Phase detection method and system

Abstract

The invention relates to the technical field of microscopic imaging, in particular to a phase detection method and system, and the method comprises the steps: emitting incident light; the incident light is divided into pump light and exciting light, and the exciting light is divided into reference field exciting light and to-be-measured field exciting light; the reference field exciting light, the to-be-measured field exciting light and the pump light are focused to the surface of a sample table to generate a partial degenerate four-wave mixing effect and generate nonlinear signal information, and the optical paths of the reference field exciting light, the to-be-measured field exciting light and the pump light guided into the surface of the sample table are the same; the reference field exciting light, the to-be-measured field exciting light and the pump light are guided into the surface of the sample table through the same optical path, the phase matching condition is met, the nonlinear signal intensity is maximized, the phase error introduced by the optical path difference is eliminated, the measurement accuracy is ensured, the time synchronization is realized, the optical path calibration is simplified, and the detection stability is improved.

Description

Technical Field

[0001] The present invention relates to the field of microscopic imaging technology, and in particular to a phase detection method and system. Background Art

[0002] Optical microscopy is a technique that uses visible light and optical lens systems to magnify and image tiny objects or structures. This technique collects light emitted, reflected, or transmitted by the object to form an observable image. The near-field light field is the light field within a range of approximately one to several wavelengths from the light source or sample. Within this region, the light field's amplitude, phase, and polarization state are strongly influenced by the light source or sample surface details. By measuring these parameters in the near-field light field, it is possible to study the tiny structures on the sample surface.

[0003] The existing technology uses partially degenerate four-wave mixing technology to achieve near-field optical microscopy imaging. The four-wave mixing effect is a nonlinear optical effect. Three beams of light interact in a nonlinear medium to produce a fourth beam of light. The process is called four-wave mixing imaging. When two of the beams participating in the four-wave mixing have the same frequency, it is called partially degenerate four-wave mixing. The fourth beam of light produced is a nonlinear signal light, which can be further used for optical signal detection and processing.

[0004] However, optical changes in nanoscale structures are usually accompanied by multiple changes in amplitude, phase, polarization, and frequency. Most existing detection methods are unable to maintain the consistency of multiple physical quantities when multiple beams of input light reach the sample detection table during the coupling analysis change process, resulting in energy instability or phase mismatch, making it difficult to meet the high-precision characterization requirements of complex nanoscale and transient processes. Summary of the Invention

[0005] In order to solve the problem that the existing near-field optical phase detection method cannot maintain the consistency of the time when light reaches the sample, the present invention provides a phase detection method and system.

[0006] In order to solve the above technical problems, the present invention provides the following technical solutions: a phase detection method, comprising the following steps: emitting incident light; dividing the incident light into pump light and excitation light, and dividing the excitation light into reference field excitation light and test field excitation light; The reference field excitation light, the test field excitation light and the pump light are focused onto the surface of the sample stage to produce a partially degenerate four-wave mixing effect and generate nonlinear signal information, and the reference field excitation light, the test field excitation light and the pump light have the same optical path when introduced into the surface of the sample stage; the nonlinear signal information is obtained and measured.

[0007] Preferably, focusing the reference field excitation light, the test field excitation light, and the pump light onto the surface of the sample stage to generate a partially degenerate four-wave mixing effect and generate nonlinear signal information further includes the following steps: The excitation light of the field to be measured is focused onto the surface of the sample stage after optical delay and polarization modulation, and excites the field to be measured on the surface of the sample stage.

[0008] Preferably, focusing the reference field excitation light, the measured field excitation light, and the pump light onto the surface of the sample stage to generate a partially degenerate four-wave mixing effect and generate nonlinear signal information comprises the following steps: The reference field excitation light is phase-modulated to generate a first reference field excitation light and a second reference field excitation light. The first reference field excitation light and the second reference field excitation light have the same frequency. The first reference field excitation light and the second reference field excitation light interfere with the field to be measured on the surface of the sample stage to generate an interference field.

[0009] Preferably, before obtaining and measuring the nonlinear signal information, the method further includes the following steps: The initial phases of the first reference field excitation light and the second reference field excitation light are controlled to be equal, and the initial phases of the first reference field excitation light and the second reference field excitation light are modulated four times in a row with a phase increment of 1 / 4 cycle to obtain the intensity information of the first interference field, the second interference field, the third interference field and the fourth interference field after the first, second, third and fourth modulations, respectively.

[0010] Preferably, the intensity information of the interference field represents the intensity information of the field to be measured, and the nonlinear signal information represents the intensity information of the interference field. Collecting and measuring the nonlinear signal information includes the following steps: The intensity information of the first interference field is subtracted from the intensity information of the third interference field to obtain a first difference expression; the intensity information of the second interference field is subtracted from the intensity information of the fourth interference field to obtain a second difference expression; and the first difference expression and the second difference expression are combined to calculate the phase distribution of the field to be measured.

[0011] Preferably, focusing the reference field excitation light, the test field excitation light, and the pump light onto the surface of the sample stage to generate a partially degenerate four-wave mixing effect and generate nonlinear signal light further comprises the following steps: The pump light is focused onto the surface of the sample stage after optical delay and polarization modulation. After polarization modulation, the polarization mode of the pump light matches the polarization mode of the nonlinear signal.

[0012] To solve the above technical problems, the present invention provides another technical solution as follows: a phase detection system for implementing the steps of the above phase detection method, the system comprising: An incident light excitation module, used for emitting incident light; A beam splitting module, used to split the incident light into pump light and excitation light, and to split the excitation light into reference field excitation light and measured field excitation light; an optical transmission module, configured to focus the reference field excitation light, the test field excitation light, and the pump light onto the surface of the sample stage to generate a partially degenerate four-wave mixing effect and generate nonlinear signal light, wherein the reference field excitation light, the test field excitation light, and the pump light have the same optical path length when introduced into the surface of the sample stage; The acquisition and calculation module is used to acquire and calculate the nonlinear signal information.

[0013] Preferably, the phase detection system further comprises a modulation module for performing optical delay and polarization modulation on the excitation light of the field to be measured, and for performing polarization modulation and optical delay on the pump light.

[0014] Preferably, the modulation module is also used to phase-modulate the reference field excitation light to generate a first reference field excitation light and a second reference field excitation light, and to control the initial phases of the first reference field excitation light and the second reference field excitation light to be equal, and to modulate the initial phases of the first reference field excitation light and the second reference field excitation light with a phase increment of 1 / 4 cycle for four consecutive times to obtain the intensity information of the first interference field, the second interference field, the third interference field and the fourth interference field after the first, second, third and fourth modulations respectively.

[0015] Preferably, the acquisition and measurement module is used to subtract the intensity information of the third interference field from the intensity information of the first interference field to obtain a first difference expression; use the intensity information of the second interference field to subtract the intensity information of the fourth interference field to obtain a second difference expression; and combine the first difference expression and the second difference expression to calculate the phase distribution of the field to be measured.

