RESUMO
In this work, we define the efficiency signal conversion numerical parameter, Veff, useful to evaluate the operation efficiency of femtosecond-Optical Parametric Oscillator (fs-OPO) cavities considering the astigmatism effect. For the validation of the Veff, we have performed experimental measurements. We present different high efficiency home-made singly resonant fs-OPO cavities, with signal tuneability from 1.1 µm to 1.6 µm based on a 0.5 mm Periodically Poled Lithium Niobate doped with MgO (MgO:PPLN) crystal. We have also defined the pump energy threshold per crystal unit length, ζp,th. Pump threshold, achieved by following the Veff, was 142 mW at 810 nm, and ζp,th = 2.10 nJ/mm, the lowest value, in comparison with other studies. The Veff is based on an ABCD matrix Gaussian beam propagation method, which calculates the mode coupling between the pump and signal beams along the crystal under different cavity configurations taking into account the astigmatism. The model was compared and tested with 3 different experimental singly resonant fs-OPO ring cavity configurations that we have defined as single-folded, two-folded, and direct-pump cavity.
RESUMO
In this work we present an Autocorrelation z-scan technique to measure, simultaneously, the spatial and temporal distribution of femtosecond pulses near the focal region of lenses. A second-order collinear autocorrelator is implemented before the lens under test to estimate the pulse width. Signals are obtained by translating a Two Photon Absorption (TPA) sensor along the optical axis and by measuring the second-order autocorrelation trace at each position z. The DC signal, which is typically not considered important, is taken into account since we have found that this signal provides relevant information. Experimental results are presented for different lenses and input wavefronts.
