CN102636258A

CN102636258A - Optical test method for electron spin diffusion transport kinetics based on pure phase liquid crystal spatial light modulator

Info

Publication number: CN102636258A
Application number: CN2012101419812A
Authority: CN
Inventors: 赖天树; 李佳明; 闫涌
Original assignee: Sun Yat Sen University
Current assignee: Sun Yat Sen University
Priority date: 2012-05-08
Filing date: 2012-05-08
Publication date: 2012-08-15
Anticipated expiration: 2032-05-08
Also published as: CN102636258B

Abstract

Invented a dynamic optical test method for electron spin diffusion transport based on a phase-only liquid crystal spatial light modulator, combining a one-dimensional pure phase liquid crystal spatial light modulator and a time-resolved pump-detector device. The principle of the experimental device is as follows: As shown in the accompanying drawings. The one-dimensional phase-only liquid crystal spatial light modulator 7 is located in the overlapping region of the pump light 2 and the probe light 3, and simultaneously modulates the circular polarization degrees of the cross-sections of the pump light 2 and the probe light 3 into a one-dimensional spatial periodic distribution. Such a modulated light field is imaged onto the sample 9 by the imaging lens 8 . The modulated pump light excites a spin-polarized transient grating in the sample, and the modulated probe light measures the decay kinetics of this spin-polarized transient grating. Analytical models of electron spin diffusion transport kinetics in one-dimensional sinusoidal and square-wave space-period modulation light fields with circular polarization are given. The invention has the advantages of simple experimental device and operation, uses absorption saturation effect to test spin diffusion transport kinetics, and has the advantages of high sensitivity.

Description

A Dynamic Optics Test Method for Electron Spin Diffusion Transport Based on Pure Phase Liquid Crystal Spatial Light Modulator

技术领域 technical field

本发明涉及一种电子自旋扩散输运动力学光学测试方法。其特点是利用纯相位型液晶空间光调制器(POLCSLM)直接调制泵浦与探测光束的偏振态分布，产生圆偏振度一维周期变化的调制光场，分别激发瞬态电子自旋光栅和探测其衰减动力学。在半导体电子自旋扩散输运动力学测量领域具有重要应用价值。The invention relates to a dynamic optical test method for electron spin diffusion transport. Its characteristic is that the polarization state distribution of the pump and probe beams is directly modulated by a pure phase liquid crystal spatial light modulator (POLCSLM), and a modulated light field with a one-dimensional periodic change in the degree of circular polarization is generated to respectively excite the transient electron spin grating and the probe beam. its decay kinetics. It has important application value in the field of measurement of semiconductor electron spin diffusion transport dynamics.

