CN113567400A - Device capable of measuring second harmonic of substance under ultrahigh pressure condition and application thereof - Google Patents
Device capable of measuring second harmonic of substance under ultrahigh pressure condition and application thereof Download PDFInfo
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
- G01N21/63—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light optically excited
Abstract
The invention discloses a device capable of measuring the second harmonic of a substance under an ultrahigh pressure condition, which comprises a laser excitation part, a polarization part and a light source part, wherein the laser excitation part is used for providing incident laser and converting the incident laser into polarized light; the microscopic light path part changes the light path of the polarized light until the polarized light is focused on a sample to be measured, excites the second harmonic and enables the second harmonic to return along the original light path of the incident laser; the object carrying part comprises a diamond anvil cell press for placing and fixing a sample to be tested; and a signal receiving section that receives the laser signal of the second harmonic returned from the microscopic optical path section and converts the laser signal into an electric signal. By the device, under the condition of changing environmental pressure, external interference is eliminated, so that the secondary harmonic intensity of the collected powder sample is accurately changed along with the pressure, the secondary harmonic intensity of the single crystal sample under the pressure change along with the polarization angle of the incident laser, and finally, in-situ high-voltage secondary harmonic measurement in the DAC is realized. The invention also discloses a method for measuring the second harmonic of the substance under the condition of ultrahigh pressure.
Description
Technical Field
The invention relates to the technical field of nonlinear optical in-situ measurement under extreme conditions. And more particularly, to a device capable of measuring the second harmonic of a substance under ultra-high pressure conditions and applications thereof.
Background
A Diamond Anvil Cell (DAC) is the only scientific device capable of generating million-atmosphere static pressure at present and is the most important scientific instrument in the field of high-pressure science and technical research. In recent years, by utilizing various in-situ measurement methods on DAC, a plurality of pressure-induced singular physical properties are discovered, important physical parameters related to an atomic arrangement structure, a lattice vibration mode, an electronic energy level structure and the like are obtained, and physical properties of a plurality of substances in an ultrahigh pressure environment, such as structures, electricity, optics, chemical bonds and the like, are known. However, to date, the measurement of second harmonics within DACs is still in the infancy. There is currently little work in DAC arrangements to test samples for second harmonic because of the many uncertainty factors associated with the measurement of second harmonic. If the measurement of the second harmonic of the sample under high pressure can be realized, the progress of the nonlinear optics field under high pressure can be promoted, and meanwhile, the combination with other testing methods under high pressure is more favorable for providing wider visual field for high pressure scientific research, more novel high pressure phenomena are revealed, and the development of high pressure science is promoted.
The high-voltage in-situ second harmonic measurement is realized on the DAC, and the method has important significance for a plurality of scientific researches. On the structural chemistry level, only the point group crystallized in non-centrosymmetric crystal has the second harmonic effect, so that the structural information of the material can be well identified by realizing the in-situ detection of the second harmonic in DAC, and the technology can become an important central-non-central structure judgment means under high pressure. In addition, the second harmonic is also a method for detecting fine magnetic sequences in a few magnetic semiconductors with high sensitivity, the combination of the optical second harmonic and the magnetic properties under high voltage can better expand the novel physical phenomena under high voltage, and the combination of the optical second harmonic and the magnetic properties under high voltage is still blank at present. Finally, the combination of optical second harmonic wave and properties of ferroelectricity, piezoelectricity, pyroelectricity and the like under high voltage is beneficial to better exploring a novel photoelectric functional material, and a new idea is provided for exploring the relationship of material structure and performance.
