Synchronous measurement device for phase and polarization parameters of nonlinear material

Abstract

The invention mainly relates to the field of nonlinear optical material measurement, in particular to a nonlinear material phase and polarization parameter synchronous measurement device which is composed of a main light path, a laser light path, a reference light path and a detection light path. A 4f coherent imaging system formed by combining a microscope objective can capture fine phase shift in a micro area of a nonlinear material, nonlinear optical response of a measurement and analysis material in a polarization state under the action of strong laser is introduced, and synchronous measurement of the phase of the nonlinear material and optical nonlinear polarization parameters is realized.

Description

Technical Field

[0001] The present invention mainly relates to the field of measurement of nonlinear optical materials, and more specifically to a device for synchronously measuring the phase and polarization parameters of nonlinear materials. Background Art

[0002] With the rapid development of optical technologies, especially in the fields of laser technology, optical communication, and optoelectronic devices, the demand for nonlinear optical materials has increased significantly. These materials are commonly used in ultrafast optics, optical switches, optical limiters, optical modulators, and all-optical networks. Therefore, accurately measuring the nonlinear refractive index of materials is crucial for the development of high-performance optical devices and materials. The concept of nonlinear optics was first proposed in 1961, and the second harmonic generation effect was experimentally verified for the first time. The research at this stage mainly focused on the theoretical exploration of nonlinear optical effects, especially third-order nonlinear polarization. The Z-scan technique has greatly promoted the progress of nonlinear optical material research. Although this method has achieved certain success in the laboratory, in the face of more complex material systems and actual application requirements, existing measurement methods still have some limitations. A nonlinear imaging technique (NIT-PO) based on the 4f phase coherent imaging technique with PO is used to measure the nonlinear refractive index of materials. This method is inspired by the phase-contrast principle in the Zernike spatial filtering experiment, which converts the tiny phase change on the object plane into a detectable intensity change on the image plane by enhancing the phase contrast, and is particularly suitable for nonlinear effect detection. However, in the study of the nonlinear effects of materials at the micron and sub-micron scales, due to the limitations of spatial resolution and sensitivity of the traditional Z-scan technique, and the insufficient dynamic range of the traditional 4f phase coherent imaging technique in the detection of micro-region nonlinear effects, there are certain technical bottlenecks.

[0003] By combining the 4f phase coherent imaging, micro-region optical measurement technology, and polarization technology, the resolution, focusing accuracy, and sensitivity of the system are improved, making it suitable for the synchronous detection of the phase and polarization parameters of micro-region nonlinear materials. Constructing a stable, efficient, highly integrated, and easy-to-operate device for synchronously measuring the phase and polarization parameters of nonlinear materials is the problem to be solved by the present invention. Summary of the Invention

[0004] The present invention relates to an optical system that combines 4f coherent imaging, micro-area optical measurement technology, and polarization technology. By introducing a spatial light modulator (SLM) to replace the traditional fixed-phase object, dynamic and programmable phase modulation can be achieved, improving the flexibility and adaptability of the system. A 4f imaging system is composed of two microscopic objective lenses with the same nominal parameters, enabling the system to measure subtle phase shifts in a tiny area. By introducing the measurement of the polarization state, polarization information under the same detection conditions can be synchronously obtained for analyzing the nonlinear optical response of materials under the action of intense laser light. Through this design, the resolution, focusing accuracy, and sensitivity of the system have been significantly improved, making it suitable for the nonlinear material phase measurement of material micro-areas. By combining the characteristics of polarized light, researchers can more accurately and comprehensively measure and analyze the nonlinear optical behavior of materials.

[0005] The present invention is realized through the following technical solutions: A device for synchronously measuring the phase and polarization parameters of nonlinear materials includes a vertical main optical path and laser optical path channels, reference optical path channels, and detection optical path channels that are perpendicular to the main optical path respectively. The main optical path includes a first beam splitter prism, a second beam splitter prism, a first microscopic objective lens, a three-dimensional translation system and a sample holder, a second microscopic objective lens, a third beam splitter prism, and a plane mirror, which are used to realize the functions of beam transmission and 4f coherent imaging. The laser optical path channel includes a pulsed laser, a variable density attenuator, a polarizer, a beam expander system, a variable aperture diaphragm, a first beam splitter prism, and a spatial light modulator, which are used to provide incident light and modulate the incident light spot. The reference optical path channel includes a first photoelectric image sensor. The reference optical path can ensure the reliability of experimental data. Especially when there are fluctuations in the light source energy, this optical path can correct the errors caused by laser fluctuations for calibrating and monitoring the energy of each laser pulse. The detection optical path channel includes a second photoelectric image sensor and a third photoelectric image sensor for spot acquisition.

[0006] In the above technical solution, the pulsed laser in the laser optical path channel emits excitation light. After being attenuated by the variable density attenuator, it enters the polarizer for polarization. Then, after being expanded by the beam expander system, the spot size is adjusted by the adjustable diaphragm to select a part with a relatively uniform central spot, and it enters the first beam splitter prism. Under the action of the first beam splitter prism, a beam of light coaxial with the laser optical path enters the reflective spatial light modulator. The spatial light modulator adjusts the excitation light and reflects it back to the first beam splitter prism to access the main optical path. Under the action of the second beam splitter prism, one beam of light serves as the reference light, and one beam of light is the detection light; the reference light enters the reference optical path channel, and the detection light accesses the detection optical path channel after passing through the first microscopic objective lens, the optical material, the second microscopic objective lens, and the third beam splitter prism.

[0007] As a further technical solution, the laser optical path channel consists of a pulsed laser, a variable density attenuation sheet, a polarizer, a beam expander system, a variable aperture diaphragm, a first beam splitter prism, and a spatial light modulator. The pulsed laser, the variable density attenuation sheet, the polarizer, the beam expander system, the variable aperture diaphragm, the first beam splitter prism, and the spatial light modulator are horizontally arranged in a straight line from right to left in sequence and are fixedly connected. The laser optical path channel is connected to the main optical path through the first beam splitter prism. The laser emitted by the pulsed laser, after passing through the variable density attenuation sheet, the polarizer, the beam expander system, the variable aperture diaphragm, the first beam splitter prism, and the spatial light modulator, the incident light spot adjusted by the spatial light modulator is circular with a radius of R a And the phase change light spot in the central part of the incident light spot is circular with a radius of L p .

[0008] As a further technical solution, the spatial light modulator is a reflective phase modulator, which can be arbitrarily adjusted between 0 and 2π for the phase distribution of the incident light beam through the control of the computer.

[0009] As a further technical solution, the first, second, and third beam splitter prisms are non-polarizing beam splitter prisms with the same size.

[0010] As a further technical solution, the main optical path consists of a first beam splitter prism, a second beam splitter prism, a first microscope objective, a three-dimensional translation system and a sample holder, a second microscope objective, a third beam splitter prism, and a plane mirror. The first beam splitter prism, the second beam splitter prism, the first microscope objective, the three-dimensional translation system and the sample holder, the second microscope objective, the third beam splitter prism, and the plane mirror are vertically arranged in a straight line from top to bottom in sequence and are fixedly connected. The outgoing light beam is incident on the spatial light modulator, and the reflected light beam is incident on the second beam splitter prism again; The second beam splitter prism divides the incident light beam into two beams of light. The reflected light beam is incident on the first photoelectric image sensor, and the transmitted light beam is incident on the first microscope objective; The outgoing light beam is incident on the sample stage; The outgoing light beam passes through the second microscope objective; The outgoing light beam is incident on the third beam splitter prism. The incident light beam is divided into two beams of light. The reflected light beam is incident on the second photoelectric image sensor, and the transmitted light beam is incident on the plane mirror. The light beam reflected by the plane mirror is incident on the third photoelectric sensor.

[0011] As a further technical solution, the plane mirror is placed at 45° along the main optical path.

[0012] As a further technical solution, the reference optical path channel is composed of a first photoelectric image sensor and a second beam splitter prism of the main optical path, which are arranged horizontally in a straight line perpendicular to the main optical path from right to left and are connected to the main optical path by the second beam splitter prism. The relative position of the sensor and the incident light is adjusted to make the center line of the sensor coincide with the optical axis, and the position of the sensor is adjusted along the optical axis direction to make the incident light wave accurately hit the target surface, which is used as a comparison reference value and monitors the stability of the reference light spot.

