Third harmonic generation at sapphire wafers with different cut axis

摘要

Nonlinear optical responses of transparent materials have been utilized in many applications, such as short-wavelength light generation, optical modulation, and non-destructive study of the sample characteristics. When a laser beam is focused onto a nonlinear crystal, the polarization state of the outcoming beam is dependent on the polarization state of the incident beam together with focused spot location inside the sample. This can be utilized for in-depth understanding of third harmonic generation mechanisms. As both the incident angle of the laser beam and the sample thickness affect the third harmonic generation yield, in this paper, we controlled the incident beam focus locations at different depth planes in order to check the sapphire thickness effect and also adjusted the tilt angle to test the incident angle effect on harmonic generation. Our result can be utilized in industrial and scientific applications, for example, when optical components or waveguides are manufactured in sapphire based on nonlinear optics, the polarization dependence will determine the quality and efficiency of micromachining. Polarization dependence can help distinguish the nonlinear phenomenon from other phenomenon occurring inside the sapphire and test the material characteristics like structural symmetry. In addition, by choosing a suitable orientation of the crystal with respect to the light beam, phase matching can be realized.