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 a fiber CPA system consisting of 8 diode-pumped amplifier channels, which are coherently combined to 300 W and compressed to <200 fs. These pulses are then post-compressed in two subsequent hollow-core fiber modules. (Fig 1.) [1,2]
The HR-2 laser system is a fivefold more powerful laser built on a similar architecture as HR-1. This system has a fiber CPA with 16 combined amplifier channels of updated design, capable of producing 10 mJ (260 fs) pulses at 100 kHz (1 kilowatt average power). The efficiency of the grating compressor has also been significantly improved. Post-compression occurs inside a stretched hollow-core fiber module with a pressure gradient. HR2 is specified to provide 5mJ, 6 fs pulses at 100kHz and 1030nm central wavelngth. The post-compression layout is still under development and expected to be finalized early 2021. Nevertheless, the generation of > 3mJ sub-10fs pulses has already been demonstrated .
Fig1. Schematic layout of the HR-1 laser.
Table 1 shows the output specifications of both laser systems. Currently the long pulse mode of HR1 is available for experiments at ELI-ALPS until 2021 Q1, when it will receive factory upgrades to reach the final specifications. HR2 is also in the last stages of development and it is expected to become available from 2021 Q2, while the full HR1 beam with the specified parameters is estimated to be available after 2021 Q3 for users.
Table 1. Parameters of HR 1 and HR 2 lasers as specified.
The average power of both systems can be lowered to 1W, for experiment pre-alignment purposes. Continuous power control of HR-1 (from 10-100% of power) without change of the other parameters is available in long pulse operation mode. Power control for short pulse mode is under implementation. The pulse duration of both laser systems can be tuned (from CPA pulse duration down to the shortest available pulse) by using a different configuration of the post-compression stages. The ongoing development of the HR-2 laser targets <200 mrad of CEP-stability, with the goal being stability of < 100 mrad. The final CEP-stabilization method will be implemented on HR-1 laser as well during the factory upgrade in 2021 Q2-Q3. Due to the high average power, user-based optical and optomechanical elements can suffer significant thermal loading, so careful design and pointing stabilization to the final target is highly recommended.
Measured parameters of HR-1
Output beam profile of HR-1
Output spectra of HR-1 in long pulse (a) and short pulse (b) mode.
Typical autocorrelation signal for HR-1 in long pulse (47 fs ACF) and short pulse (10-14 fs ACF) modes.
Typical power stability curve from HR-1 turn-on (measured in long pulse mode) (± 0.08 % RMS after 30 minutes)
Typical power stability curve from HR-1 turn-on (measured in short pulse mode) (± 0.54 % RMS after 15 minutes)
1. Hädrich et al, Opt.Lett 41, 4332
2. T.Eidam et al, CLEO Europe 2017, (CJ_12_6).
3. T.Nagy et al, Optica Memorandum 6, p. 1423 (2019)