[0013] As a further technical solution, the detection optical path channel is composed of a second photoelectric sensor and a third photoelectric sensor adjusted in parallel. The relative positions of the second and third photoelectric sensors and the incident light are adjusted to make the center line of the sensor coincide with the optical axis, and the position of the sensor is adjusted along the optical axis direction to make the incident light wave accurately hit the target surface, which is used to receive the detection light spot information and polarization information.

[0014] As a further technical solution, the computer is connected to the pulsed laser, the spatial light modulator, the first, second and third photoelectric image sensors, the three-dimensional translation system and the sample holder. The computer controls the laser output, receives the data of the photoelectric image sensors, controls the movement of the three-dimensional translation system, and processes the received data.

[0015] As a further technical solution, the three-dimensional translation system and the sample holder include a three-dimensional translation stage, a translation stage control system, and a sample stage. A nonlinear material to be measured is loaded on the sample stage, and the translation stage control system is connected to the computer and receives the control signal sent by the computer.

[0016] As a further technical solution, the optical material is an organic material, an inorganic material or a semiconductor material.

[0017] As a further technical solution, the magnification and numerical aperture parameters of the first and second micro-objective lenses are the same. The distance between the two micro-objective lenses is adjusted so that the object-side foci of the two coincide and are located in the nonlinear material to be measured.

[0018] As a further technical solution, the parameters of the first and second photoelectric image sensors are the same and are connected to the computer.

[0019] As a further technical solution, the third photoelectric image sensor is a polarization detection image sensor, and a polarization array mask plate is closely arranged in front of the detection target surface.

[0020] As a further technical solution, the optical elements and the opto-mechanical components are all installed on an anti-vibration optical platform, and the relative positions of the components are adjusted so that the optical axes of the components coincide with the light beam.

[0021] As a further technical solution, the application method of the nonlinear material phase and polarization parameter synchronous measurement device includes: Step 1: The detection light passes through the first microscope objective lens, the sample, the second microscope objective lens and reaches the third beam splitter prism. The incident light beam is divided into two beams of light. Among them, the reflected light beam is incident on the second photoelectric image sensor, and the transmitted light beam is incident on the plane mirror. The light beam reflected by the plane mirror is incident on the third photoelectric sensor. The detection light spot is received by the second photoelectric image sensor as the background light spot.

[0022] Step 2: Adjust the laser energy of the pulsed laser so that the excitation light cannot cause nonlinear effects on the optical material. The detection light spot is received by the second photoelectric image sensor as the linear light spot, and the polarization information when no nonlinear effect occurs is received by the third photoelectric image sensor.

[0023] Step 3: Adjust the laser energy of the pulsed laser so that the excitation light can cause nonlinear effects on the optical material. The detection light spot is received by the second photoelectric image sensor as the nonlinear light spot, and the polarization information when the nonlinear effect occurs is received by the third photoelectric image sensor.

[0024] Step 4: Use data processing software to process the background light spot, the linear light spot and the nonlinear light spot. By continuously iterating and fitting, find the situation that is closest to the actual light field distribution to achieve the phase detection of the nonlinear material, and analyze the polarization information received by the third photoelectric image sensor before and after the nonlinear effect occurs.

[0025] The advantages of the present invention are as follows: (1) The present invention forms a synchronous measurement device with nonlinear material phase and polarization parameters through the main optical path, the laser optical path channel, the reference optical path channel and the detection optical path channel. Introducing a spatial light modulator to replace the traditional phase object can achieve more flexible phase modulation and increase the sensitivity of the optical system.

[0026] (2) The present invention uses two microscope objective lenses to form a 4f optical system, which improves the resolution of the system and the signal-to-noise ratio. At the same time, the high focusing ability of the objective lens can make the light beam form a smaller and more accurate light spot on the surface of the sample, thereby effectively limiting the action range of the light. The focusing accuracy and the system sensitivity have been significantly improved. A polarizer and a polarization camera are introduced to simultaneously obtain polarization parameters and synchronously detect the nonlinear polarization change, which is especially suitable for the synchronous measurement of nonlinear material phase and polarization parameters in a small area. Description of the Drawings

[0027] Figure 1 It is a schematic diagram of a synchronous measurement device for nonlinear material phase and polarization parameters according to an embodiment of the present invention.

