Speckle contrast reduction by linear and nonlinear photonic devices
Speckle contrast <; 3.5% was achieved by means of (i) wavelength-diversity using spectrally-broad nonlinear photonic green lasers over the 520-545nm range and (ii) polarization- and phase-diversity using birefringent nano-photonic devices.
Upconversion blue laser by intracavity frequency self-doubling of periodically poled lithium tantalate parametric oscillator.
We report a design for upconversion 435 nm blue lasers based on simultaneously fulfilling the nonlinear processes of optical parametric oscillation (OPO) and second-harmonic generation (SHG) in a 7.9 mum periodically poled lithium tantalate (PPLT). The uncoated 15-mm-long PPLT device exhibits a low threshold of 150 mW and a differential slope efficiency of 22.6%, rendering 56 mW blue generation when pumped by a pulsed 532 nm green laser with an average power rating of 400 mW. These observations were attributed to a quasi-phase-matching (QPM) structural design with a 75% domain duty cycle to ensure the concurrence of frequency doubling with the first-order QPM-OPO PPLT device via the second-order QPM-SHG process.
Theoretical Analysis of Multimode Pumped Second-Harmonic Generation
Type I and Type II second-harmonic generations (SHG) with a randomly phased multimode pump have been theoretically analyzed by considering phase mismatch and fundamental bandwidth effect. The equations obtained in the paper are formulated in a very concise and analytic form, which can be used to evalute both conversion efficiency and spectrum. We found that the previously recognized multimode enhancement effect does not exist in Type II SHG. The issue of harmonic instability due to multimode pumping has been also discussed.