HETERODYNE-DETECTION OF THE COMPLETE ELECTRIC-FIELD OF FEMTOSECOND 4-WAVE-MIXING SIGNALS

A novel optimized heterodyne method that recovers the complete electri c field of any four-wave mixing signal at its point of origin is demon strated. A tracer pulse is sent along the signal path and characterize d at the sample by frequency-resolved optical gating. Spectral interfe rometry is used to determine the phase difference between the tracer a nd a reference pulse, the absorptive change in tracer phase in the sam ple, and the reference-signal phase difference. Together, these measur ements allow calculation of the signal phase at the sample. The phase of three pulse-scattering signals from solutions of the infrared dye I R 144 in methanol determines the absolute signal-emission time within 0.5 fs. (C) 1998 Optical Society of America [S0740-3224(98)01108-4] OC IS codes: 320.7100, 190.4830, 300.6310.