背景技术 Background technique

超大规模半导体微电子集成器件目前遭遇到了散热难和量子尺寸效应的限制，所以，目前的CPU制作不能朝更高集成度发展，而只能朝多CPU方向发展。如何突破这样的限制，发展超大规模纳电子集成器件，是目前国际上的研究热点。半导体自旋电子学正是为此目标而诞生的，其目标是要研制出低功耗、高速度的纳米电子器件，解决目前超大规模微电子集成器件遇到的困难，实现更高集成度的超大规模集成制造。基于电子自旋相干态，甚至可能实现半导体量子逻辑与计算器件。然而，实现半导体自旋电子器件，需要研究解决的基本问题之一是半导体中电子自旋输运过程所涉及的基本问题。对此问题，目前理论研究较多，而实验研究相当少，但少数的实验研究结果却发现了重要的新现象，如自旋库仑拖拽效应、爱因斯坦关系不成立等，显示出自旋输运动力学中包含丰富的物理新现象。实验研究少的主要原因在于目前没有简单高灵敏度的实验测试技术。目前报道的唯一实验测试技术是瞬态自旋光栅衍射测量法。这种方法的实验测试系统非常复杂，需要四束激光，并排列成特殊的几何结构。其中两束作为泵浦光，它们的偏振正交，迭加合成产生一个圆偏振度一维周期变化的光场，此光场激发半导体样品，则可以产生电子自旋极化光栅，即瞬态自旋光栅。而另外两束光中，一束作为瞬态自旋光栅的衰减动力学衍射测量的探测光，另一束作为衍射信号光外差放大的参考光。所以，不仅装置复杂，操作难度也很大。另一方面，衍射信号也相当弱，探测灵敏度也不高，即使使用了光外差放大技术。此外，这种技术中瞬态自旋光栅由两束光的合成光场激发，容易受到两束光之间的相位差涨落干扰，引起噪声。这些问题阻碍了自旋输运动力学实验研究的广泛开展。因而，发展实验装置和操作简单，探测灵敏度高的自旋输运测试新技术，是非常必要的，将能够促进自旋输运动力学实验研究的广泛、深入开展。本发明正是要发展这样的新方法。Ultra-large-scale semiconductor microelectronic integrated devices are currently encountering heat dissipation difficulties and limitations of quantum size effects. Therefore, the current CPU production cannot develop towards higher integration, but can only develop towards multiple CPUs. How to break through such limitations and develop ultra-large-scale nanoelectronic integrated devices is currently a research hotspot in the world. Semiconductor spintronics was born for this purpose. Its goal is to develop low-power, high-speed nanoelectronic devices, solve the difficulties encountered in current ultra-large-scale microelectronic integrated devices, and achieve higher integration. VLSI Manufacturing. Based on electron spin coherent states, it is even possible to realize semiconductor quantum logic and computing devices. However, to realize semiconductor spintronic devices, one of the basic problems that needs to be studied and solved is the fundamental problem involved in the electron spin transport process in semiconductors. At present, there are many theoretical studies on this problem, but relatively few experimental studies. However, a few experimental studies have found important new phenomena, such as the spin Coulomb drag effect, and the failure of the Einstein relationship, etc., showing that the spin input Kinematics contains a wealth of new physical phenomena. The main reason for the lack of experimental research is that there is currently no simple and highly sensitive experimental testing technology. The only experimental testing technique reported so far is transient spin grating diffractometry. The experimental test system for this approach is very complex, requiring four laser beams arranged in a special geometry. Two of them are used as pump light, their polarizations are orthogonal, superimposed and synthesized to generate a light field with one-dimensional periodic change of circular polarization degree, this light field excites the semiconductor sample, and then the electron spin polarization grating can be produced, that is, the transient spin grating. Among the other two beams, one beam is used as the probe beam for the attenuation dynamics diffraction measurement of the transient spin grating, and the other beam is used as the reference beam for the heterodyne amplification of the diffracted signal beam. Therefore, not only the device is complicated, but also the operation is very difficult. On the other hand, the diffraction signal is also rather weak, and the detection sensitivity is not high, even with the optical heterodyne amplification technique. In addition, the transient spin grating in this technique is excited by the synthetic light field of two beams of light, which is easily disturbed by the phase difference fluctuation between the two beams of light, causing noise. These problems hinder the extensive development of experimental studies on spin transport dynamics. Therefore, it is very necessary to develop experimental devices and new technologies for spin transport testing with simple operation and high detection sensitivity, which will promote the extensive and in-depth development of spin transport dynamics experimental research. The present invention is precisely to develop such a new method.

发明内容 Contents of the invention

本发明发展了一种简单的电子自旋扩散输运动力学光学测试方法。它组合一个纯相位型液晶空间光调制器(商业化产品)与传统的泵浦-探测实验装置。换句话讲，只需要在传统的泵浦-探测实验装置中增加一个纯相位型液晶空间光调制器，即可实现电子自旋输运的测量。实验装置原理如图1所示。图中7为纯相位型液晶空间光调制器。显然，此装置极其简单，只有一束泵浦光2和一束探测光3。更重要的是本发明测量的是瞬态自旋光栅的吸收饱和变化。如图1所示，探测器10直接测量探测光3透过样品9后的光功率变化，而不是象目前报道的衍射测量法那样测量探测光通过样品后的衍射信号强度。已经有实验研究报道，同一个瞬态光栅引起的探测光的透射功率变化是其引起的探测光的衍射功率的200倍以上。所以，使用吸收饱和效应测量能提高测试灵敏度200倍以上。因此，本发明不仅简化了实验装置结构和降低了实验操作难度，而且极大地提高了探测灵敏度。The invention develops a simple electron spin diffusion transport dynamic optical test method. It combines a phase-only liquid crystal spatial light modulator (commercial product) with a conventional pump-probe experimental setup. In other words, it is only necessary to add a phase-only liquid crystal spatial light modulator to the traditional pump-probe experimental setup to realize the measurement of electron spin transport. The principle of the experimental device is shown in Figure 1. 7 in the figure is a phase-only liquid crystal spatial light modulator. Obviously, this device is extremely simple, only one beam of pump light 2 and one beam of probe light 3 . More importantly, what the present invention measures is the absorption saturation change of the transient spin grating. As shown in FIG. 1 , the detector 10 directly measures the change in optical power of the probe light 3 passing through the sample 9 , instead of measuring the intensity of the diffraction signal after the probe light passes through the sample as in the currently reported diffraction measurement method. Experimental studies have reported that the change in the transmitted power of the probe light caused by the same transient grating is more than 200 times the diffraction power of the probe light caused by it. Therefore, using the absorption saturation effect measurement can improve the test sensitivity by more than 200 times. Therefore, the invention not only simplifies the structure of the experimental device and reduces the difficulty of the experimental operation, but also greatly improves the detection sensitivity.

