High power gain for stimulated Raman amplification in CuAlS2

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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 Raman amplification. Observation of a high value of absolute scattering efficiency S/L dΩ (where S is the fraction of incident power that scatters into the solid angle d Ω and L is the optical path length with S/L dΩ=9.5×10−5 cm−1 sr−1), together with relatively narrow linewidth (Γ=5.1 cm−1, full width at half maximum at room temperature and Γ=1.5 cm−1 at 8 K for the strongest Γ1 phonon mode of CuAlS2 at 314 cm−1) indicate that CuAlS2 has the highest value of the stimulated Raman gain coefficient gs/I where I is the incident laser power density. The calculated value of this gain is gs/I=2.1×10−6 cm−1/W at 300 K and 5.0×10−6 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 H2) investigated so far. The calculations show that cw Raman oscillator operation in CuAlS2 is feasible with low power threshold of pump laser.