10
1 Resonance Methods for Increasing Sensitivity of Interferometry …
and each of them has its own amplitude-phase distribution on the resonator edge
and which differs from the distribution of the rest, then different modes will create
its own independent interference patterns in the hologram plane. In other words, in
those parts of the hologram where each mode interferes itself, there will be a contrast
interference pattern, and in the region of overlap of different modes the interference
pattern will be blurred. Meanwhile, the more modes there are in the radiation, the
faster the contrast of the total interference pattern in the hologram plane is decreasing.
A hologram will reconstruct the wave field only in the part where pattern contrast is
distinct from zero, i.e., within the visibility of interference pattern. Thus, scanning
the hologram by a narrow beam, for example, by the beam of He–Ne laser, in the
reconstructed image of the diffuse screen only those parts of the laser edge will be
seen, which during the hologram recording have been radiating this mode. Hereof,
by reconstructing different hologram parts, it is possible to identify the number of
modes generated by the laser. In this regard, it is important to note that for obtaining
the image of the mode field full structure, the diffuse screen is chosen in such a
way that the radiation from the whole points of the diffuse screen reaches each
part of holograms. The variants of this method are presented below. They enable to
determine quantitatively the radiation spatial coherence degree: just holographic and
integral methods [42–44, 69]. Holographic procedure is convenient to be used as it
enables to get a peculiar spatial coherence function image for one pulse that is very
important during the studies of laser sources spatial coherence function, the radiation
of which has unstable mode structure.
1.2.1 Holographic Step and Integral Methods of Radiation
Spatial Coherence Measurement
In some cases, edge intensity distribution of laser sources, which operate in a singlemode regime as well as in a multimode regime, is quite heterogeneous. In this case,
it is almost impossible to get the linear recording of the whole hologram surface.
Therefore, the proposed method [73] for the quantitative measurement of spatial
coherence full function cannot be used in this way. The only assumption in the
proposed method [42], which can be named as a “step method,” is quasi-linearity of
the hologram recording.
It can be explained in the following way. Let the change of amplitude ratio of
hologram transmission coefficient conditioned by the exposure interference part δH
be linearly connected with δH:
T (H + δ H ) = T (H ) + f (δ H ),
(1.11)
where H = It is the average exposure; δH = δIt is the exposure version, which is
provided by the intensity interference part δI, and f =
dT
dH
is the linear amplitude
transmission coefficient. The value of the ratio f depends on the reference beam
1 Resonance Methods for Increasing Sensitivity of Interferometry …
and each of them has its own amplitude-phase distribution on the resonator edge
and which differs from the distribution of the rest, then different modes will create
its own independent interference patterns in the hologram plane. In other words, in
those parts of the hologram where each mode interferes itself, there will be a contrast
interference pattern, and in the region of overlap of different modes the interference
pattern will be blurred. Meanwhile, the more modes there are in the radiation, the
faster the contrast of the total interference pattern in the hologram plane is decreasing.
A hologram will reconstruct the wave field only in the part where pattern contrast is
distinct from zero, i.e., within the visibility of interference pattern. Thus, scanning
the hologram by a narrow beam, for example, by the beam of He–Ne laser, in the
reconstructed image of the diffuse screen only those parts of the laser edge will be
seen, which during the hologram recording have been radiating this mode. Hereof,
by reconstructing different hologram parts, it is possible to identify the number of
modes generated by the laser. In this regard, it is important to note that for obtaining
the image of the mode field full structure, the diffuse screen is chosen in such a
way that the radiation from the whole points of the diffuse screen reaches each
part of holograms. The variants of this method are presented below. They enable to
determine quantitatively the radiation spatial coherence degree: just holographic and
integral methods [42–44, 69]. Holographic procedure is convenient to be used as it
enables to get a peculiar spatial coherence function image for one pulse that is very
important during the studies of laser sources spatial coherence function, the radiation
of which has unstable mode structure.
1.2.1 Holographic Step and Integral Methods of Radiation
Spatial Coherence Measurement
In some cases, edge intensity distribution of laser sources, which operate in a singlemode regime as well as in a multimode regime, is quite heterogeneous. In this case,
it is almost impossible to get the linear recording of the whole hologram surface.
Therefore, the proposed method [73] for the quantitative measurement of spatial
coherence full function cannot be used in this way. The only assumption in the
proposed method [42], which can be named as a “step method,” is quasi-linearity of
the hologram recording.
It can be explained in the following way. Let the change of amplitude ratio of
hologram transmission coefficient conditioned by the exposure interference part δH
be linearly connected with δH:
T (H + δ H ) = T (H ) + f (δ H ),
(1.11)
where H = It is the average exposure; δH = δIt is the exposure version, which is
provided by the intensity interference part δI, and f =
dT
dH
is the linear amplitude
transmission coefficient. The value of the ratio f depends on the reference beam