Coherent interaction of picosecond pulses in a fluorescent medium and the timing of pulse trains for two-wavelength excite and probe measurements

Abstract

Coherent interaction between two cw, picosecond pulse trains of the same wavelength absorbed by a fluorescent material and the effect on the emission has been studied. As the path difference between the two beams is varied, the infra-red emission from colour centres in KCl: Na or KCl: Li fluctuates in phase with the transmitted intensity of the weaker of the two beams. The effect may be applied to the accurate relative timing of cw pulse trains of different wavelengths for use in two-wavelength, excite and probe measurements. A small fraction of the pump pulse train is superimposed on the probe beam and passes along precisely the same optical path. Coherent interaction between the two pulse trains at the pump frequency causes modulation of the transmitted probe beam intensity when pump and probe pulses are accurately synchronised.