From Phase Conjugate Laser Optics
Institute of Applied Physics, Russian Academy of Science, 603950 Nizhny Novgorod, Russia


Self-pumped phase conjugation (SPPC) of a laser beam can be accomplished by
joint stimulated scattering of the self-intersecting optical beam in a nonlinear layer
with a feedback loop. One of the most promising effects for the SPPC is stimulated
scattering of Rayleigh type. It is well known that the stimulated Rayleigh scatterings
(SRSs) can be caused by different origin of light-induced refractive index changes,
such as thermal heating in absorbing media, molecule reorientation under electric
field of the optical wave, photochromic effect, and so on. The SRS effects are easily
observed in different media for a wide variety of optical wavelengths. For example,
stimulated thermal scattering caused by the thermally induced nonlinearity was
realized in gases, liquids, and solid states for optical beams with wavelengths
ranging from UV to middle IR [1–3]. However, the increment of backward SRS is
typically quite small due to fast relaxation of the small-period scattering grating.
Therefore, a simple scheme of the backward Rayleigh-type scattering is scarcely
applicable for the phase conjugation. On the other hand, the strong increment of
near-forward SRS provides another attractive possibility for SPPC of laser beams
with long pulse duration. The SPPC can be caused by joint near-forward SRS of two
intersecting optical waves, when one strong wave, E2, is formed from another wave,
E1, after one round trip through a feedback loop (Fig. 10.1). The geometry is similar
to that for the SPPC in photorefractive media [4]. The principles of the SPPC by
joint stimulated scattering will be discussed in more detail in Sections 10.2.1–
10.2.3. One of the most promising nonlinear media for realization of SPPC by the
joint stimulated scattering, nematic liquid crystals (NLCs), will be introduced

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Lasers are devices that produce intense beams of monochromatic, coherent radiation. The word "laser" is an acronym for Light Amplification by Stimulated Emission of Radiation.
Diode Lasers
Diode lasers use light-emitting diodes to produce stimulated emissions in the form of coherent light output. They are also known as laser diodes.
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Ion lasers function by stimulating the emission of radiation between two levels of an ionized gas. They provide moderate to high continuous-wave output of typically 1 mW to 10 W.
Helium Neon Lasers
Helium neon (HeNe) lasers have an emission that is determined by neon atoms by virtue of a resonant transfer of excitation of helium. They operate continuously in the red, infrared and far-infrared regions and emit highly monochromatic radiation.
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