本发明的光学原理如图1所示。其关键特征在于引入空间光调制器7。它是一个一维纯相位型液晶阵列或称空间光调制器。一维阵列中每个单元或象素都是一个可控相位延迟片(双折射片)，而不同象素的相位延迟量是可以独立设置的。如果设置一维阵列液晶中各象素的相位延迟量随其位置周期性的在0-2π之间变化，则可实现其透射光横截面上偏振态的一维周期变化调制，等效于目前报道的实验方法中用两束正交偏振泵浦光迭加合成的光场。The optical principle of the present invention is shown in FIG. 1 . Its key feature is the introduction of a spatial light modulator 7 . It is a one-dimensional pure phase liquid crystal array or spatial light modulator. Each unit or pixel in the one-dimensional array is a controllable phase retardation film (birefringent film), and the phase retardation of different pixels can be set independently. If the phase retardation of each pixel in the one-dimensional array liquid crystal is set to change periodically between 0-2π with its position, the one-dimensional periodic modulation of the polarization state on the cross-section of the transmitted light can be realized, which is equivalent to the current In the reported experimental method, two orthogonally polarized pump beams are used to superimpose the synthesized light field.

图1所示，传统的时间分辨泵浦-探测装置1输出线偏振泵浦光脉冲2和探测光脉冲3，分别通过1/2波片4和5后，再通过透镜6聚焦在纯相位型液晶空间光调制器7上；如果旋转1/2波片4和5的方位角，使泵浦光2和探测光3的偏振方向均与7的快或慢轴成45度角，并设置7的各象素的相位延迟量随其位置周期性的在0-2π之间变化，则透过7的泵浦光2与探测光3变成同旋向的圆偏振度一维空间周期调制的光场。反之，如果再旋转波片5的方位角90度，则2和3变成正交线偏振，它们透过7后变成相反旋向的圆偏振度一维空间周期调制的光场。成象透镜8将7成象(可缩小或放大)到样品9上，结果，圆偏振度一维空间周期调制的泵浦光场激发样品9，在样品内产生电子自旋极化度一维空间周期变化，但总电子浓度空间均匀的电子布居，即所谓瞬态自旋光栅(TSG)。而相同或相反旋向的圆偏振度一维同周期空间调制探测光3测量TSG的瞬态圆二色饱和吸收变化或透射变化，则能反映电子自旋输运动力学。值得强调的是正是探测光3具有与泵浦光2同周期的圆偏振度空间调制，才能够测量到电子自旋输运动力学。反之，如果探测光3为非空间调制的圆偏振光，则对自旋输运动力学不灵敏。下面将以两个实例来说明本发明的实施方式。As shown in Fig. 1, the traditional time-resolved pump-probe device 1 outputs linearly polarized pump light pulse 2 and probe light pulse 3, which pass through the 1/2 wave plate 4 and 5 respectively, and then focus on the phase-only pulse through lens 6 On the liquid crystal spatial light modulator 7; if the azimuth angles of 1/2 wave plates 4 and 5 are rotated, the polarization directions of the pump light 2 and the probe light 3 are all at an angle of 45 degrees with the fast or slow axis of 7, and set 7 The phase delay of each pixel varies periodically between 0-2π with its position, and the pump light 2 and probe light 3 that pass through 7 become one-dimensional space-period modulation of the circular polarization degree of the same hand. light field. Conversely, if the azimuth angle of the wave plate 5 is rotated by 90 degrees, 2 and 3 become orthogonal linear polarizations, and after passing through 7, they become a light field modulated by one-dimensional spatial period of circular polarization in the opposite direction. The imaging lens 8 images the image 7 (can be reduced or enlarged) on the sample 9. As a result, the pump light field modulated by the circular polarization one-dimensional space period excites the sample 9, and generates a one-dimensional electron spin polarization in the sample. The electron population whose spatial period varies but the total electron concentration is spatially uniform is the so-called transient spin grating (TSG). The one-dimensional spatially modulated probe light with the same or opposite handedness degree of circular polarization can measure the transient circular dichroic saturation absorption change or transmission change of TSG, which can reflect the electron spin transport dynamics. It is worth emphasizing that it is the spatial modulation of the degree of circular polarization of the probe light 3 with the same period as the pump light 2 that enables the measurement of electron spin transport dynamics. Conversely, if the probe light 3 is non-spatially modulated circularly polarized light, it is insensitive to spin transport dynamics. The implementation of the present invention will be described below with two examples.

附图说明 Description of drawings

图1电子自旋扩散输运动力学实验测试装置原理图Figure 1 Schematic diagram of the experimental test device for electron spin diffusion transport dynamics

