CN101839763B - High-brightness controllable pseudo-thermal light source based on liquid crystal light valve modulation - Google Patents

Abstract

The invention discloses a high-brightness controllable pseudothermal light source based on a liquid crystal light valve modulation method, which includes a pulsed laser, an adjustable beam expander collimation system, a polarizer, a first analyzer, and an adjustable aperture diaphragm , Liquid crystal light valve, second analyzer, liquid crystal light valve control system. The pulsed laser, the adjustable beam expander collimation system, the polarizer, the first analyzer, and the adjustable aperture diaphragm are located on the same optical axis, and the optical axis is located on the incident light optical axis of the liquid crystal light valve , another second analyzer is located on the optical axis of the reflected light from the liquid crystal light valve corresponding to the optical axis of the incident light. The laser output from the laser is finally irradiated on the liquid crystal light valve controlled by the liquid crystal light valve control system. By controlling the liquid crystal light valve, a dynamic speckle field is obtained, which is a pseudothermal light field. The thermal fluctuations of the high-brightness controllable pseudothermal light source produced by the present invention can be truly recorded by the photoelectric detection system with limited passband, and by controlling the RGB image loaded on the liquid crystal light valve, the intersection of the real thermal light field can be obtained Spectral purity conditions, and the pseudothermal optical field generated at each moment is controllable.

Description

A High Brightness Controllable Pseudothermal Light Source Based on Liquid Crystal Light Valve Modulation

technical field

The invention relates to an optical component and an optical system, in particular to a high-brightness controllable pseudothermal light source based on liquid crystal light valve modulation.

Background technique

There are two basic difficulties in the experimental measurement of thermo-optic fluctuations: first, the coherence time of thermo-optic light is very short, even for the quasi-monochromatic light emitted by the best line spectrum light source, the coherence time can only reach 10 ^-11 - 10 ^-10 seconds; Second, the response time of the existing photodetectors reaches 10 ^-9 seconds at the fastest. Therefore, the existing photodetectors cannot measure the instantaneous intensity of thermal optical field fluctuations [see Qi Kangnan, Qin Kecheng, Cheng Lu. Introduction to Statistical Optics, P410].

In order to overcome these two difficulties, Martienssen and Spiller invented a continuous pseudothermal light source in 1964 [see W.Martienssen, E.Spiller, "Coherence and Fluctuations in LightBeams", American Journal of Physics 32, 8 (1964). ]. In 2006, in order to overcome the problem that the continuous pseudothermal light source does not meet the cross-spectrum purity conditions of the real thermal optical field, Han Shensheng and others from the Shanghai Institute of Optics and Fine Mechanics of the Chinese Academy of Sciences invented a high-brightness pulsed pseudothermal light source [see Liu Honglin , Zhang Minghui, Wei Qing. Abstracts of the Twelfth National Conference on Quantum Optics. 2006.]. The above technology is used to simulate the fluctuation of the real thermo-optic field; due to the long coherence time, the thermo-optic fluctuation can be detected by the existing photodetector; and because it can better simulate the correlation of the real thermo-optic field Statistical properties, so it provides conditions for the study of fields related to thermal-optical field fluctuations. However, the above-mentioned pseudothermal light sources also have certain limitations, which are mainly manifested in:

1. There are large mechanical changes in the rotating frosted glass sheet, which causes inconvenience to the actual engineering application.

2. The repeatability of the experiment is poor, and it is difficult to accurately calibrate.

Contents of the invention

The technical problem to be solved by the present invention is to provide a high-brightness controllable pseudothermal light source based on liquid crystal light valve modulation.

The thermal fluctuation of the pseudothermal optical field can be truly recorded by the existing photoelectric detection system without mechanical changes. As long as the RGB image signal loaded on the liquid crystal light valve is controlled, the liquid crystal light valve can be controlled to modulate and generate Pseudothermal light source, high experimental repeatability.

Technical solution of the present invention is as follows:

A high-brightness controllable pseudothermal light source based on liquid crystal light valve modulation, which consists of a pulsed laser 1, an adjustable beam expander collimator system 2, a polarizer 3, a first analyzer 4, and an adjustable aperture diaphragm 5. Liquid crystal light valve 6, second analyzer 7 and liquid crystal light valve control system 11, the pulsed laser 1, adjustable beam expander collimation system 2, polarizer 3, first analyzer 4, The aperture adjustment diaphragm 5 is located on the same optical axis 9, the optical axis 9 is located on the incident light optical axis of the liquid crystal light valve 6, and the optical axis 9 forms a certain angle with the normal line of the liquid crystal light valve 6, when desired Said angle is less than 6° when a purely phase-modulated light field is obtained. The second analyzer 7 is located on the reflected light optical axis 10 corresponding to the above-mentioned incident light optical axis 9, and the laser light output by the pulsed laser 1 is irradiated on the liquid crystal light controlled by the liquid crystal light valve control system 11. On the valve 6, by changing the control signal loaded on the liquid crystal light valve, the desired speckle field, that is, the pseudothermal optical field, is obtained.