[0028] In the figure: pulsed laser S01, variable density attenuator S02, polarizer S03, beam expander system S04, variable aperture diaphragm S05, first beam splitter prism S06, spatial light modulator S07, second beam splitter prism S08, first microscope objective S09, three-dimensional translation system and sample holder S10, sample stage S11, second microscope objective S12, third beam splitter prism S13, plane mirror S14, first photoelectric image sensor S15, second photoelectric sensor S16, third photoelectric sensor S17, computer S18. Detailed implementation

[0029] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only one embodiment of the present invention, rather than all embodiments. These embodiments are provided to enable a more thorough understanding of the present invention and to convey the scope of the present invention completely to those skilled in the art. Embodiment

[0030] A device for synchronously measuring the phase and polarization parameters of a nonlinear material provided by the present invention uses a cage structure to build the device, including a main optical path, a laser optical path channel, a reference optical path channel, and a detection optical path channel. The main optical path is placed perpendicular to the horizontal base, and the laser optical path channel, the reference optical path channel, and the detection optical path channel are arranged perpendicular to the main optical path from top to bottom and connected to the main optical path. Cage optical mechanical components are used to load optical elements, and the cage optical mechanical components are connected by cage support rods.

[0031] The first microscope objective S09 is fixed on a cage mounting plate. The cage mounting plate loading the first microscope objective S09 is installed directly below the cage cube loading the second beam splitter prism S08. The cage cube and the cage mounting plate are connected by a cage assembly support rod, and the height of the first microscope objective S09 is adjusted up and down by adjusting the positions of the cage mounting plate and the cage support rod.

[0032] The second microscope objective S12 is fixed on a cage mounting plate. The cage mounting plate loading the second microscope objective S12 is installed directly above the cage cube loading the third beam splitter prism S13. The cage cube and the cage mounting plate are connected by a cage assembly support rod, and the height of the second microscope objective S12 is adjusted up and down by adjusting the positions of the cage mounting plate and the cage support rod.

[0033] After the pulsed laser S01 emits laser light, it is expanded and collimated by the beam expander system S04 and then passes through a neutral density attenuator. The attenuation value of the attenuator is adjusted to ensure that other components will not be damaged by the beam energy. After entering the polarizer, the two-dimensional object defined is a linearly polarized monochromatic plane wave at normal incidence as: , Equation 1 In Equation (1): ω is the angular frequency of the light wave; k is the wave vector; E0 is the amplitude of the optical field; τ is the width of the laser pulse. In Equations (1) to (7), x, y, and z are spatial coordinates, the z-axis direction is the optical axis, t is the time parameter, and i is the imaginary unit. Since the experiment is concerned with the image intensity, for simplicity, the time term is omitted. The light beam enters the spatial light modulator S07, and the phase distribution of the incident light beam can be arbitrarily adjusted between 0 and 2π. The modulated excitation light can be expressed as: , Equation (2) In Equation (2): R a and L p represent the spot radius and the phase change spot radius of the central part, respectively; is the phase delay of the phase change spot of the central part; circ() is the circular function, with a value of 1 inside the circle and 0 outside the circle.

[0034] After passing through the first beam splitter prism S06, one beam of light enters the main optical path. After passing through the second cube beam splitter prism S08, the laser is divided into two beams of light. One beam is the reference light that enters the reference optical path channel, and the other beam is the detection light. The detection light will sequentially pass through the first microscopic objective lens S09, the three-dimensional translation system and the sample holder S10, the sample stage S11, the second microscopic objective lens S12, the third beam splitter prism S13, and the plane mirror S14, and then enter the detection optical path. The images are collected by the second photoelectric sensor S16 and the third photoelectric sensor S17. A 4f system is composed of two identical objective lenses. By adjusting the distance between the two microscopic objective lenses, the object-side foci of the two are set to coincide and located in the nonlinear material to be measured. Then, the electric field distribution on the spectral plane of the 4f system is: , Equation (3) In Equation (3): FT is the Fourier transform symbol; f1 is the focal length of the objective lens; λ is the wavelength of the incident laser. u and v are the spatial coordinates at the focal plane.

