The correct identification of the third-order nonlinear optical effect of stimulated Raman scattering (SRS) led in the last years to a versatile method to generate new laser wavelengths resulting from a photon-phonon-interaction. There is the possibility to down- (Stokes) or up-shifting (anti-Stokes) of the pump laser frequency. The size of the frequency shift depends on the Raman-active material and the excitability of their SRS-promoting vibration-modes. Prominent Raman crystals include BaNO3 and other nitrates, KGW and other tungstates, YVO4 and other vanadates as well as diamond. Recently, we observed SRS in the laser crystal LuAlO3 with one SRS-active phonon mode and the natural crystal Spodumene (α-LiAlSi2O6), which has three corresponding SRS-active vibration modes.
Selective amplification of one particular spectral line generated through SRS is possible by placing the Raman crystal into a frequency-selective optical resonator, whose optical feedback is selective for only one Stokes- or anti-Stokes component. Raman lasers can be used in many applications, e.g. differential absorption LIDAR systems (DIAL, Light Detection and Ranging) to detect trace gases like carbon dioxide (CO2), ozone (O3) or water vapor (H2O). Various pumping schemes and resonator designs have been investigated focusing on good conversion efficiency, high spatial beam quality and high pulse energy of the output beam. The DIAL technique requires laser sources with high average output power combined with an excellent beam quality (M2 < 2). One possible solution can be found in an effect called beam-cleanup, which takes place by using Raman lasers and amplifiers.
The emission of commercial solid-state lasers is shifted by Raman lasers to selected wavelengths suitable for trace gas detection. High power Raman lasers based on Ba(NO3)2, diamond and silicon detect CO2, O3 and H2O. Raman lasers base on the physical effect of stimulated Raman scattering. Two new Raman crystals (Spodumene and LuAlO3) are investigated and their SRS-spectra is shown.
In this work we report on hybrid organic/inorganic sol-gel based optical waveguides in slab configuration grown both on glass and silicon substrates by spin-coating process. The samples were obtained using Zr(IV)-propoxide as inorganic precursor and 3-glycidoxypropyltrimethoxisilane (GLYMO) as organic component in molar ratio of 3/1. Optical characterization of each layer has been accomplished performing refractive index measurements at different wavelengths in the visible and near infrared regions using an home-made experimental setup developed in our laboratory. Measurements have evidenced a difference between the in-plane and out-of-plane refractive index. We found that the amount of the optical anisotropy depends on the speed of spinning deposition and on the curing temperature. In particular the anisotropy increases with the increasing of speed deposition and with the increasing of curing temperature. Results were also confirmed by spectroscopic ellipsometric measurements. We attributed the optical anisotropy to a preferential orientation of the organic groups of the alkoxysilane precursor (GLYMO) during spin coating deposition.
In this work we report on the preliminary results of compatibility, fabrication and characterization of two planar polymeric multilayer structures for electro-optic applications. The structures are composed by three polymeric layers grown on glass substrate. Buffer and cladding layers were synthesized using polymethylmethacrylate (PMMA). The guiding layers were composed by Polysulfone (PSU) and by a mixture of PMMA and polycarbonate (PC) both doped with Disperse Red 1 (DR1) molecules as nonlinear active units. Linear and nonlinear optical characterization of the structures by refractive index, absorption, optical losses, Second Harmonic Generation (SHG) and time stability measurements have been carried out.
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