[0016] Compared with the prior art, the phase detection method and system provided by the present invention have the following beneficial effects: 1. The present invention provides a phase detection method, in which three beams of light: reference field excitation light, test field excitation light and pump light are obtained by splitting the incident light. Therefore, the reference field excitation light, the test field excitation light and the pump light have the same frequency. When the three beams of light reach the sample surface, a partially degenerate four-wave mixing effect will occur on the sample surface, and the sample surface will re-radiate new nonlinear signal light. The nonlinear signal light carries nonlinear signal information, and its frequency is a combination of the frequencies of the three input light waves. By observing and measuring the frequency, intensity and other characteristics of the nonlinear signal information, information such as the molecular structure and energy level transition of the sample can be obtained; in the partially degenerate During the four-wave mixing process, the light beams must meet in a way that can achieve phase matching. Phase matching ensures that energy is effectively transferred from the input light beam to the generated nonlinear signal light. The optical path directly affects the phase of the light. When the optical path is different, a phase difference will occur between the light beams, resulting in a serious phase mismatch. Once the phase is mismatched, the four-wave mixing effect will be greatly suppressed, and the signal information of the nonlinear signal light will be weakened. The optical path of the reference field excitation light, the test field excitation light and the pump light introduced into the sample stage surface is adjusted to be the same to meet the phase matching condition. The more accurate the compensation of similar optical path, the stronger the signal of the nonlinear signal light.

[0017] 2. The present invention provides a phase detection method, in which the excitation light of the field to be measured is derived from the splitting of the excitation light, and the optical path reaching the surface of the sample stage needs to be the same as that of the excitation light of the reference field. Therefore, the excitation light of the field to be measured is optically delayed and compensated by a delay line to reduce the phase drift and interference fringe jitter caused by the optical path difference, thereby improving the measurement accuracy and stability. The optical delay can be adjusted according to experimental requirements to adapt to different experimental conditions and sample characteristics. When the excitation light of the field to be measured interacts with the sample to generate the field to be measured, the phase, amplitude and other characteristics of the light will change, which can characterize the optical properties or physical characteristics of the sample, such as the refractive index, absorption coefficient or nonlinear optical response. These changes can reflect the internal structure and composition of the sample, and obtain information about the sample structure, composition and dynamics. In the present invention, the field to be measured carries the phase change of the sample surface and is the main object of phase detection.

[0018] 3. The present invention provides a phase detection method, in which the first reference field excitation light and the second reference field excitation light interfere with the field to be measured on the surface of the sample stage, and the phase difference and other information between the field to be measured and the reference field are measured and compared through interference. The interference field contains the interaction information between the field to be measured and the reference field, which can be used to improve the measurement accuracy and sensitivity. Since the first reference field excitation light and the second reference field excitation light have the same frequency and are equal to the optical path of the field to be measured, the formed interference field produces a stable interference pattern in space, thereby realizing phase comparison and measurement between the field to be measured and the reference field.

[0019] 4. The present invention provides a phase detection method, which uses a four-step phase shift technology to move the phase of the interference field, thereby analyzing the phase recovery process of the light field to be measured, and extracting the phase distribution of the light field in an analytical manner. It can realize the characterization of the near-field light field phase information on the basis of non-scanning near-field characterization; four times of modulation and measurement with a phase increment of 1 / 4 cycle can obtain more comprehensive interference field intensity information, thereby more accurately calculating the phase difference between the field to be measured and the reference field. At the same time, the four modulations provide multiple independent measurement data points, making the measurement results more stable, reducing measurement errors, and improving measurement sensitivity.

[0020] 5. The present invention provides a phase detection method. In actual measurement, the intensity information of the light field is the easiest to measure. The intensity information of the four-order interference field is measured and calculated. The light field information of the interference field represents the light field information of the field to be measured, and the nonlinear signal information represents the intensity information of the interference field, reflecting that the intensity and phase of the light field of the interference field are related. Therefore, in the process of realizing phase detection, the phase of the field to be measured can be determined by the light field intensity information, and finally the phase distribution of the light field to be measured is obtained; the interference field intensity information modulated four times with a fixed interval phase difference, that is, a phase adjustment algorithm, is used to combine the two difference expressions, comprehensively consider the signal changes under different phase modulations, calculate the phase distribution of the field to be measured, and improve the accuracy and stability of phase measurement.

[0021] 6. The present invention provides a phase detection method. In the four-wave mixing process, pump light is the main energy source, which uses energy to drive the nonlinear process, so that the medium in the sample can produce a nonlinear response. The intensity of the pump light directly affects the intensity of the nonlinear signal. If the pump light has a higher power, the nonlinear effect is significant enough to be detected. At the same time, in the nonlinear optical process, the pump light must also meet phase matching. After passing through the optical delay line, its optical path reaching the surface of the sample stage is equal to that of other excitation lights, such as the reference field excitation light and the test field excitation light. The optical path matching ensures that all light beams arrive at the surface of the sample stage at the same time, thereby realizing effective nonlinear interaction; after the pump light is polarization modulated, its polarization direction matches the polarization direction of the nonlinear signal, thereby improving the generation efficiency of the nonlinear signal and enhancing the intensity of the nonlinear signal; at the same time, the pump light acts as an "optical probe" with fast imaging speed, high stability, and a large enough area to be scanned at one time.

[0022] 7. An embodiment of the present invention also provides a phase detection method system, which has the same beneficial effects as the above-mentioned phase detection method and will not be described in detail here. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0024] Figure 1 is a flow chart of a phase detection method provided by the first embodiment of the present invention.

[0025] Figure 2 The frame of the phase detection system provided by the second embodiment of the present invention is Figure 1 .

[0026] Figure 3 The frame of the phase detection system provided by the second embodiment of the present invention is Figure 2 .

[0027] Figure 4 This is a demonstration and verification diagram of the phase detection method provided by the third embodiment of the present invention.

[0028] Description of the accompanying drawings: 100, phase detection system; 101, incident light excitation module; 102, beam splitting module; 103, optical transmission module; 104, acquisition and measurement module; 105, modulation module; 106, first modulation module; 107, second modulation module; 108, third modulation module; 1. Seed laser; 2. Optical parametric oscillator; 3. First linear polarizer; 4. First half-wave plate; 5. Second translation stage; 6. Dichroic mirror; 7. Filter; 8. Quarter-wave plate; 9. Third linear polarizer; 10. Imaging lens; 11. Long working distance objective lens; 12. Sample; 13. Oil immersion objective lens; 14. Beam combiner; 15. Second half-wave plate; 16. Plane mirror; 17. Third focusing lens; 18. Second focusing lens; 19. First focusing lens; 20. Spatial light modulator; 21. Third half-wave plate; 22. Beam splitter; 23. First translation stage; 30. Camera imaging module; 31. Fourth focusing lens. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and implementation examples. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0030] See also Figure 1 The present invention provides a phase detection method for detecting a near-field light field, and the phase detection method includes the following steps: Step S1, emitting incident light; Step S2, dividing the incident light into pump light and excitation light, and dividing the excitation light into reference field excitation light and test field excitation light; Step S3, focusing the reference field excitation light, the test field excitation light, and the pump light onto the surface of the sample stage to generate a partially degenerate four-wave mixing effect and generate nonlinear signal information, and the reference field excitation light, the test field excitation light, and the pump light have the same optical path length when introduced into the sample stage surface; Step S4: Acquire and measure nonlinear signal information.

[0031] It can be understood that the same optical path allows the reference field excitation light, the measured field excitation light and the pump light to better meet the phase matching conditions of partially degenerate four-wave mixing in space and time, which can effectively improve the conversion efficiency of the four-wave mixing process and generate stronger nonlinear signal information.

[0032] Specifically, optical elements such as lenses and mirrors are used to guide the reference field excitation light, the test field excitation light, and the pump light to the focal point of the sample stage. The optical path of each beam of light is adjusted by adjusting the position or angle of the mirror or lens so that the optical paths of the reference field excitation light, the test field excitation light, and the pump light reach the same length, effectively enhancing the nonlinear signal intensity generated by the partially degenerate four-wave mixing effect.

[0033] Under phase matching conditions, the phase relationship between the reference field excitation light, the measured field excitation light and the pump light is stable, thereby generating a clear and strong interference field and four-wave mixing signal. The same optical path reduces the phase noise and signal distortion caused by the optical path difference, improves the accuracy of measuring the nonlinear characteristics of the sample, and can more accurately obtain sample information when detecting small changes in the sample such as refractive index changes, concentration changes, etc.

[0034] As a non-limiting embodiment, optionally, in step S3, the reference field excitation light and the test field excitation light are combined using a beam combiner, and the reference field excitation light and the test field excitation light are re-gathered and focused on the same position on the sample stage surface through the same optical path modulation.

[0035] The same optical path ensures that the reference field excitation light and the measured field excitation light form a stable interference field on the sample surface.

[0036] Specifically, in step S1, a seed laser is obtained as the incident light. The seed laser is emitted by a laser. The wavelength, pulse width, repetition frequency, and average output power of the seed laser are not limited and can be set according to specific needs. It should be understood that in order to better emit the pump light and excitation light in step S2, the incident light should have a high light intensity.

[0037] Preferably, the laser is a femtosecond laser.

[0038] It is understood that in step S2, the incident light is divided into two parts, that is, the incident light is divided into pump light and excitation light. A beam splitter can be used to achieve a preset energy distribution ratio, stably dividing the incident light into two parts. One part is used for wavelength down-conversion. The excitation light obtained after conversion should have the same parameters such as pulse width and repetition frequency as the seed laser to better generate a partially degenerate four-wave mixing effect with the pump light.

[0039] Optionally, a 1:4 beam splitter is used to split the incident light into two parts with an energy ratio of 1:4, wherein the part with an energy ratio of 20% is directly emitted as pump light, and the part with an energy ratio of 80% is used for wavelength down-conversion. After the conversion, a beam of near-infrared laser is emitted, and this near-infrared laser is used as excitation light to excite the field to be measured.

[0040] Furthermore, the excitation light is divided into two paths, namely reference field excitation light and measured field excitation light. The reference field excitation light is used to excite and generate a reference light field, and the measured field excitation light is used to excite the measured field.

[0041] Optionally, a 50:50 beam splitter is used to obtain two excitation light beams of equal energy.

[0042] It can be understood that three beams of light are split: reference field excitation light, test field excitation light and pump light; the reference field excitation light, test field excitation light and pump light have the same frequency. When the three beams of light reach the sample surface, a partially degenerate four-wave mixing effect will occur on the sample surface, and the sample surface will re-radiate new nonlinear signal light. The nonlinear signal light carries nonlinear signal information, and its frequency is a combination of the frequencies of the three input light waves. By observing and measuring the frequency, intensity and other characteristics of the nonlinear signal information, information such as the molecular structure and energy level transition of the sample can be obtained.

[0043] Specifically, the surface of the sample stage in step S3 may be a substrate coated with a metal film layer.

[0044] As a non-limiting embodiment, the substrate may be a cover glass, and the metal film layer may be gold, silver, aluminum or other common noble metal film layers.

[0045] It can be understood that when the reference field excitation light and the field to be measured excitation are focused on a very small area, the light field has a higher spatial intensity, and this light field usually appears as a tightly focused light beam; when the reference field excitation light and the field to be measured excitation are less focused, the light field can be coupled through the surface and excite the surface plasmon mode. This mode propagates along the metal surface, forming a plasmon field that interacts with the metal surface and the incident light field.

[0046] Specifically, the reference field excitation light is modulated to generate an interference field, which is focused onto the sample surface together with the test field excitation light and the pump light. The focusing concentrates the light energy in a small area on the sample surface. The atoms or molecules on the surface of the sample stage will be affected by the light field. Under the action of the strong light field, the polarization state of the sample will change. This polarization is not a simple linear response, but will produce nonlinear polarization. According to the principle of nonlinear optics, when the three light fields (the interference field after modulation of the reference field excitation light, the test field excitation light and the pump light) interact in the sample, new light waves will be generated, that is, a partially degenerate four-wave mixing effect will be generated, generating nonlinear signal light; the nonlinear signal light is then characterized by imaging technology.

[0047] Specifically, the basic principle of characterizing and acquiring nonlinear signals of four-wave mixing is that in the nonlinear process of the light field, photons follow the conservation of energy and momentum, which can be expressed by the formula and formula Expression, among which and They respectively refer to the frequency and wave vector of the i-th wave.

[0048] The wave vector mapping of the evanescent field can be achieved through the energy and momentum conservation conditions, especially the wave vector matching condition. The evanescent field refers to the field that cannot propagate in free space due to attenuation when the wave propagates on the surface of the medium. Usually, its wave vector lies outside the free-space dispersion cone and therefore cannot be directly captured by far-field detection equipment such as cameras or spectrometers. However, through the partially degenerate four-wave mixing effect, when the wave vector matching condition is met, the evanescent field wave vector originally located outside the dispersion cone will be converted into a wave vector located within the free-space dispersion cone through a nonlinear process. The signal that was originally unable to be directly detected in the near field will be converted into nonlinear signal light that can be detected in the far field.

[0049] Understandably, the four-wave mixing effect is caused by a third-order nonlinear effect, which occurs in almost all crystalline materials. Therefore, this effect can be used to detect the surface of almost any sample, with high reusability.

[0050] Furthermore, the optical path refers to the product of the length of the path that light propagates in a medium and the refractive index of the medium. In the present invention, the optical path that the reference field excitation light, the test field excitation light, and the pump light travel to the surface of the sample stage is the same, which means that the actual physical path length they travel from the light source to the surface of the sample stage multiplied by the refractive index of the medium on their respective propagation paths is equal.

[0051] Specifically, the control of the optical path is achieved by adjusting the layout of the optical system.

[0052] Optionally, a free-space optical delay system is added during the propagation of the excitation light of the field to be measured so that the optical path traversed by the reference field excitation light and the excitation light of the field to be measured is the same; a free-space optical delay system is added during the propagation of the pump light so that the optical path traversed by the reference field excitation light, the excitation light of the field to be measured and the pump light is the same.

[0053] The optical path lengths of the excitation light and pump light of the field to be measured can be adjusted by different free-space optical delay systems. Specifically, the optical path length of the excitation light of the field to be measured is adjusted by a first free-space optical delay system; and the optical path length of the pump light is adjusted by a second free-space optical delay system.

[0054] Specifically, the free-space optical delay system can include multiple structures such as a mirror group and a translation stage to limit the minimum step size, improve the nonlinear signal intensity, eliminate phase errors, and achieve femtosecond time synchronization.

[0055] The same optical path ensures the consistency of each light beam in time and phase.