图1中，1为传统的时间分辨泵浦-探测装置，包括飞秒激光器，非共线双臂干涉仪和光学延迟线；2和3分别为来自1中双臂干涉仪两个臂的光束，2强于3，故作为泵浦光，而3较弱，作为探测光；4和5为1/2波片，分别控制2和3的偏振方向；6为聚焦透镜，将2和3聚焦到7上同一点；7为一维纯相位型液晶空间光调制器(1D-POLCSLM)，调制通过它的光束2和3的横截面上的偏振态的空间分布；8为成象透镜，成象7到样品9上，放大率可根据需要设置；10为光电探测器，测量探测光3透过样品9中由2激发的瞬态自旋光栅后被感应的透射功率变化量。In Fig. 1, 1 is a traditional time-resolved pump-probe device, including a femtosecond laser, a non-collinear dual-arm interferometer and an optical delay line; 2 and 3 are the beams from the two arms of the dual-arm interferometer in 1, respectively , 2 is stronger than 3, so it is used as pump light, and 3 is weaker, it is used as probe light; 4 and 5 are 1/2 wave plates, which control the polarization directions of 2 and 3 respectively; 6 is a focusing lens, which focuses 2 and 3 to the same point on 7; 7 is a one-dimensional pure phase liquid crystal spatial light modulator (1D-POLCSLM), modulating the spatial distribution of the polarization state on the cross-section of the light beams 2 and 3 passing through it; 8 is an imaging lens, forming Like 7 to the sample 9, the magnification can be set according to needs; 10 is a photodetector, which measures the induced transmission power variation after the probe light 3 passes through the transient spin grating excited by 2 in the sample 9.

具体实施方式 Detailed ways

依据上述原理，本发明已具体实施了两个实例，分别产生圆偏振度一维正弦型和方波型空间周期调制光场，并用于电子自旋扩散输运动力学测量，获取电子自旋扩散系数。According to the above principles, the present invention has concretely implemented two examples, respectively generating one-dimensional sinusoidal and square-wave space-period modulation light fields of the degree of circular polarization, and using them in the measurement of electron spin diffusion transport kinetics to obtain the electron spin diffusion coefficient .

实例一圆偏振度一维正弦型空间周期调制光场产生与电子自旋扩散输运动力学测量Example 1 Generation of circular polarization one-dimensional sinusoidal space-period modulation light field and measurement of electron spin diffusion transport kinetics

设xy坐标位于1D-POLCSLM平面上，y轴平行于象素长边，而x轴描述象素的一维位置分布。通过控制器设置各象素的相位延迟量满足如下关系：Let the xy coordinates lie on the 1D-POLCSLM plane, the y axis is parallel to the long side of the pixel, and the x axis describes the one-dimensional position distribution of the pixel. The phase delay of each pixel is set by the controller to satisfy the following relationship:

$φ φ ((i i)) = = \frac{22 π π}{Λ Λ} RMod RMod ((\frac{i i}{Λ Λ})) - - - - - - ((11))$

式中函数RMod()表示两数相除，取整余数，产生周期为Λ，幅度为2π的锯齿波。引入此函数是考虑到液晶的相位延迟量有限，所以，本实例中只使用0-2π范围的相位延迟量；i＝0，l，…，M-1，为1D-POLCSLM的象素位置编号；M为1D-POLCSLM阵列的总象素数；Λ为整数，表示调制周期，以象素的宽度Δx为单位，即实际的空间周期为Λ*Δx。In the formula, the function RMod() means that two numbers are divided, and the remainder is rounded to generate a sawtooth wave with a period of Λ and an amplitude of 2π. This function is introduced in consideration of the limited phase delay of the liquid crystal, so only the phase delay in the range of 0-2π is used in this example; i=0, l,..., M-1, which is the pixel position number of 1D-POLCSLM ; M is the total number of pixels of the 1D-POLCSLM array; Λ is an integer, representing the modulation period, taking the width Δx of the pixel as the unit, that is, the actual spatial period is Λ*Δx.

那么，透过1D-POLCSLM后，光束2和3的圆偏振度的一维空间周期调制为：Then, after passing through the 1D-POLCSLM, the one-dimensional space-period modulation of the degrees of circular polarization of beams 2 and 3 is:

P(i)＝sin(φ(i)) (2)P(i)＝sin(φ(i)) (2)

当A＞＞1时，即一个调制周期包含许多个调制象素，相当于密采样。这时，调制相位的离散化效应可以忽略，而近似为x坐标的连续函数。方程(1)和(2)可以近似为如下的x连续函数：When A>>1, that is, one modulation cycle includes many modulation pixels, which is equivalent to dense sampling. At this time, the discretization effect of the modulation phase can be ignored, and it is approximated as a continuous function of the x coordinate. Equations (1) and (2) can be approximated as continuous functions of x as follows:

$φ φ ((x x)) = = \frac{22 π π}{Λ Λ * * Δx Δx} RMod RMod ((\frac{x x}{Λ Λ * * Δx Δx})) - - - - - - ((33))$

$P P ((x x)) = = sin sin ((φ φ ((x x)))) \approx \approx sin sin ((\frac{22 π π}{Λ Λ * * Δx Δx} x x)) - - - - - - ((44))$

设入射线偏振光强度为I₀，受到7调制后，透射光的左、右旋圆偏振分量强度的空间调制可表示为：Assuming that the intensity of the incident ray polarized light is I ₀ , after being modulated by 7, the spatial modulation of the intensity of the left-handed and right-handed circular polarization components of the transmitted light can be expressed as:

