348
4 Speckle-Optical Methods and Devices for Studying …
It is suggested that a lens raster is used instead of one lens, which conducts Fourier
transformation, to determine the shift of separate areas of the surface. And the relative
aperture of a separate lens of the raster must be not less that the lens aperture, which
creates the image of the surface on the hologram.
A registering device (e.g., a TV camera, a photodiode array) conjugated with a
microcomputer or a memory block records Fourier transformation with the frequency
ν and the obtained information is stored or processed in real time. To get shift of
some area from time moment t 1 to moment t 2 , it is enough to calculate the value
S =
t 2
t 1
υ(t)dt
(4.77)
This process gives the possibility to follow the deformations of strongly changing
surfaces, including structure-varying surfaces.
The Yung’s fringes must register in the focal plane with a TV camera, which is
conjugated with an automated system of interferogram processing, due to which the
period and direction of fringes with the frequency of 2 Hz can be estimated. In its
turn, this will give the possibility to measure the velocity of different areas of the
plate and then to determine shift of these areas in different moments of time through
microcomputer integration.
Also the described method can be implemented in the scheme presented in
Fig. 4.19b. The laser Ls generates the first radiation pulse, which is divided on a mirror
into an object and a reference beam. Passing through the optical shutter, the object
beam incidents on the moving or deformed object P. The reflected from the object
light passes through the objective L 1 , which forms an image of the object covered with
a speckle-structure on the dynamic hologram DH. The lasers Ls 1 and Ls 2 create radiation pulses after time τ. During this time, the electro optical shutter does not allow
radiation with wavelength λ 2 passing onto the object. The object was illuminated
with radiation with the wavelength λ 2 , and the dynamic hologram is reconstructed
with radiation with the wavelength λ 1 . The lens and the lens raster conduct Fourier
transform of the speckle-structure formed by the object and reconstructed from the
hologram. In this case, the registering system should provide heterodyne detection
of Yung’s fringes. It is enough for this to use three photodiodes for each element of
the raster as the input of the registering device.
The third scheme of the device for the probable implementation of this method is
presented in Fig. 4.19c. During the first pulse, the radiation passes through the splitter
Bs where it is divided into an object and reference beams. Then the object beam goes
through electrooptical element E, which does not change its polarization during the
first pulse, incidents on the object under study, passes through the image-forming
system L1 and falls onto the cell DH where the dynamic hologram is recorded. During
the second pulse, the electrooptical element turns the polarization plane of the object
beam at 90° and thus the dynamic hologram is not recorded during the second pulse.
4 Speckle-Optical Methods and Devices for Studying …
It is suggested that a lens raster is used instead of one lens, which conducts Fourier
transformation, to determine the shift of separate areas of the surface. And the relative
aperture of a separate lens of the raster must be not less that the lens aperture, which
creates the image of the surface on the hologram.
A registering device (e.g., a TV camera, a photodiode array) conjugated with a
microcomputer or a memory block records Fourier transformation with the frequency
ν and the obtained information is stored or processed in real time. To get shift of
some area from time moment t 1 to moment t 2 , it is enough to calculate the value
S =
t 2
t 1
υ(t)dt
(4.77)
This process gives the possibility to follow the deformations of strongly changing
surfaces, including structure-varying surfaces.
The Yung’s fringes must register in the focal plane with a TV camera, which is
conjugated with an automated system of interferogram processing, due to which the
period and direction of fringes with the frequency of 2 Hz can be estimated. In its
turn, this will give the possibility to measure the velocity of different areas of the
plate and then to determine shift of these areas in different moments of time through
microcomputer integration.
Also the described method can be implemented in the scheme presented in
Fig. 4.19b. The laser Ls generates the first radiation pulse, which is divided on a mirror
into an object and a reference beam. Passing through the optical shutter, the object
beam incidents on the moving or deformed object P. The reflected from the object
light passes through the objective L 1 , which forms an image of the object covered with
a speckle-structure on the dynamic hologram DH. The lasers Ls 1 and Ls 2 create radiation pulses after time τ. During this time, the electro optical shutter does not allow
radiation with wavelength λ 2 passing onto the object. The object was illuminated
with radiation with the wavelength λ 2 , and the dynamic hologram is reconstructed
with radiation with the wavelength λ 1 . The lens and the lens raster conduct Fourier
transform of the speckle-structure formed by the object and reconstructed from the
hologram. In this case, the registering system should provide heterodyne detection
of Yung’s fringes. It is enough for this to use three photodiodes for each element of
the raster as the input of the registering device.
The third scheme of the device for the probable implementation of this method is
presented in Fig. 4.19c. During the first pulse, the radiation passes through the splitter
Bs where it is divided into an object and reference beams. Then the object beam goes
through electrooptical element E, which does not change its polarization during the
first pulse, incidents on the object under study, passes through the image-forming
system L1 and falls onto the cell DH where the dynamic hologram is recorded. During
the second pulse, the electrooptical element turns the polarization plane of the object
beam at 90° and thus the dynamic hologram is not recorded during the second pulse.