[0056] It can be understood that in the partially degenerate four-wave mixing process, the light beams must meet in a way that can achieve phase matching. Phase matching ensures that energy is effectively transferred from the input light beam to the generated nonlinear signal light, and the optical path directly affects the phase of the light. When the optical path is different, a phase difference will occur between the light beams, resulting in serious phase mismatch. Once the phase is mismatched, the four-wave mixing effect will be greatly suppressed, and the signal information of the nonlinear signal light will be weakened. The optical path of the reference field excitation light, the measured field excitation light and the pump light introduced into the sample stage surface is adjusted to be the same to meet the phase matching condition. The more accurate the compensation of similar optical path, the stronger the signal of the nonlinear signal light.

[0057] Step S3 also includes the following steps: In step S31 , the excitation light of the field to be measured is focused onto the surface of the sample stage after optical delay and polarization modulation, and excites the field to be measured on the surface of the sample stage.

[0058] Specifically, the optical delay system causes the excitation light of the field to be measured to undergo optical delay, and the optical delay system changes the length of the propagation path of the light, thereby controlling the arrival time of the light.

[0059] Exemplarily, the optical delay system can be a free-space optical delay line composed of a pair of plane mirrors placed orthogonally on a high-precision one-dimensional translation stage. The adjustable mirror position or bias angle allows the excitation light of the field to be measured to be temporally misaligned with the reference field excitation light and the pump light, so that the three beams of light reach the surface of the sample stage at the same time.

[0060] Specifically, polarization modulation is the process of changing the polarization state of light. The polarization of light can be understood as the relationship between the vibration direction of the electric field of the light wave and the propagation direction.

[0061] For example, the polarization direction of light can be changed or one polarization state can be converted into another polarization state by using optical elements such as polarizers and wave plates.

[0062] In the present invention, the excitation light of the field to be measured is modulated by a half-wave plate to obtain a linear polarization state in any direction.

[0063] As a non-limiting embodiment, the excitation light of the field to be measured passes through a quarter-wave plate to be modulated to obtain circularly polarized light or elliptically polarized light of arbitrary rotation direction.

[0064] As another non-limiting embodiment, the field excitation light to be measured passes through a vortex wave plate to obtain the field excitation light to be measured in an arbitrary polarization state. It can be understood that in the present invention, polarization modulation is used to make the polarization state of the excitation light of the field to be measured match the polarization state of the reference field excitation light and the pump light or to generate specific interactions, thereby better exciting the field to be measured.

[0065] Step S3 includes the following steps: In step S32, the reference field excitation light is phase-modulated to generate a first reference field excitation light and a second reference field excitation light. The first reference field excitation light and the second reference field excitation light have the same frequency. The first reference field excitation light and the second reference field excitation light interfere with the field to be measured on the surface of the sample stage to generate an interference field.

[0066] Specifically, phase modulation changes the phase of the light wave to introduce a specific phase change to the reference field excitation light, preparing for subsequent interference and other processes.

[0067] Exemplarily, the reference field excitation light is loaded with dual-beam interference holographic phase modulation through a spatial light modulator, and phase detection with four-step phase shift is realized here.

[0068] After phase modulation, the original reference field excitation light is divided into two beams, namely the first reference field excitation light and the second reference field excitation light, and the frequencies of the first reference field excitation light and the second reference field excitation light remain the same as the frequency of the original reference field excitation light.

[0069] Since the frequencies of the first reference field excitation light and the second reference field excitation light are the same as the frequency of the field to be measured, and they satisfy a certain phase relationship in space, an interference field will be formed on the surface of the sample stage.

[0070] Furthermore, before step S4, obtaining and measuring the nonlinear signal information, the following steps are also included: In step S33, the initial phases of the first reference field excitation light and the second reference field excitation light are controlled to be equal, and the initial phases of the first reference field excitation light and the second reference field excitation light are modulated four times in a row with a phase increment of 1 / 4 cycle to obtain the intensity information of the first interference field, the second interference field, the third interference field, and the fourth interference field after the first, second, third, and fourth modulations, respectively.

[0071] Specifically, in step S33, the present invention applies the “four-step phase shift” technology of structured light illumination to the near-field light field characterization, and extracts the phase distribution of the light field in an analytical manner, so that we can realize the near-field light field phase information characterization based on the non-scanning near-field characterization.

[0072] It can be understood that four times of modulation and measurement with a phase increment of 1 / 4 cycle can obtain more comprehensive interference field intensity information, thereby more accurately calculating the phase difference between the field to be measured and the reference field. At the same time, four modulations provide multiple independent measurement data points, making the measurement results more stable, reducing measurement errors, and improving measurement sensitivity.

[0073] Furthermore, step S4 of collecting and calculating nonlinear signal information includes the following steps: Step S41, use the intensity information of the first interference field to subtract the intensity information of the third interference field to obtain a first difference expression; use the intensity information of the second interference field to subtract the intensity information of the fourth interference field to obtain a second difference expression; combine the first difference expression and the second difference expression to calculate the phase distribution of the field to be measured.

[0074] Understandably, in actual measurement, the easiest thing to measure is the intensity information of the light field. The intensity information of the four-time interference field is measured and calculated, and the light field information of the interference field represents the light field information of the field to be measured, and the nonlinear signal information represents the intensity information of the interference field, reflecting that the intensity and phase of the light field of the interference field are related. Therefore, in the process of realizing phase detection, the phase of the field to be measured can be determined by the light field intensity information, and finally the phase distribution of the light field to be measured is obtained; the interference field intensity information modulated four times with a fixed interval phase difference is used, that is, a phase adjustment algorithm, and the two difference expressions are combined, and the signal changes under different phase modulations are comprehensively considered to calculate the phase distribution of the field to be measured, thereby improving the accuracy and stability of phase measurement.

[0075] For example, in a non-limiting embodiment provided by the present invention, the following experimental process is performed to calculate the phase distribution of the field to be measured: In the partially degenerate four-wave mixing experiment, let the light field on the surface of the sample to be measured be Ei, and its mathematical expression is .

[0076] The introduced first reference field excitation light and the second reference field excitation light form structured light fringes. The light intensity of the first reference field excitation light and the light intensity of the second reference field excitation light can be written as:

[0077]

[0078] Where ν represents the amplitude of the first reference field excitation light and the second reference field excitation light, k represents the wave vector, k= , ϕ represents the phase of the reference light, μ(x,y) represents the amplitude of the light field to be measured at (x,y), φ(x,y) represents the phase of the light field to be measured at (x,y), and x is the spatial coordinate variable.

[0079] More specifically, kx reflects the spatial phase change of the reference light. The signs before kx in E1 and E2 are opposite, indicating that the spatial phase change trends of the first reference field excitation light and the second reference field excitation light are opposite.

[0080] The first reference field excitation light E1 and the second reference field excitation light E2 interfere with the light field to be measured, forming a new light field distribution Et, whose light field intensity expression is: Among them, Et represents the intensity information of the interference field, μ represents the amplitude of the light field to be measured, ν represents the amplitude of the reference field excitation light, and x represents the spatial coordinate variable. represents the phase of the field to be measured, and ϕ represents the initial phase of the reference field excitation light.

