An increasing number of scientific applications require highly energetic ultrafast laser system like OPA pumping, THz generation or filamentation. To address their requirements, a compact diode-pumped Terawatt-class laser was developed, this laser can deliver 220 mJ pulses at 50 Hz repetition rate and 415 fs pulse duration. The system is based on a CPA scheme starting with a synchronizable oscillator, a spectral shaper, then a regenerative amplifier and two multipass amplifiers. The laser’s modular structure allows for an upgrade with additional amplification stage. In order to maintain a large spectrum throughout the whole amplification, a spectrum modulator is used to shape the spectral amplitude of the seeded pulses. It allows the versatile shaping of the spectral bandwidth to efficiently compensate the spectral narrowing induced by the amplifiers. This spectrally shaped pulse is then seeded to a regenerative amplifier based on a Yb:CaF2 crystal. Thanks to its wide emission cross section and excellent storage efficiency, the pulse energy reached 30 mJ with a spectral bandwidth of 6nm centered at 1030 nm. This spectral shape is adapted to the two amplification stage which are based on Yb:YAG crystal. The first amplification multipass stage allows to increase the pulse energy to 90 mJ. The main amplification stage then increases the energy to 250 mJ. The energy is compressed by a pair of highly efficient gratings. The pulses are successfully compressed down to 415 fs with an output energy of 220 mJ. The beam after compression has an excellent spatial Gaussian shape, a remarkable pointing stability and a high Strehl ratio.
High power high energy lasers have recently emerged as potential solution for several applications such as secondary rays generation, nuclear fusion and medical therapy. One major limitation of such systems for high energy extraction is the laser-induced damage threshold (LIDT) of laser components.
In this context, many studies have been devoted to the determination of the LIDT of laser materials under certain operational conditions and the identification of the limiting factors at the nanoseconds and femto/sub-picoseconds regime 1–3.However, these measurements do not consider that in most high intensity laser chains such as chirped pulsed amplification (CPA), pulses are stretched to larger duration such as hundreds of picoseconds. Thus, measuring the LIDT of laser materials under stretched pulses irradiation becomes critical.
In this work, we report a study of the influence of the coating treatment and fatigue in the LIDT of Yb:YAG crystals under stretched pulses by means of 1-on-1, Rasterscan and S-on-1 tests. We use a 1mJ, 1kHz laser (S-Pulse model from Amplitude Systèmes) modified to support 150 ps-pulse duration. We show a lower LIDT of the AR-coating compared to that of the HR-coating (7J/cm2) and preliminary outcomes point out a non-deterministic effect of the fatigue at this regime of pulse duration. These results show the importance of testing critical components at hundred-picoseconds regime for high power and high energy lasers.
1. Sozet, M. et al. Laser damage density measurement of optical components in the sub-picosecond regime. 40, 2–5 (2015).
2. Smith, A. V & Do, B. T. Bulk and surface laser damage of silica by picosecond and nanosecond pulses at 1064 nm. (2008).
3. Jensen, L. O. et al. Investigations on SiO 2 / HfO 2 mixtures for nanosecond and femtosecond pulses a Laser. 7842, 1–10 (2017).
A high intensity Gamma source is required for Nuclear Spectroscopy, it will be delivered by the interaction between accelerated electron and intense laser beams. Those two interactions lasers are based on a multi-stage amplification scheme that ended with a second harmonics generation to deliver 200 mJ, 5 ps pulses at 515 nm and 100 Hz.
A t-Pulse oscillator with slow and fast feedback loop implemented inside the oscillator cavity allows the possibility of synchronization to an optical reference. A temporal jitter of 120 fs rms is achieved, integrated from 10 Hz to 10 MHz.
Then a regenerative amplifier, based on Yb:YAG technology, pumped by fiber-coupled QCW laser diodes, delivers pulses up to 30 mJ. The 1 nm bandwidth was compressed to 1.5 ps with a good spatial quality: M2 of 1.1. This amplifier is integrated in a compact sealed housing (750 x 500 x 150 mm), which allows a pulse-pulse stability of 0.1 % rms, and a long-term stability of 1,9 % over 100 hours (with +/-1°C environment).
The main amplification stage uses a cryocooled Yb:YAG crystal in an active mirror configuration. The crystal is cooled at 130 K via a compact and low-vibration cryocooler, avoiding any additional phase noise contribution, 340 mJ in a six pass scheme was achieved, with 0.9 of Strehl ratio. The trade off to the gain of a cryogenic amplifier is the bandwidth reduction, however the 1030 nm pulse was compressed to 4.4 ps. As for the regenerative amplifier a long-term stability of 1.9 % over 30 hours was achieved in an environment with +/-1°C temperature fluctuations
The compression and Second Harmonics Generation Stages have allowed the conversion of 150 mJ of uncompressed infrared beam into 60 mJ at 515 nm.
We report on a diode pumped ultrafast amplifier based on Yb:CaF2 delivering 32 mJ, at a repetition rate of up to 200 Hz, with a central wavelength of 1030nm. The pulses have spectral bandwidth of 5.5 nm, supporting a theoretical pulse duration of 250 fs, are compressed to 300 fs in a compressor based on reflection gratings with a transmission efficiency up to 89%. This laser source constitutes an ideal source for pumping nonlinear crystals through Optical Parametric Amplification or Optical rectification. It is also well adapted for seeding ultrafast high energy amplifiers based on Yb:YAG crystals
A high intensity Gamma source is required for Nuclear Spectroscopy, it will be delivered by the interaction between accelerated electron and intense laser beams. Those two interactions lasers are based on a multi-stage amplification scheme that ended with a second harmonics generation to deliver 200 mJ, 3.5 ps pulses at 515 nm and 100 Hz.
A t-Pulse oscillator with slow and fast feedback loop implemented inside the oscillator cavity allows the possibility of synchronization to an optical reference. A temporal jitter of 120 fs rms is achieved, integrated from 10 Hz to 10 MHz.
Then a regenerative amplifier, based on Yb:YAG technology, pumped by fiber-coupled QCW laser diodes, delivers pulses up to 30 mJ. The 1 nm bandwidth was compressed to 1.5 ps with a good spatial quality: M2 of 1.1. This amplifier is integrated in a compact sealed housing (750x500x150 cm), which allows a pulse-pulse stability of 0.1% rms, and a long-term stability of 1,9% over 100 hours (with +/-1°C environment).
The main amplification stage uses a cryocooled Yb:YAG crystal in an active mirror configuration. The crystal is cooled at 130 K via a compact and low-vibration cryocooler, avoiding any additional phase noise contribution, 340 mJ in a six pass scheme was achieved, with 0.9 of Strehl ratio. The trade off to the gain of a cryogenic amplifier is the bandwidth reduction, however the 1030 nm pulse was compressed to 3.5 ps.
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