High-power 2 micron optical-parametric frequency converter with sub-picosecond pulse duration

摘要

Ultrashort pulse lasers with pulse durations < 1 ps make it possible to cold process a wide range of materials, whileintroducing virtually no heat into the workpiece. Industrial ultrashort pulse lasers are currently mainly limited to thewavelength range around 1 μm and below. With optical parametric frequency conversion, however, the addressablewavelength can be extended to the IRB range (1.5 to 3.0 μm).Based on a commercially available laser emitting at a wavelength of 1030 nm, the system presented here generates laserlight at a wavelength of 2.06 μm in a two-stage process. First, in an optical parametric generator (OPG), part of the pumppower is converted into the degenerated signal and idler field (2.06 μm). In an optical parametric amplifier (OPA), thisfield is further amplified by the remaining pump power. An optional seeding with a narrow-band diode laser can be usedto influence the output bandwidth in a targeted manner.An output power of 18.5 W was generated from approximately 80 W input power. At a pulse repetition rate of 800 kHz,this corresponds to a pulse energy of approximately 23 μJ. Moreover, a beam quality M2 of 1.8 and 2.0 in horizontal andvertical direction was achieved. The pulse duration at 2 μm at this operating point is about 600 fs at a pump pulseduration of 900 fs. At an operating point with optimized power, a maximum output power of about 28 W, correspondingto about 35 μJ of pulse energy, was generated. The overall conversion efficiency at this working point was more than 35percent.