beam splitting lens 4 to enter a collection light path, and the collection light path consists of a filter 5, a convex lens 6 and a signal acquisition device 7; the second polaroid 8 fixed on the electric rotating table is controlled by software to rotate 360 degrees and synchronously acquire second harmonic data, so that an angular distribution diagram of the second harmonic component in the same polarization state as the incident laser can be obtained. The angular distribution map can be used for rapidly and accurately judging a specific sample such as single-layer MoS2The direction of the crystal axis.
The utility model also provides a polarization resolution second harmonic testing method, which comprises the following steps:
step S1, calibrating the light path to make the optical axes of the excitation laser, the quarter slide 3 and the microscope objective 9 on the same straight line;
step S2, calibrating the first polaroid 2 and the quarter-wave slide 3, rotating the quarter-wave slide 3 to enable the polarization direction of emergent light from the first polaroid 2 to form an angle of 45 degrees with the optical axis of the polaroid 2 so as to generate circularly polarized light, rotating the second polaroid 8 for a circle, measuring the output power of the second polaroid by using a power meter, and repeatedly adjusting the angle of the quarter-wave slide 3 so that the intensity of the emergent light is not changed along with the rotation of the second polaroid 8.
Step S3, placing the sample 10 on a sample stage, turning on laser, adjusting the power of the laser, ensuring that the signal acquisition device 7 can acquire clear second harmonic signals, electrically controlling the second polarizer 8 to rotate 360 degrees by using the control computer 11, and synchronously acquiring second harmonic spectrum signals by using the signal acquisition device 7, wherein the initial position of the second polarizer 8 is set to be the horizontal direction, and the rotation step length is set to be 5 degrees.
Step S4, determining the crystal axis direction of the sample 10 according to the collected second harmonic signal angular distribution diagram (as shown in fig. 2) and the initial polarization direction of the second polarizer 8.
Specifically, the second harmonic is based on the second-order nonlinear interaction between light and a substance, and when laser with frequency omega exceeding a certain power is irradiated on a material with a non-centrosymmetric structureWhen the material is loaded, the material can send out a second harmonic signal with the frequency of 2 omega. The second harmonic signal is very sensitive to the structure of the sample, and the information such as the crystal axis direction of the sample can be detected by detecting the second harmonic signal resolved by polarization. In a single layer of MoS2For example, the material has a 3 rd order rotational symmetry structure, as shown in FIG. 2. Assuming that the initial position of the second polarizing plate 8 is the horizontal direction, the angular distribution of the second harmonic signal having the same polarization direction as that of the excitation light is calculated by the following formula:
wherein theta is an included angle between the polarization direction of the second harmonic and the horizontal direction, I0Is the maximum of the second harmonic signal,
namely single-layer MoS2The angle between the plane of symmetry of (a) and the horizontal direction. The angular distribution map is a plurality of angular distributions I calculated according to the above formula||Is drawn.
Therefore, the crystal axis direction of the two-dimensional material can be accurately determined by detecting the second harmonic signal resolved by polarization.
The utility model improves the existing device for detecting the crystal axis of the two-dimensional material by using a second harmonic optical method, and the microscopic imaging method is simpler, has more accurate measurement result and wider application range. The utility model adopts common optical components, has low cost, can be widely used for crystal axis detection of two-dimensional materials, and is suitable for popularization.
Although the embodiments of the present invention have been described with reference to the accompanying drawings, various changes or modifications can be made by the owner within the scope of the appended claims, and the scope of the present invention should be covered by the owner as long as the protection scope of the present invention is not exceeded by the claims.
Claims (4)
1. A polarization resolution second harmonic testing device is characterized by comprising a laser, a first polaroid, a quarter glass, a beam splitting lens, a second polaroid, a microscope objective and a sample which are arranged in sequence, a filter, a focusing lens and a signal acquisition device which are arranged in sequence, the optical axis of the first polaroid and the optical axis of the quarter glass sheet form an angle of 45 degrees, the spectroscope is used for transmitting circularly polarized light output from the quarter glass sheet and then sequentially passing through the second polaroid and the microscope objective lens to be focused on a sample, the second harmonic signal emitted by the sample passes through the microscope objective lens and the second polaroid in sequence, is reflected by the spectroscope plate to enter the collection light path, passes through the filter plate and the focusing lens on the collection light path in sequence and is collected by the signal collecting device, the polaroid is fixed on the electric rotating table, and the signal acquisition device and the electric rotating table are both connected with the control computer.
2. The polarization-resolved second harmonic testing apparatus of claim 1, wherein the beam splitter is a dichroic mirror or a semi-reflective semi-transparent mirror.
3. The polarization-resolved second harmonic testing apparatus of claim 1, wherein the signal acquisition device is a spectrometer or a photodetector.
4. The polarization-resolving second harmonic testing apparatus of claim 1, wherein the light path of the beam splitting optics is at a 90 ° angle to the collection light path.
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN114441454A (en) * | 2021-12-31 | 2022-05-06 | 中国人民解放军国防科技大学 | Polarization resolution second harmonic testing device and method |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN114441454A (en) * | 2021-12-31 | 2022-05-06 | 中国人民解放军国防科技大学 | Polarization resolution second harmonic testing device and method |
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