We report simultaneous frequency conversion and amplitude modulation in an optical second harmonic generator by electro-optically controlling the relative phase between the 1064-nm fundamental and the 532-nm second harmonic fields in a dispersion crystal section between two periodically poled lithium niobate (PPLN) sections. Theoretical derivation and experimental demonstration were carried out for two novel crystal configurations, including a linear cascaded configuration in which a 1-cm dispersion section is sandwiched between two 2-cm PPLN sections, and a folding- crystal configuration in which the mixing waves traverse twice in a 2-cm PPLN section through total internal reflections in a 1.5-cm dispersion section. Due to the coherence enhancement in the constructive phase between the two SHG fields in the two PPLN sections, we measured a 30% increase in conversion efficiency compared to a continuous 4-cm PPLN under the same condition. The measured half-wave voltage for the amplitude modulation is 1.1 volt x d micrometers /l_d(cm), where d is the separation of the electrodes and l_d is the length of the electrodes.

The objective of this investigation is to apply wavelet image processing to Four-Wave Mixing (FWM) for the purpose of defining beam interaction both within and outside the nonlinear crystal. This will allow a better understanding of beam quality and allow for better performance of potential devices.

Nitrogen lasers have been used since many years to make dye solutions to lase. A nitrogen laser (337.1 nm) TEA at atmospheric pressure has been built in our laboratory. It has been characterized and used to pump cells of different sizes containing different dyes: Rhodamine 6G, Coumarin 440, DOTCI and pyranine. As a preliminary result it has been shown that pyranine can lase, and this happens at very low threshold. Moreover, we have found that, independently on the dye concentration in the solvent, the dyes under consideration can be grouped into two major classes of behavior: Rhodamine 6G and DOTCI can lase both axially and transversally; Coumarin 440 and pyranine can lase only axially. Other intriguing features will be discussed and attention will be devoted to simultaneous multiple beam generation, superfluorescence and distributed axial pumping of dye solutions.

Chalcogenide glasses in the [Ge-Se-S-As] system have been synthesized and studied with respect to their nonlinear optical properties from third and second order. Z-scan and Mach Zehnder interferometry measurements of the nonlinear refractive index (n₂) and nonlinear absorption ((beta) ) have been performed at 1064 nm. Some z-scan measurements have been also realized at 1430 nm. The results have been correlated to the structures of the glasses and the figure of merit has been calculated with the purpose of a potential utilization of these glasses in the realization of ultra- fast all-optical switches. Nonlinearities as high as 850 times the nonlinearity of silica glass have been obtained and some glasses exhibit at 1430 nm nonlinear optical characteristics suitable for telecommunication applications. The all-optical poling of a chalcohalogenide glass has been realized with a Q-switch mode-locked Nd:YAG laser at 1064 nm emitting 45 ps pulses at a repetition rate of 10 Hz with frequency doubling at 532 nm. A nonlinear coefficient d_eff equals 2.8 10^-17 m/V similar to that of the reference glass Schott SF 57 has been obtained. The thermal poling of a chalcogenide glass also has been realized and a transient second order nonlinear susceptibility (chi) ⁽²) has been observed.

All-optical poling technique permits purely optical orientation of molecules. The experiment consists of two steps: the writing (so-called seeding) period and the readout one. In the seeding phase two beams, the fundamental one ((omega) ) and its second harmonic (SH, 2(omega) ) illuminate the sample and print in the medium the second order (chi) ⁽²) susceptibility grating with a periodicity satisfying the condition of phase matching for SH generation. In the readout period only the fundamental beam irradiates the sample, and the second harmonic generation is observed at the sample output. Efficient all-optical poling requires optimisation of the seeding beam intensities and their relative phase difference. We propose a novel technique for non-perturbative monitoring of the all-optical poling process and the easy method of orienting molecules without any necessity of taking into account the phase difference between seeding beams.

Steady-state and laser-induced transient absorption around the surface plasmon resonance of copper nanoparticle composites, fabricated by ion implantation, have been studied by optical measurements. Negative ion implantation has been applied to generate the Cu nanoparticles in amorphous SiO₂, crystalline MgOn(Al₂O₃), LiNbO₃, SrTiO₃ and TiO₂ with various refractive indices and optical energy gaps. The surface plasmon resonance in the steady-state absorption resulted from formation of nanoparticles in the substrates and shifted to red with increasing refractive index of the matrix. The nanoparticle fabrication by the negative ion implantation was succeeded in all the insulating substrates used, and it is capable to tune the resonance band to 1.7 - 2.2 eV (730 - 560 nm) by selecting of the matrix. However, there remained a problem that the plasmon band in LiNbO₃, SrTiO₃ and TiO₂ with narrow energy gap overlapped radiation-induced defect band. Laser-induced transient absorption was measured with a technique of pump-probe femtosecond spectroscopy. The bleaching plasmon band recovered in several picoseconds due to energy transfer from the excited electron system to the phonon system via the electron-phonon interaction. The transient absorption is also affected by radiation damage in the matrices with the narrow energy gap.

We investigated the operation of a diode-pumped Yb:YAG laser passively Q-switched, by Cr⁴⁺:YAG, Cr⁴⁺:LuAG, and Cr⁴⁺:GSGG saturable absorbers. The results presented here are focused towards the design of a passively Q-switched Yb:YAG microlaser. The free-running performance of both rod and a disk Yb:YAG is characterized, and experimental parameters such as gain and loss are evaluated. These values, together with the value of the stimulated emission cross section, e.g. (sigma) _emequals3.3x10^-20 cm² were found to fit between our experimental results and an existing numerical model which relates the experimental and physical parameters to the minimal threshold pumping power. Q-switched pulses with maximum peak power of approximately equals 10.4-kW, and energy of approximately equals 0.5 mJ/pulse were extracted with 30% extraction efficiency.

We present a temperature-dependent Sellmeier equation for congruent and stoichiometric LiTaO₃. The refractive indices in the range of 0.39-4.1 micrometers were determined by scanning the pump lasers wavelength and finding the QPM second harmonic wavelength for a series of period- temperature pairs, and from QPM OPO measurements. The obtained new Sellmeier coefficients were used to calculate the QPM wavelengths of the idler and signal for a PPSLT OPO pumped at 1064 nm. An OPO based on PPSLT was demonstrated. The idler-tuning range was 4.1828-3.9898 micrometers for temperatures of 40-200 degree(s)C. The obtained wavelengths were in good agreement with our predictions.

We have demonstrated Raman amplification in small core As-Se fiber. We observed over 20 dB of gain in a 1.1-meter length of fiber pumped by a nanosecond pulse of approximately 10.8 W peak power at 1.50 micrometers . The peak of the Raman gain was shifted by approximately 230 cm^-1 to 1.56 micrometers . The Raman gain coefficient is estimated to be about 2.3 x 10^-11 m/W, over 300 times greater than that of silica. The large Raman gain coefficient coupled with the large IR transparency window of these fibers shows promise for development of As-Se Raman fiber lasers and amplifiers in the near, mid and long IR spectral regions.