阅读说明：本技术 动态光场有效空间相干分布的测量方法及测量系统 (Method and system for measuring effective spatial coherence distribution of dynamic light field ) 是由 陈亚红 王飞 蔡阳健 于 2020-05-25 设计创作，主要内容包括：本发明公开了一种动态光场有效空间相干分布的测量方法及测量系统,包括以下步骤：在待测动态光场的一侧依次设置傅里叶变换透镜和光探测器,所述傅里叶变换透镜的焦距为f,所述傅里叶变换透镜与待测光场的光源距离为f,所述傅里叶变换透镜与光探测器的距离为f；所述光探测器采集待测动态光场经过傅里叶变换透镜聚焦后的焦点处的光谱密度分布；使用光探测器测试获得动态光场在光源处的光强分布；计算获得待测动态光场的相干分布。其可以测量具有任意统计特性的动态光场的有效相干分布,步骤简单,测量速度快,成本低。(The invention discloses a method and a system for measuring the effective spatial coherence distribution of a dynamic light field, which comprises the following steps: the method comprises the following steps that a Fourier transform lens and an optical detector are sequentially arranged on one side of a dynamic light field to be detected, the focal length of the Fourier transform lens is f, the distance between the Fourier transform lens and a light source of the light field to be detected is f, and the distance between the Fourier transform lens and the optical detector is f; the optical detector collects the spectral density distribution of the dynamic light field to be measured at the focus after the dynamic light field is focused by the Fourier transform lens; obtaining the light intensity distribution of the dynamic light field at the light source by using a light detector; and calculating to obtain the coherence distribution of the dynamic light field to be detected. The method can measure the effective coherent distribution of the dynamic light field with any statistical characteristic, and has the advantages of simple steps, high measuring speed and low cost.)

1. A method for measuring the effective spatial coherence distribution of a dynamic light field is characterized by comprising the following steps:

s1, sequentially arranging a Fourier transform lens and an optical detector on one side of the dynamic optical field to be detected, wherein the focal length of the Fourier transform lens is f, the light source distance between the Fourier transform lens and the optical field to be detected is f, and the distance between the Fourier transform lens and the optical detector is f; the optical detector collects the spectral density distribution I (rho) of the dynamic light field to be measured at the focus after the dynamic light field is focused by the Fourier transform lens;

s2, obtaining the light intensity distribution I (r) of the dynamic light field at the light source by using a light detector test;

s3, calculating to obtain the coherent distribution of the dynamic light field to be measuredWherein, lambda is the wavelength of the dynamic optical field to be measured,is composed ofThe fourier transform of (d).

2. The method for measuring the effective spatial coherence distribution of a dynamic light field according to claim 1, wherein said S2 comprises:

and replacing the Fourier transform lens in the S1 with an imaging lens, and testing by the optical detector to obtain the light intensity distribution I (r) of the dynamic light field to be tested.

3. The method of claim 2 wherein the focal length of the imaging lens is f/2.

4. The method of claim 1 wherein the light detector is a CCD.

5. The method of claim 1 wherein the light detector is CMOS.

6. A test light path for dynamic light field effective spatial coherence distribution, which is characterized in that the test light path is based on the method for measuring dynamic light field effective spatial coherence distribution according to any one of claims 1 to 5.

7. A system for measuring the effective spatial coherence distribution of a dynamic light field is based on the method for measuring the effective spatial coherence distribution of a dynamic light field in any one of claims 1 to 5, and is characterized by comprising a data acquisition module, wherein the data acquisition module stores a first data set and a second data set, the first data set is the spectral density distribution I (p) of the dynamic light field to be measured at the focus after the dynamic light field is focused by a Fourier transform lens, and the second data set is the light intensity distribution I (r) of the dynamic light field at a light source.

8. The system for measuring the effective spatial coherence distribution of a dynamic light field according to claim 7, further comprising a data operation module, wherein the data operation module stores the operation formula in S3.

Technical Field

The invention relates to the technical field of photoelectricity, in particular to a method and a system for measuring effective spatial coherence distribution of a dynamic light field.

Background

Due to inevitable physical phenomena such as quantum random effect in the stimulated radiation process, all optical fields in nature, including artificial optical fields in laboratories, are dynamically and randomly fluctuated. The randomness of dynamic random fluctuation light fields is researched, and the time-space statistical coherence characteristics of the dynamic light fields are essentially researched. The dynamic light field spatial coherence distribution refers to the distribution of a cross spectrum density function between any two points on a light field cross section, the cross spectrum density function between any two points on the dynamic light field cross section researched by people in the past meets Gaussian distribution, and the light field is also called as a dynamic light field with Gaussian spatial coherence distribution.

In recent years researchers found that the spatial coherence distribution of a dynamic light field is not limited to gaussian distribution only, and in 2007, italian scientist f. Later, researchers found that in an attempt to construct spatial coherent distributions of different distributions, light field regulation can be conveniently and effectively achieved by constructing the spatial coherent distribution of the light field, and some peculiar transmission characteristics are achieved. Such as: in 2011, Lajunen et al constructed a dynamic light field with non-uniform spatial coherence distribution, which showed self-focusing characteristics during transmission. In 2014, chenyihong et al proposed a dynamic light field with a partially coherent vector having a special spatial coherent distribution, which can effectively regulate and control the polarization state distribution of the light field, such as generating a radially polarized light field and an angularly polarized light field. Afterwards, Chen Asia red et al generate a self-splitting optical field by regulating and controlling the spatial coherent distribution of the dynamic optical field, and the optical field has important application prospects in multi-particle capture and control.

In fact, in the specific example of implementing the light field regulation and control by the light field spatial coherence distribution, what plays a decisive role is the effective spatial coherence distribution of the light field, which depends on the actual spot size, the larger the spot is, the wider the effective spatial coherence distribution of the light field is, and the smaller the spot is, the narrower the effective spatial coherence distribution of the light field is. Therefore, it is important how to measure the effective coherence distribution of the dynamic light field.

Due to the important role played by the effective spatial coherent distribution of the dynamic light field in the light field regulation, the measurement of the effective spatial coherent distribution of the dynamic light field becomes the key and difficult problem in the research field.

Up to now, there are three main methods for measuring the effective spatial coherence distribution of the light field:

first, the effective spatial coherence distribution of the dynamic light field is recovered by using a fourth-order correlation function of light intensity between two points measured by point-by-point scanning of two single-photon detectors on a cross section of the dynamic light field light source, which is mentioned in the literature (f.wang and y.cai, "Experimental analysis of fractional coherence beam with a fractional coherence optics," j.opt.soc.a. 24,1937-1944(2007)), the point-by-point scanning method in the method is very time-consuming, and the method can only be used for measuring a one-dimensional distribution of the effective spatial coherence distribution, and cannot measure a two-dimensional structure of the effective spatial coherence distribution.

Second, in the literature (y.chen, f.wang, l.liu, c.zhao, y.cai, and o.korotkova, "Generation and propagation of a partial coherent vector beam with spatial correlation functions," physics.rev.a 89,013801 (2014)), it takes a set (2000 in the experiment) of instantaneous light intensity distribution maps of dynamic light fields at the light source by means of a Charge Coupled Device (CCD), extracts data of the taken light intensity distribution maps by MATLAB software, and performs correlation processing thereon to obtain a distribution of squares of the modes of the light field effective spatial correlation distribution, which is much less in time consumption than the first method, and is capable of measuring a two-dimensional spatial distribution of the squares of the light field effective spatial correlation distribution; however, the second method has certain defects, on one hand, it has high requirements for building an optical path, and on the other hand, it can only measure amplitude information of effective spatial coherent distribution of an optical field, and cannot measure phase information of the effective spatial coherent distribution.

Third, chinese patent No. CN201910791478.3 discloses a method for realizing complex coherence measurement of random light field by using light intensity correlation, which can measure amplitude and phase of coherent distribution of dynamic light field, but is limited to measuring dynamic light field with gaussian statistical distribution, and is no longer applicable to dynamic light field with arbitrary statistical distribution.

Disclosure of Invention

The technical problem to be solved by the invention is to provide a method and a system for measuring the effective spatial coherence distribution of a dynamic light field, which can measure the effective coherence distribution of the dynamic light field with any statistical characteristic, and have the advantages of simple steps, high measuring speed and low cost.

