Post-Compression of a Q-Switched Laser in a Multi-Pass Cell

The two most notable methods for producing short laser pulses are mode-locked and Q-switched lasers. While mode-locked lasers generate pulses in the pico- (ps) to femtosecond (fs) range, Q-switched lasers typically produce pulses at the nanosecond (ns) or 100 ps level [1]. Thus, mode-locking has been the superior technology when ultrashort pulses or high peak powers are required. On the other hand, Q-switched lasers can have great advantages owing to their simplicity, compactness, low costs, and the large pulse energies that can be generated [2]. To bridge the parameter gap between mode-locked and Q-switched lasers, pulse post-compression appears attractive. One possible method is self-phase-modulation (SPM) in optical fibers [3]. However, stimulated-Raman-scattering limits the possible peak powers to far below 1 kW and thus pulse energies to lower than μJ level for ns pulses [3]. Another SPM-based method are Multi-pass cells (MPCs), which have become a standard technology for post-compression of mode-locked lasers [4]. However, MPCs have not yet been used to compress Q-switched laser pulses due to their inherently low peak powers. Here, we demonstrate a new MPC type, facilitating post-compression of pulses with order-of-magnitude lower peak power than typical bulk-MPCs [4]. We use a fused silica block as the nonlinear medium and compress 1 mJ pulses from the nanosecond down to the picosecond regime.