${I I}_{σ σ}^{&PlusMinus; &PlusMinus;} ((x x)) = = \frac{{I I}_{00,, σ σ}}{22} [[11 &PlusMinus; &PlusMinus; P P ((x x))]] = = \frac{{I I}_{00,, σ σ}}{22} [[11 &PlusMinus; &PlusMinus; sin sin ((\frac{22 π π}{Λ Λ * * Δx Δx} x x))]] - - - - - - ((55))$

式中左端上标“±”表示“右/左”旋圆偏振光；σ＝2或3，分别表示泵浦束2和探测束3。方程左右两端的“±”号对应关系为同时取上或下符号。下同。In the formula, the superscript "±" on the left end means "right/left" circularly polarized light; σ=2 or 3 means the pump beam 2 and the probe beam 3, respectively. The corresponding relation of "±" signs at the left and right ends of the equation is to take up or down signs at the same time. The same below.

方程(5)描述的圆偏振度正弦型空间周期调制光由8成象到9上，则样品前表面上的调制光强为：The circular polarization degree sinusoidal space-period modulation light described by equation (5) is imaged from 8 to 9, then the modulated light intensity on the front surface of the sample is:

${I I}_{σ σ}^{&PlusMinus; &PlusMinus;} ((x x)) = = \frac{{I I}_{00,, σ σ}}{22 {Q Q}^{22}} [[11 &PlusMinus; &PlusMinus; sin sin ((\frac{22 π π}{Λ Λ * * Δ Δ {x x}^{' '}}))]] - - - - - - ((66))$

式中Q为成象透镜8的放大率，Δx′＝Q*Δx。In the formula, Q is the magnification of the imaging lens 8, Δx'=Q*Δx.

受调制泵浦光，激发样品，产生电子自旋极化度正弦调制的电子浓度分布，可表示为：modulated pump light, Exciting the sample produces an electron concentration distribution with a sinusoidal modulation of the electron spin polarization, which can be expressed as:

${n no}_{&PlusMinus; &PlusMinus;} ((x x)) = = \frac{{n no}_{00}}{22} [[11 &PlusMinus; &PlusMinus; Δ Δ n no sin sin ((\frac{22 π π}{Λ Λ * * Δ Δ {x x}^{' '}}))]] - - - - - - ((77))$

式中左端下标“±”表示电子自旋极化“向上/向下”；n₀为光激发的总电子浓度，是空间均匀的；Δn为电子的自旋极化度，取值为0～1，依赖于样品的能带结构和带间激发光学选择定则。In the formula, the subscript "±" at the left end indicates the electron spin polarization "up/down"; n ₀ is the total electron concentration excited by light, which is uniform in space; ~1, depends on the band structure of the sample and the optical selection rules for interband excitation.

电子的自旋极化分布为：The spin polarization distribution of electrons is:

$S S ((x x)) = = {n no}_{+ +} ((x x)) - - {n no}_{- -} ((x x)) = = {n no}_{00} Δ Δ n no sin sin ((\frac{22 π π}{Λ Λ * * Δ Δ {x x}^{' '}} x x)) - - - - - - ((88))$

方程(8)即所谓瞬态自旋光栅(TSG)。显然，本发明用1D-POLCSLM调制单束泵浦光即产生了TSG，比目前报道的双束泵浦光迭加场产生TSG简单。Equation (8) is the so-called transient spin grating (TSG). Apparently, the present invention uses 1D-POLCSLM to modulate a single pump light to generate TSG, which is simpler than the TSG generated by superposition field of double pump light reported so far.

方程(7)和(8)描述的瞬态自旋极化空间分布是由一个泵浦光脉冲激发瞬间注入的，由于电子-空穴复合、自旋弛豫和扩散输运效应，它们将随时间演化，并由如下方程描述：The transient spin polarization spatial distribution described by equations (7) and (8) is injected instantaneously by a pump light pulse excitation, and due to electron-hole recombination, spin relaxation and diffusion transport effects, they will follow the time evolution, and is described by the following equation:

${n no}_{&PlusMinus; &PlusMinus;} ((x x,, t t)) = = \frac{{n no}_{00}}{22} {e e}^{- - t t / / {τ τ}_{r r}} [[11 &PlusMinus; &PlusMinus; Δ Δ n no sin sin ((\frac{22 π π}{Λ Λ' '} x x)) {e e}^{- - (({((22 π π / / Λ Λ' '))}^{22} {D D.}_{s the s} + + 22 / / {τ τ}_{s the s})) t t}]] - - - - - - ((99))$

或or

$S S ((x x,, t t)) = = {n no}_{00} Δ Δ n no sin sin ((\frac{22 π π}{Λ Λ' '} x x)) {e e}^{- - [[{((22 π π / / Λ Λ' '))}^{22} {D D.}_{s the s} + + 22 / / {τ τ}_{s the s} + + l l / / {τ τ}_{r r}]] t t} - - - - - - ((1010))$

式中Λ′＝Λ*Δx′，D_s为电子自旋扩散系数，正是它反映自旋扩散输运动力学；τ_r和τ_s分别为电子-空穴复合寿命和电子自旋弛豫寿命。where Λ′=Λ*Δx′, D _s is the electron spin diffusion coefficient, which reflects the spin diffusion transport kinetics; τ _r and τ _s are the electron-hole recombination lifetime and electron spin relaxation lifetime, respectively .