Although high-voltage in-situ second harmonic measurement in DACs is of such great significance, few researchers have implemented high-voltage in-situ second harmonic testingReports of related work may be rare and rare. The earliest high-voltage in-situ second harmonic measurements were made in 1997 by Simon et al testing SiO using a Mao-Bell type DAC2The in-situ second harmonic of (1) is changed, but due to the limitation of equipment technology, the experimental result only collects data of 10 points in a pressure range of 30GPa, and the reliability is not high from the change trend of the data. Subsequently, Bayarjargal et al modified the process and tested ZnO, Cr2O3The high-voltage in-situ second harmonic of the materials corresponds to the high-voltage in-situ second harmonic, but the testing mode basically refers to the method of Simon et al, so the testing result is still fuzzy, and the variation trend of the second harmonic is difficult to explain. Meanwhile, the work of testing the intensity of the second harmonic of the material under pressure along with the change of the polarization angle of the incident laser is still blank. The second harmonic intensity of the material can visually reflect the information of the elements in the material along with the change of the polarization angle of the incident laser, and the structural change of the material caused along with the pressure change can be reflected after the pressure is introduced, but no high-voltage equipment capable of realizing the work exists at present.
Disclosure of Invention
The first purpose of the invention is to provide a device capable of measuring the second harmonic of a substance under the condition of ultrahigh pressure, and by the device, under the condition of changing the environmental pressure, external interference (such as sample thickness, environmental light and other factors) is eliminated, so that the second harmonic intensity of a powder sample is accurately collected along with the change of the pressure and the second harmonic intensity of a single crystal sample under pressure change along with the change of the polarization angle of incident laser, and finally, in-situ high-pressure second harmonic measurement in a DAC is realized.
Another object of the present invention is to provide a method for measuring the second harmonic of a substance under ultra-high pressure conditions.
In order to achieve the first purpose, the invention adopts the following technical scheme:
an apparatus for measuring the second harmonic of a substance under ultra-high pressure conditions, comprising:
a laser excitation unit that supplies incident laser light and converts the incident laser light into polarized light;
the microscopic light path part changes the light path of the polarized light until the polarized light is focused on a sample to be measured, excites the second harmonic and enables the second harmonic to return along the original light path of the incident laser;
the object carrying part comprises a diamond anvil cell press for placing and fixing a sample to be tested; and
and a signal receiving unit for receiving the second harmonic laser signal returned from the microscope optical path unit and converting the laser signal into an electrical signal.
Further, the laser excitation portion includes:
a laser providing incident laser light;
and the polarizer can freely rotate and receives and converts the incident laser into polarized light.
Further, the laser is a picosecond laser; the incident laser wavelength is 1064 nm.
Furthermore, the microscopic light path part comprises a plurality of total reflection mirrors, a first beam splitter and an objective lens positioned between the total reflection mirrors and the sample to be detected.
Further, the signal receiving section includes:
the optical filter is positioned between the photomultiplier and the first beam splitter and is used for receiving the laser which penetrates through the first beam splitter and has the wavelength of the incident laser wavelength 1/2;
the photomultiplier receives the laser signal having the wavelength of the incident laser 1/2 transmitted through the filter, and converts the laser signal into an electrical signal.
Further, the device also comprises a viewing camera and a searchlight.
In order to achieve the second purpose, the invention adopts the following technical scheme:
a method of measuring the second harmonic of a substance under ultra-high pressure conditions, comprising the steps of:
placing a sample to be tested in a sample cavity of a diamond anvil cell press;
the laser excitation part provides incident laser and converts the incident laser into polarized light;
changing the light path of the polarized light until the polarized light is focused on a sample to be tested, and exciting the sample to be tested to generate second harmonic;
the second harmonic wave is returned along the original optical path along with the reflected incident laser;
receiving the returned laser signal of the second harmonic and converting the laser signal into an electrical signal.
Further, the polarized light focused on the sample to be measured completely covers the sample to be measured.
Further, the polarization angle of the polarized light is changed, and the returned laser signal intensity of the second harmonic wave under different polarization angles is tested and recorded.
Further, ruby and pressure transmission medium are arranged in the sample cavity, wherein the pressure transmission medium is filled in the sample cavity, and a sample to be detected is located in the center of the sample cavity and is not in direct contact with the ruby.
