New crystalline materials for nonlinear frequency conversion, electro-optic modulation, and mid-infrared gain media.

摘要

New crystalline materials were investigated for applications in frequency conversion of near-infrared wavelengths and as gain media for tunable mid-infrared solid-state lasers. GaCa₄O(BO₃)₃ (GdCOB), YCa₄O(BO₃)₃ (YCOB), LaCa₄O(BO ₃)₃ (LaCOB), and Gd_0.275Y_0.725Ca ₄O(BO₃)₃ were characterized for frequency conversion of 1 μm lasers. For type I doubling at 1064 nm, LaCOB, GdCOB, and YCOB were found to have effective coupling coefficients (d_eff) of 0.52 ± 0.05, 0.78 ± 0.06, and 1.12 ± 0.07 pm/V, respectively. LaCOB was measured to have angular and thermal sensitivities of 1224 ± 184 (cm-rad)−1 and 0.10 (cm-°C)−1 , respectively. The effective coupling coefficient for type II non-critically phasematched (NCPM) doubling at 1064 nm in Gd_0.275Y_0.725Ca ₄O(BO₃)₃ was measured to be 0.37 ± 0.04 pm/V. We predict LaCOB to have a type I NCPM fundamental wavelength of 1042 ± 1.5 nm. Due to its low angular and thermal sensitivities for doubling near 1047 nm, LaCOB has potential for frequency doubling of high-average power Nd:LiYF₄ and Yb:Sr₅(PO₄)₃F lasers. LaCOB, GdCOB, and YCOB were also investigated for optical parametric oscillator applications and we determined that they may have potential in a Ti:sapphire pumped oscillator.; The effective linear electro-optic coefficients (r_eff) were measured along dielectric directions in YCOB and a maximum r_eff of 10.8 pm/V was found. For a crystal with a 5:1 aspect ratio, the corresponding half-wave voltage at 1064 nm would be 19.6 kV. Therefore a Pockels cell composed of two YCOB crystals with 5:1 aspect ratios would have a required half-wave voltage 10 kV.; Moderate coupling coefficients (3 x KH₂PO₄), low thermal sensitivities, ease of growth to large sizes, non-hygroscopicity, and favorable polishing and coating characteristics make LaCOB, GdCOB, and YCOB attractive for frequency conversion of high-average power near-infrared lasers.; Absorption and emission cross-sections of ∼10−18 cm2 were measured for Fe2+:ZnSe in the 4 μm region at temperatures below 220 K. Luminescence lifetimes were found that ranged from 5–110 μs below 220 K. Tunable lasing action was demonstrated for the first time in Fe2+:ZnSe with a tuning range from 3.98 μm (20 K) to 4.54 μm (180 K). The Fe 2+:ZnSe laser had thresholds ≤50 μJ and slope efficiencies ≤10% with 0.6% output coupling.