3.1 The Holographic Method of Contouring of Static …
199
1. If the absorption line is rather narrow and the absorption coefficient as the
function of the wavelength changes rather fast, then the absorption on one of the
used wavelengths can be much more intensive than on the other wavelength. Then,
the formula for the contrast is transformed to the following form
(3.23)
From (3.23), it follows that the value of the contrast is determined only by absorption and wavelength corresponding to one of the exposures. Realization of this case
is possible if gaseous media are used as immersion.
2. If the refraction coefficient remains almost constant under changes of wavelengths between the exposures, then κ 1 = κ 2 = κ. Such spectral lines are typical for
liquid media and the refractive index for two wavelengths can also be considered as
identical. Then taking into account (3.20), (3.21) simplifies to
(3.24)
Comparison of (3.23) and (3.24) shows that for the obtained identical values of
the depth distance and the thickness of the absorbing layer, on which the contrast
incidents to the minimal recorded value, gaseous media are preferable as the value of
the absorption index from (3.23) will be significantly lower than the corresponding
value in (3.24). This leads to the fact that the intensity of the interference patter is
greater due to the absolute value if the object is placed in gaseous immersion.
To illustrate the possibilities of the method of absolute surface relief estimation
let us show the normalized intensity distribution (see Fig. 3.5a) and the dependence
of contrast (Fig. 3.5b) on the thickness of the absorbing layer between the object
(Fig. 3.4) and the wall of the chamber calculated for a wedge-shaped surface. The
parameters corresponding to the sodium vapor were chosen for the calculation:
λ 1 = 589.5 nm, x 1 = 0.004, n 1 = 1.004,
λ 2 = 620 nm, x 2 = 5.4 × 10
−7
, n 2 = 1.000,
R 1 a 1 = R 2 a 2 .
To simplify the calculation the intensity distribution of the beams illuminating
the object was supposed to be homogeneous. As to define the absolute surface relief
the contrast of the interference pattern is used, this distribution does not play an
important role.
Thus, application of the absorbing medium in the two-long-wave contouring
method makes it possible to determine the absolute surface relief of the objects
which have an arbitrary shape. Owing to the fact that different sources exist, which
emit two wavelengths simultaneously, this method makes it possible to register the
shape of moving objects or time-changing objects
199
1. If the absorption line is rather narrow and the absorption coefficient as the
function of the wavelength changes rather fast, then the absorption on one of the
used wavelengths can be much more intensive than on the other wavelength. Then,
the formula for the contrast is transformed to the following form
(3.23)
From (3.23), it follows that the value of the contrast is determined only by absorption and wavelength corresponding to one of the exposures. Realization of this case
is possible if gaseous media are used as immersion.
2. If the refraction coefficient remains almost constant under changes of wavelengths between the exposures, then κ 1 = κ 2 = κ. Such spectral lines are typical for
liquid media and the refractive index for two wavelengths can also be considered as
identical. Then taking into account (3.20), (3.21) simplifies to
(3.24)
Comparison of (3.23) and (3.24) shows that for the obtained identical values of
the depth distance and the thickness of the absorbing layer, on which the contrast
incidents to the minimal recorded value, gaseous media are preferable as the value of
the absorption index from (3.23) will be significantly lower than the corresponding
value in (3.24). This leads to the fact that the intensity of the interference patter is
greater due to the absolute value if the object is placed in gaseous immersion.
To illustrate the possibilities of the method of absolute surface relief estimation
let us show the normalized intensity distribution (see Fig. 3.5a) and the dependence
of contrast (Fig. 3.5b) on the thickness of the absorbing layer between the object
(Fig. 3.4) and the wall of the chamber calculated for a wedge-shaped surface. The
parameters corresponding to the sodium vapor were chosen for the calculation:
λ 1 = 589.5 nm, x 1 = 0.004, n 1 = 1.004,
λ 2 = 620 nm, x 2 = 5.4 × 10
−7
, n 2 = 1.000,
R 1 a 1 = R 2 a 2 .
To simplify the calculation the intensity distribution of the beams illuminating
the object was supposed to be homogeneous. As to define the absolute surface relief
the contrast of the interference pattern is used, this distribution does not play an
important role.
Thus, application of the absorbing medium in the two-long-wave contouring
method makes it possible to determine the absolute surface relief of the objects
which have an arbitrary shape. Owing to the fact that different sources exist, which
emit two wavelengths simultaneously, this method makes it possible to register the
shape of moving objects or time-changing objects