Generation of intense sub-20-fs vacuum ultraviolet pulses compressed by material dispersion

Efficient (∼10%) generation of vacuum ultraviolet femtosecond pulses via four-wave mixing in hollow-core fibers

We report the generation of the fifth harmonic of Ti:sapphire, at 160 nm, with more than 4 µJ of pulse energy and a pulse length of 37 fs with a 1 kHz repetition rate. The vacuum ultraviolet pulses are produced using four-wave difference frequency mixing in a He-filled stretched hollow-core fiber, driven by a pump at 267 nm and seeded at 800 nm. Guided by simulations using Luna.jl, we are able to optimize the process carefully. The result is a conversion efficiency of ∼10% from the 267 nm pump beam.

Efficient generation of the 7th harmonic of Ti:sapphire (114.6 nm) vacuum ultraviolet pulses with 60 fs duration by non-collinear four-wave mixing in argon

The recent advances in femtosecond vacuum UV (VUV) pulse generation, pioneered by the work of Noack et al., has enabled new experiments in ultrafast time-resolved spectroscopy. Expanding on this work, we report the generation of 60 fs VUV pulses at the 7th harmonic of Ti:sapphire with more than 50 nJ of pulse energy at a repetition rate of 1 kHz. The 114.6 nm pulses are produced using non-collinear four-wave difference-frequency mixing in argon. The non-collinear geometry increases the phase-matching pressure, and results in a conversion efficiency of ∼10^-3 from the 200 nm pump beam. The VUV pulses are pre-chirp-compensated for material dispersion with xenon, which has negative dispersion in this wavelength range, thus allowing almost transform-limited pulses to be delivered to the experimental chamber.

Generation of intense subcycle optical pulses in a gas

The generation of intense subcycle laser pulses during the propagation of two-color femtosecond pulses in a gas medium is investigated theoretically and experimentally. Four-wave mixing induced by the laser pulses in a gas medium generates multi-octave laser radiation from the ultraviolet to the infrared, which forms stable subcycle laser pulses after a certain propagation distance in a gas medium with group-velocity dispersion. The intense subcycle laser pulses would allow the coherent control of the waveforms of soft-x-rays generated via high-harmonic generation.

Efficient generation of below-threshold harmonics for high-fidelity multi-photon physics in the VUV spectral range

We demonstrate the generation of microjoule level, sub-20-fs, Ti:Sa fifth-harmonic pulses utilizing a loose-focusing geometry in a long Ar gas cell. The VUV pulses centered at 161.8 nm reach pulse energies of 1.1 μJ per pulse, while the corresponding pulse duration is measured with a second-order, fringe-resolved autocorrelation scheme to be 18±1  fs. Nonresonant, two-photon ionization of Kr and three-photon ionization of Ne verify the fifth-harmonic pulse high-intensity content and indicate the feasibility of multi-photon VUV pump-VUV probe studies of ultrafast atomic and molecular dynamics.

Generation of sub-17 fs vacuum ultraviolet pulses at 133 nm using cascaded four-wave mixing through filamentation in Ne

The sixth harmonic (6ω, 133 nm) of a Ti:sapphire laser is generated using cascaded four-wave mixing in filamentation propagation of the fundamental (ω) and the second harmonic (2ω) pulses through Ne gas. The method provides the 6ω pulse energy higher than 5 nJ/pulse at 1 kHz and a pulse duration shorter than 17 fs without dispersion compensation.

Enhanced XUV pulse generation at 89 nm via nonlinear interaction of UV femtosecond filaments

We demonstrated efficient generation of ultrafast extreme ultraviolet (XUV) pulses at 89 nm from an intense 267 nm UV femtosecond filamentation in argon gas. The XUV pulse generation efficiency was significantly enhanced through UV filament termination from the argon gas into the background vacuum that prevented backconversion of the generated third-harmonic XUV to the fundamental-wave UV pulses. This was further combined with noncollinear UV filament interaction that produced volume-plasma to pre-extract XUV pulses from the filament core, resulting in further XUV enhancement. The generated 89 nm XUV pulses reached what is so far, to our knowledge, the highest pulse energy of 190 nJ.

Simultaneous generation of sub-20 fs deep and vacuum ultraviolet pulses in a single filamentation cell and application to time-resolved photoelectron imaging

Sub-20 fs pulses of the third, fourth, and fifth harmonics of a Ti:sapphire laser are simultaneously generated using cascaded four-wave mixing in filamentation propagation of the fundamental frequency and the second harmonic pulses in Ne gas. Reflective optics under vacuum are employed after the four-wave mixing to minimize material dispersion of the optical pulses. The cross-correlation between 198 and 159 nm pulses of 18 fs is achieved without dispersion compensation. This new light source is applied to time-resolved photoelectron imaging of carbon disulfide (CS₂).

Generation of tunable sub-45 femtosecond pulses by noncollinear four-wave mixing

Generation of sub-45 fs vacuum UV (VUV) pulses tunable across the spectral range of 146-151 nm at 1 kHz repetition rate is reported. The pulses are produced using noncollinear difference-frequency four-wave mixing between the third-harmonic of an amplified Ti:sapphire laser and the signal wavelength of an infrared optical parametric amplifier (ω(VUV)=2ω(TH)-ω(IR)) in krypton and argon. The generated VUV pulses have energies as high as 90 nJ. Pulse duration measurements are realized by cross correlation between the VUV pulses and the laser fundamental wavelength using pump-probe ionization in xenon.