SU607460A1 - Holographic interferometer - Google Patents

Description

The drawing shows the principal optical scheme of a holographic interferometer.

UH consists of a coherent radiation source 1 (laser, collimator i, beam-splitting plate 6 dividing the beam into two parts 6 (and 5 (and / 2), flat mirror 4: diffuse diffuser b, working zone o, hologram 7, oooect B, the photo system of the system U, which includes iU, diaphragm ii, lens 12 and photo recorder 15, mounted along beam vi, mirrors 14, 15, and negative lens ib installed along beam li / 2.

The proposed holographic interferometer works as follows. The pre-coherent laser radiation 1 is collimated by the optical system 2. The collimated beam is divided into two parts 3i and 32 by means of a separator plate 6. The beam performs the functions of a signal beam. With the help of mirror 4, this beam is directed to the diffuser b. The scattered beam shines through the working area b and drops onto the hologram 7.

The h beam is used as a reference beam. By the mirrors 14 and 15, the reference beam is directed to the negative lens 16. At the output of lens ib, a diverging beam is formed, illuminating the hollow frame at an angle a relative to the normal to its surface.

A hologram is recorded by the method of two exposures. At the first exposure, the object under study is present in the working zone b. Before the second exposure, the hologram 7 is shifted in its own plane along one of the coordinate axes, for example, by the value,. The second exposure is carried out in the absence of the object.

After the corresponding photo processing, the hologram is set on the former place and illuminated by a beam of hours. The hologram reconstructs two sets of point light sources located in the diffuse diffuse plane scattered, displaced relative to each other by the value A.

Light emanating from the corresponding points, for example, A and L, the image of the diffuser 5, enters the lens 8 mounted in front of the photographic system 9. The rays propagating parallel to the optical axis of the system will be collected in the rear focal point 5 of the lens 8. By moving the lens 8 (points S) with respect to the front focal point of the photographic system 9, it is possible to create various interference conditions between the respective beams in the observation plane 13. From the positions of the geometrical optics, To obtain an analytical expression defining in each fixed position of the lens 8 the distance a from its focal plane to the photographic system 9 (lens lUj. This expression looks like:

   -, -,

e D

where l is the radiation wavelength, / 1 and / 2 are the focal lengths of the lens and photographic system, respectively,

D - the displacement of the hologram in its own plane along the coordinate axes X or Y,

e - width of interference

lanes settings. From the formula it follows that if

  /./1-/2/-.Д-0.

This ratio is zero if e 00, e is l / p (2), where p is the angle between the interfering rays. The width of the strip is equal to the circumference when

p and. Under the condition a - / 2, from the photographic system Y, the corresponding Ls come out at a zero angle of interference | C 0. On the plane of the screen 13, a uniformly illuminated field is observed,

corresponding to the setting of the interferometer on an ultra-fine strip.

In case the lens 8 is installed from the photographic system 9 at a distance of a C / 2, then at the output of the system the corresponding L & C will intersect behind the rear focal point of the system at a certain angle. At the same time, interference fringes of finite width (e const) are formed in the observation plane i3. As the value of a decreases, the angle p between the interfering beams decreases. According to (2J decrease; i increases the width of the interference fringes. Therefore, by successive movement of the lens 8 along the optical axis of the system, the holographic interferometer setting and the width of the end bands can be changed. emanating from the respective sources K and A in a certain way. If the lens 8 is set so that point 5 is between the front focal point and the main plane of the lens 10 (), then the interferometer achieves a change in the sign of the phase (angle) of the interfering rays. The latter means that the images of the sources A and A

are in antiphase with respect to their initial position on the diffuser 5. A change in the sign of the phase (angle) of the interfering rays leads to the formation of interferograms of the alternating sign with respect to the gradient of optical inhomogeneity, when the objective 8 is set relative to the photographic system 9 at a distance of c / a a change in the sign of the phase of the corresponding rays occurs. The interferogram recorded under this condition characterizes the initial setting of the interferometer, determined by the direction and magnitude of the displacement of the hologram between the exposures.

Thus, the proposed holographic interferometer allows one to obtain interference patterns that correspond to the setting for an infinite wide band and a band of finite width of various widths and a variable sign of the phase (angle) of the interfering rays. Due to this versatility of the proposed interferometer, the range of adjustment of the interferometer in one experiment significantly increases and the accuracy of interference measurements increases.

Claims (2)

1.Colier R. et al. Optical holography, M., “Mir, 1973, p. 477. 2. Matulka R. D., Collins D. I. Determination of treedimensional densijti fields from holographic interferograms. J, “Appl. Phys., 1971, 42, No. 3, 1109-1119.