Generation of watt level mid-infrared wavelengths using intra-cavity ZnGeP 2 OPO within a 2.1µm Ho:YAG laser

Abstract

We report on watt level mid-infrared (MIR) wavelength generation using intra-cavity ZnGeP₂ (ZGP) optical parametrical oscillator (OPO) within a 2.1μm Ho:YAG laser. A compact cavity of less than 50cm was designed for the intra-cavity OPO setup. With the same laser setup, watt level of both 2.1μm and MIR wavelengths were generated. An average output power of >20W of 2.1μm and >1W of MIR wavelength at 10 KHz repetition rate were achieved from a 46W Tm fiber pump laser. The Ho:YAG laser was resonantly pumped by a 1.9μm Tm:fiber laser and nanosecond pulses were generated using an electro-optics q-switch modulator. With the use of a λ/4 waveplate and a thin film polarizer, a variable output coupler for the Ho:YAG laser was formed where we could optimize the output coupling to achieve 21W of 2.1μm wavelength. MIR wavelengths were generated using commercial ZGP crystals from Inrad. A HR mirror for the MIR wavelengths was inserted into the Ho:YAG cavity to form the intra-cavity ZGP OPO. The rear mirror of the Ho:YAG cavity act as the output coupler with R=70% for the MIR wavelengths. Optimizing of the MIR generation was done by tuning the phase-matching angle of the ZGP and adjusting the cavity length of the OPO. A preliminary result of the intra-cavity ZGP OPO generates >1W of MIR wavelength.