A unified miniature optically pumped NH 3 FIR laser (unified mini OPFIR cavity laser),including a mini TEA CO 2 pump laser, was developed. The optimum operation of the unified mini-OPFIR cavity laser was studied experimentally. The relations among FIR laser output power, operating gas pressure, length and coupling condition of the cavity were measured. lt was found that the very wide band FIR laser emission was a common feature of the mini OPFIR cavity laser. This will be a new way for wide range frequency tuning of FIR laser.