The liquid crystal light valve adopts a phase-only high-resolution matrix type liquid crystal light valve. The computer generates an RGB image signal and transmits it to the driving circuit of the liquid crystal light valve to drive the liquid crystal light valve. The value of each point of the RGB image determines the value of the liquid crystal light valve. The phase shift of the output beam, controlling the value of each point of the RGB image can control the phase shift of each point of the liquid crystal light valve, thereby modulating the spatial phase distribution of the beam.

The period T of the control signal loaded on the liquid crystal light valve is equal to the interval Δt of the laser pulse output by the pulsed laser:

Δt=T

In the same cycle of the liquid crystal light valve control system, the pulse used to trigger the laser is delayed by 20 ms than the pulse used to trigger the liquid crystal light valve, so as to stabilize the modulation result of the liquid crystal light valve.

In the RGB image loaded on the liquid crystal light valve by the liquid crystal light valve control system, in the same period, the values of each point on the image are irrelevant; the values of each point on the two images in different periods are mutually related Also irrelevant.

The extinction ratio of the polarizer 3 and the first analyzer 4 is 500:1. Since the liquid crystal light valve of pure phase modulation is more sensitive to the polarization state of the incident light, by adjusting the polarizer 3 and the first analyzer device 4, so that the laser beam incident on the liquid crystal light valve is as linearly polarized as possible, and the polarization direction is parallel to the slow axis direction of the liquid crystal light valve.

Technical effect of the present invention:

The pseudothermal light source has all the statistical characteristics of the thermal optical field, and solves the difficulties in the original technical background:

High brightness, because the energy of a single speckle field pulse is determined by the energy of a single laser pulse, and because a pure phase-modulated liquid crystal light valve is used, the output modulated laser energy loss is small.

Without mechanical changes, since the liquid crystal light valve only needs to control the RGB image information loaded on it, it can change the output light field, so different light field modulations can be realized without changing the optical path.

Good repeatability, under the same experimental conditions, the same light field can be obtained by loading the same RGB image information, which provides the possibility for calibration.

Description of drawings

Fig. 1 is a structural block diagram of a high-brightness controllable pseudothermal light source device based on a liquid crystal light valve modulation method according to the present invention. In the figure:

1: pulsed laser, 2: adjustable beam expander collimation system, 3: polarizer, 4: first analyzer, 5: adjustable aperture diaphragm, 6: liquid crystal light valve, 7: second analyzer 8: Pseudothermal optical field, 9: Optical axis of incident light, 10: Optical axis of reflected light, 11: Liquid crystal light valve control system.

Fig. 2 is a spatial intensity distribution diagram of a speckle field generated in an embodiment of the present invention within a coherent time.

Detailed ways

The present invention will be further described below in conjunction with the embodiments and accompanying drawings, but the protection scope of the present invention should not be limited thereby.

Please refer to Fig. 1. Fig. 1 is a structural block diagram of a high-brightness controllable pseudothermal light source device based on liquid crystal light valve modulation in the present invention, which is also an embodiment of the present invention. It can be seen from the figure that the present invention is based on liquid crystal light valve modulation. Pseudo-controlled thermal light source, which consists of a pulsed laser 1, an adjustable beam expander collimator system 2, a polarizer 3, a first analyzer 4, an adjustable aperture stop 5, a liquid crystal light valve 6, a second analyzer 7 and liquid crystal light valve control system 11, the pulsed laser 1, adjustable beam expander collimation system 2, polarizer 3, first analyzer 4, adjustable aperture diaphragm 5 are located on the same optical axis 9 , the optical axis 9 is located on the optical axis of the incident light of the liquid crystal light valve 6, and the optical axis 9 forms a certain angle with the normal line of the liquid crystal light valve 6, when it is desired to obtain a pure phase modulated light field, the The angle is less than 6°. The second analyzer 7 is located on the reflected light optical axis 10 corresponding to the above-mentioned incident light optical axis 9, and the laser light output by the pulsed laser 1 is irradiated on the liquid crystal light controlled by the liquid crystal light valve control system 11. On the valve 6, by changing the control signal loaded on the liquid crystal light valve, the desired speckle field, that is, the pseudothermal optical field, is obtained.

The pulsed laser 1 of this embodiment adopts a semiconductor pulsed laser with a wavelength of 650 nm.