[0081] In step S33, the phases of the first reference field excitation light and the second reference field excitation light are changed to ϕ, ϕ+π / 2, ϕ+π, and ϕ+3π / 2, respectively. We can obtain the intensity distribution of the total interference field under four different reference light phases, which are recorded as I1, I2, I3, and I4 respectively. Further calculation can be solved to obtain the phase of the field to be measured:

[0082] in, represents the phase distribution of the field to be measured, I1, I2, I3, and I4 represent the intensity information corresponding to the four interference patterns obtained by changing the phase of light, and ϕ represents the initial phase of light.

[0083] From the phase representation of the field to be measured, it can be seen that the excitation light of the first reference field and the excitation light of the second reference field have a specific spatial phase distribution form. The light field to be measured and the reference light field are linearly superimposed to obtain the light field distribution of the interference field. After the excitation light of the first reference field and the excitation light of the second reference field are superimposed and interfere with the light field to be measured, the intensity of the interference field will be modulated by the phase of the light field to be measured. By collecting interference patterns under different phase shift conditions, I1, I2, I3, and I4 are obtained. Using the above-mentioned phase formula of the field to be measured, the phase of the light field to be measured can be demodulated.

[0084] It can be understood that the first reference field excitation light and the second reference field excitation light interfere with the field to be measured on the surface of the sample stage, and the phase difference and other information between the field to be measured and the reference field are measured and compared through interference. The interference field contains the interaction information between the field to be measured and the reference field, which can be used to improve the measurement accuracy and sensitivity. Since the frequency of the first reference field excitation light and the second reference field excitation light is the same and the optical path is equal to that of the field to be measured, the interference field formed produces a stable interference pattern in space, thereby realizing phase comparison and measurement between the field to be measured and the reference field.

[0085] Optionally, during the interference intensity calculation process, the derivation process of the interference field intensity is gradually simplified by setting the first reference field excitation light and the second reference field excitation light to have the same amplitude and the same initial phase.

[0086] Furthermore, the intensity information of the interference field represents the intensity information of the field to be measured, and the nonlinear signal information represents the intensity information of the interference field.

[0087] Specifically, when the light field to be measured interferes with the reference light field, according to the principle of wave superposition, the interference field is the result of the interaction between the two, and the intensity information of the field to be measured is obtained by calculating the intensity information of the interference field.

[0088] During the interference process of light, when the light intensity reaches a certain level or in some special media, nonlinear optical effects will occur. The nonlinear process generates nonlinear signals. Nonlinear signals are an indirect way to obtain the intensity information of the interference field. By detecting the intensity, frequency, phase and other information of these nonlinear signals, the intensity information of the interference field can be inferred.

[0089] Step S3 also includes: In step S34, the pump light is focused onto the surface of the sample stage after optical delay and polarization modulation. After polarization modulation, the polarization mode of the pump light matches that of the nonlinear signal.

[0090] It can be understood that the intensity of the pump light directly affects the intensity of the nonlinear signal. If the pump light has a higher power, the nonlinear effect is significant enough to be detected. At the same time, in the nonlinear optical process, the pump light must also meet phase matching. After passing through the optical delay line, its optical path reaching the surface of the sample stage is equal to that of other excitation lights, such as the reference field excitation light and the test field excitation light. The optical path matching ensures that all light beams arrive at the surface of the sample stage at the same time, thereby realizing effective nonlinear interaction; after the pump light is polarization modulated, its polarization direction matches the polarization direction of the nonlinear signal, improving the generation efficiency of the nonlinear signal and enhancing the intensity of the nonlinear signal; at the same time, the pump light acts as an "optical probe" with fast imaging speed, high stability, and a large enough area to be scanned at one time.

[0091] Specifically, due to the high energy of the pump light, in partially degenerate four-wave mixing, the pump light photons can interact with the photons in other light fields. Through the conversion of energy and momentum, part of the energy is converted into nonlinear signal light, generating new nonlinear signal light. After polarization modulation, the polarization mode of the pump light matches the polarization mode of the nonlinear signal, thereby enhancing the nonlinear signal.

[0092] It is understandable that there is no fixed execution order between step S31 to step S34. They can be executed in any order according to actual needs, and some steps can be performed simultaneously.

[0093] See also Figure 2-Figure 3 A second embodiment of the present invention provides a phase detection system 100 for implementing the above-mentioned phase detection method. The phase detection system 100 includes: An incident light excitation module 101, configured to emit incident light; The beam splitting module 102 is used to split the incident light into pump light and excitation light, and to split the excitation light into reference field excitation light and measured field excitation light; The optical transmission module 103 is used to focus the reference field excitation light, the test field excitation light, and the pump light onto the surface of the 12 samples to generate a four-wave mixing effect and generate nonlinear signal light. The reference field excitation light, the test field excitation light, and the pump light have the same optical path length when introduced to the surface of the 12 samples. The acquisition and calculation module 104 is used to acquire and calculate nonlinear signal information.

[0094] Specifically, the incident light excitation module 101 includes a laser and an optical parametric oscillator 2 which are arranged in sequence.

[0095] Specifically, the phase detection system 100 further includes 12 samples placed at preset positions.

[0096] Furthermore, the acquisition and measurement module 104 is provided with an imaging device close to the sample 12 .

[0097] The beam combiner 14 is arranged close to the sample 12 and away from the imaging device.

[0098] It can be understood that the laser is used to emit seed laser as incident light, and the optical parametric oscillator 2 is used to receive the incident light and divide the incident light into two parts, one part is directly emitted as pump light, and the other part is emitted as excitation light after wavelength down-conversion; the beam splitter 22 arranged at a distance from the optical parametric oscillator 2 is used to divide the excitation light into reference field excitation light and measured field excitation light.

[0099] Specifically, the beam splitting module 102 includes a first beam splitting module 102 and a second beam splitting module 102 . The first beam splitting module 102 is used to split the incident light into pump light and excitation light. The second beam splitting module 102 is used to split the excitation light into reference field excitation light and measured field excitation light.

[0100] Furthermore, the second beam splitting module 102 splits the excitation light into reference field excitation light and measured field excitation light, and forms a reference field light path and a measured field light path respectively.

[0101] It can be understood that the separation of the reference field optical path and the measured field optical path makes it possible to independently control and modulate the two beams of light, providing a basis for subsequent interference measurement and phase analysis.

[0102] Furthermore, the phase detection system 100 further includes a modulation module 105 for optically delaying and polarization modulating the excitation light of the field to be measured, and for optically delaying and polarization modulating the pump light.

[0103] Specifically, the modulation module 105 includes a first modulation module 106 and a second modulation module 107. The first modulation module 106 is used to perform optical delay and polarization modulation on the excitation light of the field to be measured, and the second modulation module 107 is used to perform optical delay and polarization modulation on the pump light.

[0104] Exemplarily, in the optical path of the field to be measured, the first modulation module 106 is provided with a first free-space optical delay system, which is composed of a pair of plane mirrors 16 placed orthogonally on the first translation stage 23 and arranged opposite to each other.

[0105] It can be understood that the first translation stage 23 carries a group of plane mirrors 16. The group of plane mirrors 16 causes light to reflect multiple times between the mirrors, thereby increasing the optical path and achieving light delay. When the first translation stage 23 moves, the position of any plane mirror 16 in the group of plane mirrors 16 changes, causing the path length of light propagating in the system to change. There is a linear relationship between the displacement distance Δx and the change in optical path, thereby achieving precise delay control of light. A smaller step size means higher delay accuracy, which can detect smaller phase changes, thereby improving the measurement resolution and sensitivity of the system.

