ABSTRACT
Ultrashort ultraviolet (UV) pulses are pivotal for resolving ultrafast electron dynamics. However, their efficient generation is strongly impeded by material dispersion and two-photon absorption, in particular, if pulse durations around a few tens of femtoseconds or below are targeted. Here, we present a new (to our knowledge) approach to ultrashort UV pulse generation: using the fourth-harmonic generation output of a commercial ytterbium laser system delivering 220â fs UV pulses, we implement a multi-pass cell (MPC) providing 5.6â µJ pulses at 256â nm, compressed to 30.5â fs. Our results set a short-wavelength record for MPC post-compression while offering attractive options to navigate the trade-off between upconversion efficiency and acceptance bandwidth for UV pulse production.
ABSTRACT
The generation of below-threshold harmonics in gas-jets constitutes a promising path towards optical frequency combs in the vacuum ultra-violet (VUV) spectral range. Of particular interest is the 150â nm range, which can be exploited to probe the nuclear isomeric transition of the Thorium-229 isotope. Using widely available high-power, high-repetition-rate Ytterbium-based laser sources, VUV frequency combs can be generated through the process of below-threshold harmonic generation, in particular 7th harmonic generation of 1030â nm. Knowledge about the achievable efficiencies of the harmonic generation process is crucial for the development of suitable VUV sources. In this work, we measure the total output pulse energies and conversion efficiencies of below-threshold harmonics in gas-jets in a phase-mismatched generation scheme using Argon and Krypton as nonlinear media. Using a 220 fs, 1030â nm source, we reach a maximum conversion efficiency of 1.1 × 10-5 for the 7th harmonic (147â nm) and 0.78 × 10-4 for the 5th harmonic (206â nm). In addition, we characterize the 3rd harmonic of a 178 fs, 515â nm source with a maximum efficiency of 0.3%.
ABSTRACT
In this work, we demonstrate postcompression of 1.2 ps laser pulses to 13 fs via gas-based multipass spectral broadening. Our results yield a single-stage compression factor of about 40 at 200 W in-burst average power and a total compression factor >90 at reduced power. The employed scheme represents a route toward compact few-cycle sources driven by industrial-grade Yb:YAG lasers at high average power.