Ida Zsuzsanna Kozma, Peter Baum, Stefan Lochbrunner

Parametrically generated pulses have broad tunability in the near IR and visible spectral region, and the noncollinear geometry provides ultrabroadband pulses. Most organic molecules have their electronic absorption in the blue and UV spectral region. region. Therefore it is essential to extend the available spectral range to shorter wavelengths and to develop schemes for efficient generation of ultrashort optical pulses tunable in the blue and UV. Tunable UV pulses can be generated from parametrically generated pulses by frequency doubling, quadrupling or upconversion with a powerful near IR pulse (sum frequency mixing (SFM)). Since larger pulse energies and higher pulse energy and beam profile stability can be achieved with the SFM process, we developed a new SFM scheme for efficient pulse generation. The possible schemes for mixing the 130 fs pulse of the Ti:sapphire chirped pulse amplifier (CPA) and the 150 fs chirped pulse of the tunable NOPA source are presented here. inefficient energy transfer complicated adjustment of 2 compressors good tunability pulse lengthening due to bad temporal overlap efficient energy transfer good temporal overlap for all spectral components         We showed that the nonlinear frequency conversion via SFM of ultrashort tunable visible pulses from a NOPA is best performed when the pulses are deliberately left chirped. The mixing with stretched pulses from the Ti:sapphire pump system leads to UV pulses with energies of several µJ and a broad tuning range of 295 - 450 nm.   No compressor is needed in the visible and therefore tuning of the UV wavelength is easy and requires only tuning of the NOPA and a fine tuning of the temporal overlap in the SFM crystal. The generated pulses were compressed to sub-30 fs throughout the entire tuning range (20 fs at 348 nm) with a newly designed prism compressor, which avoids the need for broadband polarization-rotation elements.

"Widely tunable sub-30 fs ultraviolet pulses by chirped sum frequency mixing" Ida Z. Kozma, Peter Baum, Stefan Lochbrunner and Eberhard Riedle Opt. Express 11, 3110 - 3115 (2003) Details