3 Holographic Interferometry for Studying …
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interest where it is possible to record surface relief changing in time by regulating the
interval between radiation pulses. In pulse radiation, the contoured maps in sphere
motion are obtained [77]. Real-time contouring was conducted with krypton ion laser
and electro optical crystal with minimal mentioned in literature depth interval equal
to 2.67 μm [78]. The contoured maps of retina were obtained [79], wear of artificial bones was studied, tests of mirrors [80] and aspherical surfaces [81, 82] were
conducted, and reflective index of acrylic rubber was defined [59]. Thus, the analysis of the literature shows that the main advantage of the two-long-wave contouring
method is the possibility to study shape of objects in motion or changing their shape
with time. This advantage comparing to other contouring methods occurs due to laser
equipment improvement and, in particular, development of modes, in which lasers
simultaneously generate several wavelengths.
Almost at the same time with the two-long-wave contouring method the immersion method appeared [70]. This method is double exposed in its essence and is
implemented in the following way. The object under study is placed in the immersion chamber with a flat window. Before the first exposure, the chamber is filled
with liquid or gas with the refractive index n 1 , and before the second exposure with
the refractive index n 2 . After recording the double-exposed hologram contour, bands
were observed on the object surface.
The immersion method was used to obtain contoured maps of a punch for turbine
bucket producing [83], and it was used for the study of wear [84].
It is easy to see that if to produce a cell, transparent window of which has internal
surface with a relief opposite to the relief of the standard, then the layer thickness of
the liquid will characterize the difference relief [85]. The contoured map of the relief
gradient can be obtained if the surface under study moves in the transverse direction
relative to its transparent replica serving as the cell window [86].
Another contouring method is the so-called two sources method [69]. In the holographic version of this method, the hologram is exposed twice by movement of
illuminating source. The depth interval between the bands in this case depends on
changing the object entrance angle. But as while hologram recording side illumination of the object must be used, then its surface appears to be partially black-out. The
solution of this situation can be found in illuminating the object from different sides
[87] or in implementing hologram recording in colliding beams [88]. Along with
this at solution of each particular task, the selection of the method of surface relief
research must be conducted after detailed study of advantages and disadvantages of
these methods, as they nearly differ according to their metrological characteristics
(the depth interval obtained). Moreover, from the analysis of the literature it is seen
that the holographic contouring methods make it possible to solve several types of
tasks: to detect the surface relief, difference of the two reliefs, to examine the surface
relief gradient and the medium refractive index. In all approaches, the assumption
was used that the sequence order of planes cutting the object is known; i.e., the shape
of the object is known to be regular. But for objects with a surface shape, which
is beforehand unknown, with random alternate convexities and concavities or while
comparing shapes of two surfaces such an assumption leads to errors, and that is why
185
interest where it is possible to record surface relief changing in time by regulating the
interval between radiation pulses. In pulse radiation, the contoured maps in sphere
motion are obtained [77]. Real-time contouring was conducted with krypton ion laser
and electro optical crystal with minimal mentioned in literature depth interval equal
to 2.67 μm [78]. The contoured maps of retina were obtained [79], wear of artificial bones was studied, tests of mirrors [80] and aspherical surfaces [81, 82] were
conducted, and reflective index of acrylic rubber was defined [59]. Thus, the analysis of the literature shows that the main advantage of the two-long-wave contouring
method is the possibility to study shape of objects in motion or changing their shape
with time. This advantage comparing to other contouring methods occurs due to laser
equipment improvement and, in particular, development of modes, in which lasers
simultaneously generate several wavelengths.
Almost at the same time with the two-long-wave contouring method the immersion method appeared [70]. This method is double exposed in its essence and is
implemented in the following way. The object under study is placed in the immersion chamber with a flat window. Before the first exposure, the chamber is filled
with liquid or gas with the refractive index n 1 , and before the second exposure with
the refractive index n 2 . After recording the double-exposed hologram contour, bands
were observed on the object surface.
The immersion method was used to obtain contoured maps of a punch for turbine
bucket producing [83], and it was used for the study of wear [84].
It is easy to see that if to produce a cell, transparent window of which has internal
surface with a relief opposite to the relief of the standard, then the layer thickness of
the liquid will characterize the difference relief [85]. The contoured map of the relief
gradient can be obtained if the surface under study moves in the transverse direction
relative to its transparent replica serving as the cell window [86].
Another contouring method is the so-called two sources method [69]. In the holographic version of this method, the hologram is exposed twice by movement of
illuminating source. The depth interval between the bands in this case depends on
changing the object entrance angle. But as while hologram recording side illumination of the object must be used, then its surface appears to be partially black-out. The
solution of this situation can be found in illuminating the object from different sides
[87] or in implementing hologram recording in colliding beams [88]. Along with
this at solution of each particular task, the selection of the method of surface relief
research must be conducted after detailed study of advantages and disadvantages of
these methods, as they nearly differ according to their metrological characteristics
(the depth interval obtained). Moreover, from the analysis of the literature it is seen
that the holographic contouring methods make it possible to solve several types of
tasks: to detect the surface relief, difference of the two reliefs, to examine the surface
relief gradient and the medium refractive index. In all approaches, the assumption
was used that the sequence order of planes cutting the object is known; i.e., the shape
of the object is known to be regular. But for objects with a surface shape, which
is beforehand unknown, with random alternate convexities and concavities or while
comparing shapes of two surfaces such an assumption leads to errors, and that is why