Further, the sample to be detected is in a state of normal pressure, high pressure or ultrahigh pressure.
The invention has the following beneficial effects:
the device provided by the invention can be used for testing the substance in-situ high-voltage second harmonic, and the testing method is accurate, so that the blank that the second harmonic intensity of the tested material under pressure changes along with the polarization angle of the incident laser is made up. In the invention, a method for measuring the second harmonic of a substance under an ultrahigh pressure condition by using the device is provided, an in-situ high-pressure second harmonic test method is provided, the position of an excited sample is fixed in the test process, the oscillation of the second harmonic signal caused by the change of the thickness of the sample is eliminated, meanwhile, the external interference is eliminated by adopting a noise deduction mode to ensure that the obtained signal completely comes from the sample to be tested, finally, an objective lens replacement mode is used for dealing with a smaller sample (if a high-pressure environment is obtained, a small diamond anvil surface is required to be used, so that the size of the sample is limited), and a measurable pressure window is popularized to be near hundreds of GPa. In addition, the invention also provides a method for testing the second harmonic polarization curve of the single crystal sample under pressure for the first time, and the method can more intuitively express the change condition of the microstructure of the sample under pressure through the change condition of the second harmonic polarization curve. In conclusion, the method can clearly and accurately describe the change conditions of the second harmonic waves of the powder and the single crystal sample under the pressure, and the obtained data can more reliably and intuitively reflect the change conditions of the internal microstructure of the sample. The in-situ measurement of the second harmonic wave in the high-voltage environment is really solved.
Drawings
The following describes embodiments of the present invention in further detail with reference to the accompanying drawings.
Fig. 1 shows a schematic diagram of the structure of the device for measuring the second harmonic of a substance under ultra-high pressure conditions in the present invention.
Fig. 2 shows a graph of the second harmonic signal as a function of laser current.
Fig. 3 shows the results of the second harmonic signal test on the KDP sample in embodiment 1 of the present invention.
Fig. 4 shows the results of the second harmonic signal test against barium metaborate (BBO) in example 2 of the present invention.
FIG. 5 shows the results of in-situ second harmonic polarization curve test on potassium titanyl phosphate (KTP) as a single crystal sample in example 3 of the present invention.
FIG. 6 shows the results of in-situ second harmonic polarization curve testing of a single crystal sample, Cesium Borate (CBO), in example 4 of the present invention.
Detailed Description
In order to more clearly illustrate the invention, the invention is further described below with reference to preferred embodiments and the accompanying drawings. Similar parts in the figures are denoted by the same reference numerals. It is to be understood by persons skilled in the art that the following detailed description is illustrative and not restrictive, and is not to be taken as limiting the scope of the invention.
As shown in fig. 1, one embodiment of the present invention provides a device that can measure the second harmonic of a substance under ultra-high pressure conditions. The device includes:
a laser excitation unit a for supplying incident laser light and converting the incident laser light into polarized light;
the microscopic light path part b changes the light path of the polarized light until the polarized light is focused on a sample to be measured, excites the second harmonic and enables the second harmonic to return along the original light path of the incident laser;
a carrying part c comprising a diamond anvil cell press 10 for placing and fixing a sample to be measured; and
and a signal receiving unit d for receiving the second harmonic laser signal returned from the microscopic optical path unit and converting the laser signal into an electric signal.
In some specific examples, the laser excitation part a comprises
A laser 1 that supplies incident laser light;
and the polarizer 4 which can freely rotate receives and converts the incident laser into polarized light.
Illustratively, a suitable laser 1 may be a picosecond laser, preferably a 1064nm picosecond laser.
In the laser excitation portion a, the received incident laser beam is converted into polarized light by the polarizer 4. Due to the arrangement of the polarizer 4, the device can be better applied to detection of single crystal, polycrystal and other powdery samples.
In some preferred examples, the laser excitation portion a further includes an analyzer 3, and the analyzer 3 is located between the incident laser 1 and the polarizer 4, and can be used to detect the degree of deflection of the polarized light.
