Femtosecond OPO pumped by a high power ytterbium rod-type fiber laser mode locked at harmonic repetition rates

Abstract

Given their interest in multiple, most notably in spectroscopy, high-speed optical sampling, optical frequency comb, super-continuum generation, and others, high repetition rate (HRR) femtosecond lasers have attracted a lot of attention in the last decade. In rare-earth-doped fiber, the HRR can be achieved by controlling the nonlinear polarization rotation in long and heavily doped erbium or ytterbium fibers. However, it is usually difficult to tune the central wavelength of oscillators by providing pulses at an HRR. Further extension in the IR can be achieved through pumping an optical parametric oscillator (OPO) by amplifying the output of an HRR laser system. Compared with SHG and SFG, OPOs generate pulses that can be tuned on a broad spectral range, with limited pulse-to-pulse energy fluctuations and almost a TEM00 beam profile. Hence, one of the simplest and efficient ways to generate tunable HRR femtosecond pulses on a broad spectral range is to pump an OPO with a high-power laser oscillator, where one can adjust the PRR. We perform an experiment using an ytterbium rod-type fiber that provides more than 4.5W output power and tens of nJ per pulses, in which the PRR is controlled by nonlinear polarization rotation. The pulses delivered by this laser are further used to pump an OPO. The OPO is shown to work without any further adjustments. The femtosecond signal pulse delivered by this singly resonant OPO is tunable from 1450nm to 1700nm.