Polarization dependent multiphoton absorption in ZnO thin films

Abstract

We present a simple non-destructive approach for studying the polarization dependence of nonlinear absorption processes in semiconductors. The method is based on measuring the yield of the near UV photoluminescence as a function of polarization and intensity of femtosecond laser pulses. In particular, we investigated the polarization dependence of three photon laser absorption in intrinsic and Al-doped ZnO thin films. Both specimen show stronger emission for linearly polarized excitation compared to circular polarization. The ratios for the three-photon absorption coefficients are about 1.8 and independent of the doping. It is shown that Al-doped films have lower threshold for stimulated emission in comparison to the intrinsic films.

Polarization Dependent Excitation and High Harmonic Generation from Intense Mid-IR Laser Pulses in ZnO

“…Polycrystalline ZnO thin films were synthesized by RF-magnetron sputtering on sapphire substrates. Scanning electron microscope (SEM) and X-ray diffraction (XRD) characterization of the samples reveal a 300 nm thick film with columnar crystalline grains, grown in the <001> direction, with a size of 120–150 nm, as published in [ 24 ]. The polished ZnO single crystal sample exhibits a thickness of 100 µm and a crystalline orientation of <001>.…”

“…The use of thin films to study the polarization dependence of light absorption is important to rule out nonlinear propagation effects like self-focusing, which can be present in the bulk sample [ 29 ]. A previous work [ 24 ], using the same thin films, showed the dependence of three photon absorptions of near infrared light (0.8 µm) on the laser ellipticity. There, the PL signal decreases by a factor 1.8 when circular compared to when linear polarized laser light was used.…”