[0035] For a simplified model, only the third-order nonlinear optical effect is considered here. The nonlinear absorption coefficient can be set as β, and the linear absorption coefficient and the third-order nonlinear refractive coefficient are expressed as ɑ0 and n2, respectively. Then, the optical electric field after exiting the sample can be expressed as: , Equation (4) In Equation (4): L eff is the effective thickness, and . If the nonlinear sample is a lossless Kerr medium, that is, both β and ɑ0 are 0, then the formula can be simplified to: , Equation (5) In this way, the light intensity distribution detected by the second photoelectric sensor S16 on the exit surface of the 4f system can be expressed as: , Equation (6) FT in Equation 6 -1 is the inverse Fourier transform, H(u,v,t) is the coherent transfer function of the lens, defined as , N A is the numerical aperture of the objective lens, and G is the magnification. Considering the response of the photoelectric sensor to the energy flux distribution of the laser pulse, the image can be expressed as: , Formula 7 The above formulas can be combined to simulate the spatial distribution of the laser beam collected by the second photoelectric sensor in the detection light path.

[0036] The detection light source is a pulsed laser with a pulse width of 21ps (FWHM) and a wavelength of 532nm.

[0037] The spatial light modulator is a pure phase type spatial light modulator with a phase modulation range of 0-2π and a pixel resolution of 1920*1080.

[0038] The first, second and third beam splitter prisms are non-polarizing beam splitter prisms with the same size, and the beam splitting ratios are all 5:5.

[0039] The first and second microscope objectives are 20x infinite conjugate microscope objectives with the same nominal parameters.

[0040] The first and second photoelectric image sensors are CMOS sensors with a pixel resolution of 2048*2048 and a frame rate of 30fps.

[0041] The third photoelectric image sensor is a CMOS camera with a micro-polarization mask plate. Each unit of the polarization mask plate contains 2*2 polarization masks with different polarization states, and the polarization directions are 0 degrees, 45 degrees, 90 degrees and 135 degrees respectively.

[0042] The optical elements and optomechanical components are installed on a vibration-isolating optical platform. The computer synchronously controls the pulse laser, SLM, the first photoelectric sensor, the second photoelectric sensor, the third photoelectric sensor three-dimensional translation stage, the translation stage control system, and the sample stage. The nonlinear material to be tested is loaded on the sample stage. The relative positions of the components are adjusted so that the optical axis of the component coincides with the light beam. First, the optical material is not placed, and the detection light spot is received as the background light spot by the second photoelectric sensor. Then the laser energy of the pulse laser is adjusted and the optical material is placed so that the excitation light cannot cause the optical material to produce a nonlinear effect. The detection light spot is received as a linear light spot by the second photoelectric sensor, and the polarization information when no nonlinear effect occurs is received by the third photoelectric sensor. The laser energy of the pulse laser is adjusted so that the excitation light can cause the optical material to produce a nonlinear effect. The detection light spot is received as a nonlinear light spot by the second photoelectric sensor, and the polarization information when the nonlinear effect occurs is received by the third photoelectric sensor.

[0043] Using data processing software, process the above background light spots, linear light spots, and nonlinear light spots. Take the nonlinear light spot as the simulated input, modify the size of n2 and continuously iterate and fit to find the situation closest to the actual light field distribution, so as to obtain the phase parameter of the micro-region nonlinear material. Use image software to compare and analyze the polarization information before and after the material undergoes the nonlinear effect.

