Study of an injection-seeded supra-atmospheric CO(2) laser operated below emission threshold with a ring cavity

The dynamics and tuning range of an injection-seeded supra-atmospheric CO(2) laser operated at a pressure of 10 atm with a ring cavity are studied theoretically and experimentally. When the losses of such a laser are sufficiently high, the short lifetime of the gain does not permit the buildup of intense pulses that start from spontaneous emission noise; the laser is then said to be operated below emission threshold. Under such circumstances, injection seeding with a few milliwatts of a single-mode signal permits nearly full extraction of the available power. The extraction efficiency is shown to depend in a sensitive manner on the frequencies of a cavity mode and of the injected signal. When these two frequencies are mismatched, a lower power is extracted, and two-mode emission takes place. The laser is shown to be tunable over 41 transition lines of the CO(2) spectrum.