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

Ultrashort pulse lasers with pulse durations < 1 ps make it possible to cold process a wide range of materials, while introducing virtually no heat into the workpiece. Industrial ultrashort pulse lasers are currently mainly limited to the wavelength range around 1 μm and below. With optical parametric frequency conversion, however, the addressable wavelength 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 laser light at a wavelength of 2.06 μm in a two-stage process. First, in an optical parametric generator (OPG), part of the pump power is converted into the degenerated signal and idler field (2.06 μm). In an optical parametric amplifier (OPA), this field is further amplified by the remaining pump power. An optional seeding with a narrow-band diode laser can be used to 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 and vertical direction was achieved. The pulse duration at 2 μm at this operating point is about 600 fs at a pump pulse duration of 900 fs. At an operating point with optimized power, a maximum output power of about 28 W, corresponding to about 35 μJ of pulse energy, was generated. The overall conversion efficiency at this working point was more than 35 percent.