如何测量方程(9)或(10)描述的动力学过程是本发明的又一重要内容。如图1所示，和泵浦光2具有相同圆偏振度一维空间周期调制的探测光3，

(如方程(6)所示)，透过样品9中的TSG，由探测器10测量TSG感应的探测光3的透射功率变化量随延迟时间的变化。这完全不同于目前国际上报道的测量线偏振探测光3透过TSG后的衍射信号功率随延迟时间的变化。本发明探测方法的探测灵敏度极大地提高。How to measure the kinetic process described by equation (9) or (10) is another important content of the present invention. As shown in Figure 1, the probe light 3 having the same degree of circular polarization as the pump light 2 is one-dimensionally space-periodically modulated,

(as shown in Equation (6)), through the TSG in the sample 9 , the detector 10 measures the variation of the transmission power variation of the probe light 3 induced by the TSG with the delay time. This is completely different from current international reports measuring the variation of the diffracted signal power with the delay time after the linearly polarized probe light 3 passes through the TSG. The detection sensitivity of the detection method of the invention is greatly improved.

探测器10测量到的探测光透过TSG后的透射功率变化动力学可表示为：Probe light measured by detector 10 The dynamics of the transmission power change after passing through the TSG can be expressed as:

$ΔP ΔP ((t t)) = = A A {e e}^{- - t t / / {τ τ}_{r r}} {{11 + + B B {e e}^{- - [[{((22 π π / / Λ Λ' '))}^{22} {D D.}_{s the s} + + 22 / / {τ τ}_{s the s}]] t t}}} - - - - - - ((1111))$

式中A和B为拟合参数，0＜B＜1，依赖样品的能带结构和光激发带间跃迁选择定则。In the formula, A and B are fitting parameters, 0<B<1, which depends on the energy band structure of the sample and the selection rule of the transition between photoexcited bands.

因为样品的电子-空穴复合寿命τ_r和电子自旋弛豫寿命τ_s能够单独测量，是已知的，已有多种成熟的测试方法报道。所以，用方程(11)最优化拟合本实例调制方法实验测试到的动力学数据，就能获取描述电子自旋扩散输运动力学的电子自旋扩散系数D_s。Because the electron-hole recombination lifetime τ _r and the electron spin relaxation lifetime τ _s of the sample can be measured separately, it is known that a variety of mature test methods have been reported. Therefore, the electron spin diffusion coefficient D _s describing the electron spin diffusion transport kinetics can be obtained by using equation (11) to optimally fit the kinetic data experimentally tested by the modulation method of this example.

实例二圆偏振度一维方波型空间周期调制光场产生与电子自旋扩散输运动力学测量Example 2 Generation of circular polarization one-dimensional square wave space-period modulation light field and measurement of electron spin diffusion transport dynamics

当光的圆偏振度的一维空间调制周期小，仅少数几个象素，如Λ＜10时，方程(3)和(4)描述的连续近似调制就不成立。实例一所描述的自旋输运扩散动力学不再成立。因而，对于小周期调制，本发明实例发展一种圆偏振度一维方波型空间周期调制光场产生，并用于电子自旋扩散输运动力学测量。When the one-dimensional spatial modulation period of the circular polarization degree of light is small, only a few pixels, such as Λ<10, the continuous approximate modulation described by equations (3) and (4) does not hold. The spin transport diffusion dynamics described in Example 1 no longer hold. Therefore, for small-period modulation, the example of the present invention develops a circular polarization degree one-dimensional square-wave space-period modulation optical field generation, and is used for electron spin diffusion and transport dynamics measurement.

设置空间光调制器7的周期相位如下：Set the periodic phase of the spatial light modulator 7 as follows:

$φ φ ((x x)) = = {Σ Σ}_{q q = = - - M m / / 22}^{M m / / 22} \frac{π π}{22} rect rect ((\frac{x x + + ΛΔx ΛΔx / / 22 - - 22 qΛΔx qΛΔx}{ΛΔx ΛΔx})) + + \frac{33 π π}{22} rect rect ((\frac{x x - - ΛΔx ΛΔx / / 22 - - 22 qΛΔx qΛΔx}{ΛΔx ΛΔx})) - - - - - - ((1212))$

式中函数定义：

其余符号意义同实例一。The function definition in the formula:

The meanings of other symbols are the same as those in Example 1.

