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Nonlinear Optical Elements

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Development of Nonlinear Optical elements for Parametric Generation in the Mid-IR Region

Tech Area / Field

  • PHY-OPL/Optics and Lasers/Physics
  • CHE-THE/Physical and Theoretical Chemistry/Chemistry

Status
3 Approved without Funding

Registration date
28.09.1997

Leading Institute
Design and Technological Institute of Monocrystals , Russia, Novosibirsk reg., Novosibirsk

Project summary

Optical parametric oscillators (OPO) are considered now as the most promising devices for obtaining coherent radiation, in which the wavelength is continuously tuned over a wide spectral range. Although parametric oscillation was demonstrated in the 60's years for the first time and the first commercial devices appeared in the 70's, its extensive development was pampered by the absence of available laser sources for OPO pumping as well as by shortages of known nonlinear crystals.

In contrast to the VUV-near IR range which is well covered by tunable lasers or OPO on LBO, BBO and KTP crystals, the middle IR region is handled much more weakly and thus the task of search for new nonlinear crystals and development of their growth technique is of great current interest. Meanwhile the mid-IR range (2 to 20 mkm) is particularly important thanks to the fact that the majority of chemical compounds have specific vibrational/rotational spectra and their detection and identification are possible, thus making it possible to solve various fundamental and applied tasks. In medicine thus the remote diagnostics of issues and blood as well as therapy is possible. The valuable information regarding diseases, aging and so on can be obtained. OPO's are promising for remote monitoring of the surrounding environment, atmosphere, including global changes as a result of technological effects such as a greenhouse effect, ozone layer distortions leading to climate transformations. Of great importance is OPO use for workplace and technological processes testing, detection of industrial contaminations and escapes in gas transport.

In the present proposal the efforts will be concentrated on growth and monitoring of new nonlinear crystals such as LiInS2, LilnSe2 and LiInSxSe2-x solid solutions as well as GaSe, in which nonlinear susceptibility is comparable or even higher than that of wellknown AgGaS2, AgGaSe2 and ZnGeP2 crystals and which cover the spectral range from 2 to 18 mkm. There are several additional reasons, which make the Li-containing crystals very attractive for nonlinear optics:


1. LiInS2 and its analogues are crystallized in a mm2 space group like KTP and are related to pyroelectrics or even to ferroelectrics where the periodic domain structure can be created and the quasi-phase-matching operation (QPM) can be realized. The latter allows us to widen considerably the spectral range of generated frequencies and to increase the nonlinear conversion efficiency.
2. The Ag ion replacement by the lighter Li ion results in increase of frequencies of crystal lattice vibrations and of the Debye temperature. It brings to intensifying of U-processes in phonon-phonon interactions and to the increase of thermal conductivity values, which in turn, is accompanied by an increase of optical damage threshold.
3. The change of crystal lattice type allows us to avoid the difference in sign of the thermal expansion coefficients along various directions and the creation of stresses and {112} microdomain defects, which are typical for 42m structures. Thus the new crystals are expected to have more available growth technology.
4. The more rarefied crystal structure relative to a chalcopyrite one of AgGaS2, AgGaSe2 and ZnGeP2 facilitates the nonlinear crystal doping by transition metals and rare earths ions when creating the polyfunctional elements of laser schemes.

In the present proposal the complex approach to a problem of working out of nonlinear optical elements is realized. It includes all stages, beginning from the purification of initial reagents and finishing with protecting/antireflection coatings and creation of certain elements of laser schemes. The main physical parameters of the grown crystals, which are responsible for laser applications, will be determined. Use of the powerful complex of physical methods including X-ray techniques, optical and ESR spectroscopy allows us to investigate the real structure in detail and work out methods of correction/compensation for unacceptable parameters and as a result to realize the potential capabilities of nonlinear crystals in the maximum extent.

The proposal will be fulfilled by a group of highly-skilled specialists on growth and investigation of their physical properties from the Design and Technological Institute of Monocrystals and from the Institute of Mineralogy and Petrography of the Siberian Branch of the Russian Academy of Sciences, who participated for a long time in various military programs.

The present proposal is supported actively by the leading organizations in nonlinear optics such as the Lawrence Livermore National Laboratory of the University of California in U.S.A. and the Observatory of Paris (France), which are ready to take an active part in the fields of:


- Characterization of nonlinear crystals and the optical elements from them, using the available laser technique;
- Theoretical and experimental optimization of nonlinear interactions in proper types of OPO for high-speed and high-resolution spectroscopy, frequency standards and so on;
- Working out of CW and pulsed coherent light sources based on the developed nonlinear crystals, which cover the mid-IR range and their use for detection of various molecular complexes, atmospheric monitoring and solution of metrological tasks.


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