SU1485190A1 - Shadow apparatus - Google Patents

Description

The invention relates to the field of optical instrumentation and can be used in various fields of experimental physics in the study of transparent inhomogeneities. The shadow device contains a laser 1 installed in series, a collimator including, for example, an expansion lens 2, a swiveling mirror 3, a spherical mirror 4 and a meniscus 5, a receiving optical system consisting of a focusing lens including a meniscus 6, a spherical mirror 7 and a swiveling mirror 8, as well as from a collimating lens 9, a visualizing filter made in the form of two transmitting volume holograms 10, 11 and a lens system 12, 13, as well as a photographic recorder 14. Holograms 10, 11 are registered in collimated

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The hologram 10 is optically conjugated with the focusing and collimating lenses with the object under study 15 and set at an angle of 5 Bragg to the optical axis of the collimating lens 9. The lens system 12, 13 and the hologram 11 are installed in the first order diffraction of the hologram 10. The hologram 11 is installed with the possibility of rotation in the plane ιθ of the bone inclination of the hologram 10, and the photo recorder is located in the first order of the diffraction of the hologram II and is optically conjugated

with the object under study 15. The radiation diffracts at this object at different angles, and the diffraction efficiency of holograms 10, 11 and, consequently, their transmission depends on the magnitude of these angles, which ensures the visualization of phase inhomogeneities. Due to the work of holograms 10, 11 in wide parallel beams, the quality of shadow patterns increases, and due to the fact that the transverse oscillations of the holograms do not change the intensity in the reconstructed beam, the susceptibility to vibrations is reduced. 1 il.

The invention relates to optical instrumentation and can be used in various fields of experimental physics in the study of transparent inhomogeneities. five

The purpose of the invention is to improve the quality of shadow paintings while reducing susceptibility to vibrations.

The drawing shows the optical scheme of the device.

The shadow device contains a laser 1 installed in series, a collimator including, for example, an expansion lens 2, a turning mirror 3, a spherical mirror 4 and a meniscus 5, a receiving optical system consisting of a focusing lens, including a meniscus 6, a spherical mirror 7 and a swivel mirror 8, as well as from a collimating lens 9, an imaging filter made in the form of two transmissive volume _n holograms 10 and 11 and a lens system 12 and 13, as well as a photographic recorder 14. The holograms 10 and 11 are recorded in collimated The hologram 10 is optically conjugated with focusing and colliding lenses with the object under study 15 and mounted at a Bragg angle to the optical axis of the collimating lens 9. The lens system 12 and 13 and the hologram 11 are set to the first diffraction order of the hologram 10. The hologram 11 is installed 30 rotatably in the plane of inclination of the hologram 10, and the photo recorder is located in the first diffraction order of the hologram 11 and is optically conjugated with the object under study 15.

The shadow device works as follows.

The beam of light from laser 1 expands in the collimator and shines through the object under study 15, which is usually placed between the collimator and the receiving part. In the near part, focusing is performed.

wide collimated beam, and lens 9 builds the image of the investigated heterogeneity. The beam collimated by lens 9 diffracts on the hologram 10 and, having passed the lens system 12 and 13, again diffracts on the hologram 11. The photographic recorder 14 selects the diffracted first-order diffraction wave and records the shadow pattern of the object under study. For the visualization of inhomogeneities, a system of two holograms 10 and 11 is used. Each hologram is recorded when two collimated beams interfere with a sufficiently large angle between the beams and has a certain selectivity to the direction of propagation of the restoring beam. For such a hologram, the value δο characterizing the angular deviation of the reducing beam from the Bragg angle Θο, at which the diffraction efficiency of the hologram becomes zero, is determined by the expression

x _ ^{3λ 0} ^ ππΓδηΘο '

where λ is the wavelength of the radiation used to record the hologram;

n is the average value of the index of breakdown of the photoemulsion;

T is the emulsion thickness.

