Noncritically Phase-Matched Ktp And KnbO 3 For Tunable Lasers At Room Temperature

Abstract

ABSTRACT In this paper, we report the first systematical analyses of the room temperature noncritical phase match­ ing (NPM) curves for biaxial crystals of KTP and KNbO3. The advantages and potential applications using these NPM conditions are explored, with an emphasis on tunable lasers in diode-pumped systems. 1. INTRODUCTION Nonlinear crystals operated at the noncritical phase-matching(NPM) conditions, particularly at room tem­ perature, are always desirable for high-efficiency frequency conversions. Crystals at the NPM provide sev­ eral advantages over that of the critically-phase-matched: (1) maximum effective nonlinear coefficient (deff) in most of the crystals, except for crystals such as beta-barium-borate(BBO) with deff = d22cos0 = 0, for 6 = 90 degrees; (2) maximum angular, spectral and temperature bandwidths; and (3) minimum Poynting vector walk-off, where the first-order dispersion of k-vector vanishes and only the second-order dispersion contri­ butes to the phase mismatching.KTP crystals operated at the critical-phase-matching(CPM) conditions have been widely used for fre­ quency doubling of Nd:YAG(1064 nm) laser, were the NPM usually cannot be temperature-tuned due to the rather small temperature-gradient of the refractive indexes. High temperature NPM operations have been identified in several crystals usch as MgO-doped lithium niobate and potassium niobate in doubling Nd:YAG lasers and diode lasers.[l,2] Angle-tuned CPM in KTP crystal for tunable IR lasers was recently reported.[3-6] In this paper, we report the room temperature NPM using KTP and KNbO3 for various fre­ quency conversions including second harmonic generation(SHG), sum-frequency-mixing(SFM) and differ- ence-frequency-mixing(DFM). These high-efficiency NPMs operated at room temperature promise the potential applications for the generature of coherent sources ranging from visible to mid-IR, particularly in the diode-laser-pumped systems. The tuning ranges at various polarization configurations will be analyzed and specific examples in diode-pumped systems will be explored.