3.3 Laser-Holographic Complex …
263
line of mirrors for equalizing waves of reference and object beams. The mirror 5 has
a two-sided reflecting covering (6, 9). After the beam splitter 4 the laser radiation
gets onto the mirror 5, reflects from it and goes along the path 5–10 coinciding in
direction with arrows in Fig. 3.44. The beam splitter 10 directs half of the radiation
to the expander of the reference beam 14, after which the light is reflected from the
mirror 16 and gets to the hologram 18. The radiation passed through the beam splitter
is reflected by the mirror 11 mounted on the piezoceramics for phase shift formations,
then it passes through the expander 15, is reflected by the mirror 17 and gets onto
the hologram 18. The shutters 12, 13 work in such a way that during interferogram
recording only one of the channels of the reference beams is opened by the ruby
laser radiation. The first pulse goes along the path 10–11–13–15–17–18. The shutter
12 is closed. After the first pulse passed the shutter 13 closes, the shutter 12 opens
and the radiation goes along the path 10–12–14–16–18. Thus, the first hologram on
a double-exposure interferogram is recorded with the reference beam of the mirror
17, and the second one—with the reference beam from the mirror 16. While reading
the interferogram with radiation of the He–Ne laser 2, which goes along the path
2–4–5–6–7–8–9–10 and further, both shutters open and two reference beams from
the mirrors reconstruct the interferogram of the object with “living” fringes. Further
processing of the interferogram is conducted according to the method described in
Sect. 3.3.6.
Intensity is measured in each point of the image, and I 1 (x, y) for the moment
when the mirror 11 is in position 0, I 2 corresponds to the mirror 11 in position B(+δ),
I 3 (x, y)—to the mirror in position A(−δ). Further, the phase distribution is calculated
according to (3.79).
The conducted experiments proved functionality of the scheme. In the image, the
“living” interference fringes were observed, which displaced during the shift of the
mirror 11. The scheme offered in Fig. 3.44 is much easier, cheaper and more reliable
in work than the scheme in Fig. 3.42.
Moreover, if there is no need for accurate calculation of shifts and the quantitative
estimation of the fringe image character is enough as, for example, in a case of
non-destructive testing, then after removing the beam splitter 10, we will get the
scheme of a classical interferometer with one reference beam 11, 13, 15, 17, 18.
A scheme of compensation node of path difference between the reference and the
object beams was developed. It is based on using the mirror optical loop (Fig. 3.38).
There was shown the possibility of determining not only the quantities, but also
relative shift directions of points on the surface under study while using the scheme
of hologram recording and reconstruction with two spatially separated reference
beams. Thus, the conducted work gave the possibility to optimize the choice of
methods of the developed equipment, i.e., using two reference beams the phase shift
for measurements of the phase with the accuracy, which corresponds to analogs
of interference holographic systems, and to demonstrate reading and processing of
images having eliminated the impact of dispersion. The study of the conditions of
recording the focused images on photothermoplastic materials gave the possibility
to improve the principle optical scheme of this device.
263
line of mirrors for equalizing waves of reference and object beams. The mirror 5 has
a two-sided reflecting covering (6, 9). After the beam splitter 4 the laser radiation
gets onto the mirror 5, reflects from it and goes along the path 5–10 coinciding in
direction with arrows in Fig. 3.44. The beam splitter 10 directs half of the radiation
to the expander of the reference beam 14, after which the light is reflected from the
mirror 16 and gets to the hologram 18. The radiation passed through the beam splitter
is reflected by the mirror 11 mounted on the piezoceramics for phase shift formations,
then it passes through the expander 15, is reflected by the mirror 17 and gets onto
the hologram 18. The shutters 12, 13 work in such a way that during interferogram
recording only one of the channels of the reference beams is opened by the ruby
laser radiation. The first pulse goes along the path 10–11–13–15–17–18. The shutter
12 is closed. After the first pulse passed the shutter 13 closes, the shutter 12 opens
and the radiation goes along the path 10–12–14–16–18. Thus, the first hologram on
a double-exposure interferogram is recorded with the reference beam of the mirror
17, and the second one—with the reference beam from the mirror 16. While reading
the interferogram with radiation of the He–Ne laser 2, which goes along the path
2–4–5–6–7–8–9–10 and further, both shutters open and two reference beams from
the mirrors reconstruct the interferogram of the object with “living” fringes. Further
processing of the interferogram is conducted according to the method described in
Sect. 3.3.6.
Intensity is measured in each point of the image, and I 1 (x, y) for the moment
when the mirror 11 is in position 0, I 2 corresponds to the mirror 11 in position B(+δ),
I 3 (x, y)—to the mirror in position A(−δ). Further, the phase distribution is calculated
according to (3.79).
The conducted experiments proved functionality of the scheme. In the image, the
“living” interference fringes were observed, which displaced during the shift of the
mirror 11. The scheme offered in Fig. 3.44 is much easier, cheaper and more reliable
in work than the scheme in Fig. 3.42.
Moreover, if there is no need for accurate calculation of shifts and the quantitative
estimation of the fringe image character is enough as, for example, in a case of
non-destructive testing, then after removing the beam splitter 10, we will get the
scheme of a classical interferometer with one reference beam 11, 13, 15, 17, 18.
A scheme of compensation node of path difference between the reference and the
object beams was developed. It is based on using the mirror optical loop (Fig. 3.38).
There was shown the possibility of determining not only the quantities, but also
relative shift directions of points on the surface under study while using the scheme
of hologram recording and reconstruction with two spatially separated reference
beams. Thus, the conducted work gave the possibility to optimize the choice of
methods of the developed equipment, i.e., using two reference beams the phase shift
for measurements of the phase with the accuracy, which corresponds to analogs
of interference holographic systems, and to demonstrate reading and processing of
images having eliminated the impact of dispersion. The study of the conditions of
recording the focused images on photothermoplastic materials gave the possibility
to improve the principle optical scheme of this device.