3.1 The Holographic Method of Contouring of Static …
207
3.1.6 Multi-angle Method of Surface Relief Contouring
The increase of accuracy in holographic contouring can be reached in two ways: due
to decrease of the depth interval between the bands or due to narrowing of interference
maxima. In the latter case, the location of contours on the surface of the object under
study can be more accurately calculated.
As it was previously stipulated, the multi-long-wave method [22, 28–31] and
the multi-immersion medium [96] method are applied for obtaining contour maps
with narrower interference lines. But both interference methods are rather difficult
to implement in experiments, and that is why there was a task to develop an easier
and flexible method for obtaining narrow interference contours. As it is known the
suggested in the work [68, 69] contouring method with two spaced sources is the
simplest of the holographic methods of surface-shape detection nowadays. In the
work [88], it is shown that the depth interval between the bands on the reconstructed
image can be decreased at changing the observation angle. This makes it possible
to conduct a detailed study of the shape of the object. Moreover, in the two-source
method, the depth interval can be reduced through the increase of the incidence angle
between two waves illuminating the object under study. But the side illumination
relative to the observer leads to darkening of almost half of the studied surface. To
eliminate this disadvantage, several methods are suggested [88, 97, 98]. Two-sided
lateral illumination of the object and image filtration on the reconstruction stage are
used during holographic moire contouring [97]. In case when the object is registered
in colliding beams under surface illumination from the side of the observer, the
number of shaded areas significantly decreases [88].
Based on the two-source method with registration in colliding beams, a technique
of contour maps forming with narrower interference fringes is suggested. The object
is illuminated with a collimated beam through the hologram, and the light reflected
from the object forms an object beam. The exposed hologram is m-fold registered and
either the object-hologram (G) system or the illuminating beam turns through angle
α between the exposures. Hologram recording can also be implemented under the
object illumination simultaneously by m beams evenly spaced along the angle. The
scheme of the experiment is presented in Fig. 3.9. As a result of the interference of
m waves with amplitudes, which are proportional to
a m = exp
i
2π z
λ
cos α m −
1
cos β
+ tgβ sin α m
,
(3.35)
where λ is the wavelength; z is the distance between the hologram and the object; α m =
α+mα is the inclination angle of mth illuminating wave; and β is the observation
angle.
The object crosses the system of interference fringes characterizing by the
intensity distribution.
207
3.1.6 Multi-angle Method of Surface Relief Contouring
The increase of accuracy in holographic contouring can be reached in two ways: due
to decrease of the depth interval between the bands or due to narrowing of interference
maxima. In the latter case, the location of contours on the surface of the object under
study can be more accurately calculated.
As it was previously stipulated, the multi-long-wave method [22, 28–31] and
the multi-immersion medium [96] method are applied for obtaining contour maps
with narrower interference lines. But both interference methods are rather difficult
to implement in experiments, and that is why there was a task to develop an easier
and flexible method for obtaining narrow interference contours. As it is known the
suggested in the work [68, 69] contouring method with two spaced sources is the
simplest of the holographic methods of surface-shape detection nowadays. In the
work [88], it is shown that the depth interval between the bands on the reconstructed
image can be decreased at changing the observation angle. This makes it possible
to conduct a detailed study of the shape of the object. Moreover, in the two-source
method, the depth interval can be reduced through the increase of the incidence angle
between two waves illuminating the object under study. But the side illumination
relative to the observer leads to darkening of almost half of the studied surface. To
eliminate this disadvantage, several methods are suggested [88, 97, 98]. Two-sided
lateral illumination of the object and image filtration on the reconstruction stage are
used during holographic moire contouring [97]. In case when the object is registered
in colliding beams under surface illumination from the side of the observer, the
number of shaded areas significantly decreases [88].
Based on the two-source method with registration in colliding beams, a technique
of contour maps forming with narrower interference fringes is suggested. The object
is illuminated with a collimated beam through the hologram, and the light reflected
from the object forms an object beam. The exposed hologram is m-fold registered and
either the object-hologram (G) system or the illuminating beam turns through angle
α between the exposures. Hologram recording can also be implemented under the
object illumination simultaneously by m beams evenly spaced along the angle. The
scheme of the experiment is presented in Fig. 3.9. As a result of the interference of
m waves with amplitudes, which are proportional to
a m = exp
i
2π z
λ
cos α m −
1
cos β
+ tgβ sin α m
,
(3.35)
where λ is the wavelength; z is the distance between the hologram and the object; α m =
α+mα is the inclination angle of mth illuminating wave; and β is the observation
angle.
The object crosses the system of interference fringes characterizing by the
intensity distribution.