A Mid-IR Optical Parametric Oscillator Pumped by an Actively Q-Switched Ho:YAG Ceramic Laser*Supported by the National Natural Science Foundation of China under Grant Nos 61308009, 61405047 and 50990301, the Fundamental Research Funds for the Central Universities under Grant Nos HIT.NSRIF.2014044 and HIT.NSRIF.2015042, and the Science Fund for Outstanding Youths of Heilongjiang Province under Grant No JQ201310. (August 2015)