3.3 Laser-Holographic Complex …
261
1 is the ruby laser; 2 is the beam splitter; 3 is the illuminating lens (negative); 4,
5 are the flat mirrors; 6 is the device for reference beams separating; 7, 7
are the
polarizers; 8 is the piezoelectric flat mirror; 9 is the device of frequency shift; 10,
12 are the telescopic systems; 11 is the device for input of phase shift; 13 is the
reversible carrier; 14 is the optical scheme for interferogram formation; 15 is the
registration system; 16 is the He–Ne laser; 17 is the λ/4 plate; 18 is the device for
electronic processing of signal and input them into computer; 19 is the computer; 20
is the display; 21 is the λ/2 plate.
Holograms are recorded with a pulse ruby laser. Spatial separation of reference
beams is conducted with the device 6. The λ/2 plate 21 and λ/4 plate 17 serve for
matching reference beam polarizations if KDP crystal with a doubly refracting prism
(or with two crossed polarizers) is used as the device 6.
This scheme provides possibility to implement the method of detecting relative
quantities, speeds and shift directions. For this purpose, the device of frequency
shift is inserted into the reference beams. This device can be in a form of a rotating
diffractive grating and a device for inputting the set phase shift 11, in particular, an
optical compensator. The piezoceramic oscillating mirror 8 can be used instead of the
grating 9. Both a reversible thermoplastic carrier and high-resolution photographic
plates can be used as the registering medium. In a case with the plates, the size of the
holograms can be rather big—30 × 40 cm
2 , and that is why observations from three
directions can be conducted and the spatial shift vector can be determined. In this
case, the system of expressions like (3.62) is composed and solved. For recording
and reconstructing such a hologram, it is reasonable to use spherical reference waves,
and that is why instead of the telescopic systems 10, 12, it is required to establish
microdiaphragm lenses. It is possible to use one lens, through which both reference
and reconstructing waves will pass at a small angle. Hologram reconstruction is
conducted with the continuous He–Ne laser 16 and the radiation should be spread
from it along the same paths as from it 1. The λ/4 crystal plate 17 is necessary for
efficient spatial separation of reference beams with the device 6.
The obtained electrical signals are processed with the device 18, digitalized and
inputted using the computer 19. The interference pattern is simultaneously displayed
in real time on the screen 20 for visual observation and control. The computer
processes the obtained data, determines the shift field and displays it in a way convenient for interpretation. It is worth mentioning that as the object is illuminated by the
spherical wave, the illumination direction along the surface of the object changes and
that should be taken into account while determining the shifts according to (3.62).
Using a two-pulse laser gives the possibility to estimate relative shift speed of
points on the surface under study, which are calculated according to formula μ =
0.5 Nλ/t, where t is the quantity of time interval between pulses; N is the number of
interference fringes between the analyzed and the initial points. If the phase method
of hologram processing is used when there is no counting of interference fringes and
shift quantities and the determination is conducted through a change of phase shifts,
the relative shift speeds can be calculated according to formula μ = L z /t where L z is
the longitudinal shift component.
261
1 is the ruby laser; 2 is the beam splitter; 3 is the illuminating lens (negative); 4,
5 are the flat mirrors; 6 is the device for reference beams separating; 7, 7
are the
polarizers; 8 is the piezoelectric flat mirror; 9 is the device of frequency shift; 10,
12 are the telescopic systems; 11 is the device for input of phase shift; 13 is the
reversible carrier; 14 is the optical scheme for interferogram formation; 15 is the
registration system; 16 is the He–Ne laser; 17 is the λ/4 plate; 18 is the device for
electronic processing of signal and input them into computer; 19 is the computer; 20
is the display; 21 is the λ/2 plate.
Holograms are recorded with a pulse ruby laser. Spatial separation of reference
beams is conducted with the device 6. The λ/2 plate 21 and λ/4 plate 17 serve for
matching reference beam polarizations if KDP crystal with a doubly refracting prism
(or with two crossed polarizers) is used as the device 6.
This scheme provides possibility to implement the method of detecting relative
quantities, speeds and shift directions. For this purpose, the device of frequency
shift is inserted into the reference beams. This device can be in a form of a rotating
diffractive grating and a device for inputting the set phase shift 11, in particular, an
optical compensator. The piezoceramic oscillating mirror 8 can be used instead of the
grating 9. Both a reversible thermoplastic carrier and high-resolution photographic
plates can be used as the registering medium. In a case with the plates, the size of the
holograms can be rather big—30 × 40 cm
2 , and that is why observations from three
directions can be conducted and the spatial shift vector can be determined. In this
case, the system of expressions like (3.62) is composed and solved. For recording
and reconstructing such a hologram, it is reasonable to use spherical reference waves,
and that is why instead of the telescopic systems 10, 12, it is required to establish
microdiaphragm lenses. It is possible to use one lens, through which both reference
and reconstructing waves will pass at a small angle. Hologram reconstruction is
conducted with the continuous He–Ne laser 16 and the radiation should be spread
from it along the same paths as from it 1. The λ/4 crystal plate 17 is necessary for
efficient spatial separation of reference beams with the device 6.
The obtained electrical signals are processed with the device 18, digitalized and
inputted using the computer 19. The interference pattern is simultaneously displayed
in real time on the screen 20 for visual observation and control. The computer
processes the obtained data, determines the shift field and displays it in a way convenient for interpretation. It is worth mentioning that as the object is illuminated by the
spherical wave, the illumination direction along the surface of the object changes and
that should be taken into account while determining the shifts according to (3.62).
Using a two-pulse laser gives the possibility to estimate relative shift speed of
points on the surface under study, which are calculated according to formula μ =
0.5 Nλ/t, where t is the quantity of time interval between pulses; N is the number of
interference fringes between the analyzed and the initial points. If the phase method
of hologram processing is used when there is no counting of interference fringes and
shift quantities and the determination is conducted through a change of phase shifts,
the relative shift speeds can be calculated according to formula μ = L z /t where L z is
the longitudinal shift component.