Steady state mode-locking of the Nd:YVO 4 laser operating on the 1.34 μm transition using intracavity SHG in BIBO or PPMgSLT

Abstract

Passive mode-locking of Nd-lasers operating on the 4 F 3/2 4 I 13/2 transition is problematic for semiconductor saturable absorber mirrors (SESAMs) not only because of difficulties in their fabrication process but also in relation to the achievable parameters and damage resistivity. We investigate an alternative approach based on second-order nonlinearity inside the laser cavity which utilizes negative χ (2) -lens formation in a SHG crystal assisted by nonlinear reflection of the so-called frequency-doubling nonlinear-mirror (FDNLM). This approach has been previously employed only for mode-locking of Nd-lasers emitting at 1.06 μm. Here we demonstrate passive mode-locking of a diode-pumped Nd:YVO 4 laser operating at 1342 nm based on negative χ (2) -lensing assisted by the FDNLM effect. Using a 7-mm-long BiB 3 O 6 (BIBO) nonlinear crystal or 10-mm-long and 1-mm-thick periodically-poled Mg-doped stoichiometric lithium tantalate (PPMgSLT) crystal and output couplers highly-reflecting at the second-harmonic with optimized transmission at the fundamental, we achieve average output powers in the steady-state mode-locked regime of the order of 1 W at pulse durations in the 4-7 ps range. Such a combination of high output power and short pulse duration is superior with respect to the results previously reported with SESAM mode-locked Nd-lasers operating on this transition. Higher average powers have been obtained for this laser transition only by the complex additive mode-locking technique. In our case the average power limit is set by the maximum power achievable in the fundamental transversal mode in the continuous-wave (CW) regime. The shortest pulses (FWHM of 3.7 ps) can be very well fitted by sech 2 temporal shape assumption.