In order to solve the technical problem, the invention provides a method and a system for measuring the effective spatial coherence distribution of a dynamic light field, which comprises the following steps:

s1, sequentially arranging a Fourier transform lens and an optical detector on one side of the dynamic optical field to be detected, wherein the focal length of the Fourier transform lens is f, the light source distance between the Fourier transform lens and the optical field to be detected is f, and the distance between the Fourier transform lens and the optical detector is f; the optical detector collects the spectral density distribution I (rho) of the dynamic light field to be measured at the focus after the dynamic light field is focused by the Fourier transform lens;

s2, obtaining the light intensity distribution I (r) of the dynamic light field at the light source by using a light detector test;

s3, calculating to obtain the coherent distribution of the dynamic light field to be measuredWherein, lambda is the wavelength of the dynamic optical field to be measured,is composed ofThe fourier transform of (d).

Preferably, the S2 includes:

and replacing the Fourier transform lens in the S1 with an imaging lens, and testing by the optical detector to obtain the light intensity distribution I (r) of the dynamic light field to be tested.

Preferably, the focal length of the imaging lens is f/2.

Preferably, the light detector is a CCD.

Preferably, the light detector is a CMOS.

The invention discloses a system for measuring the effective spatial coherence distribution of a dynamic light field, which comprises a data acquisition module, wherein the data acquisition module stores a first data set and a second data set, the first data set is the spectral density distribution I (rho) of the dynamic light field to be measured at a focus after the dynamic light field is focused by a Fourier transform lens, and the second data set is the light intensity distribution I (r) of the dynamic light field at a light source.

Preferably, the system further comprises a data operation module, and the data operation module stores the operation formula in S3.

The invention has the beneficial effects that:

1. the measuring device is simple, and the cost of measuring the effective coherent distribution of the dynamic light field is saved.

2. The method has simple measurement steps and high measurement speed, and the effective coherent distribution structure of the dynamic light field can be recovered only by measuring the light field distribution of the dynamic light field light source to be measured and the far field spectral density distribution.

3. The method can measure the effective coherent distribution of the dynamic light field with any statistical characteristic, thereby having universal applicability.

Drawings

FIG. 1 is a schematic diagram of the construction of the optical path of the present invention

The reference numbers in the figures illustrate: 1. a light source of the dynamic light field to be detected; 2. a Fourier transform lens; 4. a light detector; 5. and (4) a computer.

Detailed Description

The present invention is further described below in conjunction with the following figures and specific examples so that those skilled in the art may better understand the present invention and practice it, but the examples are not intended to limit the present invention.

Referring to fig. 1, the invention discloses a method for measuring the effective spatial coherence distribution of a dynamic light field, which comprises the following steps:

s1, sequentially arranging a Fourier transform lens 2 and an optical detector 4 on one side of a dynamic light field to be detected, wherein the focal length of the Fourier transform lens 2 is f, the distance between the Fourier transform lens 2 and a light source 1 of the light field to be detected is f, and the distance between the Fourier transform lens 2 and the optical detector 4 is f; the optical detector 4 collects the spectral density distribution I (rho) of the dynamic light field to be measured at the focus after the dynamic light field is focused by the Fourier transform lens;

s2, obtaining the light intensity distribution I (r) of the dynamic light field at the light source by using a light detector test, which specifically comprises:

and replacing the Fourier transform lens in the S1 with an imaging lens, and testing by the optical detector to obtain the light intensity distribution I (r) of the dynamic light field to be tested. The focal length of the imaging lens is f/2.

S3, calculating to obtain the coherent distribution of the dynamic light field to be measuredWherein, lambda is the wavelength of the dynamic optical field to be measured,is composed ofThe fourier transform of (d).

The light detector is a CCD or a CMOS. The light detector 3 transmits the acquired data to the computer 4.

