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A great variety of ultrafast lasers is available commercially, many of them are originated from research and development in academic laboratories. While the commercial systems are usually stand alone, few-purpose systems, the academic ones are more versatile with a trade-off in reliability and robustness. In this paper we describe a laser system, where robust industrial components are complemented with unique in house developments and researches. The many-arm system hence offers reliable performance with versatile parameters for many disciplines, ranging from nonlinear optics, through high harmonic generation, and material sciences to diagnostic development and industrial applications.

The laser systems of the TeWaTi group at the University of Szeged, Hungary is implemented on a single and a double chirped pulse amplification scheme (Fig.1). The 7 fs, CEP-stabilized seed pulses of the system are generated by a Femtolasers Rainbow CEP4 Ti:sapphire oscillator at a 75 MHz repetition rate, which have a spectrum spanning from 650 nm to 950 nm. The feed-forward-type stabilization provides better than 50 mrad RMS noise in the CEP. The oscillator beam is divided, one part can be used for broadband interferometric applications, while the other part is directed into the preamplifier.

 

 

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Fig.1. Schematic flowchart of the TeWaTi laser systems at University of Szeged.

 

 

 

A uniquely designed broadband multipass bulk stretcher based on a 20 cm SF57 glass slab with a transmission of 80% stretches the seed pulses to 30 ps. To keep the temporal contrast high, the preamplifier was chosen a multipass Ti:Sapphire type, pumped with 20 mJ pump pulses from a custom tailored Nd:YLF laser at 200 Hz repetition rate and a peak-to-peak stability better than 0.2%. In order to broaden the bandwidth, to tune the dispersion, and to control the CEP, the pulses are steered to a Pockels cell and an acousto-optical programmable filter after the first 5 pass. The shaped pulses then steered back to the amplifier to a further 5 passes, and to be compressed with a grism compressor. The resulting 1.5 mJ, 20 fs, CEP-stabilized, pulses are used directly to HHG and pump-probe experiments, or steered into a tunable NOPA stage for time resolved spectroscopy applications in the visible spectral range. The NOPA is pumped by the 2nd harmonic of the preamplifier beam and amplifies a white light seed, keeping the pulses synchronized to the laser system.

 

The second, power amplifier stage aims for TW pulse power. Prior to compression, part of the preamplified pulses are expanded to 300 ps by a regenerative-type multipass Offner stretcher, the five-pass Ti:sapphire amplifier increases the pulse energy to 70 mJ with a 10 Hz, 400 mJ flashlamp-pumped Spectra-Physics Nd:YAG laser. The final, grating compressor provides at least 50 mJ pulses with 25 fs duration, centered at 800 nm for various nonlinear optical experiments, material science, surface processing, and damage threshold measurements.

 

A reliable and affordable laser system is described, providing HHG, fs pump-probe, and material science experiments with pulses of CEP stabilized 0.1 TW peak power, tunable broadband VIS-NIR, and 2 TW peak power, respectively