6
1 Resonance Methods for Increasing Sensitivity of Interferometry …
radiation coherence length of 36 mm and allows using it for the holography and resonance interferometry purposes [41, 47]. Moreover, in this case, with the Rhodamine
6G concentration corresponding to the absorption constant of 12 cm
−1 for λ =
347.2 nm under the change of pumping energy from 0.03 to 0.05 J single-frequency
or two-frequency generation mode was produced (Fig. 1.2c, d). The spectrogram
(Fig. 1.2c) also shows radiation frequency tuning with the Fabry–Perot interferometer slope (four generation pulses with the interferometer sequential slope). Meanwhile, grating slope does not change. Wavelength-tuned interval in the case of singlefrequency mode covered spectral region of 25 nm that was achieved by simultaneous
slope of the grating and interferometer. In this case, the generation energy peak
was 0.002 J. By sloping Fabry–Perot interferometer without changing the diffraction grating position, it was possible to tune laser frequency as well as to change
the spectral intensity relations between the generation lines. The interferometer base
increase resulted in the decrease of the interval between the generation lines.
By doubling the dye concentration in the solution and increasing pumping energy
to 0.065 J, simultaneous generation mode of four wavelengths with 1.8 nm path was
produced. Meanwhile, the width of each component was 0.03 nm (see Fig. 1.2e).
Simultaneous generation of several wavelengths with equidistant path between them
is of the utmost interest in the area of dye lasers practical use, in particular, in
holographic interferometry to outline the relief of the time-dependent surfaces. At
the same time, it is necessary to admit that if the aspects of radiation frequency
selection (the control of time coherence of pulsed dye lasers radiation) have been
studied quite well, then spatial coherence of dye laser radiation with laser pumping
has not been studied. It is connected with the fact that the challenge of the laser
source practical use is the absence of measuring and controlling methods of one
of the most important characteristics of their radiation—spatial coherence. And the
most difficult thing is to study spatial coherence of the laser radiation with unstable
mode structure. The problem has appeared how to measure spatial coherence of the
pulsed Rhodamine 6G laser radiation with the laser pumping. In 1974, L. V. Tanin
published the studies on this laser radiation coherence characteristics using his own
methods in order to find resources of laser application for solving holography tasks
[39, 55]. This will be in detail discussed below.
1.2 Spatial Coherence of Rhodamine 6G Laser Radiation
with Laser Pumping and Its Measuring Methods
In the holographic experimental practice, it is often necessary to know a quantitative variable, which describes interference pattern contrast produced during the
use of radiation sources under study. As such, a radiation characteristic mutualcoherence function is taken. This function describes the correlation between radiation
electrostatic field amplitude in arbitrary points of space r 1 and r 2 and time t and t +
τ [56]:
1 Resonance Methods for Increasing Sensitivity of Interferometry …
radiation coherence length of 36 mm and allows using it for the holography and resonance interferometry purposes [41, 47]. Moreover, in this case, with the Rhodamine
6G concentration corresponding to the absorption constant of 12 cm
−1 for λ =
347.2 nm under the change of pumping energy from 0.03 to 0.05 J single-frequency
or two-frequency generation mode was produced (Fig. 1.2c, d). The spectrogram
(Fig. 1.2c) also shows radiation frequency tuning with the Fabry–Perot interferometer slope (four generation pulses with the interferometer sequential slope). Meanwhile, grating slope does not change. Wavelength-tuned interval in the case of singlefrequency mode covered spectral region of 25 nm that was achieved by simultaneous
slope of the grating and interferometer. In this case, the generation energy peak
was 0.002 J. By sloping Fabry–Perot interferometer without changing the diffraction grating position, it was possible to tune laser frequency as well as to change
the spectral intensity relations between the generation lines. The interferometer base
increase resulted in the decrease of the interval between the generation lines.
By doubling the dye concentration in the solution and increasing pumping energy
to 0.065 J, simultaneous generation mode of four wavelengths with 1.8 nm path was
produced. Meanwhile, the width of each component was 0.03 nm (see Fig. 1.2e).
Simultaneous generation of several wavelengths with equidistant path between them
is of the utmost interest in the area of dye lasers practical use, in particular, in
holographic interferometry to outline the relief of the time-dependent surfaces. At
the same time, it is necessary to admit that if the aspects of radiation frequency
selection (the control of time coherence of pulsed dye lasers radiation) have been
studied quite well, then spatial coherence of dye laser radiation with laser pumping
has not been studied. It is connected with the fact that the challenge of the laser
source practical use is the absence of measuring and controlling methods of one
of the most important characteristics of their radiation—spatial coherence. And the
most difficult thing is to study spatial coherence of the laser radiation with unstable
mode structure. The problem has appeared how to measure spatial coherence of the
pulsed Rhodamine 6G laser radiation with the laser pumping. In 1974, L. V. Tanin
published the studies on this laser radiation coherence characteristics using his own
methods in order to find resources of laser application for solving holography tasks
[39, 55]. This will be in detail discussed below.
1.2 Spatial Coherence of Rhodamine 6G Laser Radiation
with Laser Pumping and Its Measuring Methods
In the holographic experimental practice, it is often necessary to know a quantitative variable, which describes interference pattern contrast produced during the
use of radiation sources under study. As such, a radiation characteristic mutualcoherence function is taken. This function describes the correlation between radiation
electrostatic field amplitude in arbitrary points of space r 1 and r 2 and time t and t +
τ [56]: