A universal method for improving the detection sensitivity of four-wave transverse shearing interferometer

Abstract

The present invention discloses a method for improving the detection sensitivity of a four-wave lateral shearing interferometer, which belongs to the field of optical precision detection. The method only needs to sample an interference fringe pattern, and the wavefront slope sensitivity of the four-wave lateral shearing interferometer can be increased by two times through fringe processing. The advantage of the present invention is that it solves the problem that the traditional four-wave lateral shearing interferometer needs to adjust the distance between the grating and the camera target surface to improve the sensitivity, the operation is complicated, and the adjustment error is large. The principle is clear and the operation is convenient.

Description

Technical Field

[0001] The invention belongs to the field of advanced optical detection, and in particular relates to a method generally used for improving the detection sensitivity of a four-wave lateral shearing interferometer. Background Art

[0002] Four-wave lateral shearing interferometer is a grating type lateral shearing interferometer. The measured light is diffracted by the grating, and more than 90% of the diffracted light energy is concentrated in four beams of first-order diffracted light. These four beams are transmitted forward along their respective diffraction angles, and finally coherently superimposed to form interference fringes. By processing the interference fringes, the wavefront slopes in the two orthogonal directions of x and y are obtained. The measured wavefront can be restored by the wavefront restoration algorithm using the wavefront slope. Four-wave lateral shearing interferometer has a series of advantages such as large dynamic range, anti-vibration, and achromatism. It has been applied in a series of fields such as biomedicine, laser diagnosis, and adaptive optics. At present, four waves have been increasingly valued by scientists from various countries.

[0003] The sensitivity of the four-wave lateral shearing interferometer in detecting phase is determined by the shear amount. The greater the shear amount, the higher the detection sensitivity. Therefore, the traditional four-wave lateral shearing interferometer achieves the purpose of increasing the detection sensitivity by changing the physical distance between the grating and the CCD and increasing the shear amount. However, not only is the process of moving the grating complicated to implement, but the movement of the grating will also cause adjustment errors such as the tilt of the grating. The present invention proposes a method that can double the sensitivity of the four-wave lateral shearing interferometer through data processing without changing any hardware device. Summary of the invention

[0004] The purpose of the present invention is to make up for the shortcomings of the current technology and propose a method generally applicable to improving the detection sensitivity of a four-wave transverse shearing interferometer.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] A method for improving the detection sensitivity of a four-wave lateral shearing interferometer, the method comprising the following steps:

[0007] Step 1: Collect and obtain a four-wave transverse shearing interference fringe pattern, and its light intensity expression is:

[0008]

[0009] Where I is the interference fringe intensity, I0 is the interference fringe background intensity distribution, s is the shear amount of the four first-order diffracted lights along the x direction or y direction, k is the wave number, p is the amplitude grating period, W is the wavefront distribution to be measured, and represent the wavefront slopes in the x-direction and y-direction, respectively, and They represent the wavefront slopes at 45° and -45° from the X-axis respectively;

[0010] Step 2: Perform Fourier transform on equation (1) to obtain the spectrum distribution of light intensity I, take out the spectrum in the X direction and Y direction and perform inverse Fourier transform to obtain a new light intensity expression:

[0011]

[0012] Step 3: Square I1 and get the new light intensity expression:

[0013]

[0014] Step 4: Use Fourier transform to find the phase of I2 to get the wavefront slope in the X and Y directions. Using the wavefront slopes in these two orthogonal directions The measured wavefront W can be restored by the wavefront restoration method.

[0015] Furthermore, in step 4, the wavefront restoration method is implemented by the following expression:

[0016]

[0017] Where W is the measured wavefront, FT represents Fourier transform, and u and v are the horizontal and vertical coordinate variables of the spectrum respectively.

[0018] In the light intensity distribution I2 obtained after processing, the coefficient of the phase to be measured, i.e., the wavefront slope, is increased by two times, so the sensitivity is also increased by two times. Compared with the traditional method of improving sensitivity, the method of the present invention does not require the improvement of the experimental device, but can effectively improve the sensitivity through simple calculation, which is easier to implement and is applicable to all four-wave lateral shearing interferometers.

