Since resonant absorption of light caused by a variety of different molecular bond occurs in the mid-infrared (MIR) wavelength region, many applications using tunable MIR lasers have been reported. However, the applicable fields of the MIR tunable lasers have been restricted by their large size and high cost equipments. Therefore, we are developing a compact tunable MIR laser using an optical parametric oscillator (OPO). To obtain a long term stability and a high conversion efficiency, a diode-pumped and Q-switched Tm,Ho:YAG ceramic laser with a wavelength of 2.1 μm was adopted for the pump source. A maximum output energy of 40 mJ was obtained with the Tm,Ho:YAG ceramic laser at a pulse width of 150 ns and a repetition rate of 10 Hz. An experiment was performed using a singly-resonant OPO with a ZnGeP2 crystal pumped by another OPO with a wavelength of 2.1 μm. A threshold pump fluence of 0.2 J/cm2 and a slope efficiency of 60% were obtained at a signal and idler wavelengths of 3.3 and 5.6 μm, respectively. Using these results and a theoretical model calculation, the maximum output energy of MIR-OPO pumped with the Tm,Ho:YAG ceramic laser was estimated to be about 20 mJ.© (2009) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.