Nonlinear Compression of Intense Optical Pulses at 1.55 μm by Multiple Plate Continuum Generation

Intense ultrashort laser pulses at 1.55 μm are generated by a home-built light source and compressed to 20 fs by multiple plate continuum (MPC) and Fourier pulse shaping. The entire system consists of three building blocks, responsible for seed generation, optical parametric chirped pulse amplification (OPCPA), and nonlinear compression. A commercial Yb:KGW amplifier pumps a difference frequency generator and an optical parametric amplifier (OPA) to generate 1 kHz, 44 fs, 10 μJ, carrier-envelope phase stable seed pulses at 1.55 μm. A grating-lens pair stretches the seed pulses to 50 ps by introducing a great amount of normal group delay dispersion (GDD). After that, the chirped pulse energy is boosted to 5 mJ by two OPA stages pumped by a commercial Nd:YAG amplifier (30 mJ, 85 ps). To compress the amplified pulses, a grating pair compressor providing an adequate amount of anomalous GDD is employed. The OPCPA system eventually delivers 3 mJ and 80 fs pulses, limited by the phase-matching bandwidth of nonlinear crystals. To further compress the pulse duration, pulses are sent to an MPC stage, which consisted of nine pieces of 200-μm-thick quartz plates. The OPCPA output spectrum is broadened by four times and compressed to 20 fs (3.6 carrier cycles) by a femtosecond Fourier-transform pulse shaper. The pulses are characterized by polarization gating cross-correlation frequency-resolved optical gating. Due to the high pondermotive force, an intense and long-wavelength laser system like this is useful in seeding a MeV-level electron accelerator and generating coherent soft X-ray high-harmonic generation.