Diffraction efficiency curve

The holograms smoothly change from the maximum when the beam is incident on the hologram at the Bragg angle о o to zero, if the angle of incidence of the restoring beam differs from the Bragg angle by the amount bo. Since the beam incident on the hologram 10 contains rays deflected by the object under study 15 and, therefore, the incidence angles of which differ from the Bragg angle, the diffraction efficiency of the hologram 10 for these rays differs from the maximum one more significant the greater the angle of deflection of the rays by the object. Thus, the volume hologram installed in the image plane

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impressions allows visualization of the investigated heterogeneity and is a filter of spatial frequencies. In this case, filtering is carried out in the image plane in a wide beam, which makes it possible to exclude coherent diffraction noise.

We will calculate the required value of T when the working field diameters are ~ 20 mm and the registration field is 20 mm. In practical studies, the angles of deflection of light rays by objects are usually εο — 10 ^- - ^10-5 rad. In the field of the visualizing hologram (the registration area), the beam is compressed, and, therefore, the deflection angles increase and reach values of ε>. = 10 ^-2 ^ 10 ^-4 happy. From the above relation for bb at λ = 0 6328 μm, n = 1.52 (gelatin), Θο = 3Ο ° and bo == 1О ^-2, it follows that G ≈ 40 μm. Such a thickness of the emulsion is provided, for example, in two combined photographic plates of the LOI-2 or PE-2 type. The value of b _{0 is} reduced by special irrigation of bichromated gelatin to a thickness of T ~ 500 μm, using Reoxane photosensitive materials, etc. In this example, the diffraction efficiency of the hologram 10 for rays whose deviation from the Bragg angle is within ε _Γ = = 0 -10 ^-2 glad, changes from maximum to zero, and for rays, the angular deviations of which exceed ε _Γ = 10 ^-2 rad, is equal to zero.

The above reasoning is also valid for a hologram 11. Holograms 10 and 11 can be registered and processed under the same conditions. When installing the hologram 11 at the Bragg angle to the beam reconstructed from hologram 10, the diffraction efficiency curves of the two holograms coincide and the angular selectivity of the system of two holograms corresponds to the parameter for one hologram. Rotation of the hologram 11 at a certain angle leads to a shift of the diffraction efficiency curve of this hologram relative to the diffraction efficiency curve of the hologram 10, i.e., to the formation of the overlap zone of the two curves. The interval of angles corresponding to the formed overlap zone can be much smaller than bo. Thus, the interval of visualization of the angles of deflection of the rays in the inhomogeneity, which is provided by the filter consisting of two holograms 10 and 11, can be made arbitrarily small, and the sensitivity of the device is quite high. It should be noted that a significant overlap of the diffraction efficiency profiles of holograms reduces the measurement range. Interval of visualized angles

5 (refractive index gradients) depends on the angle of rotation of the hologram holder 11. Thus, it is possible to visualize different areas of the object and control the sensitivity of measurements, and

Ιθ of quantitative measurements is associated with obtaining a calibration dependence of the radiation intensity in the photographic recorder on the angle of rotation of the hologram 11. The use of holograms as imaging filters does not limit the shape of the source

15 light and eliminates diffraction noise when using coherent radiation. In addition, the proposed device eliminates the influence of vibrations, since the transverse oscillations of the holograms do not change the intensity in the reconstructed beam, for which the diameter of the hologram is sufficient to choose larger than the diameter of the beam. The use of holograms to visualize inhomogeneities in a shadow instrument at the same time provides an additional advantage, which consists in the possibility of correcting the aberrations of the optical system of a shadow instrument.

Claims (1)

Claim A shadow device containing a laser, a collimator and a receiving optical system installed in series, including a focusing lens, an imaging filter and a photographic recorder optically coupled to the object under investigation, characterized in that 35 of the quality of shadow patterns while reducing the susceptibility to vibrations, a collimating lens is inserted into it, installed behind the focusing lens, and the imaging filter is made in the form of two 4θ transmissive volume holograms recorded in collimated beams and a system of lenses that optically match the holograms with each other, the first hologram being optically coupled with a focusing and collimating lenses with <5 the object being tracked and set at the Bragg angle to the optical axis of the collimating objective, the system of conjugating lenses and the second hologram is set in the first diffraction order of the first hologram, the second hologram is installed with the possibility of rotation in the plane of inclination of the first hologram, and the photoregulation trattoria located in the first order of diffraction of the second hologram.