Compressed OPO pulses provide tunable femtosecond infrared output

Compressed OPO pulses provide tunable femtosecond infrared output

David Hanna and colleagues at the Optoelectronics Research Centre (Southampton, England) are operating a synchronously pumped optical parametric oscillator (OPO) based on periodically poled lithium niobate (PPLN) using 4-ps pum¥pulses at 1047 nm from a commercial diode-pumped CW modelocked Nd:YLF laser (DPM-1000-120 from Microlase; Glasgow, Scotland). An OPO resonator slightly longer than the exact matched length produces signal pulses compressed by a factor of 20--to 200-250-fs pulses. Essentially all of the pum¥energy is transferred into these short pulses, and the OPO produces higher peak powers than the pum¥laser. The nonresonant idler beam also showed compression.

Hanna says the effect is stable over a signal-beam tuning range of 1.7 to 1.9 µm and idler-beam tuning range of 2.3 to 2.7 µm and depends on high gain--which the PPLN offers because of its high nonlinearity--as well as grou¥velocity dispersion. "This is an extremely easy way of achieving compression," says Hanna. "It is very efficient and it gives infrared tunability . . . and avoids the cost and complexity of an argon and Ti:sapphire laser, which is currently the standard route to femtoseconds and tunability. We think this is an important ste¥in making femtosecond technology more accessible."