High-power optical parametric frequency converters with addressable wavelengths in the IR

摘要

Based on established short pulse lasers with an output wavelength around 1μm optical parametric frequency converters open up the spectral range between 1.4 and 4.0μm for the first time in a power range of interest to laser material processing. The systems can be flexibly adapted as regards wavelength, pulse parameters and spectral properties to the requirements of various applications. We will discuss technical implementation and characterization of different optical parametric generators (OPG) based on periodically poled Lithium Niobate (PPLN) to show the parameter flexibility of this approach as well as current technical limits. Actual design examples will address output wavelengths between 1.6μm and 3.4μm with output powers ranging from several watts to tens of watts. The pulse parameters of these lasers range from a pulse duration of 9 ps with a repetition rate of 86 MHz to 1.5 ns and 100 kHz. The spectral bandwidth of the OPG examined can be very large. In particular, spectral bandwidths of about 100 nm are measured at the degenerated point, where the output wavelength is equal to twice the pump wavelength. Even beyond this point, a spectrum of typically a few tens of nanometers width generally accompanies a large conversion efficiency (>50 %). For applications that require a narrower spectrum, the OPG can be operated in a seeded mode, where only a few milliwatts of power from a continuously emitting laser diode are sufficient to seed a pulsed high power OPG efficiently and reduce the bandwidth to few nanometers.