Thick Film, Orientation-Patterned Gallium Arsenide for Nonlinear Optical Frequency Conversion


Optical frequency conversion using quasi-phasematched (QPM) nonlinear optical crystals is a powerful technique for generating coherent radiation in wavelength ranges where lasers are not readily available. For generation of mid-infrared (mid-IR) light, which is desirable for applications such as spectroscopy, IR countermeasures, and remote sensing, QPM GaAs is an ideal material because of its broad IR transmis- sion range and large nonlinear coefficient. Orientation-patterned gallium arsenide (OP-GaAs) is a type of QPM GaAs that has been recently developed. In OP-GaAs, periodic inversions of the crystallographic orientation are epitaxially grown into the material. The growth process involves molecular beam epitaxy, lithographic definition of QPM periods, and hydride vapor phase epitaxy. Significant progress has been made in increasing the quality of thick-film OP-GaAs material; periods as small as 30 µm have been grown in 0.5-mm-thick films, and overall thicknesses of 1 mm have been achieved. Furthermore, OP-GaAs loss measurements showed attenuation coefficients of 0.005 cm−1 , measured at 2-µm wavelength. The improved material quality has allowed the demonstration of efficient nonlinear optical frequency conversion in the mid-infrared wavelength range in OP-GaAs. This thesis discusses growth improvements and demonstrations of nonlinear optical devices in bulk OP-GaAs.

Using thick-film orientation-patterned GaAs, optical parametric generation and oscillation were demonstrated. We showed generation of extremely broadband infrared radiation in OP-GaAs using optical parametric generation. Also, a nanosecond- duration optical parametric oscillator based on OP-GaAs was built and used to explore the polarization dependence of three-wave mixing in OP-GaAs. High symmetry in the nonlinear susceptibility tensor of GaAs together with lack of birefringence allow effcient nonlinear optical mixing with circularly polarized or even depolarized waves; this property is not seen in most nonlinear optical crystals, which mix only linearly polarized waves. Efficient pumping of an OP-GaAs OPO with circularly polarized and depolarized light was achieved. We also investigated implications of polarization- independent phasematching that is present in GaAs and other cubic nonlinear optical crystals.


April, 2008