Elena Fedulova

Energy scaling of Kerr-lens mode-locked thin-disk oscillators

Geometric scaling of a Kerr-lens mode-locked Yb:YAG thin-disk oscillator yields femtosecond pulses with an average output power of 270 W. The scaled system delivers femtosecond (210-330 fs) pulses with a peak power of 38 MW. These values of average and peak power surpass the performance of any previously reported femtosecond laser oscillator operated in atmospheric air.

High-power multi-megahertz source of waveform-stabilized few-cycle light

Waveform-stabilized laser pulses have revolutionized the exploration of the electronic structure and dynamics of matter by serving as the technological basis for frequency-comb and attosecond spectroscopy. Their primary sources, mode-locked titanium-doped sapphire lasers and erbium/ytterbium-doped fibre lasers, deliver pulses with several nanojoules energy, which is insufficient for many important applications. Here we present the waveform-stabilized light source that is scalable to microjoule energy levels at the full (megahertz) repetition rate of the laser oscillator. A diode-pumped Kerr-lens-mode-locked Yb:YAG thin-disk laser combined with extracavity pulse compression yields waveform-stabilized few-cycle pulses (7.7 fs, 2.2 cycles) with a pulse energy of 0.15 μJ and an average power of 6 W. The demonstrated concept is scalable to pulse energies of several microjoules and near-gigawatt peak powers. The generation of attosecond pulses at the full repetition rate of the oscillator comes into reach. The presented system could serve as a primary source for frequency combs in the mid infrared and vacuum UV with unprecedented high power levels.

Kerr effect in multilayer dielectric coatings

We report the utilization of the optical Kerr effect in multilayer dielectric coatings, previously discussed only theoretically. We present the design and realization of multilayer dielectric optical structures with layer-specific Kerr nonlinearities, which permit tailoring of the intensity-dependent effects. The modulation depth in reflectance reaches up to 6% for the demonstrated examples of dielectric nonlinear multilayer coatings. We show that the nonlinearity is based on the optical Kerr effect, with the recovery time faster than the laser pulse envelope of 1 ps. Due to high flexibility in design, the reported dielectric nonlinear multilayer coatings have the potential to open hitherto unprecedented possibilities in nonlinear optics and ultrafast laser applications.

Highly-dispersive mirrors reach new levels of dispersion

A highly-dispersive mirror with the unprecedented group delay dispersion of -10000 fs2 in the wavelength range of 1025-1035 nm is reported. Reproducible production of a coating with such a high dispersion was possible due to the recently developed robust synthesis technique. Successful employment of the new highly-dispersive mirror in an oscillator is demonstrated.

Power-scaling a Kerr-lens mode-locked Yb:YAG thin-disk oscillator via enlarging the cavity mode in the Kerr-medium

We report on a purely hard-aperture Kerr-lens mode-locked Yb:YAG thin-disk oscillator delivering 230-W, 11.5-μJ, 330-fs (30 MW) in air. To our knowledge this is the highest average power achieved from KLM oscillators so far.

Dielectric optical coatings at high peak intensities

Recent developments in the synthesis, production and characterization of multilayer optical coatings provide precise group-delay dispersion control over broadband spectral ranges. High laser induced damage threshold of dielectric coatings allow exposing them at high intensity laser radiation on the order of 10–1000 GW/cm2. Until now these coatings have been considered in the linear regime only. At the same time, at the intensities close to the laser-induced damage threshold optical coating exhibit nonlinear effects. Namely, intensity dependent addition to the refractive index n2I (Kerr effect) cause variation of the reflectance coefficient [1]. The coatings with predictable increase of reflectance at high intensities can be used for the development of innovative elements for ultrafast optics, special edge filters with extremely steep reflectance slope in the vicinity of the central wavelength were designed, produced and carefully investigated. The coatings exhibit predictable increase of reflectance at high intensities.

Characterization of Nonlinear Effects in Edge Filters

A specially designed and produced edge filter with pronounced nonlinear effects is carefully characterized. The nonlinear effects are estimated at the intensities close to the laser-induced damage.

Power and energy scaling of Kerr-lens mode-locked thin-disk oscillators

The goal of this contribution is to provide a guideline for Kerr-lens mode-locking (KLM) of thin-disk oscillators. This includes cavity design, hard and soft-aperture optimization, handling of thermal effects in intra-cavity optics as well as methods of average power and energy scaling. The main differences and similarities between mode-locking of Ti:sapphire bulk and Yb:YAG thin-disk oscillators are presented.

High power Kerr-lens mode-locking of Yb:YAG and Yb:CALGO thin-disk oscillators

A scaling approach allows reaching 270-W, 14.4-µJ, 330-fs (38 MW) from a KLM Yb:YAG thin-disk oscillator, the highest average power of any KLM-oscillator. Progress on applying this concept to the Yb:CALGO disk-medium is also reported.

Investigation of Laser-Induced Currents in Large-Band-Gap Dielectrics

Applying few-cycle laser pulses to dielectrics increases their ac-polarizability, allowing for switching currents at the frequency of light. We report on the dependence of these ultrafast currents on material band gap and sample geometry.