218
3 Holographic Interferometry for Studying …
Main directions of the crystal phase plates λ/2 are oriented at the angles of 0 and
90° to the direction of oscillation of linearly polarized laser beam, and the second
reference beam is overlapped. Then, the optically neutral medium was changed for
an optically active one in the chamber 17, and the second hologram was recorded on
the same photoplate. During the second exposure, the hologram was recorded with
the help of the reference beam formed by the mirror 8, and the first reference beam
was overlapped. The plate 7 was placed diagonally.
During the reconstruction, the holographic plate 11 was illuminated simultaneously by two reference waves, and the plate 7 was in a diagonal state.
The contoured map of the surface was observed behind the diagonally situated
crystal phase plate 14 (λ/4) and the polarizer 15; in the image plane formed by the
telescopic system 10, 13, 14, the contoured map was visually observed with the
microscope 19. Polarization of the reconstructed waves was turned into one plane
with the analyzer 15. While turning the polarizer 16 clockwise the rings on the
contoured map were subtended to the center, i.e., to more approximate points of the
surface. This shows that the surface is convex. Thus, using this method convexes and
concavities of the surface under study are easy to determine. The principle possibility
of practical realization of this method is experimentally proved (see Fig. 3.19). Due
to the results of the polarization measurements, the surface relief contoured maps in
several sections were formed (Fig. 3.20).
As it follows from the above mentioned the described holographic polarization
method of surface relief study makes it possible to determine not only the height but
also the direction of the relief change, i.e., to distinguish convexes from concavities.
Scanning of the surface under study with contoured lines allows changing the
height of the relief in any point, detecting local defects of the surface and increasing
the accuracy of estimation of the relief height in any analyzed point at the expense
of movement from the linear measurements to the angular one.
Thus, this holographic method of surface contouring based on changing the polarization state of object waves makes it possible to determine the height as well as the
direction of the relief of the surface under study, and to increase the spatial resolution.
3.1.9 Increasing Spatial Resolution of Holographic
Multi-beam Methods of Surface Relief Contouring
It is known that implementation of the multi-beam interference makes it possible to
narrow the interference lines and in such a way to enhance the accuracy of determination of coordinates of lines maxima. Applied to holographic contouring methods, this
leads to the increase of the accuracy of relief detection [28, 103]. For example, in the
work [28], it is suggested to use dye laser generating radiation with different wavelengths for multi-beam topograms forming. In the work [103], the multi-immersion
method is used for the same reason; i.e., the object under study is placed in a chamber
with the immersion medium, and before each hologram registration, the refractive
3 Holographic Interferometry for Studying …
Main directions of the crystal phase plates λ/2 are oriented at the angles of 0 and
90° to the direction of oscillation of linearly polarized laser beam, and the second
reference beam is overlapped. Then, the optically neutral medium was changed for
an optically active one in the chamber 17, and the second hologram was recorded on
the same photoplate. During the second exposure, the hologram was recorded with
the help of the reference beam formed by the mirror 8, and the first reference beam
was overlapped. The plate 7 was placed diagonally.
During the reconstruction, the holographic plate 11 was illuminated simultaneously by two reference waves, and the plate 7 was in a diagonal state.
The contoured map of the surface was observed behind the diagonally situated
crystal phase plate 14 (λ/4) and the polarizer 15; in the image plane formed by the
telescopic system 10, 13, 14, the contoured map was visually observed with the
microscope 19. Polarization of the reconstructed waves was turned into one plane
with the analyzer 15. While turning the polarizer 16 clockwise the rings on the
contoured map were subtended to the center, i.e., to more approximate points of the
surface. This shows that the surface is convex. Thus, using this method convexes and
concavities of the surface under study are easy to determine. The principle possibility
of practical realization of this method is experimentally proved (see Fig. 3.19). Due
to the results of the polarization measurements, the surface relief contoured maps in
several sections were formed (Fig. 3.20).
As it follows from the above mentioned the described holographic polarization
method of surface relief study makes it possible to determine not only the height but
also the direction of the relief change, i.e., to distinguish convexes from concavities.
Scanning of the surface under study with contoured lines allows changing the
height of the relief in any point, detecting local defects of the surface and increasing
the accuracy of estimation of the relief height in any analyzed point at the expense
of movement from the linear measurements to the angular one.
Thus, this holographic method of surface contouring based on changing the polarization state of object waves makes it possible to determine the height as well as the
direction of the relief of the surface under study, and to increase the spatial resolution.
3.1.9 Increasing Spatial Resolution of Holographic
Multi-beam Methods of Surface Relief Contouring
It is known that implementation of the multi-beam interference makes it possible to
narrow the interference lines and in such a way to enhance the accuracy of determination of coordinates of lines maxima. Applied to holographic contouring methods, this
leads to the increase of the accuracy of relief detection [28, 103]. For example, in the
work [28], it is suggested to use dye laser generating radiation with different wavelengths for multi-beam topograms forming. In the work [103], the multi-immersion
method is used for the same reason; i.e., the object under study is placed in a chamber
with the immersion medium, and before each hologram registration, the refractive