Non-critical phase-matched second harmonic generation by β´-Gd 2(MoO4)3 in the near infrared

A two-crystal walkoff-compensated β-barium metaborate optical parametric oscillator was used to locate the noncritical (90°) phase-matching (NCPM) wavelengths for type II second-harmonic generation along the crystallographic a- and b-axes of a crystal of β´-gadolinium molybdate and to measure their spectral and angular acceptances. The relative second-harmonic intensity versus wavelength curves exhibited peaks at 1.403 μm and 1.410 μm, respectively, with full widths at half maximum of 7.2 nm and 7.3 nm. The relative second-harmonic intensity versus external angular orientation curves had full widths at half maximum for propagation along the a - and b-axes of 13.6° and 14.1° θ_ext and 71.5° and ~92.3° φ_ext, respectively. These large spectral and angular acceptances are typical of noncritical phase-matching. The discrepancy between calculated and experimental NCPM wavelengths is attributed to the errors inherent in measuring and extrapolating refractive indices