The liquid crystal light valve 6 of this embodiment adopts the XY area phase type liquid crystal light valve Model A512 of BNS Company, which is a pure phase high-resolution matrix type liquid crystal light valve, and an RGB image signal is generated by a computer and sent to the liquid crystal light valve. The drive circuit, and then drive the liquid crystal light valve. The value of each point of the RGB image determines the phase offset of the corresponding pixel output beam of the liquid crystal light valve. Controlling the value of each point of the RGB image can control the phase of each point of the liquid crystal light valve. shift, thereby modulating the spatial phase distribution of the beam.

The period T of the control signal loaded on the liquid crystal light valve 6 in this embodiment is equal to the interval Δt of the laser pulses output by the pulsed laser 1:

Δt=T

In the liquid crystal light valve control system 11 of this embodiment, in the same cycle, the pulse used to trigger the pulsed laser 1 is delayed by 20 ms from the pulse used to trigger the liquid crystal light valve 6 to stabilize the modulation result of the liquid crystal light valve.

In the RGB image loaded on the liquid crystal light valve 6 by the liquid crystal light valve control system 11 of the present embodiment, in the same cycle, the values of each point on the image are irrelevant; the values of each point on the two images in different cycles, are also unrelated to each other.

The extinction ratio of the polarizer 3 and the first analyzer 4 in this embodiment is 500:1. Since the liquid crystal light valve with pure phase modulation is more sensitive to the polarization state of the incident light, by adjusting the polarizer 3 and the first analyzer device 4, so that the laser beam incident on the liquid crystal light valve 6 is as linearly polarized as possible, and the polarization direction is parallel to the slow axis direction of the liquid crystal light valve 6.

The extinction ratio of the second analyzer 7 of the present embodiment is 500:1, due to the light field modulated by the liquid crystal light valve, the polarization state will change to a certain extent, through the effect of the second analyzer 7, the obtained The pseudothermal light field is linearly polarized light.

After the laser pulse is collimated, filtered and analyzed, it is projected onto the liquid crystal light valve 6, and the size of the light spot is determined by the adjustable aperture stop 5. To make full use of each pixel on the liquid crystal light valve, it is recommended that the size of the aperture stop be equal to the effective area of the liquid crystal light valve.

Fig. 2 is a spatial intensity distribution diagram of the speckle field generated by the embodiment of the present invention within the coherence time, and its high contrast indicates that the pseudothermal light source is suitable for detection within the coherence time.

Claims (5)

1. A high-brightness controllable pseudothermal light source based on a liquid crystal light valve modulation method, which consists of a pulsed laser (1), an adjustable beam expander collimation system (2), a polarizer (3), a first polarizer device (4), adjustable aperture diaphragm (5), liquid crystal light valve (6), second analyzer (7) and liquid crystal light valve control system (11), it is characterized in that: The liquid crystal light valve (6) adopts a phase-only high-resolution matrix type liquid crystal light valve; The pulsed laser (1), the adjustable beam expander collimation system (2), the polarizer (3), the first analyzer (4), and the adjustable aperture stop (5) are located on the same optical axis ( 9), the optical axis (9) is located on the incident light optical axis of the liquid crystal light valve (6), and the optical axis (9) forms a certain angle with the normal line of the liquid crystal light valve (6). When obtaining a purely phase-modulated light field, said angle is less than 6°; The second analyzer (7) is located on the reflected light axis (10) corresponding to the incident light axis; The laser light output by the pulsed laser (1) is irradiated on the liquid crystal light valve (6) controlled by the liquid crystal light valve control system (11), and by changing the control signal loaded on the liquid crystal light valve (6), the obtained The required speckle field is the pseudothermal optical field. 2. A high-brightness controllable pseudothermal light source based on a liquid crystal light valve modulation method according to claim 1, characterized in that: the period T of the control signal loaded on the liquid crystal light valve (6) is the same as the The interval Δt of the laser pulses output by the pulsed laser (1) is equal: Δt=T. 3. A high-brightness controllable pseudothermal light source based on liquid crystal light valve modulation according to claim 1, characterized in that: the liquid crystal light valve control system (11) is used to trigger pulses in the same cycle The pulse of the laser (1) is delayed by at least 20 ms from the pulse used to trigger the liquid crystal light valve (6). 4. A high-brightness controllable pseudothermal light source based on a liquid crystal light valve modulation method according to claim 1, characterized in that: the liquid crystal light valve control system (11) is loaded on the liquid crystal light valve (6) RGB image, in the same period, the value of each point on the image is irrelevant; the value of each point on the two images in different periods is also irrelevant to each other. 5. A high-brightness controllable pseudothermal light source based on liquid crystal light valve modulation according to claim 1, characterized in that: the extinction of the polarizer (3) and the first analyzer (4) The ratio is 500:1, and the laser beam incident on the liquid crystal light valve (6) is linearly polarized by adjusting the polarizer (3) and the first analyzer (4), and the polarization direction is the same as that of the liquid crystal light valve (6). ) parallel to the slow axis.

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