[0019] The present invention has the following beneficial effects:

[0020] (1) The present invention solves the problem that the traditional four-wave transverse shearing interferometer needs to adjust the physical distance between the grating and the camera target surface to improve the sensitivity, the operation is complicated, and the adjustment error is large;

[0021] (2) The invention has clear principles, simple calculations, clear principles, and convenient operation;

[0022] (3) The present invention is applicable to any four-wave lateral shearing interferometer and has strong versatility. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 A flowchart of a method generally used to improve the detection sensitivity of a four-wave lateral shearing interferometer;

[0024] Figure 2 Figure I is the shearing interference fringe pattern collected by the four-wave lateral shearing interferometer;

[0025] Figure 3 Schematic diagram of spectrum distribution of fringe pattern I;

[0026] Figure 4 It is the distribution diagram of fringe diagram I1;

[0027] Figure 5 It is the distribution diagram of fringe diagram I2;

[0028] Figure 6 This is a schematic diagram of the spectrum distribution of fringe pattern I2. DETAILED DESCRIPTION

[0029] In order to better illustrate the purpose, technical solutions and advantages of the present invention, a further detailed description is given below in conjunction with the accompanying drawings, but this should not limit the protection scope of the present invention at all.

[0030] A method generally used to improve the detection sensitivity of a four-wave transverse shearing interferometer, such as Figure 1 As shown, the method comprises the following steps:

[0031] Step 1: The four-wave lateral shearing interferometer camera collects a shearing interference fringe pattern. The fringe distribution is as follows: Figure 2 The light intensity expression is shown in formula (1). The interference fringe I is subjected to Fourier transform, and the spectrum distribution is shown in Figure 3 shown.

[0032]

[0033] Step 2: Take out Figure 3 The spectrum in the X and Y directions is transformed by inverse Fourier transform to obtain the new light intensity distribution I1 as shown in Figure 4 As shown, the light intensity expression is shown in formula (2).

[0034]

[0035] Step 3: Square I1 to get the new light intensity distribution I2 as Figure 5 As shown, the light intensity expression is shown in formula (3). From the new interference fringe expression formula (3), it can be seen that the wavefront slope The coefficients of are doubled compared to those in equation (1). At this time, the sensitivity of the wavefront slope is also doubled.

[0036]

[0037] Step 4: Calculate the Fourier transform of I2, and its spectrum distribution is as follows Figure 6As shown, take out Figure 6 The positive first-order spectrum in the X and Y directions, Moving both spectra to the center of the frequency domain, the expression becomes By performing an inverse Fourier transform on the new spectrum, the wavefront slopes in the X and Y directions can be obtained. The measured wavefront can then be restored using the wavefront restoration method.

[0038] Among them, the wavefront restoration method is optional, as shown in the following expression,

[0039]

[0040] Where W is the measured wavefront, FT represents Fourier transform, and u and v are the horizontal and vertical coordinate variables of the spectrum respectively.

[0041] The method for improving the detection sensitivity of a four-wave transverse shearing interferometer described in the present invention is that in the light intensity distribution obtained after fringe processing, the coefficient of the phase to be measured, that is, the wavefront slope, is increased by two times, so the sensitivity is also increased by two times. Compared with the traditional method of improving sensitivity, the method of the present invention does not require the improvement of the experimental device, and can effectively improve the sensitivity through simple calculations, which is easier to implement and is applicable to all four-wave transverse shearing interferometers.

Claims

1. A method for improving the detection sensitivity of a four-wave transverse shearing interferometer, characterized in that: The method comprises the following steps: Step 1: Collect and obtain a four-wave transverse shearing interference fringe pattern, and its light intensity expression is: （1） Where I is the interference fringe intensity, is the background light intensity distribution of interference fringes, Four first-order diffraction beams along Direction or The shear amount in the direction is the wave number, p is the amplitude grating period, W is the wavefront distribution to be measured, and Represents wavefront Direction and The wavefront slope in the direction and They represent the wavefront slopes at 45° and -45° from the X-axis respectively; Step 2: Perform Fourier transform on equation (1) to obtain the spectrum distribution of light intensity I, take out the spectrum in the X direction and Y direction and perform inverse Fourier transform to obtain the new light intensity expression: （2） Step 3: Taking the square, we get the new light intensity expression: （3） Step 4: The wavefront slopes in the X and Y directions can be obtained by using the Fourier transform method to obtain the phase. , Using the wavefront slopes in these two orthogonal directions , , the measured wavefront W can be restored by the wavefront restoration method; The wavefront restoration method is implemented by the following expression: （4） Where W is the measured wavefront, FT represents Fourier transform, and u and v are the horizontal and vertical coordinate variables of the spectrum respectively.

Images