显然，方程(12)描述一个周期为2ΛΔx或者2Λ个象素，半个周期幅值为π/2，另半个周期幅值为3π/2的方波型周期函数。泵浦光2和探测光3通过7后，将变成圆偏振度为+1和-1的方波型周期调制光场。Obviously, Equation (12) describes a square-wave periodic function with a period of 2ΛΔx or 2Λ pixels, half of the period with an amplitude of π/2, and the other half with an amplitude of 3π/2. After pumping light 2 and probe light 3 pass through 7, they will become square-wave periodically modulated light fields with degrees of circular polarization of +1 and -1.

设入射线偏振光强为I₀，则透过7的圆偏振度一维方波型空间周期调制光强可表示为：Assuming that the incident ray polarization intensity is I ₀ , the one-dimensional square-wave space-period modulation light intensity with a degree of circular polarization of 7 can be expressed as:

${I I}_{σ σ}^{&PlusMinus; &PlusMinus;} ((x x)) = = {I I}_{00,, σ σ} {Σ Σ}_{q q = = - - M m / / 22}^{M m / / 22} rect rect ((\frac{x x &PlusMinus; &PlusMinus; ΛΔx ΛΔx / / 22 - - 22 qΛΔx qΛΔx}{ΛΔx ΛΔx})) - - - - - - ((1313))$

通过成象透镜8将7成象到9上，则在样品前表面上的调制光强为：7 is imaged onto 9 through the imaging lens 8, then the modulated light intensity on the front surface of the sample is:

${I I}_{σ σ}^{&PlusMinus; &PlusMinus;} ((x x)) = = \frac{{I I}_{00,, σ σ}}{{Q Q}^{22}} {Σ Σ}_{q q = = - - M m / / 22}^{M m / / 22} rect rect ((\frac{x x &PlusMinus; &PlusMinus; ΛΔx ΛΔx' ' / / 22 - - 22 qΛΔx qΛΔx' '}{ΛΔx ΛΔx' '})) - - - - - - ((1414))$

方程(14)描述的方波型周期调制泵浦光场，

激发样品9，产生电子自旋极化周期变化的电子浓度分布：The square-wave periodic modulation pump light field described by equation (14),

Excite sample 9 to produce an electron concentration distribution with periodic changes in electron spin polarization:

${n no}_{&PlusMinus; &PlusMinus;} ((x x)) = = \frac{{n no}_{00}}{22} {Σ Σ}_{q q = = M m / / 22}^{M m / / 22} [[11 &PlusMinus; &PlusMinus; Δn Δn * * rect rect ((\frac{x x + + ΛΔ ΛΔ {x x}^{' '} / / 22 - - 22 qΛΔ qΛΔ {x x}^{' '}}{ΛΔ ΛΔ {x x}^{' '}})) \overset{- -}{+ +} Δn Δ n * * rect rect ((\frac{x x - - ΛΔ ΛΔ {x x}^{' '} / / 22 - - 22 qΛΔ qΛΔ {x x}^{' '}}{ΛΔ ΛΔ {x x}^{' '}}))]] - - - - - - ((1515))$

式中左端下标“±”号与右端远算符号“±”和

的对应关系为同时取上或下符号。In the formula, the subscript "±" at the left end and the far calculation symbol "±" at the right end and

The corresponding relationship is to take the up or down sign at the same time.

方程(15)描述的电子自旋极化周期分布是由单个泵浦脉冲瞬时激发的，即TSG。它会由于电子-空穴复合，自旋弛豫和扩散输运而随时间演化。时间演化由自旋扩散方程控制，解可表示为：The periodic distribution of electron spin polarization described by equation (15) is instantaneously excited by a single pump pulse, ie, TSG. It evolves with time due to electron-hole recombination, spin relaxation and diffusive transport. The time evolution is governed by the spin-diffusion equation, and the solution can be expressed as:

${n no}_{&PlusMinus; &PlusMinus;} ((x x,, t t)) = = \frac{{n no}_{00}}{22} {e e}^{- - t t / / {τ τ}_{r r}} {{11 \overset{- -}{+ +} \frac{44 Δn Δ n}{π π} {Σ Σ}_{m m = = 00}^{\infty \infty} \frac{11}{22 m m + + 11} sin sin ((\frac{((22 m m + + 11)) 22 π π}{{Λ Λ}^{' '}} x x)) {e e}^{- - [[{((((22 m m + + 11)) 22 π π / / {Λ Λ}^{' '}))}^{22} {D D.}_{s the s} + + 22 / / {τ τ}_{s the s}]] t t}}} - - - - - - ((1616))$

式中Λ′＝2Λ*Δx′，为光场的调制周期。Where Λ'=2Λ*Δx' is the modulation period of the light field.