Further, a first filter 2 is provided between the laser 1 and the analyzer 3.
In some preferred examples, the microscope optical path part b comprises a plurality of total reflection mirrors 5,7,9, a first beam splitter 6 and an objective lens 10 positioned between the total reflection mirrors 9 and the sample to be measured. The reflection by the total reflection mirrors 5,7,9 and the first beam splitter 6 functions to change the optical path of the resulting polarized light so that the polarized light can be irradiated onto a sample to be measured. In the present embodiment, the number of total reflection mirrors is not limited, and may be specifically determined according to the need of an actual optical path. For example, the number of the cells is 2 to 8. The polarized light can be completely focused on the sample to be measured by the focusing action of the objective lens 10.
The sample to be measured is irradiated by the polarized light to excite the second harmonic wave, and the excited second harmonic wave returns along the incident laser original light path along with the reflected polarized light.
In this embodiment, there is no specific requirement for the selection of the anvil press 11 for placing and fixing the sample to be measured, and it is sufficient to generate a super-high atmospheric pressure static pressure. The sample to be tested is fixed in the sample cavity of the diamond anvil cell press 11.
In some embodiments, the stage section c further comprises a stage 15 for carrying the diamond anvil press 11.
In still other embodiments, the signal receiving part d comprises
A third filter 13, which is located between the photomultiplier 14 and the first beam splitter 6, and receives the laser beam having the wavelength of the incident laser wavelength 1/2 that has passed through the first beam splitter 6;
the photomultiplier 14 receives the laser signal having the wavelength of the incident laser 1/2 transmitted through the third filter 13, and converts the laser signal into an electrical signal to display the laser intensity information thereof.
In order to better focus the laser spot on the surface of the sample and determine the position of the laser spot, in some examples, the device further comprises a viewing camera and a searchlight. So that the laser spot can be better focused on the surface of the sample, and the position of the laser spot can be determined. Wherein, the observation camera can be a CCD camera. Furthermore, a second beam splitter 8 is further disposed at the laser path of the microscope path portion b, and is configured to reflect light emitted by the observation camera and the searchlight to a direction along the original laser path, so as to achieve better observation and photographing effects.
In yet another embodiment of the present invention, there is provided a method of measuring a second harmonic of a substance under ultra-high pressure conditions, the method comprising the steps of:
placing a sample to be tested in a sample cavity of a diamond anvil cell press 11;
the laser excitation part a provides incident laser and converts the incident laser into polarized light;
changing the light path of the polarized light until the polarized light is focused on a sample to be tested, and exciting the sample to be tested to generate second harmonic;
the second harmonic part generated by excitation returns along the original optical path along with the reflected incident laser;
and receiving the returned laser signal of the second harmonic wave, and converting the laser signal into an electric signal.
In some preferred examples, the polarized light focused on the sample to be tested completely covers the sample to be tested, so as to obtain more accurate test results.
In some preferred examples, the polarization angle of the polarized light is changed, and the returned second harmonic laser signal intensity at different polarization angles is tested and recorded.
In still other preferred examples, the sample cavity of the diamond anvil cell press 11 is further provided with ruby and a pressure transmission medium, wherein the pressure transmission medium fills the sample cavity, and the sample to be measured is located at the center position in the sample cavity and is not in direct contact with the ruby. In this embodiment, the sample to be measured is a massive solid, which is dense and rough and is favorable for light reflection. While the thickness is not too thick to avoid crushing upon pressurization.
In some preferred examples, the sample to be tested is in a state of normal pressure or high pressure or ultrahigh pressure.
In this embodiment, there is no particular requirement for the selection of the diamond anvil press, but it is preferable that the diamond anvil be a diamond of high optical transmission (Type-II diamond).
