Available Equipment (ELI-ERIC)

HR1: The High Repetition rate laser system provide millijoule level, few-cycle laser pulses at 100 kHz repetition rate, ideally suited for experiments relying on high statistics. The laser systems work in the near infrared, at 1030 nm wavelength. CEP control is not yet demonstrated, but phase-tagging is possible.

This laser can be used alone, or as a driver of GHHG beamlines, or the TAS setup.

Brief description of the available set up

The High Repetition rate (HR-1) laser system provides millijoule level, few-cycle laser pulses at 100 kHz repetition rate. This makes experiments relying on statistics of large number of shots possible or much faster. The laser system works in the near infrared, at 1030 nm wavelength.

Description of key areas of science

Key applications (for now) include high-harmonic generation (attosecond XUV pulses / pulse trains, see HR GHHG beamlines), and various pump-probe experiments (for example, see Transient Absorption Spectrometer). The direct beam is available for users as well.

Full description of system:

The ELI ALPS HR-1 laser system is designed to produce sub-2 cycle, 1 mJ, CEP-stabilized laser pulses at 100 kHz repetition rate at 1030 nm. The system is an ytterbium fiber chirped-pulse amplifier system. The main amplifier uses 8 parallel (diode-pumped) large mode area photonic crystal fiber amplifiers, which are coherently combined to > 200 W and compressed to 280 fs. These pulses are then post-compressed in two subsequent multi-pass cells, first to < 35fs and then to 6.2 fs. (Fig 1.) The concept was first demonstrated in [1] with the hollow-core fiber method. This technique had its limitations, so the system was upgraded to use multi-pass cells [5], which handle high average power and pulse energy better and have higher efficiency.

 Figure 1: Schematic layout of the HR-1 laser.

Table 1 shows the specification of the systems at the output of the lasers.

Table 1: Parameters of HR 1 lasers as specified.

The average power of the system can be lowered to circa 1W, being able to provide a beam for pre-alignment of an optical setup. (In this pre-alignment case, post-compression stages receive only minimum power, so spectral bandwidth is limited.) Continuous power control of HR-1 (from 10-100% of power) without change of the other parameters is already available for long pulse mode. Power control for short pulse mode (and almost an octave of bandwidth) requires using custom-design beamsplitters, so only discrete steps are possible.

The pulse duration can be slightly tuned by using a bit lower power level in the post-compression stages, resulting in longer pulses and narrower wavelength range.

CEP stability has not yet been demonstrated, but expected to be available by the start of the experiment period of this call.

Main experimental geometries 

Typically pump-probe geometries were used in the experimental setups so far.

The main beam is provided to HHG beam lines through beam transport tube in vacuum.

The main beam can be made available on the optical table in the lab as well.

There is a 30 fs / 20 W split beam available at the lab as well, for experiments needing smaller power only.

Available target systems 

The main target areas for these lasers are the HR GHHG Gas and HR GHHG Condensed attosecond beamlines situated in the neighbouring laboratories, containing a quasi-static gas cell target. For the 20W output of the laser the transient absorption spectrometer (TAS) setup provides a target area. It is also possible to install the user’s own setup on the optical table in the laser laboratory.,

Available metrology

Power, spectrum, pulse duration (autocorrelator and D-scan), and it is possible to measure pointing stability, energy stability, beam profile and wavefront for the users as well.

CEP-tagging is possible (as an analog signal by Stereo-ATI electronics or a recorded data on computer).

References

[1] Hädrich et al, Opt.Lett 41, 4332
https://doi.org/10.1364/OL.41.004332

[2] E. Shestaev et al, Opt. Lett 45, 6350
https://doi.org/10.1364/OL.409410

[3] T.Nagy et al, Optica Memorandum 6, p. 1423 (2019)
http://dx.doi.org/10.1364/OPTICA.6.001423

[4] E. Shestaev et al, Opt. Lett. 45, 97-100 (2020)
https://doi.org/10.1364/OL.45.000097

[5] S. Hädrich et al, Opt.Lett 47, 1537
https://doi.org/10.1364/OL.450991