The invention discloses a system for measuring the effective spatial coherence distribution of a dynamic light field, which comprises a data acquisition module, wherein the data acquisition module stores a first data set and a second data set, the first data set is the spectral density distribution I (rho) of the dynamic light field to be measured at a focus after the dynamic light field is focused by a Fourier transform lens, and the second data set is the light intensity distribution I (r) of the dynamic light field at a light source. The present invention further includes a data operation module, which stores the operation formula in S3.

The measurement principle of the invention is as follows:

the reference (e.wolf, Introduction to the Theory of science and polarization of Light, 2007) knows that the statistical properties of dynamic Light fields can be expressed by a mutual Coherence function between two points, which can be expressed as:

i (r) in formula (1)₁)，I(r₂) Respectively represent r on the light source surface₁And r₂Light intensity distribution at two points, gamma (r)₁-r₂) Is represented by r₁And r₂The mutual interference function between two points, namely the coherent distribution structure of the dynamic optical field.

After the dynamic light field is focused by a fourier transform lens with f, the spectral density distribution at the focal point can be expressed as:

whereinIs composed ofThe fourier transform of (a) the signal,is gamma (r)₁-r₂) The fourier transform of (d).Representing a convolution. According to the convolution theorem, equation (2) can be expressed as:

in the formula (3), the first and second groups,

by appropriately transforming equation (3), an expression of the spatial coherence distribution structure of the dynamic light field can be obtained:

as can be seen from the formula (5), the effective spatial correlation structure distribution of the dynamic light field to be measured can be determined by measuring the light intensity distribution I (r) of the dynamic light field at the light source and the spectral density distribution I (ρ) at the focal point after being focused by the fourier transform lens, and the amplitude and phase distribution of the effective spatial coherence distribution structure can be measured at the same time.

The specific operation steps of this embodiment are as follows: the invention prepares a dynamic light field light source 1 to be measured with a self-splitting characteristic effective coherent distribution structure according to a scheme provided in a generation device and a generation method of a self-splitting light beam (Chenyihong, Queenfei, Chua Yangjian) and a patent number CN 201410399805.8).

A Charge Coupled Device (CCD) can be used for recording and storing a two-dimensional gray scale image of the light intensity distribution of a dynamic light field to be detected at a light source, wherein the CCD is a Grasshopper3 series professional CCD developed by Point Grey, and the specific model is GS3-U3-14S5M, and the specific parameters are horizontal resolution 1384, vertical resolution 1036 and frame frequency/line frequency 30 fps.

Irradiating the dynamic light field to be measured onto a Fourier lens 2 which is focused to 400 mm, wherein the distance from the light source surface of the dynamic light field to be measured to the thin lens surface is 400 mm; and then, placing the professional CCD used in the previous step at a focal plane which is 400 mm away from the rear of the thin lens for measuring and storing a two-dimensional gray scale image of spectral density distribution of the dynamic light field to be measured after being focused. And (3) importing the two-dimensional gray-scale maps stored in the two steps into MATLAB, and respectively carrying out fast Fourier transform and corresponding processing (the calculation process refers to a measurement principle), so that the amplitude and phase distribution of the effective coherent distribution structure of the dynamic light field to be measured can be obtained.

The CCD recording and storing steps are as follows: firstly, connecting the CCD to a desktop computer with a professional Windows 10 system through a USB 3.0 interface, wherein the default desktop computer is provided with software which is provided by Point Grey and is named as Point Grey, and the software is used for observing and storing images received by the CCD; after the CCD is connected to a computer, the CCD is aligned to the detected light beam, and the Point Grey software is opened to record and save the image received by the CCD.

The working principle of the invention is as follows:

1. the measuring device is simple, and the cost of measuring the effective coherent distribution of the dynamic light field is saved.

2. The method has simple measurement steps and high measurement speed, and the effective coherent distribution structure of the dynamic light field can be recovered only by measuring the light field distribution of the dynamic light field light source to be measured and the far field spectral density distribution.

3. The method can measure the effective coherent distribution of the dynamic light field with any statistical characteristic, thereby having universal applicability.

The above-mentioned embodiments are merely preferred embodiments for fully illustrating the present invention, and the scope of the present invention is not limited thereto. The equivalent substitution or change made by the technical personnel in the technical field on the basis of the invention is all within the protection scope of the invention. The protection scope of the invention is subject to the claims.