[0106] Specifically, a set of plane reflectors 16 placed orthogonally make the excitation light of the field to be measured go through a "Z"-shaped path, and the optical path length increases. The relationship between the displacement distance Δx of the first translation stage 23 and the optical delay experienced by the excitation light of the field to be measured is: Optionally, the first translation stage 23 can provide a minimum step length of less than 21 microns.

[0107] Furthermore, a beam combiner 14 is provided near the sample 12 in the phase detection system 100 .

[0108] The reference field excitation light and the measured field excitation light modulated by the first free-space optical delay system and the spatial light modulator 20 are combined by a beam combining mirror 14 arranged near the sample 12. After combining, the reference field excitation light and the measured field excitation light have the same optical path.

[0109] It can be understood that the combined reference field excitation light and the measured field excitation light have the same optical path to ensure that they have a stable phase relationship when reaching the 12 samples, thereby generating clear interference fringes, eliminating the phase error caused by the difference in optical paths, and improving the measurement accuracy.

[0110] Specifically, the pump light forms a pump light optical path in the phase detection system 100 .

[0111] In this embodiment, the second modulation module 107 is provided with a second free-space optical delay system in the pump light path. The second free-space optical delay system is composed of a pair of plane mirrors 16 placed orthogonally on the second translation stage 5 and arranged opposite to each other.

[0112] As can be understood, the two orthogonally positioned plane mirrors 16 cause the incident pump light to exit in parallel after undergoing a certain geometric displacement. Simultaneously, the second translation stage 5 moves parallel to the incident direction of the pump light, enabling precise adjustment of the time delay between the pump light and the excitation light. The relationship between the displacement distance Δx of the second translation stage 5 and the optical delay Δl experienced by the incident laser light, i.e., the pump light, is Δl = 2Δx.

[0113] Specifically, the second translation stage 5 moves along the direction in which the pump light enters or exits the second translation stage 5. Optionally, the second translation stage 5 can provide a minimum step length of less than 42 microns.

[0114] It is understandable that the second translation stage 5 should have precise displacement control, which can achieve nanometer or micrometer level accuracy, so as to more accurately eliminate the optical delay between the excitation light and the pump light, and should provide smooth and vibration-free movement.

[0115] The pump light is modulated by the second free space optical delay system and reaches the sample 12, and has the same optical path as the excitation light after the reference field excitation light and the measured field excitation light are introduced into the surface of the sample 12.

[0116] It can be understood that when light propagates through a medium, the optical path length is equal to the product of the medium's refractive index and the geometric path length. When the pump light, the combined excitation light from the reference field and the excitation light from the field to be measured, reaches the 12 sample surfaces with the same optical path length, it means that they take the same amount of time to propagate along the optical path. This consistent optical path ensures a stable distribution of interference fringes.

[0117] After the excitation light excites the sample 12, the time for the detection light to reach the sample 12 is precisely controlled by the second free-space optical delay system, and the dynamic process of the sample 12 is captured by the imaging device. In this embodiment, the excitation light is the reference field excitation light and the measured field excitation light, and the detection light is the pump light.

[0118] The second free-space optical delay system cooperates with the first free-space optical delay system to ensure that the pump light and the excitation light coincide in time at the sample 12, thereby improving the measurement signal-to-noise ratio.

[0119] Furthermore, the imaging device in the acquisition and measurement module 104 includes: a filter 7, which is used to filter the nonlinear signal light and remove background noise; a quarter-wave plate 8, which is used to process the polarization state of the nonlinear signal light and convert it into linearly polarized light; a third linear polarizer 9, which is used to analyze the polarization state of the nonlinear signal light; an imaging lens 10, which is used to focus and image the nonlinear signal light; and a camera imaging module 30, which is used to perform a single exposure imaging of the nonlinear signal light 30.

[0120] It can be understood that the short-wave cutoff type dichroic mirror 6 is arranged between the free-space optical delay line and the long focusing objective lens, so that the pump light can pass through without change, generating a partially degenerate four-wave mixing effect, and then the nonlinear signal light can be reflected separately to the imaging device for imaging, which can avoid interference and make the system have higher multiplexing.

[0121] Furthermore, the modulation module 105 also includes a third modulation module 108, which is used to phase-modulate the reference field excitation light to generate a first reference field excitation light and a second reference field excitation light, and to control the initial phases of the first reference field excitation light and the second reference field excitation light to be equal, and to modulate the initial phases of the first reference field excitation light and the second reference field excitation light with a phase increment of 1 / 4 cycle for four consecutive times to obtain the intensity information of the first interference field, the second interference field, the third interference field and the fourth interference field after the first, second, third and fourth modulations respectively.

[0122] Specifically, in the reference field optical path, the third modulation module 108 is provided with a spatial light modulator 20 to load dual-beam interferometric holographic phase modulation, and implements four-step phase shift phase loading here, that is, the initial phases of the first reference field excitation light and the second reference field excitation light are modulated four times in a row with a phase increment of 1 / 4 cycle, and the intensity information of the first interference field, the second interference field, the third interference field and the fourth interference field after the first, second, third and fourth modulations are obtained respectively.

[0123] The four-step phase shift method introduces phase differences of 0, π / 2, π, and 3π / 2 in sequence, collects four interference patterns, and thus calculates the phase information of the object being measured.

[0124] Furthermore, the acquisition and measurement module 104 is also used to subtract the intensity information of the third interference field from the intensity information of the first interference field to obtain a first difference expression; use the intensity information of the second interference field to subtract the intensity information of the fourth interference field to obtain a second difference expression; and combine the first difference expression and the second difference expression to calculate the phase distribution of the field to be measured.

[0125] It can be understood that the phase calculation method of four-step phase shift interferometry in the present invention extracts the phase distribution of the field to be measured by performing differential operations on four interference patterns. The differential operation can effectively offset the low-frequency noise in the system, and the measurement module 104 can fully obtain four complete interference patterns at one time, thereby improving the anti-interference ability, ensuring the optimization of measurement efficiency and the accuracy of phase solution.

[0126] As a non-limiting embodiment, see Figure 4 The specific detection steps of a phase detection method provided by the third embodiment of the present invention in the phase detection system 100 are as follows: The seed laser 1 emits incident light, which is then divided into pump light and excitation light in the optical parametric oscillator 2.

[0127] Specifically, the pump light forms a pump light path in the system, in which the pump light passes through the first linear polarizer 3 and modulates the polarization state to obtain linearly polarized light with higher polarization purity. The pump light is modulated by the first half-wave plate 4 to obtain linearly polarized light with any polarization direction.

[0128] Again, the pump light is coupled into a second free-space optical delay system, which comprises a combination of two plane mirrors 16 disposed on a second translation stage 5. The second free-space optical delay system ensures that the optical path from the pump light to the surface of the sample 12 is the same as that of the excitation light.

[0129] Finally, the pump light passes through the dichroic mirror 6 and is incident on the long working distance objective lens 11 and is focused onto the gold film sample 12. The focusing position is the light field area to be measured excited by the excitation light.

[0130] Furthermore, for the excitation light, the excitation light passes through the second linear polarizer to modulate the polarization state to obtain linearly polarized light with higher polarization purity.

[0131] The excitation light is split by the beam splitter 22 into reference field excitation light and test field excitation light.

