Nonlinear Optical Absorption Study Of Indium Nitride Thin Film

The investigation on nonlinear optical absorption properties of semiconductors have recently received intensive research interest both in theoretically and experimentally. As we know, saturable absorption (SA) has been extensively applied in laser physics, such as mode locking and optical bistability and so on. Two-photon absorption (TPA) and reverse saturable absorption (RSA) have been studied for numerous optical device applications including optical switching and most importantly optical limiters. Therefore, the study of nonlinear optical absorption properties of InN thin film is of very important and has practical significance.Among different experimental methods of nonlinear optics Z-scan technique is considered one of the simplest and most accurate methods for nonlinear parameters. Both the sign and magnitude of the total nonlinear absorption and nonlinear refractive index can be deduced. It is widely applied in the investigation of nonlinear optical processes in semiconductors. In this article, the basic third-order nonlinear optical processes in media have been reviewed firstly. Then the principle of Z-scan technique together with the brief description of the instruments has been introduced. Based on the detailed calculation of optical transmission spectrum profile, the basic optical parameters of InN have been yielded. By using Z-scan technique the nonlinear optical absorption properties of InN thin film under different pulsed laser and wavelengths have been well studied.Through the open-aperture transmission Z-scan (TZ-scan) technique, we studied the nonlinear optical absorption of InN thin film under ns, ps and fs pulsed lasers, respectively. And different absorption mechanisms have been analyzed. It is found there exist different absorption processes under different pulsed laser. In 6 ns and 38 ps pulsed TZ-scan measurements at 532 nm, SA effects induced by one-photon transition were observed directly. And the film showed SA effect induced by two-photon transition in 38 ps pulsed TZ-scan measurement at 1064 nm. In 100 fs pulsed TZ-scan measurement at 800 nm TPA was the dominated process at low optical intensity. However, as the incident laser intensity increased, the TPA coefficient trended to saturable value. All the results indicate that InN film is a kind of good satirable absorber. The strong SA properties measured in ns and ps lasers suggest that it may be a material with potential application in laser pulse compression, while the TPA presented in fs laser underpin the future development in the optical limiting. This work was supported by Natural Science Foundation of China (contract Nos.10734020).