Sudipta Gangopadhyay

AgGaGeS4 Crystals for Nonlinear Laser Device Applications

A mid-infrared frequency converter with a nonlinear crystal, AgxGaxGe(1-x)S4 (AgGaGeS4), for x=0.5 has been reported by the second harmonic generation of tunable CO2 laser radiation. Two pole coefficients of Sellmeier equations are also presented.

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.

A simple technique of enhancement of efficiency in optical frequency conversion

A simple technique for enhancement of conversion efficiency focusing by cylindrical lens of the interacting beams in three wave nonlinear interaction has been reported by generating second and third harmonics of 1064nm radiation in a Li2B4O7 crystal and compared the generated beam energy focusing by spherical lens. An increase in conversion efficiency of about 5.2 times has been realized in focusing by cylindrical lens than that in focusing by spherical lens.

Large enhancement in second-harmonic generation by optical feedback

An optical feedback configuration is proposed for second-harmonic generation from a secondary coherent source in a nonlinear crystal that without focusing enables one to realize same conversion efficiency as obtained in a conventional setup but with at least four times less input fundamental energy. The effectiveness of the scheme is confirmed.

Singly-resonant optical parametric oscillator based on KTA crystal

Tunable mid-infra-red radiation by singly resonant optical parametric oscillation based on KTA crystal pumped by multi-axial Gaussian shape beam from Q-switched Nd:YAG laser has been demonstrated. Threshold energy of oscillation at different idler wavelengths for different cavity length has been demonstrated. Single pass conversion efficiency of incident pump energy to infra-red wavelength has also been measured.

Walk-Off Compensated UV generation in Lithium Tetraborate crystals

As high as 21 mJ of energy at 288.5 nm is produced for the first time in Lithium Tetraborate crystals utilizing Type-I twin crystal walk-off compensated second harmonic generation. In the process it is shown that unless one uses the walk-off compensated configuration, the effect of walk-off degrades the conversion efficiency of the second harmonic generation even when the so-called aperture length is much greater than the actual length of the crystal as well as the crystal has an appreciably low value of walk-off angle.

Large enhancement of second harmonic generation in Li/sub 2/B/sub 4/O/sub 7/ crystals

A simple multipass configuration (MPC) is designed using twin crystals that substantially enhances the conversion efficiency of extra cavity SHG by simultaneous employment of focusing and compensation of double refraction. A newly developed crystal lithium tetraborate (Li/sub 2/B/sub 4/O/sub 7/ or LB4) to demonstrate the feasibility of the scheme since the crystal has effective nonlinearity which is only 1/6th times that of KDP. The configuration improves the conversion efficiency of SHG in this crystal from 4.7 to 21% at the same level of fundamental intensity. Thus the designed MPC can be used for any other nonlinear crystals with higher nonlinearity as well.