Effect of counterintuitive time delays in nonlinear mixing

The effect of varying the relative arrival time of the two laser pulses emp loyed in doubly resonant four-wave sum mixing, enhanced by induced transpar ency, is studied with the aim of optimizing the efficiency of vacuum-ultrav iolet generation. With atomic hydrogen as the nonlinear medium, pulsed radi ation with wavelengths of 243 and 656 nm and durations of 8 and 14 ns, resp ectively, is mixed to generate 103-nm coherent radiation. It is shown that by delaying the arrival time of the ground-state pump beam (243 nm) by 2.5- 3.5 us relative to the arrival of the upper-state coupling beam (656 nm), i t is possible to enhance the generated intensity by a factor of 2 or more. (C) 2000 Optical Society of America. OCIS codes: 190.4380, 270.1670, 260.52 10, 020.6580, 270.4180.