Despite much recent progress in developing ultrafast laser systems with pulse duration less than 25 fs in the near-infrared, many applications in solid state physics, surface science, biophysics, and chemistry 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 ultraviolet. 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.