2ND-HARMONIC POWER OF KTIOPO4 WITH DOUBLE-REFRACTION

Second harmonic (SH) power of the type-II phase matching in KTiOPO4 (KTP) is calculated for the fundamental beams of TEM00 mode within the near field approximation (parallel Gaussian beam) taking the beam walk-off effect among the two fundamental and the SH beams into account. The slit intensity and the total SH power are calculated as functions of the beam radius and the crystal length. Two approximations are made for the SH power calculation at tight beam focusing condition. The measurements of the SH power in KTP are carried out for three crystals of 6, 3, and 1.5 mm thickness. The effective nonlinear coefficient for Nd:YAG incident radiation is estimated to be 4.3 pm/V with 10% uncertainty, taking the enhancement factor due to the multimode structure of the laser beam into account.