CN100442044C - Phase recovery method in neutron interferometer - Google Patents

Abstract

A phase recovery method in a neutron interferometer, comprising the following steps: 1) shooting a neutron interference pattern that does not contain object phase information; 2) taking another neutron interference pattern that contains object information; 3) Place the medium interference pattern photo without object phase information in the 4f optical system, take a spatial spectrum photo, that is, the spatial spectrum of the carrier fringe, and perform in-situ development, fixing, and drying; 4) in a 4f optical system , take away the neutron interference pattern photo that does not contain object information, place a neutron interference pattern containing object information, and then perform optical information processing, because a photo containing carrier fringe space spectrum has been placed in the 4f system, Therefore, the carrier fringe will not pass through the optical system, and what will be obtained will be a contour map of the phase information of the object.

Description

Phase recovery method in neutron interferometer

technical field

The invention relates to an interferometer, in particular to a phase recovery method in a neutron interferometer, which has wide application prospects in biomedicine, microelectronics, aerospace, precision measurement, archaeology and other disciplines.

Background technique

As early as 1936, people discovered the wave properties of neutrons, but it was only after 1945, with the advancement of nuclear reactor technology, that neutron diffraction and interference were applied. We know that neutrons or any other radiation sources with wave properties can be used to study the spatial arrangement of atoms in solids and obtain structural information inside atoms as long as their wavelengths and the distance between atoms are of the same order of magnitude.

According to wave theory, the neutron wavelength is given by:

λ=h/mV

In the formula, h is Planck's constant, m and V are the mass and velocity of neutrons, obviously, the wavelength of neutrons can be changed by adjusting the velocity of neutrons, and the diffraction characteristics of neutrons make it convenient for people to use a Or multiple crystals make it "monochromatic", all of which prepare the conditions for neutron interference.

For most heavy metals, the penetration depth of X-rays is limited, but neutrons can do a lot. In a sense, neutrons and X-rays are complementary to each other. In particular, hydrogen has a greater absorption of neutrons. Therefore, neutrons are very sensitive to the detection of some hydrogen-containing organic materials, such as: lubricating oil, plastics, sealing rings in metal casings, etc. For large heavy metal components, neutrons are also very valuable, especially in precision metrology and detection, neutron interferometers are especially effective.

Since the wavelength of neutrons is only on the order of one-thousandth of visible light, neutron interferometers require a high degree of perfect crystal alignment and mechanical stability, and its error and vibration amplitude do not exceed 10 ^-2 nm. People make this kind of interferometer on a whole piece of perfect crystal, because of its integrity, excellent experimental results can be obtained, and high collimation and stability can be guaranteed. The neutron interferometer consists of a whole perfect crystal divided into three pieces placed in parallel to form a neutron interferometer. The first crystal splits the neutron beam after passing through the monochromator into transmitted waves and diffracted waves. In the symmetrical experimental device arrangement, the intensities of the two beams are completely equal at the exact Bragg position of the crystal; the middle crystal The role of the mirror is similar to that of two beams of light; the third crystal acts as an analysis crystal. The sample is placed in the optical path of one of the beams, between the beamcombining crystal and the analyzing crystal, and thereby introduces a phase change that distorts the wavefront. Interfering the object light passing through the sample with the reference light produces interference fringes, which are very sensitive to the phase shift of the probe beam passing through the sample.

It is usually difficult to ensure that the angle between the two neutron beams is zero, so the measured phase distribution is superimposed on a group of parallel fringes, which brings difficulties to the analysis of the phase distribution of the object.

Contents of the invention

Aiming at the above-mentioned shortcomings in the prior art, the present invention proposes a phase recovery method in a neutron interferometer, thereby removing the carrier fringe and obtaining a contour map of the phase distribution of the object.

From physical optics, we already know that the intensity distribution of the interference pattern of two-beam interference can be expressed by the following formula:

I(x,y)=a(x,y)+b(x,y)cos(2πf ₀ x+Φ(x,y)) (1)

In the formula, f ₀ is the carrier frequency, f ₀ =1/d, d is the spacing of the carrier fringes, and the spacing of the interference fringes is determined by the angle between the object light and the reference light. The so-called carrier fringe is the interference fringe directly obtained by the interferometer when the sample to be measured is not placed. We assume that the carrier fringe is parallel to the y-axis, Φ(x, y) is the phase shift caused by the incident neutron beam due to the sample to be tested, a(x, y) is the background light intensity, and b(x, y) is the image contrast. It can be seen from the above formula that the interference pattern is formed by superimposing the phase distribution of the object on the carrier fringe, which corresponds to the contour map of the phase distribution of the object, that is, the phase distribution of the object deflects the carrier fringe.

To obtain the phase distribution of the sample, the carrier fringe on the interference pattern needs to be eliminated first. Below we use the Fourier transform method to achieve this goal.

We rewrite (1) into the following exponential form:

I(x, y) = a(x, y) + c(x, y) exp(i2πf ₀ x) + c ^* (x, y) exp(-i2πf ₀ x) (2)

in,

$\mathrm{<span\; class="notranslate">\; c</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; b</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; i\&Phi;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

Perform one-dimensional Fourier transform on (2) to get:

I _F (f, y) = a _F (f, y) + c _F (ff ₀ , y) + c ^* _F (f + f ₀ , y) (4)

It can be known from formula (4) that the interference field will appear three sharp peaks far apart in the Fourier frequency domain, and the distance between them is f ₀ . The peaks on the left and right correspond to the third and second terms of equation (4) respectively, and only these two peaks contain the phase distribution information of the object to be measured. We can take out the wave peak on the right alone, and perform a one-dimensional Fourier inverse transform on it to obtain c(x, y), and then according to formula (3), we can directly obtain the phase distribution of the object. Therefore, in order to recover the phase of the object from the interference pattern, the following steps are followed:

1) Shoot a neutron interference pattern that does not contain object phase information;

2) Take another neutron interference pattern containing object information;

3) Place the photo of the neutron interference pattern that does not contain the phase information of the object in a 4f optical system, take a photo of the spatial spectrum, that is, the spatial spectrum of the carrier fringe, and perform in-situ development, fixing, and drying;

4) In the 4f optical system, take away the neutron interference pattern photo that does not contain object information, place a neutron interference pattern containing object information, and then perform optical information processing, because a photo containing A photo of the spatial spectrum of the carrier fringe, so the carrier fringe will not pass through the optical system, and what is obtained is a contour map of the phase information of the object.

Technical effect of the present invention:

Because in the prior art, the phase information is superimposed on the carrier fringe, it is impossible to obtain the contour map of the phase information of the object through the neutron interference photo, and the invention overcomes this defect.

Detailed ways

In order to recover the phase of the object from the interference pattern, the following steps are followed:

1) Shoot a neutron interference pattern that does not contain the phase information of the object.

2) Take another neutron interference pattern containing object information.

3) Place the medium interference pattern photo without object phase information in the 4f optical system, take a spatial spectrum photo, that is, the spatial spectrum of the carrier fringe, and perform in-situ development, fixing, and drying.

4) In the 4f optical system, take away the neutron interference pattern photo that does not contain object information, place a neutron interference pattern containing object information, and then perform optical information processing, because a photo containing A photo of the spatial spectrum of the carrier fringe, so the carrier fringe will not pass through the optical system, and what is obtained is a contour map of the phase information of the object.

Claims (1)

1. A phase recovery method in a neutron interferometer, characterized in that it comprises the following steps: 1) Shoot a neutron interference pattern that does not contain object phase information; 2) Take another neutron interference pattern containing object information; 3) Place the photo of neutron interference pattern that does not contain the phase information of the object in the 4f optical system, take a photo of the spatial spectrum, that is, the spatial spectrum of the carrier fringe, and perform in-situ development, fixing, and drying; 4) In a 4f optical system, take away the neutron interference pattern photo that does not contain object information, place a neutron interference pattern containing object information, and then perform optical information processing, because a photo of neutron interference pattern that contains object information has been placed in the 4f system The photo contains the spatial frequency spectrum of the carrier fringe, so the carrier fringe will not pass through the optical system, and what will be obtained will be a contour map of the phase information of the object.