However, in order to enable more accurate measurements of the second harmonic of a material being measured under pressure conditions, particularly ultra high pressure conditions, in some examples the pre-treatment of the diamond anvil press 11 in use is optimised. Specifically, first, the diamond anvil cell press 11 apparatus will be assembled; the upper and lower anvil faces of the diamond anvil cell press 11 are placed opposite to each other and rotated 180 degrees relative to each other, and then the upper and lower anvil faces are still perfectly overlapped with each other, so that the diamond is not damaged under high pressure. The shims (typically T301 steel plates were selected as the shim material that was tested to not produce an interference signal) were then pre-pressed to a thickness that varied for diamond shim pre-pressing of varying diameter anvil surfaces. And punching a hole in the center of the indentation by using laser to create a sample cavity, and cleaning the gasket in an ultrasonic mode so as to avoid introducing impurities to interfere with the experimental result. The pad is then repositioned to the center of the anvil surface so that the center of the sample chamber coincides with the center of the anvil surface. The thickness of the sample being tested is typically one-half of the thickness of the sample chamber to prevent thinning of the sample under high pressure and thus damage to the sample. The pressure calibration mode refers to a ruby calibration means. The sample to be tested (powder needs to be pre-pressed to be dense, and a single crystal sample needs to ensure the integrity of the sample) and the ruby are put into a sample cavity filled with a pressure transmission medium (generally low-viscosity silicone oil is adopted, and whether the pressure transmission medium interferes with an experimental result or not needs to be detected before testing), attention needs to be paid to the fact that the sample is placed at the center of the sample cavity as far as possible and keeps a certain distance from the ruby, and therefore the change of a second harmonic signal caused by the absorption of the ruby to laser is avoided. Finally the diamond anvil press is closed to complete the assembly phase of the device.
The optical path diagram of the second harmonic measurement is shown in fig. 1, the light source of the incident light adopted by the invention is a 1064nm picosecond laser, the laser excitation part a excites the incident light to firstly pass through the first optical filter 2 and then pass through the polarizer 4 to form polarized light, wherein the polarizer 4 can be used for changing the polarization angle of the incident light; the plan condition of the incident light is checked through the analyzer 3, then the incident light passes through a series of total reflection mirrors 5,7,9, a first beam splitter 6 and a lens 10 to focus an incident light spot on a sample, the size of the spot can be changed along with the amplification factor of an objective lens 10, the 20-time objective lens can focus the spot to 40 micrometers, and the 10-time objective lens can focus the spot to 80 micrometers at present, so that the aim of dealing with samples with different sizes is achieved. The second harmonic signal generated by the excitation of the sample to be detected returns to the laser excitation part a along the light path along with the reflected incident light, the signal intensity is detected by adopting the photomultiplier tube 14, and meanwhile, the filter 13 is used in front of the photomultiplier tube 14 to filter out all laser with the wavelength except 532nm, so that the influence of stray light is accurately eliminated. For the observation aspect of the sample, the scheme adopts an illumination and observation module, and a camera and a searchlight are connected to determine the position of the sample.
