Ultrashort pulsed laser coherence measurements by single-pulse holography and four-wave mixing

We present a technique for determining coherence times of single femtosecond or picosecond pulses by a holographic method that measures the diffraction efficiency of a holographically recorded, time dispersed interference pattern. The results are discussed in terms of recent transient grating interpretations that use fourth-order coherence functions. Picosecond coherence times are measured for single 532-nm pulses, short-cavity dye-laser (SCDL) pulses, and a train of cw mode-locked dye-laser pulses. Nonrandom background coherence effects in a Nd:YAG (532-nm) laser are observed with both four-wave mixing measurements of average coherence and single-shot holographic measurements under operating conditions of spectral broadening. The SCDL has a coherence time of 2.8 psec, and both techniques measured random background coherence artifacts over the 22-psec pulse duration.