Analysis of various optical pumping schemes for liquid oxygen lasers

Singlet oxygen generated by optical pumping in liquid oxygen/air medium has recently been reported as a potential gain medium for high power lasers at 1580 nm, by USA’s defense agency DARPA. However, the details with reference to the underlying physics of this laser and the potential pumping techniques for achieving lasing are still unclear. The present paper investigates numerically the population kinetics of both upper and lower lasing levels viz. O2$(^{1}\Delta_{g})_{v=0}$ and O2$(^{3}\Sigma_{g})_{v=1}$ states in liquid oxygen and discusses the criticality involved in obtaining lasing with this medium. Isotopic liquid oxygen and liquid air medium where improved conditions for lasing are anticipated, as compared to that in natural liquid oxygen, have also been considered in the present study. The studies have been carried out for optical pumping by both continuous and pulsed mode lasers at 1064 nm and 634 nm wavelengths. The temporal variation of small signal gain in each case has been investigated along with limitations of the same from point of view of lasing. The available and extractable power from all three medium for an optimum pumping case has also been discussed. The studies reveal that liquid air has high potential for very high power lasers as compared to both natural and isotopic liquid oxygen.