We accurately measured the second-order nonlinear-optical coefficients of LaBGeO5 (LBGO) at the fundamental wavelength of 532 nm using the wedge technique. The values of d33, d22 and d31(=d32) were determined to be 1.15, 1.41 and 0.75 pm/V, respectively. The values are much larger than those estimated from our measured results at 1064 nm using Miller’s rule. Moreover, d33 is smaller than d22, the magnitude relation of which is inverse at 1064 nm. Then we need to remeasure at 1064 nm as well as measure the other d components.
We recently fabricated a large-aperture quasi-phase matching stack of 53 GaAs plates using the room-temperature bonding. Although 29 times higher second-harmonic power was obtained than from a 9-plate stacked device, its surface profile was degraded and the positions with high transmittance were limited. By putting the GaAs plates on YAG crystals polished to laser grade instead of directly putting on metallic stages, we confirmed that the surface flatness as well as the transmittance were improved. We are now developing additional processes, which we expect realizes 100-plate or more stacked QPM structures with low loss.
We identified eight nonlinear crystals enabling THz emission from quadratic phase-matched Difference-Frequency-Generation: YCOB, BNA, LBO, CSP, AGS, CdSe, ZnO and GaP. For all these crystals, we performed Time-Domain Spectroscopy in the same conditions to determine their absorption spectra in polarized light as well as their principal refractive indices as a function of wavelength in the 0.5-2.0 THz range. By combining previous data with the Sellmeier equations valid in their visible and infrared transparency ranges, we calculated the coherence length of Difference-Frequency-Generation associated to all possible configurations of polarization and found interesting and complementary phase-matching conditions in the eight studied crystals.
Using the room-temperature-bonding technique, we have succeeded in fabricating a quasi-phase-matching (QPM) stack of 53 GaAs plates with each thickness of 106 μm and aperture of 5.5 × 5.0 mm for second-harmonic generation of a CO2 laser at 10.6 μm. An improved process was applied which realized fine alignment of the GaAs plates on the translation stage. The fabricated 5.6 mm long, 53 plate-stacked GaAs-QPM device generated 20 times higher secondharmonic power than the previously fabricated 0.95 mm long QPM stack of nine GaAs plates.
High power blue radiation obtained by intracavity frequency-doubling of a continuous wave diode end-pumped Nd:YAG laser operating on the 4F3/2 → 4I9/2 transition is reported. The maximum output power for the randomly polarized beam at 946 nm was 3.7 W for 9.5 W absorbed pump power at 808 nm; the slope efficiency with respect to the absorbed pump power was 44%. For the polarized fundamental radiation the maximum power was 1.1 W (26% optical-to-optical efficiency with respect to the absorbed power), the laser operating with 38% slope efficiency. Intracavity frequency-doubling by a 2.0-mm thick KNbO3 crystal placed in a linear resonator yielded 159-mW single-ended blue-output with optical conversion efficiency versus the absorbed pump power of 4.8%. Using a V-type resonator increased the blue power at 418 mW with 11.6% optical conversion efficiency in absorbed power; the laser optical conversion efficiency was 6.7%, while the conversion of the available infrared power reached 50%.
A diode end-pumped Nd:YAG laser passively Q-switched by Cr4+:YAG saturable absorber and intracavity frequency-doubled by a LBO nonlinear crystal is described. Using a linear cavity the maximum average power at 1.06-μm fundamental wavelength was 3.3 W, 22.5 kHz repetition rate and 25.2-ns pulses duration. The maximum peak power was 12 kW for an average power of 1.8 W, laser pulses of 17.5-ns duration and 209.3-μJ energy. Intracavity frequency-doubling employing a V-type laser resonator yielded 532-nm green pulses of 226-μJ energy and 86-ns width at 4.2-kHz rate of repetition. The theoretical calculations based on a model of rate of equations show good agreement with the experiments at both fundamental and second-harmonic wavelengths.
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