Bulk lithium tantalate doubles diode laser output to ultraviolet wavelengths

Bulk lithium tantalate doubles diode laser output to ultraviolet wavelengths

Using periodically poled bulk lithium tantalate (LiTaO3) for second-order quasi-phasematching second-harmonic generation (SHG), researchers Kiminori Mizuuchi and Kazuhisa Yamamoto of Matsushita Electric Industrial Co. Ltd. (Osaka, Japan) frequency doubled the output of a visible (680 nm) diode laser, obtaining 1.02 µW of power at 340 nm. Lithium tantalate is a good material for ultraviolet light generation, with transparency extending to 280 nm, large nonlinear susceptibility, and high resistance to photorefractive damage. The Matsushita team created the periodic ferroelectric domain inversions in the LiTaO3 that are required for quasi-phasematching second-harmonic generation by photolithographically generating a periodic tantalum electrode pattern on the surface of the crystal, subjecting the sample to proton exchange, and applying a brief, high-voltage pulse. The poling period was 3.3 µm with a linewidth of 1.2 µm and a 75% duty cycle.

The completed device was 200 µm thick with a 10-mm interaction length. The non optimized beam waist in the crystal was 40 ¥ 100 µm; the short axis was aligned to the 200-µm thickness of the LiTaO3. Second-harmonic conversion efficiency of 0.09% was achieved, which is an order of magnitude lower than the theoretical value, primarily due to the nonoptimized beam waist. Efficiency should increase with the use of an improved source.