χ(2)-Lens Mode-Locking of a Nd:YVO4 Laser with High Average Power and Repetition Rate up to 600 MHz

Abstract

We demonstrate χ (2) -lens mode-locking of a diode pumped Nd:YVO 4 laser. The output power is 6 W, the pulse duration is 6 ps for repetition rates from 110 MHz up to 600 MHz. OCIS codes: (140.3530) Lasers, neodymium; (140.4050) Mode-locked lasersMode-locked diode-pumped lasers with high average power (>1 W) and high repetition rate (~1 GHz) have attracted significant attention because of their potential applications, especially in high-capacity telecommunication systems and time-resolved spectroscopy. Semiconductor saturable absorber mirror (SESAM) mode-locking technique has been used already to generate high repetition rate picosecond pulses with duration of 13.7 ps and 21 ps respectively [1,2]. A SESAM with low modulation depth is required in order to prevent Q-switching instabilities, because in fundamental mode-locking regime at certain intra-cavity power increasing the repetition rate leads to reducing the intra-cavity pulse energy [3]. However, utilizing a SESAM with low modulation depth prevents the pulse shortening and self-starting operation of the mode-locking regime. Moreover, the residual absorption of SESAMs can lead to heating or thermal damage of the absorber, especially for operation at high intra-cavity power and high repetition rate. As an alternative to SESAMs, χ (2) -lens mode-locking has been demonstrated with Nd:YVO 4 and Nd:GdVO 4 lasers emitting output power of several watts with transform-limited pulses [4,5]. In rhis technique two physical processes govern the mode-locking operation: resonator intensity dependent loses due to intra-cavity χ (2) -lens formation and soliton-like pulse shaping due to negative intra-cavity self-phase modulation introduced by phase mismatched SHG. Hence, χ (2) -lens mode-locking enables high power operation, because there is no residual absorption typical for saturable absorbers. Besides, soliton-like pulse shaping substantially reduces the tendency to Q-switching instabilities and supports generation of transform-limited pulses.In this work we report χ (2) -lens mode-locking of a diode-pumped Nd:YVO 4 laser. Stable and self-starting modelocking operation is achieved in the case of negative intra-cavity self-phase modulation. 6.1 ps transform-limited pulses have been generated with average output power of 6.1 W and repetition rate up to 600 MHz.The laser design is based on a linear cavity, whose length can vary from 1.5 m to 0.25 m ( fig. 1). The active medium is a 9 mm long, a-cut Nd:YVO 4 crystal with doping concentration of 0.27 at. % Nd 3+ . It is longitudinally pumped by the unpolarized radiation of a 808 nm laser diode bar coupled into a 400 µm optical fiber (NA=0.22). The output beam from the fiber is focused by a 1:1.5 reimaging unit (F1-F2) and delivered onto the active medium through the mirror M1, which transmits the pump radiation. The pump beam waist is measured to be ≈300 µm in radius and the absorbed pump power is ≈90% of the incident power. The SHG crystal is a periodically-poled 1 mol. % Mg-doped stoichiometric lithium tantalate (PPMgSLT) wit...

χ(2)-Lens Mode-Locking of a Yb:YAG Laser Using Intracavity SHG in a LBO crystal

“…However, it was demonstrated manly for Nd-doped crystalline lasers. Besides, χ (2) -lens mode-locking allows generation of transform-limitted pulses [4]. It can benefit from soliton-like pulse shaping without any dispersion compensating elements due to the intra-cavity self-phase modulation, introduced by phase mismatched SHG.…”