Spectrum of two-photon absorption coefficient for GaSe

Abstract

Summary form only given. The spectrum of the two-photon absorption (TPA) coefficient is crucial for its applications in optical power limiting, autocorrelation, two-photon luminescence, and is important for optical parametric oscillation. GaSe has a large value of second-order nonlinear coefficient and a wide transparency range (0.62-20 /spl mu/m) ideal for the efficient generation of mid- and far-IR. The value of the TPA coefficient for GaSe was measured to be very large, i.e. 110 cm/GW at the wavelength of 1.064 /spl mu/m. Such a large value could limit the applications of GaSe. However, TPA coefficient was recently measured to be 6 cm/GW at the wavelength of 700 nm. On the other hand, based on a three-band model, /spl beta/ at 700 nm is estimated by us to be 13 cm/GW. Therefore, the value obtained by Vodopyanov et al (Opt. Commun. vol. 155, p. 47, 1998) is supported by this theoretical value. However, the value obtained by Adduci et al (Phys. Rev. B vol. 15, p. 926, 1977) is a factor of about 42 larger than that predicted by the theory. Such a large difference between two experimental values has motivated us to measure the TPA coefficient spectrum for Ge. Here, we report our first results of the measurement of the spectrum of the TPA coefficient for GaSe based on the z-scan technique (Sheik-Bahae et al, IEEE J. Quantum Electron. vol. 26, p. 760, 1990) using picosecond laser pulses. We have used high peak intensities of picosecond laser pulses while keeping the average laser powers low enough to avoid any thermal effect and free-carrier effects.