650 fs pulses at 1045 nm from a passively Q-switched Nd:YVO<inf>4</inf> microchip laser system

Abstract

Summary form only given. In this contribution we present a novel concept to produce ultrashort pulses from a passively Q-switched Nd:YVO4 microchip [1] laser system reaching the sub-ps range with a tunable emission wavelength from 1030nm to 1050nm.This method comprises two stages: one that carries out the nonlinear compression of the spectrally broadened microchip pulses with a grating compressor [2] and a second stage, in which these pulses are coupled into a further waveguide for additional spectral broadening through self-phase modulation (SPM) followed by a narrow band-pass filter [3]. The high peak power and the short pulse duration of the compressed pulses result in wide SPM spectra with a nearly un-chirped region at the spectral edges, which is used for this concept. Therefore, the spectrally broadened pulses can be filtered afterwards far away from the original central wavelength, which leads in addition to temporal pulse shortening and cleaning to an adjustable wavelength shift. To the best of our knowledge the combination of nonlinear compression and subsequent spectral filtering is used the first time for generating wavelength-tunable sub-ps pulses from a Q-switched laser source.The setup of a proof-of-principle experiment (Fig. 1a) consists of a fiber-amplified Nd:YVO4 microchip laser source, which emits SPM-broadened 72 ps pulses followed by a grating compressor leading to pulse durations of 5.9 ps with a central wavelength of 1064 nm. Afterwards, these compressed pulses are coupled into a passive single-mode fiber (0.3 m long, 10 μm core diameter), in which SPM broadens the spectrum to a bandwidth of approximately 40 nm (-20 dB) (Fig. 1c). The used band-pass has a spectral transmission window of 6 nm with a tunable central filter wavelength. Subsequent filtering at the lower edge of the pulse spectrum results in pedestalfree pulses with a 650 fs full width at half maximum (FWHM) duration corresponding to an autocorrelation trace of 0.9 ps (FWHM) (Fig. 1b). At the same time the filtered pulses have been shifted from 1064 nm to 1045 nm (Fig. 1c), which is very advantageous for subsequent power amplification in Yb-doped fibers. In conclusion, the presented method appears very suitable for passively Q-switched microchip laser systems to reach the sub-ps range. Moreover, this concept seems very suitable for the integration into an all-fiber system, which would result in very compact and stable lasers delivering ultrashort pulses. Such a laser can find many applications, especially in the field of micromachining and might be a very promising alternative to conventional mode-locked laser systems.