Dispersion of femtosecond laser pulses propagating in Ar, He, Kr, N(2), Ne, Xe, and their mixtures is measured by spectrally and spatially resolved interferometry. By varying the gas pressure in a 4.5 m long tube between 0.05 mbar and ambient pressure, the first, second, and third order phase derivatives of broadband laser pulses are determined at 800 nm under standard conditions. The dispersion of gases and gas mixtures obeys the Lorentz-Lorenz formula with an accuracy of 0.7%. Based on the measured pressure dependent dispersion values in the near infrared and the refractive indices available from the literature for the ultraviolet and visible, a pressure dependent Sellmeier-type formula is fitted for each gas. These common form, two-term dispersion equations provide an accuracy between 4.1x10(-9) (Ne) and 4.3x10(-7) (Xe) for the refractive indices, from UV to near IR.

The propagation of high intensity laser beams is excessively affected by optical nonlinear effects, thereby the knowledge of the nonlinear refractive indices of the beam guiding media is indispensable in the design of laser systems and experiments. Apart from undesired self-focusing, several areas of modern laser spectroscopy can utilize optical nonlinearity, from LiDAR measurements to filamentation. In this paper we report on a direct measurement of pressure dependent nonlinear refractive index of Ar, N2, Ne, Xe, and air between 0.05 mbar and 1 bar, based on the powerful technique called spectrally and spatially resolved interferometry. In this way the total value of nonlinear refractive index is measured, that is the sum of all elementary phenomena contributing to the intensity dependent refractivity of the gases.

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The extreme light infrastructure attosecond light pulse source offers beamtime for users of various attosecond and particle sources driven by versatile laser systems. Here we report on the state of the art of a few-cycle, multi-TW, 1kHz repetition rate laser system, now fully operational in the facility. The system is based on four stages of optical parametric amplifiers (OPAs) pumped by a total of 320mJ, 80ps frequency-doubled Nd:YAG laser pulses. All OPA stages utilize double crystal configuration, which design has been also confirmed by model calculations. The 1kHz SYLOS 2 system produces 32mJ laser pulses around a central wavelength of 891nm with 6.6fs (<2.3 optical cycles) pulse duration exceeding the peak power of 4.8 TW on a daily basis. The recorded best pulse duration is 6.3fs, which corresponds to 2.12 cycles and 5.1 TW peak power. During long-term (24h) performance tests, energy stability of 1.2%, carrier-envelope phase (CEP) stability of 210mrad, and pointing stability of 0.4µrad were demonstrated, while the Strehl ratio of the beam is kept above 0.75. In order to help the alignment of all the different experiments at the facility and to reduce the workload on SYLOS 2 system, a second laser system has been developed. The so-called SYLOS Experimental Alignment (SEA) laser mimicks the performance of the SYLOS 2 laser, but at a repetition rate two orders of magnitude lower and without CEP-stabilization. The three single-crystal OPA stages of the SEA laser provide 42mJ pulse energy for the users, while having energy stability of 0.87% and sub-13fs pulse duration at a repetition rate ranging from a single shot up to 10Hz.

Spatiotemporal compression of ultrashort pulses is one of the key issues of chirped pulse amplification (CPA), the most common method to achieve high intensity laser beams. Successful shaping of the temporal envelope and recombination of the spectral components of the broadband pulses need careful alignment of the stretcher-compressor stages. Pulse parameters are required to be measured at the target as well. Several diagnostic techniques have been developed so far for the characterization of ultrashort pulses. Some of these methods utilize nonlinear optical processes, while others based on purely linear optics, in most cases, combined with spectrally resolving device. The goal of this work is to provide a review on the capabilities and limitations of the latter category of the ultrafast diagnostical methods. We feel that the importance of these powerful, easy-to-align, high-precision techniques needs to be emphasized, since their use could gradually improve the efficiency of different CPA systems. We give a general description on the background of spectrally resolved linear interferometry and demonstrate various schematic experimental layouts for the detection of material dispersion, angular dispersion and carrier-envelope phase drift. Precision estimations and discussion of potential applications are also provided.