For the pulse pumped CO
2laser we used Q-switching to investigate inversion kinetics. The pump was synchronized with the Q-switching mirror. It was possible to obtain the Q-switch pulses at any phase of the pump pulse. The repetition rate was 50 Hz and the pump pulse duration was 4 or 10 ms. It was found that there is an optimum delay in switching the cavity Q-factor after the discharge started. The giant pulse intensity increased several times after the discharge was switched from CW to pulses. The inversion rise time was 1-2 ms and its lifetime was strongly dependent on the discharge current, due to plasma heating during the current pulse. Increasing the helium percentage in the discharge prolonged the inversion lifetime because of high thermal conductivity of helium gas. Gaseous BCl
3was chosen to obtain the CO
2laser giant pulses with bleachable filter. The vibronic frequency V
3of the B
11Cl
3molecules coincides with the

lines of the CO
2laser. Rarer B
10Cl
3corresponds to less active

lines. Pure BCl
3did not give the giant pulses. Adding helium to the BCl
3cell gave the pulses. The best results came from adding very small amounts of ammonia NH
3because of the effective vibrational energy transfer between colliding BCl
3and NH
3molecules.