Experimental and theoretical investigation of the frequency sweep exhibited by a TEA CO2 laser with a ring resonator and injection of radiation

The heterodyne method was used in an experimental investigation of the frequency dynamics during operation of a TEA CO₂ laser with a ring resonator and radiation injection. The time dependence of the change in the frequency during lasing differed qualitatively from the results of other authors. The short duration of the discharge pulses and a considerable delay of lasing relative to these pulses prevented reduction in the frequency during the initial part of the pulse. Creation of a shock wave by the discharge in the anode region lowered the lasing frequency at the end of a pulse. This was attributed to a change in the mode composition of the output radiation during lasing. A theoretical analysis was made of the factors responsible for the change in the emission frequency. At the beginning of a pulse the frequency change was dominated by heating of the active medium by the discharge current pulse, whereas at the end of a pulse the dominant effect was the influence of the shock wave on the change in the mode composition. The experimental results agreed well with the theoretical calculations.