Determination of nonlinear optical coefficients and efficient type-II second-harmonic-generation for TmCOB crystals

By Maker Fringe (MF) method, all of the nonlinear optical (NLO) coefficients including d(11), d(12), d(13), d(31), d(32) and d(33) of TmCa4O(BO3)(3) (TmCOB) crystals were measured to be 0.19, 0.26, -0.61, -0.30,1.66 and -1.25 pm/V, respectively. Based on which, the second-harmonic-generation (SHG) phase-matching (PM) characteristics of TmCOB crystals in two-dimensional principal planes and three-dimensional non-principal planes (space) were theoretically calculated, such as PM tuning curves, distribution of effective NLO coefficient (d(eff)), beam walk-off angle, and angular acceptance bandwidth. At the fundamental waves of 1064 nm, the type-II optimal PM angles with largest d(eff) for principal planes and space were decided to be (52.8 degrees, 90.0 degrees) (d(eff) 0.24 pm/V) and (118.0 degrees, 77.2 degrees) (d(eff) 0.35 pm/V), respectively. The type-II SHG of TmCOB crystals was found to present large acceptance angle bandwidth (similar to 2-12 times of type-I values) and small beam walk-off angle (similar to 0.2-0.4 times of type-I values). At a high input energy of 6.89 mJ (35 ps, 10 Hz, 1064 nm), the SHG transformation efficiency for an uncoated TmCOB crystal sample cut along type-II optimal angle (118.0 degrees, 77.2 degrees) with 12 mm in length was measured to be 55.9%, which achieved the same conversion efficiency grade as type-I optimal PM.