For the second harmonic test of a sample under high pressure, firstly, the assembled diamond anvil cell is placed on a sample table after pressure calibration, and the sample table is openedAnd the searchlight and the CCD camera respectively adjust a threaded knob on the sample platform to accurately find the sample position, focus the sample to a specific position of the sample (the light spot position is checked to enable the light spot to be completely covered on the sample), and the sample position is adopted in later testing (the sample thickness can cause the change of the second harmonic signal intensity). The test software and photomultiplier tube 14 are turned on and the laser shutter is inserted while the illumination and other ambient light are turned off. At this point, the signal received by the photomultiplier tube 14 is recorded as Ibkg(i.e., background signal) and subtraction of the background signal with the program software. At this time, the laser shutter was opened to irradiate the sample with the incident laser light, and the intensity of the received signal I was recordedsample. To verify whether the second harmonic signal originates from the excitation of the sample, the incident laser current can be first adjusted, and if the signal intensity is non-linear with the current intensity, the signal can be determined to be excited by the sample as shown in fig. 2. The appropriate incident laser current intensity is then used for testing, and the current intensity is adjusted to an appropriate area, so that the photomultiplier tube is likely to be damaged if the current intensity is too large, and the photomultiplier tube is similar to a noise signal if the current intensity is too small, thereby influencing the experimental result. Determination of noise signal: the ruby used for calibrating the pressure is known not to have the second harmonic effect, so that in the whole pressurizing process, the signal intensity of the ruby is tested after the signal intensity of the sample to be tested is tested, and finally the change of the noise is recorded. The polarization curve test pre-stage work for single crystal samples under pressure is similar to the powder test. The difference is that firstly, the sample to be measured should be a single crystal with good crystallinity, so as to obtain a polarization curve with a perfect shape. Secondly, after subtracting the background signal IbkgAnd then, collecting a second harmonic signal by adopting a mode of obtaining polarized incident light by rotating the polarizer, wherein the second harmonic signal obtained by the photomultiplier is the corresponding second harmonic intensity under the polarization angle, drawing the intensities under all the angles into a curve which is a second harmonic polarization intensity curve under the pressure point, and continuously pressurizing the anvil press by the diamond to obtain an in-situ test result.
Example 1
In situ second harmonic testing of powder samples potassium dihydrogen phosphate (KDP)
In order to verify the feasibility of the experiment, the experimental scheme provided by the invention is utilized, high-voltage second harmonic measurement is carried out on part of typical materials, the experimental operation flow and experimental numerical analysis are described by taking a potassium dihydrogen phosphate (KDP, analytically pure AR 99.5%) sample as an example, and the experimental operation is as follows:
the pad was pre-pressed according to the above experiment using a pair of anvils with an anvil face size of 500 microns and a T301 steel sheet with an initial pad thickness of 250 microns, the pre-pressed thickness being about 50 microns and the laser ablated diameter of 350 microns at the center of the indentation acting as a sample cavity. And assembling the diamond anvil cell according to the experimental scheme, testing a second harmonic signal until the maximum pressure reaches 12GPa, and finally obtaining the change condition of the second harmonic signal of KDP along with the pressure.
Fig. 3 is a result of a second harmonic signal test on a KDP sample, and it can be found from experimental values that the signal of the KDP sample shows a trend of significant attenuation with the increase of pressure, and finally, the second harmonic signal of the KDP sample is almost consistent with a noise signal (ruby) before and after 5GPa, that is, the second harmonic effect disappears, which is well consistent with the transition of the structural change of non-centrosymmetric of the KDP under pressure (4GPa) reported in the literature. When the pressure is relieved to normal, the second harmonic reappears in accordance with the description in the literature that KDP undergoes reversible phase change. The experimental result means that the experimental scheme designed by the invention has certain advantages in exploring material structure phase change and second harmonic measurement precision.
Example 2
In-situ second harmonic testing of powder samples barium metaborate (BBO)
The same experimental conditions as above are used, the second harmonic signal of barium metaborate (BBO) is tested, the experimental result is shown in fig. 4, in the pressure range of 0-12GPa, the received second harmonic signal is in a steady state all the time, which indicates that the structure does not change much, and then pressurization is continued, and the signal is attenuated continuously until the signal disappears. This phenomenon indicates that for barium metaborate, a phase change occurs under pressure resulting in the disappearance of the second harmonic signal. The highest pressure point for this test was 29GPa at which the second harmonic signal completely disappeared and was identical to the ruby noise signal. After pressure relief, a stronger second harmonic signal can be obtained again, which represents that barium metaborate undergoes irreversible phase change under the pressure.
