Guided-Wave Optical Parametric Amplification in Gases: A Novel Phase-Matching Technique for Ultrafast Pulses

Abstract

Despite much recent progress in developing ultrafast laser systems with pulse duration less than 25 fs in the near-infrared1, many applications in solid state physics, surface science, biophysics, and chemistry2 require ultrafast pulses with energies >μJ in the ultraviolet (UV). In the past, third harmonic generation (THG) by sum-frequency mixingin nonlinear crystals has been used to generate light in the deep ultraviolet3. While this technique can result in conversion efficiencies of several percent, it suffers from pulse broadening due to group velocity walkoff in the medium. The resulting pulse duration of 200 fs is too long to monitor reaction dynamics in many cases, particularly in small molecules and organic species. THG by focusing high-intensity infrared pulses in a gas4,5 does not suffer from severe temporal walkoff, and thus can be used to generate very short-duration pulses. In previous work4 we demonstrated that by focusing 20 fs pulses in air or noble gases, third-harmonic light at 270 nm with 14 fs pulse duration can be generated. However, in this case, the conversion efficiency (~ 0.1%) is relatively low due to the short interaction length and poor phase matching.