Abstract
Passively modelocked diode-pumped solid-state lasers (DPSSLs) with pulse repetition rates in the gigahertz regime suffer from an increased tendency for Q-switching instabilities. Low saturation fluence intracavity saturable absorbers - such as the semiconductor saturable absorber mirrors (SESAMs) - can solve this problem up to a certain average output power limited by the onset of SESAM damage. Here we present a passive stabilization mechanism, an all-optical Q-switching limiter, to reduce the impact of Q-switching instabilities and increase the potential output power of SESAM modelocked lasers in the gigahertz regime. With a proper cavity design a Kerr lens induced negative saturable absorber clamps the maximum fluence on the SESAM and therefore limits the onset of Q-switching instabilities. No critical cavity alignment is required because this Q-switching limiter acts well within the cavity stability regime. Using a proper cavity design, a high-power diode-pumped Yb:CALGO solid-state laser generated sub-100 fs pulses with an average output power of 4.1 W at a pulse repetition rate of 5 GHz. With a pulse duration of 96 fs we can achieve a peak power as high as 7.5 kW directly from the SESAM modelocked laser oscillator without any further external pulse amplification and/or pulse compression. We present a quantitative analysis of this Kerr lens induced Q-switching limiter and its impact on modelocked operation. Our work provides a route to compact high-power multi-gigahertz frequency combs based on SESAM modelocked diode-pumped solid-state lasers without any additional external amplification or pulse compression.
Highlights
The semiconductor saturable absorber mirrors (SESAMs) (SEmiconductor Saturable Absorber Mirror) [1,2,3] has established itself as a key enabling technology for ultrafast lasers, and most if not all commercially available ultrafast lasers use the SESAM technology in industrial-compatible laser systems
SESAM modelocked diode-pumped solid state lasers (DPSSLs) have demonstrated quantum-noise limited performance [4] which benefits a large number of applications at gigahertz pulse repetition rates, such as high-speed optical communications [5,6,7], optical interconnects [8], optical clocks [9], lidar [10, 11], high-speed asynchronous optical sampling [12], analog-todigital converters [13], and optical frequency metrology [14,15,16]
We have introduced and demonstrated an all-optical Q-switching limiter to reduce Qswitching instabilities in SESAM modelocked diode-pumped Yb(5% at.)-doped CaGdAlO4 crystal (Yb)-doped solid-state lasers operating at gigahertz pulse repetition rates
Summary
The SESAM (SEmiconductor Saturable Absorber Mirror) [1,2,3] has established itself as a key enabling technology for ultrafast lasers, and most if not all commercially available ultrafast lasers use the SESAM technology in industrial-compatible laser systems. We provide a solution for further power scaling in the gigahertz pulse repetition rate regime using both low-brightness industrial-grade high-power pump laser diodes and larger mode sizes in gain and absorber, addressing both limitations at the same time. In contrast to KLM no operation close to the cavity stability regime is required We implement this Q-switching limiter in a SESAM modelocked Yb:CALGO DPSSL generating pulses as short as 96 fs with an average power of 4.1 W at a record-high pulse repetition rate of 5 GHz. The Q-switching limiter allowed for this power scaling at higher pulse repetition rates by increasing the cavity mode sizes and using highpower pumping with a commercial low-brightness laser diode array. This compact laser provides state-of-the-art performance with high power sub-100-fs pulses using a simple and robust cavity design in combination with straightforward SESAM modelocking and standard diode pumping
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