[0044] The present invention discloses a device for synchronously measuring the phase and polarization parameters of a nonlinear material. The 4f coherent imaging system combined with a microscope objective makes the system more sensitive to the phase change of the sample, capable of capturing subtle phase offsets in a tiny area. By introducing a phase-type spatial light modulator, dynamic and programmable phase modulation can be achieved, improving the flexibility and adaptability of the system. By introducing the measurement of the polarization state, the nonlinear optical response of the material under the action of strong laser light is analyzed. Through this design, the resolution, focusing accuracy, and sensitivity of the system have been significantly improved, making it suitable for realizing the phase measurement of micro-region nonlinear materials while capturing nonlinear polarization changes. By combining the characteristics of polarized light, researchers can more accurately and comprehensively measure and analyze the nonlinear optical behavior of the material. In the present invention, the parameters being the same only means that the nominal parameters of two or more components are the same, rather than referring to exactly the same actual parameters.

Claims

1. A device for synchronously measuring the phase and polarization parameters of a nonlinear material, characterized in that, Including: A pulsed laser S01, a variable density attenuator S02, a polarizer S03, a beam expander system S04, a variable aperture diaphragm S05, a first beam splitting prism S06, a spatial light modulator S07, a second beam splitting prism S08, a first microscope objective S09, a three-dimensional translation system and a sample holder S10, a sample stage S11, a second microscope objective S12, a third beam splitting prism S13, a plane mirror S14, a first photoelectric image sensor S15, a second photoelectric sensor S16, a third photoelectric sensor S17, and a computer S18; The pulsed laser outputs pulsed laser light, and the emitted light beam passes through the variable density attenuator; The emitted light beam then passes through the polarizer; The emitted light beam then passes through the beam expander system; The emitted light beam then passes through the variable aperture diaphragm; The emitted light beam then passes through the first beam splitting prism; The emitted light beam is incident on the spatial light modulator, and the reflected light beam is incident on the second beam splitting prism again; The second beam splitting prism divides the incident light beam into two beams of light, where the reflected light beam is incident on the first photoelectric image sensor, and the transmitted light beam is incident on the first microscope objective; The emitted light beam is incident on the sample stage; The emitted light beam passes through the second microscope objective; The emitted light beam is incident on the third beam splitting prism, and the incident light beam is divided into two beams of light, where the reflected light beam is incident on the second photoelectric image sensor, and the transmitted light beam is incident on the plane mirror; The light beam reflected by the plane mirror is incident on the third photoelectric sensor; The computer is connected to the pulsed laser, the spatial light modulator, the first, second, and third photoelectric image sensors, the three-dimensional translation system and the sample holder. The computer controls the laser output, receives the data from the photoelectric image sensors, controls the movement of the three-dimensional translation system, and processes the received data.

2. The synchronous measurement device for the phase and polarization parameters of a nonlinear material according to claim 1, wherein: The spatial light modulator is a reflective phase modulator, and through the control of the computer, it can arbitrarily adjust the phase distribution of the incident light beam between 0 and 2π.

3. The synchronous measurement device for the phase and polarization parameters of a nonlinear material according to claim 1, wherein: The first, second, and third beam splitting prisms are non-polarizing beam splitting prisms of the same size.

4. The synchronous measurement device for the phase and polarization parameters of a nonlinear material according to claim 1, wherein: The three-dimensional translation system and the sample holder include a three-dimensional translation stage, a translation stage control system, and a sample stage. The sample stage is loaded with the nonlinear material to be measured, and the translation stage control system is connected to the computer and receives the control signal sent by the computer.

5. The synchronous measurement device for the phase and polarization parameters of a nonlinear material according to claim 1, wherein: The magnification and numerical aperture parameters of the first and second microscope objectives are the same. The distance between the two microscope objectives is adjusted so that the object-side focal points of the two coincide and are located in the nonlinear material to be measured.

6. The synchronous measurement device for the phase and polarization parameters of a nonlinear material according to claim 1, wherein: The first and second photoelectric image sensors have the same parameters and are connected to a computer.

7. The synchronous measurement device for the phase and polarization parameters of a nonlinear material according to claim 1, wherein: The third photoelectric image sensor is a polarization detection image sensor, and a polarization array mask plate is closely arranged in front of the detection target surface.

8. The synchronous measurement device for the phase and polarization parameters of a nonlinear material according to any one of claims 1-7, wherein: The optical elements and the optomechanical components are all installed on an anti-vibration optical platform, and the relative positions of the components are adjusted so that the optical axes of the components coincide with the light beam.

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