方程(14)描述的同周期方波型圆偏振调制探测光，透过TSG后，由探测器10测量到的TSG所感应的透射功率变化的时间演化为：The same periodic square wave circularly polarized modulation probe light described by equation (14), After passing through the TSG, the time evolution of the transmission power change induced by the TSG measured by the detector 10 is:

$ΔP ΔP ((t t)) = = A A {e e}^{- - t t / / {τ τ}_{r r}} {{11 + + B B {Σ Σ}_{m m = = 00}^{\infty \infty} \frac{11}{{((22 m m + + 11))}^{22}} {e e}^{- - [[{((((22 m m + + 11)) 22 π π / / Λ Λ' '))}^{22} {D D.}_{s the s} + + 22 / / {τ τ}_{s the s}]] t t}}} - - - - - - ((1717))$

因为样品的电子-空穴复合寿命τ_r和电子自旋弛豫寿命τ_s能够单独测量，是已知的，已有多种成熟的测试方法报道。所以，用方程(17)最优化拟合本实例调制方法实验测试到的自旋扩散输运动力学数据，就能获取描述电子自旋扩散输运动力学的电子自旋扩散系数D_s。Because the electron-hole recombination lifetime τ _r and the electron spin relaxation lifetime τ _s of the sample can be measured separately, it is known that a variety of mature test methods have been reported. Therefore, the electron spin diffusion coefficient D _s describing the electron spin diffusion transport dynamics can be obtained by using Equation (17) to optimally fit the spin diffusion transport kinetic data experimentally tested by the modulation method of this example.

值得注意的是方程(17)式中高阶项的幅度按1/(2m+1)²衰减，所以，衰减得非常快。使用方程(17)最优化拟合实验动力学数据时，只需要取求和项中前几项就能获得足够的精度，并不需要计算无穷项和。It is worth noting that the magnitude of the higher-order terms in equation (17) decays by 1/(2m+1) ² , so the decay is very fast. When using equation (17) to optimally fit the experimental kinetic data, only the first few terms in the summation can be obtained to obtain sufficient accuracy, and there is no need to calculate the infinite sum.

Claims

1. the electron spin diffusion based on pure phase type LCD space light modulator transports the dynamics optical test method; Combination One-Dimensional Pure phase type LCD space light modulator and time resolution pumping-detection device is characterized in that using pure phase type LCD space light modulator while modulated pumping to become identical one-dimensional space period profile with the circular polarization of surveying hot spot; The pump light excited sample of being modulated; Produce the electron-spin polarization transient grating, and the detection light transmission spin polarization transient grating of being modulated is measured the spin diffusion and is transported dynamics; Its transmission power variable quantity has reflected then that with changing time delay the electron spin diffusion transports dynamics; Pixel unit yardstick when the modulation period of circular polarization much larger than One-Dimensional Pure phase type LCD space light modulator; And when the periodic phase of One-Dimensional Pure phase type LCD space light modulator being set, surveying in the light transmission sample transmission power variable quantity behind the transient state spin grating and describe by equation (2) with changing time delay by equation (1);

φ (i) = \frac{2 π}{Λ * Δx} RMod (\frac{i}{Λ * Δx}) - - - (1)

Function R Mod () expression two numbers are divided by in the formula, round remainder; Λ is the number of picture elements of modulation period; Δ x is the yardstick of pixel unit;

ΔP (t) = A e^{- t / τ_{r}} {1 + B e^{- [{(2 π / Λ')}^{2} D_{s} + 2 / τ_{s}] t}} - - - (2)

Λ ' is the cycle of transient state spin grating, τ in the formula _rAnd τ _sBe respectively electronics-hole-recombination life-span and electron spin relaxation life-span, available other known method independent measurement is known; A, B and D _sBe fitting parameter, the spin diffusion that obtains with equation (2) optimization match experiment measuring transports the dynamics data acquisition, and D _sThe electron spin coefficient of diffusion that will measure just.

2. a kind of electron spin diffusion based on pure phase type LCD space light modulator described in the claim 1 transports the dynamics optical test method; Be merely several pixel units when the modulation period of circular polarization; When by equation (3) periodic phase of One-Dimensional Pure phase type LCD space light modulator being set, the transmission power variable quantity in the detection light transmission sample behind the transient state spin grating is described by equation (4) with changing time delay;

φ (x) = Σ_{q = - M / 2}^{M / 2} \frac{π}{2} rect (\frac{x + ΛΔx / 2 - 2 qΛΔx}{ΛΔx}) + \frac{3 π}{2} rect (\frac{x - ΛΔx / 2 - 2 qΛΔx}{ΛΔx}) - - - (3)

Function definition in the formula, ; All the other symbolic significances are with (1) formula;

ΔP (t) = A e^{- t / τ_{r}} {1 + B Σ_{m = 0}^{\infty} \frac{1}{{(2 m + 1)}^{2}} e^{- [{((2 m + 1) 2 π / Λ^{'})}^{2} D_{s} + 2 / τ_{s}] t}} - - - (4)

M is an integer in the formula, as the summation variable; All the other symbolic significances are with (2) formula.The spin diffusion that obtains with equation (4) optimization match experiment measuring transports dynamics data, but electron gain spin diffusion coefficient D then _s