U. Chatterjee

Noncritical second harmonic generation of CO2 laser radiation in mixed chalcopyrite crystal

We have generated a tunable second harmonic of CO2 laser radiation noncritically for the first time in a potential mixed chalcopyrite crystal AgGaxIn1−xSe2. Wide angular acceptance and increased conversion as compared to AgGaSe2 have been observed and the tuning characteristics have been explained using the dispersion data of its two end crystals.

Observation of nonlinear absorption and visible photoluminescence emission in chemically synthesized Cu2+ doped ZnS nanoparticles

Nonlinear optical properties of chemically synthesized ZnS and Cu2+ doped ZnS nanoparticles of average sizes ∼2.5 nm are reported by using open aperture z-scan technique with the Nd:YAG laser second harmonic radiation at 532 nm. Tunable photoluminescence emissions in the visible region due to the increase in concentration of Cu2+ doping in ZnS are observed at room temperature. By analyzing the experimental z-scan data, it is found that three photon absorptions (3PA) are taking place in all the samples. The extracted values of 3PA coefficients of the samples are ∼109 times higher than that of bulk ZnS.

Temperature-tunable second-harmonic generation in zinc germanium diphosphide

Second‐harmonic generation of tunable CO2 laser radiation is reported and analyzed in ZnGeP2 both by angular and temperature tunings. Temperature tuning can thus be advantageously employed in this crystal for nonlinear devices.

Widely tunable deep ultraviolet generation in CLBO

Abstract In a single cut cesium lithium borate (CsLiB6O10 or CLBO) crystal we have generate deep UV radiation tunable from 195 to 265 nm (with a gap from 210 to 226 nm due to crystal cut limitation). Radiation in the 195–210 nm region is generated by noncollinear sum-frequency mixing of Nd:YAG laser radiation with the second harmonic (239–262 nm) of the dye laser radiation. However, radiation in the region of 210–237.5 nm and 236.8–265 nm is generated by third harmonic and second harmonic generation of the dye laser, respectively. All three interactions for coverage of the said range are made in the same cut CLBO crystal Type-I, θ=80° and ϕ=45°. The shorter wavelength tuning is phase-matching limited. A conversion efficiency of 14% is realised in our 5.5 mm long crystal for the generation of 241.7 nm radiation by Type-I second harmonic generation with a fundamental input beam intensity as low as 14.6 MW/cm2.

Three-photon-induced four-photon absorption and nonlinear refraction in ZnO quantum dots

Three-photon-induced four-photon absorption via excited-state absorption and self-defocusing nonlinear refraction are reported for the first time, to our knowledge, in ZnO quantum dots with average sizes of 2.0+/-0.1 nm with 1064 nm radiation from a Q-switched Nd:YAG laser at a peak intensity of 2.5 GW/cm(2). By employing the three-level two-step model, the experimental results can be explained quite satisfactorily.

Enhancement of second harmonic generation by double-pass configuration in barium borate

Double-pass type-I second harmonic generation (SHG) external to a laser cavity is reported for the first time in a BBO crystal resulting in an enhancement of the generated harmonic intensity by a factor of 3.4 from that obtained in the single-pass generation.

Noncollinear phase-matched second-harmonic generation in beta barium borate

Noncollinearly phase‐matched second‐harmonic generation is reported for the first time in beta barium borate crystal and compared with existing KDP and KD*P crystals using Nd:YAG radiation.

Tunable coherent infrared source from 5-16 µm based on difference-frequency mixing in an indium-doped GaSe crystal

A tunable coherent infrared source based on a double-difference-frequency-mixing technique in an indium-doped GaSe crystal in the last stage, with a Nd:YAG laser as the basic pump source, is reported. Angular acceptance as well as spectral acceptance has been measured. The energy output of the infrared radiation has been measured. Absorption characteristics of polystyrene and polythene sheets have been measured with the generated radiation; the main peaks correspond to spectrophotometric measurement.

Influence of composition ratio variation on optical frequency conversion in mixed crystals. I. Gradual variation of composition ratio

A theoretical model is presented to deal with optical frequency conversion in a mixed nonlinear crystal with a small linear variation in composition ratio. Using the quasi-geometrical optics method, what we believe to be new diffraction-free coupling equations are developed to describe sum and difference frequency generations. With these new frequencies, we find that an optimal crystal length exists like that in the plane-wave model. Furthermore, the optimization of generated powers with absorption, transverse index modulation, and walk-off effect are studied in detail. According to different efficiency reductions, the tolerance and acceptance of composition ratios along and vertical to the beam propagating direction are presented. Intended gradual index crystals are also discussed for their possible applications in the frequency conversion of wideband lasers and in generating pulse compressed second harmonic ultrashort pulses.

Generation of tunable 187.9–196-nm radiation in β-Ba 2 BO 4

Tunable 187.9-196-nm vacuum-ultraviolet radiation was generated at room temperature in a beta barium borate crystal by sum-frequency mixing of Nd:YAG laser radiation and the second harmonic of a dye laser pumped by the second harmonic of the same Nd:YAG laser. By use of the advantageous noncollinear phase-matching configuration, a peak power of 1.3 kW was obtained at 194 nm with input power densities as low as 79MW/cm(2) for 1064-nm and 0.65MW/cm(2) for 237.3-nm radiation.