[0132] The reference field excitation light and the to-be-measured field excitation light form a reference field excitation light optical path and a to-be-measured field excitation light optical path in the system.

[0133] Specifically, in the reference field excitation light path, the reference field excitation light is incident on the third half-wave plate 21 to modulate the linear polarization direction of the laser light to be the same as the polarization modulated by the spatial light modulator 20 .

[0134] The third modulation module 108 is provided with a spatial light modulator 20 , which implements a four-step phase shift phase loading of the reference field excitation light.

[0135] The reference field excitation light is shaped into a parallel beam by the second focusing lens 18 in the optical transmission module 103 , and is focused to the focal point of the oil immersion objective lens 13 through the first focusing lens 19 , the third focusing lens 17 , and the fourth focusing lens 31 .

[0136] The reference field excitation light is reflected by the plane reflector 16 before being focused, and then enters the beam combiner 14 .

[0137] Specifically, in the optical path of the excitation light of the field to be measured, the excitation light of the field to be measured is coupled into a first free-space optical delay system through a plane mirror 16. The first free-space optical delay system comprises a combination of two plane mirrors 16 disposed on a first translation stage 23. The first free-space optical delay system ensures that the optical path from the excitation light of the field to be measured to the surface of the sample 12 is the same as that of the excitation light of the reference field.

[0138] The excitation light of the field to be measured is modulated by the second half-wave plate 15 to obtain a linear polarization state in any direction, and then incident on the beam combiner 14. At this time, the reference field excitation light and the excitation light of the field to be measured are combined.

[0139] The combined reference field excitation light and the measured field excitation light are focused onto the surface of the sample 12 through the oil-immersion objective lens 13. When the optical delay between the reference field excitation light, the measured field excitation light and the pump light is strictly compensated by the first free-space optical delay system and the second free-space optical delay system, a partially degenerate four-wave mixing effect will occur on the surface of the sample 12, generating a nonlinear signal.

[0140] The nonlinear signal light is collected by the long working distance objective lens 11 and reflected into the collection light path by the dichroic mirror 6.

[0141] Furthermore, in the collection light path, the nonlinear signal light is further filtered by the filter 7 to remove background noise, and is derotated by the quarter-wave plate 8 to convert the circularly polarized light or elliptically polarized light of arbitrary rotation direction into linearly polarized light, and is polarized by the third linear polarizer 9.

[0142] The imaging lens 10 focuses the nonlinear signal onto the camera imaging module 30 , and the camera imaging module 30 performs a single exposure imaging on the nonlinear signal.

[0143] In the embodiments provided herein, it should be understood that "B corresponding to A" means that B is associated with A and B can be determined based on A. However, it should also be understood that determining B based on A does not mean determining B based solely on A; B can also be determined based on A and / or other information.

[0144] It should be understood that references to "one embodiment" or "an embodiment" throughout this specification mean that specific features, structures, or characteristics associated with the embodiment are included in at least one embodiment of the present invention. Therefore, the phrases "in one embodiment" or "in an embodiment" appearing throughout this specification do not necessarily refer to the same embodiment. Furthermore, these specific features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. Those skilled in the art should also be aware that the embodiments described in this specification are all optional embodiments, and the actions and modules involved are not necessarily required for the present invention.

[0145] In various embodiments of the present invention, it should be understood that the size of the serial numbers of the above-mentioned processes does not necessarily mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0146] The flow charts and block diagrams in the accompanying drawings of the present invention illustrate the possible implementation architecture, functions and operations of the system, method and computer program product according to various embodiments of the present application. In this regard, each box in the flow chart or block diagram can represent a module, program segment or a part of code, and the module, program segment or a part of code contains one or more executable instructions for realizing the specified logical function. It should also be noted that in some alternative implementation schemes, the functions marked in the box can also occur in a different order than those marked in the accompanying drawings. For example, two boxes represented in succession can actually be executed substantially in parallel, and they can sometimes be executed in the opposite order, which is determined based on the functions involved. It should be noted that each box in the block diagram and / or flow chart, the combination of the boxes in the block diagram and / or flow chart can be implemented by a dedicated hardware-based system that performs the specified function or operation, or can be implemented by a combination of dedicated hardware and computer instructions.

[0147] Compared with the prior art, the phase detection method and system provided by the present invention have the following beneficial effects: 1. The present invention provides a phase detection method, in which three beams of light: reference field excitation light, test field excitation light and pump light are obtained by splitting the incident light. Therefore, the reference field excitation light, the test field excitation light and the pump light have the same frequency. When the three beams of light reach the sample surface, a partially degenerate four-wave mixing effect will occur on the sample surface, and the sample surface will re-radiate new nonlinear signal light. The nonlinear signal light carries nonlinear signal information, and its frequency is a combination of the frequencies of the three input light waves. By observing and measuring the frequency, intensity and other characteristics of the nonlinear signal information, information such as the molecular structure and energy level transition of the sample can be obtained; in the partially degenerate During the four-wave mixing process, the light beams must meet in a way that can achieve phase matching. Phase matching ensures that energy is effectively transferred from the input light beam to the generated nonlinear signal light. The optical path directly affects the phase of the light. When the optical path is different, a phase difference will occur between the light beams, resulting in a serious phase mismatch. Once the phase is mismatched, the four-wave mixing effect will be greatly suppressed, and the signal information of the nonlinear signal light will be weakened. The optical path of the reference field excitation light, the test field excitation light and the pump light introduced into the sample stage surface is adjusted to be the same to meet the phase matching condition. The more accurate the compensation of similar optical path, the stronger the signal of the nonlinear signal light.

[0148] 2. The present invention provides a phase detection method, in which the excitation light of the field to be measured is derived from the splitting of the excitation light, and the optical path reaching the surface of the sample stage needs to be the same as that of the excitation light of the reference field. Therefore, the excitation light of the field to be measured is optically delayed and compensated by a delay line to reduce the phase drift and interference fringe jitter caused by the optical path difference, thereby improving the measurement accuracy and stability. The optical delay can be adjusted according to experimental requirements to adapt to different experimental conditions and sample characteristics. When the excitation light of the field to be measured interacts with the sample to generate the field to be measured, the phase, amplitude and other characteristics of the light will change, which can characterize the optical properties or physical characteristics of the sample, such as the refractive index, absorption coefficient or nonlinear optical response. These changes can reflect the internal structure and composition of the sample, and obtain information about the sample structure, composition and dynamics. In the present invention, the field to be measured carries the phase change of the sample surface and is the main object of phase detection.

[0149] 3. The present invention provides a phase detection method, in which the first reference field excitation light and the second reference field excitation light interfere with the field to be measured on the surface of the sample stage, and the phase difference and other information between the field to be measured and the reference field are measured and compared through interference. The interference field contains the interaction information between the field to be measured and the reference field, which can be used to improve the measurement accuracy and sensitivity. Since the first reference field excitation light and the second reference field excitation light have the same frequency and are equal to the optical path of the field to be measured, the formed interference field produces a stable interference pattern in space, thereby realizing phase comparison and measurement between the field to be measured and the reference field.