Example 3
In-situ second harmonic polarization curve test of potassium titanyl phosphate (KTP) of single crystal sample
The assembly process of the diamond anvil press for single crystal sample testing was essentially identical to that of the powder sample, with polarized incident laser light produced by rotating the polarizer during testing. The deflection angle selected in the experiment is 0-360 degrees, the step length is 2 degrees, and the test result is shown in fig. 5. The second harmonic intensity of the material is gradually reduced along with the increasing of the pressure, but the polarization curve of the material is not obviously changed, which indicates that no phase change occurs. The attenuation of the second harmonic is only the suppression of the internal polarity elements. When the pressure increased to 6.9, the second harmonic signal had become very weak, essentially comparable to the noise signal. This phenomenon shows that KTP undergoes a structural phase change of non-centrosymmetry under pressure, and the pressure point of the phase change is about 6 GPa. The experimental result is consistent with the literature result reported by the predecessor, which indicates the accuracy of the method.
Example 4
In-situ second harmonic polarization curve testing of single crystal sample Cesium Borate (CBO)
As with the above experimental conditions, the second harmonic polarization curve of the single crystal sample Cesium Borate (CBO) was tested, and the experimental result is shown in fig. 6, where the second harmonic intensity of the material gradually decreases with increasing pressure, but the shape of the polarization curve does not change, indicating that no structural phase transition occurs. Knowing that the highest pressure point 11.6GPa can still receive a second harmonic signal, the material is consistently in the original non-centrosymmetric structure in the pressure range.
It should be understood that the above-mentioned embodiments of the present invention are only examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention, and it will be obvious to those skilled in the art that other variations or modifications may be made on the basis of the above description, and all embodiments may not be exhaustive, and all obvious variations or modifications may be included within the scope of the present invention.
Claims (10)
1. An apparatus for measuring a second harmonic of a substance at ultra-high pressure conditions, comprising:
a laser excitation unit that supplies incident laser light and converts the incident laser light into polarized light;
the microscopic light path part changes the light path of the polarized light until the polarized light is focused on a sample to be measured, excites the second harmonic and enables the second harmonic to return along the original light path of the incident laser;
the object carrying part comprises a diamond anvil cell press for placing and fixing a sample to be tested; and
and a signal receiving unit for receiving the second harmonic laser signal returned from the microscope optical path unit and converting the laser signal into an electrical signal.
2. The apparatus according to claim 1, wherein the laser excitation portion includes:
a laser providing incident laser light;
and the polarizer can freely rotate and receives and converts the incident laser into polarized light.
3. The apparatus of claim 2, wherein the laser is a picosecond laser; the incident laser wavelength is 1064 nm.
4. The apparatus according to claim 1, wherein the microscope optical path portion comprises a plurality of total reflection mirrors, a first beam splitter, and an objective lens between the total reflection mirrors and the sample to be measured.
5. The apparatus according to claim 1, wherein the signal receiving section includes:
the optical filter is positioned between the photomultiplier and the first beam splitter and is used for receiving the laser which penetrates through the first beam splitter and has the wavelength of the incident laser wavelength 1/2;
the photomultiplier receives the laser signal having the wavelength of the incident laser 1/2 transmitted through the filter, and converts the laser signal into an electrical signal.
6. The apparatus of claim 1, further comprising a viewing camera and a searchlight.
7. A method for measuring the second harmonic of a substance under ultra-high pressure conditions, comprising the steps of:
placing a sample to be tested in a sample cavity of a diamond anvil cell press;
the laser excitation part provides incident laser and converts the incident laser into polarized light;
changing the light path of the polarized light until the polarized light is focused on a sample to be tested, and exciting the sample to be tested to generate second harmonic;
the second harmonic part generated by excitation returns along the original optical path along with the reflected incident laser;
receiving the returned laser signal of the second harmonic and converting the laser signal into an electrical signal.
8. The method of claim 7, wherein the polarized light focused onto the test sample completely covers the test sample.
9. The method of claim 7, wherein the polarization angle of the polarized light is changed, and the returned second harmonic laser signal intensity at different polarization angles is tested and recorded.
10. The method according to claim 7, wherein the sample to be tested is in a state of normal pressure or high pressure or ultrahigh pressure.
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