Abstract
Theoretical model for a rotating mirror Q switched CW CO laser is presented. It considers 36 vibration levels including the ground level of CO molecule. Lasing on 20 rotational lines in 18 vibration bands is considered. The lasing on these lines takes place between the rotational sublevels associated with each vibration level. Hence one is required to develop the rate equations for the 36 vibration levels, 397 rotational sublevels and also the equations for the photon densities associated with the360 lasing lines. These equations include the varying loss experienced by the lasing mode as it traverses the gain medium due to rotation of the mirror. The discharge has a thermal gradient. To take this into account we divide the gain medium into two zones, a central one matching with the laser mode and the rest of the discharge zone as the second zone. The two zones are assigned two temperatures as per the calculated average temperatures in these two zones. The calculations of how the above variables vary with time are carried out with the help of a fourth order Runge Kutta routine in the two zones separately. For each time step the model also calculates the intersection areas of the laser mode with the two zones. The actual power profiles of all the individual lasing lines are obtained by combining their powers in these two zones and the corresponding intersection areas. An important application of this laser in additional frequency generation in nonlinear crystals, require time synchronisation among interacting pulses. Our results show that in each vibration band about 12 to –13 lines operate, but only 3 to –4 among them are strong and are well synchronised in time. Their growth is determined by cascade lasing, higher gain coefficient compared to their neighbours and preference of their growth due to rotational relaxation. The results at operation of the rotating mirror at100 Hz, shows that about 222 lines operate and about 65 lines shows this synchronisation property. The results have been validated with experimental data available in the literature.
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