High power gain for stimulated Raman amplification in CuAlS2

The spontaneous Raman spectra of the chalcopyrite structure crystal CuAlS2, which is promising for nonlinear optical applications, has been investigated at 8 and 300 K. The main aim of this study is to compare the absolute spontaneous Raman scattering efficiency in CuAlS2 crystals with that of their isomorphous analog, zinc-blende structure GaP crystals, known as one of the most efficient materials for amplification. Observation of a high value of absolute scattering efficiency S/L d Omega (where S is the fraction of incident power that scatters into the solid angle d Omega and L is the optical path length with S/L d Omega=9.5X10(-5) cm(-1) sr(-1)), together with relatively narrow linewidth (Gamma=5.1 cm(-1), full width at half maximum at room temperature and Gamma=1.5 cm(-1) at 8 K for the strongest Gamma(1) phonon mode of CuAlS2 at 314 cm(-1)) indicate that CuAlS2 has the highest value of the stimulated Raman gain coefficient g(s)/I where I is the incident laser power density, The calculated value of this gain is g(s)/I=2.1X10(-6) cm(-1)/W at 300 K and 50X10(-6) cm/W, at 8 K for 514.5 nm laser excitation, and is larger than those for the appropriate vibrational modes of various materials (including GaP, LiNbO3, Ba2NbO5O15, CS2 and H-2) investigated so far. The calculations show that cw Raman oscillator operation in CuAlS2 is feasible with low power threshold of pump laser. (C) 1996 American Institute of Physics.