Bálint Kiss

4-W, 100-kHz, few-cycle mid-infrared source with sub-100-mrad carrier-envelope phase noise

We demonstrate an optical parametric chirped-pulse amplifier delivering 4-cycles (38-fs) pulses centered around 3.1 µm at 100-kHz repetition rate with an average power of 4 W and an undersampled single-shot carrier-envelope phase noise of 81 mrad recorded over 25 min. The amplifier is pumped by a ~1.1 ps, Yb-YAG, thin-disk regenerative amplifier and seeded with a supercontinuum generated in bulk YAG from the same pump pulses. Carrier-envelope phase stability is passively achieved through difference-frequency generation between pump and seed pulses. An additional active stabilization at 10 kHz combining 2f-to-f interferometry and a LiNbO3 acousto-optic programmable dispersive filter achieves a record low phase noise.

Fabrication and analysis of transmission gratings produced by the indirect laser etching technique

The diffraction efficiency of gratings etched into fused silica was measured and modelled. 950, 2120 and 3710 nm period gratings were fabricated with the use of two-beam interferometric laser-induced backside wet etching (TWIN-LIBWE). The spatial distribution of the modulation depth (MD), determined from AFM measurements, followed the spatial intensity distribution of the laser beam throughout the grooved areas. The diffraction efficiency of the fabricated gratings was measured to all allowed diffraction orders at several wavelengths (266, 532 and 654.5 nm). Within the frame of Gsolver code, a model was developed that takes into account the spatial distribution of MD. The computed diffraction efficiencies showed good agreement with the results of measurements.

Multi-W, 100-kHz, few-cycle mid-infrared source with sub-100-mrad single-shot carrier-envelope phase noise

Extension of High order Harmonics Generation (HHG) towards XUV and up to soft-x-rays relies on the development of driving sources with specific properties: mid-infrared wavelength, few-cycle pulse duration, high peak intensity, carrier-envelope phase stability and control, high energy and/or high-repetition rate. While longer wavelengths of the driving source extend the HHG cutoff energy through the λ2 dependency of the ponderomotive energy, shorter pulses lead to the higher peak intensities enhancing the HHG conversion yield and extending HHG cutoff energy even further. Additionally, few-cycle driving pulses reduce the number of produced attosecond bursts up to, ideally, a single isolated attosecond pulse. In this case, CEP stability and control is paramount for ensuring optimization and shot-to-shot reproducibility of the HHG yield and spectra.

Grating fabrication in dielectric coatings by TWIN-LIBWE

Thin films are widely used in many applications, especially, the transparent layers are commonly used as high reflective and antireflex coatings on optical elements. Moreover, several spectroscopic applications need microstructured thin films deposited on bulk dielectric. Many procedures have been developed for etching transparent dielectrics. The conventional multistep techniques (hidrofluidic etching [1], powder blasting [2], ion etching [3]) require contact mask preparation on the target surface. The laser-based direct and indirect methods, however, can provide a good alternative for micro- and submicrometer structuring of transparent dielectrics without the complicate preparation of contact masks. The laser-induced backside wet etching (LIBWE) [4] is one of the most promising and flexible and applicable indirect technique. It was recently demonstrated that the combination of LIBWE with the two-beam interferometric method (TWIN-LIBWE) is well suited for fabrication of submicrometer period gratings onto the surface of bulk fused silica [5]. In this paper we report on the fabrication of micrometer period grating structure in SiO2, and ZrO2 thin films with the use of TWIN-LIBWE.