[0150] 4. The present invention provides a phase detection method, which uses a four-step phase shift technology to move the phase of the interference field, thereby analyzing the phase recovery process of the light field to be measured, and extracting the phase distribution of the light field in an analytical manner. It can realize the characterization of the near-field light field phase information on the basis of non-scanning near-field characterization; four times of modulation and measurement with a phase increment of 1 / 4 cycle can obtain more comprehensive interference field intensity information, thereby more accurately calculating the phase difference between the field to be measured and the reference field. At the same time, the four modulations provide multiple independent measurement data points, making the measurement results more stable, reducing measurement errors, and improving measurement sensitivity.

[0151] 5. The present invention provides a phase detection method. In actual measurement, the intensity information of the light field is the easiest to measure. The intensity information of the four-order interference field is measured and calculated. The light field information of the interference field represents the light field information of the field to be measured, and the nonlinear signal information represents the intensity information of the interference field, reflecting that the intensity and phase of the light field of the interference field are related. Therefore, in the process of realizing phase detection, the phase of the field to be measured can be determined by the light field intensity information, and finally the phase distribution of the light field to be measured is obtained; the interference field intensity information modulated four times with a fixed interval phase difference, that is, a phase adjustment algorithm, is used to combine the two difference expressions, comprehensively consider the signal changes under different phase modulations, calculate the phase distribution of the field to be measured, and improve the accuracy and stability of phase measurement.

[0152] 6. The present invention provides a phase detection method. In the four-wave mixing process, pump light is the main energy source, which uses energy to drive the nonlinear process, so that the medium in the sample can produce a nonlinear response. The intensity of the pump light directly affects the intensity of the nonlinear signal. If the pump light has a higher power, the nonlinear effect is significant enough to be detected. At the same time, in the nonlinear optical process, the pump light must also meet phase matching. After passing through the optical delay line, its optical path reaching the surface of the sample stage is equal to that of other excitation lights, such as the reference field excitation light and the test field excitation light. The optical path matching ensures that all light beams arrive at the surface of the sample stage at the same time, thereby realizing effective nonlinear interaction; after the pump light is polarization modulated, its polarization direction matches the polarization direction of the nonlinear signal, thereby improving the generation efficiency of the nonlinear signal and enhancing the intensity of the nonlinear signal; at the same time, the pump light acts as an "optical probe" with fast imaging speed, high stability, and a large enough area to be scanned at one time.

[0153] 7. An embodiment of the present invention also provides a phase detection method system, which has the same beneficial effects as the above-mentioned phase detection method and will not be described in detail here.

[0154] The above is a detailed introduction to a large-scale model distillation method, device and storage medium disclosed in the embodiments of the present invention. Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core ideas. At the same time, for those skilled in the art, according to the ideas of the present invention, there will be changes in the specific implementation methods and application scopes. In summary, the content of this specification should not be understood as a limitation on the present invention. Any modifications, equivalent replacements and improvements made within the principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A phase detection method for detecting near-field light fields, characterized in that: The method comprises the following steps: emitting incident light; The incident light is divided into pump light and excitation light, and the excitation light is divided into reference field excitation light and test field excitation light; Focusing the reference field excitation light, the test field excitation light, and the pump light onto the surface of the sample stage to generate a partially degenerate four-wave mixing effect and generate nonlinear signal information, and the reference field excitation light, the test field excitation light, and the pump light have the same optical path length when introduced into the surface of the sample stage; The nonlinear signal information is acquired and measured.

2. The phase detection method according to claim 1, wherein: Focusing the reference field excitation light, the test field excitation light, and the pump light onto the surface of the sample stage to generate a partially degenerate four-wave mixing effect and generate nonlinear signal information further includes the following steps: The excitation light of the field to be measured is focused onto the surface of the sample stage after optical delay and polarization modulation, and excites the field to be measured on the surface of the sample stage.

3. The phase detection method according to claim 2, wherein: Focusing the reference field excitation light, the test field excitation light, and the pump light onto the surface of the sample stage to generate a partially degenerate four-wave mixing effect and generate nonlinear signal information includes the following steps: The reference field excitation light is phase-modulated to generate a first reference field excitation light and a second reference field excitation light. The first reference field excitation light and the second reference field excitation light have the same frequency. The first reference field excitation light and the second reference field excitation light interfere with the field to be measured on the surface of the sample stage to generate an interference field.

4. The phase detection method according to claim 3, wherein: Before obtaining and measuring the nonlinear signal information, the following steps are also included: The initial phases of the first reference field excitation light and the second reference field excitation light are controlled to be equal, and the initial phases of the first reference field excitation light and the second reference field excitation light are modulated four times in a row with a phase increment of 1 / 4 cycle to obtain the intensity information of the first interference field, the second interference field, the third interference field and the fourth interference field after the first, second, third and fourth modulations, respectively.

5. The phase detection method according to claim 4, wherein: The intensity information of the interference field represents the intensity information of the field to be measured, and the nonlinear signal information represents the intensity information of the interference field. Collecting and measuring the nonlinear signal information includes the following steps: The intensity information of the first interference field is subtracted from the intensity information of the third interference field to obtain a first difference expression; the intensity information of the second interference field is subtracted from the intensity information of the fourth interference field to obtain a second difference expression; and the first difference expression and the second difference expression are combined to calculate the phase distribution of the field to be measured.

6. The phase detection method according to claim 1, wherein: Focusing the reference field excitation light, the field excitation light to be measured, and the pump light onto the surface of the sample stage to generate a partially degenerate four-wave mixing effect and generate nonlinear signal light further includes the following steps: The pump light is focused onto the surface of the sample stage after optical delay and polarization modulation. After polarization modulation, the polarization mode of the pump light matches the polarization mode of the nonlinear signal.

7. A phase detection system, configured to implement the phase detection method according to any one of claims 1 to 6, characterized in that: The phase detection system comprises: An incident light excitation module, used for emitting incident light; A beam splitting module, used to split the incident light into pump light and excitation light, and to split the excitation light into reference field excitation light and measured field excitation light; an optical transmission module, configured to focus the reference field excitation light, the test field excitation light, and the pump light onto the surface of the sample stage to generate a partially degenerate four-wave mixing effect and generate nonlinear signal light, wherein the reference field excitation light, the test field excitation light, and the pump light have the same optical path length when introduced into the surface of the sample stage; The acquisition and calculation module is used to acquire and calculate the nonlinear signal information.

8. The phase detection system according to claim 7, wherein: The phase detection system further includes a modulation module for optically delaying and polarization modulating the excitation light of the field to be measured, and for optically delaying and polarization modulating the pump light.

9. The phase detection system according to claim 8, wherein: The modulation module is also used to phase-modulate the reference field excitation light to generate a first reference field excitation light and a second reference field excitation light, and to control the initial phases of the first reference field excitation light and the second reference field excitation light to be equal, and to modulate the initial phases of the first reference field excitation light and the second reference field excitation light with a phase increment of 1 / 4 cycle four times in a row, and obtain the intensity information of the first interference field, the second interference field, the third interference field and the fourth interference field after the first, second, third and fourth modulations respectively.

10. The phase detection system according to claim 8, wherein: The acquisition and measurement module is used to subtract the intensity information of the third interference field from the intensity information of the first interference field to obtain a first difference expression; The intensity information of the fourth interference field is subtracted from the intensity information of the second interference field to obtain a second difference expression; the first difference expression and the second difference expression are combined to calculate the phase distribution of the field to be measured.

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