Jiří Mužík

Progress in kW-class picosecond thin-disk lasers development at the HiLASE

High average power picosecond Yb:YAG thin-disk lasers are being developed at Hilase. A compact 1 mJ/100 kHz and 4 mJ/100 kHz zero-phonon-line-pumped regenerative amplifiers PERLA C with a CVBG compressor provide <2 ps long pulses in a nearly diffraction-limited beam. The output was successfully converted to 2nd and 4th harmonic frequency with high conversion efficiency. High energy, QCW-pumped beamline PERLA B is operated at 45mJ/1kHz in fundamental spatial mode and pulse length < 2ps. Its second stage amplifier is being assembled and 1.8 J was extracted. The latest development status of all thin-disk beamlines at the Hilase center is reported.

Cryogenically-cooled Yb:YGAG ceramic mode-locked laser

This work reports on a liquid-nitrogen-cooled, SESAM mode-locked Yb:YGAG (Yb:Y(3)Ga(2)Al(3)O(12)) ceramic laser. The Yb:YGAG has a similar structure to Yb:YAG, but its emission spectrum at low temperature remains much broader, which is suitable for ultrashort pulse generation and amplification. A stable pulse train with 119-MHz repetition rate was obtained at a wavelength of 1026 nm. The measured pulse duration is 2.4 ps, which is more than four times shorter than that achieved with a cryogenically-cooled Yb:YAG. Furthermore, laser performance of the Yb:YGAG ceramics in continuous-wave operation and wavelength tunability at 80 K was investigated.

Investigation and modelling of pump saturation effect on thermal load of Yb:YAG thin disk pumped at various wavelengths

Relations among absorption of pump beam, quantum defect and thermal load were investigated for pump wavelengths of 968 nm and near 940 nm in two independent, real-time measurement experiments complemented with thermal distribution simulation. Saturation of absorption at 969 nm pumping for non-lasing operational regime, which affects temperature rise and exists independently of the thin disk type, disk head construction, pump power and pump beam diameter is reported. Disk temperature dependence of absorption, quantum defect and disk geometry and large difference between absorption, disk temperature and o-o efficiency at both pump wavelengths are discussed.

Development of 2.7-μm Er:Y2O3 ceramic laser operated at room temperature

In this paper, we investigated laser performance of Er:Y2O3 ceramics at room temperature. With pulsed pumping with duty cycle of 1%, 1.02 W of peak output power was obtained at wavelength of 2.7 μm with slope efficiency of 3%. Furthermore, absorption spectra of the ceramics and temperature evolution for different pumping conditions were examined.

kW-class picosecond thin-disc prepulse laser Perla for efficient EUV generation

Abstract. The technology for extreme ultraviolet (EUV) lithography sources is maturing. Laser produced plasma (LPP) sources with usable power >100  W have been used in high-volume manufacturing (HVM) applications, and 250-W sources are expected to be introduced in HVM soon. However, a further increase of power and cleanness may benefit a powerful picosecond (ps) laser in the near-infrared and wavelength converted spectral region. The HiLASE Centre has been working in thin-disc laser technology and has demonstrated a 0.5-kW platform Perla-C based on a very compact Yb:YAG regenerative amplifier. 100-kHz ps operation has been achieved with a fundamental spatial mode and excellent long-term pointing and energy stability. It is reported on a thin-disc-based ps Yb:YAG solid-state laser technology platform Perla developed in the Czech Republic and the present performance of delivering >4  mJ, <2-ps pulses at a 100-kHz repetition rate with the potential to be upgraded to 1 kW of average power and 1-MHz pulse repetition rate. The ps laser extendibility is important for kW-class LPP sources and controlled free electron laser EUV sources in 10-kW power region.

Development of a kW-level picosecond thin-disk regenerative amplifier with a ring cavity

We report on development of a 100-kHz, 5-mJ picosecond system based on a two-stage thin-disk Yb:YAG regenerative amplifier. With a compact ring cavity, we obtained 565 W with 46.7% optical-to-optical efficiency in continuous-wave. In seeded operation, pulses with energy up to 4 mJ and 1.4-nm bandwidth were generated with 39% extraction efficiency. Pulse compression below 2 ps was so far demonstrated at lower pulse energy of 1 mJ. Full-power pulse compression and further pulse energy increase are under development.

Cryogenically-cooled Yb:YGAG ceramic picosecond oscillator

In this work, a passively mode-locked Yb:YGAG (Yb:Y3Ga2Al3O12) ceramic laser generating picosecond pulses at liquid-nitrogen temperature is demonstrated. The Yb:YGAG has a similar structure to Yb:YAG, but its emission bandwidth at cryogenic temperature remains much broader, which is advantageous for ultrashort pulse generation and amplification. Using this laser material, a stable train of pulses at a wavelength of 1026 nm was obtained, with measured pulse duration of 2.4 ps, which is more than four times shorter than that achieved with a cryogenically-cooled Yb:YAG.

1.2 W actively mode-locked Tm:YLF laser

We present a diode-pumped actively mode-locked Tm:YLF laser. Continuous-wave mode-locked regime was achieved using an acousto-optic modulator and a stable train of pulses with 150 MHz repetition rate, 220 ps pulse width and 1.2 W average output power at 1.91 μm in a nearly diffraction-limited beam was obtained. Laser characteristics in the freerunning regime with both continuous and pulsed pumping as well as humidity-related issues are also reported.