Abstract
The nonlinear absorption properties of direct (GaN) and indirect (CdI2) band gap crystals have been studied by using an open aperture Z-scan technique under fundamental (1064 nm) and frequency doubled (532 nm) wavelength respectively with 10 ns or 60 ps pulse durations. Direct band gap crystal exhibits two and three photon absorption at all input irradiances. On the other hand, at low input irradiance the indirect band gap crystal exhibits saturable absorption (SA). At higher input irradiances two and three photon absorption becomes dominant. A monotonic increase of the nonlinear absorption coefficients with increasing laser pulse duration from 60 ps to 10 ns is observed for GaN and CdI2 crystals.
Highlights
Nonlinear optical (NLO) materials play a major role in nonlinear optics and in particular they have a great impact on information technology and industrial applications
Normalised transmittance results of the open aperture Z-scan for an irradiation wavelength of 532 nm of energy 2.34 ev indicating two photon absorption (2 PA) with 10 nsec and 60 psec pulse duration, in case of Gallium Nitrate (GaN) and CdI2 crystals are shown in Figures 1 and 2 and for wavelength of 1064 nm of energy 1.17 ev indicating three photon absorption (3 PA) with 10 nsec and 60 psec pulse duration in case of GaN and CdI2 crystals are shown in Figures 3 and 4 respectively
Smaller values of two and three photon absorption coefficients in case of indirect band gap crystals as compared to direct band gap crystals have been attributed to phonon assisted transition
Summary
Nonlinear optical (NLO) materials play a major role in nonlinear optics and in particular they have a great impact on information technology and industrial applications. This effort has brought its fruits in applied aspects of nonlinear optics This can be essentially traced to the improvement of the performances of the NLO materials. The wide band gap of GaN enables this crystal to exhibits special properties for applications in optoelectronics and high power and high frequency devices. Nonlinear optical processes in GaN, such as two and three photon absorption, can lead to optical power limitations and optical damage in nitride based optoelectronics These processes can be used in numerous applications: optical limiters, photonic switches and nonlinear autocorrelation systems for ultrafast laser pulse characterization because of these potential. Ultra fast devices are the key component for the generation In this case the wide direct and indirect band gap semiconductor is the suitable candidates to calculate the nonlinear absorption parameters. Observed a switching from saturable absorption (SA) to two and three photon absorption in CdI2 indirect band gap crystal by increasing input irradiances
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