We report on the successful demonstration of the world’s first kW average power, 100 Joule-class, high-energy, nanosecond pulsed diode-pumped solid-state laser (DPSSL), DiPOLE100. Results from the first long-term test for amplification will be presented; the system was operated for 1 hour with 10 ns duration pulses at 10 Hz pulse repetition rate and an average output energy of 105 J and RMS energy stability of approximately 1%. The laser system is based on scalable cryogenic gas-cooled multi-slab ceramic Yb:YAG amplifier technology. The DiPOLE100 system comprises three major sub-systems, a spatially and temporally shaped front end, a 10 J cryo-amplifier and a 100 J cryo-amplifier. The 10 J cryo-amplifier contain four Yb:YAG ceramic gain media slabs, which are diode pumped from both sides, while a multi-pass architecture configured for seven passes enables 10 J of energy to be extracted at 10 Hz. This seeds the 100 J cryo-amplifier, which contains six Yb:YAG ceramic gain media slabs with the multi-pass configured for four passes. Our future development plans for this architecture will be introduced including closed-loop pulse shaping, increased energy, higher repetition rates and picosecond operation. This laser architecture unlocks the potential for practical applications including new sources for industrial materials processing and high intensity laser matter studies as envisioned for ELI , HiLASE , and the European XFEL . Alternatively, it can be used as a pump source for higher repetition rate PW-class amplifiers, which can themselves generate high-brightness secondary radiation and ion sources leading to new remote imaging and medical applications.
The HiLASE “Bivoj” laser system developed at CLF Rutherford Appleton Laboratory in collaboration with HiLASE team as DiPOLE100 was relocated to Dolni Brezany near Prague, Czechia at the end of 2015 and fully re-commissioned at the end of 2016. In 2016, the system demonstrated average output power of 1kW generating pulses of 105 J at 10 Hz repetition rate for the first time in the world. Since then the system has been subjected to several testing campaigns in order to determine some of its key characteristics. Beam quality, wavefront quality, pointing stability, energy stability and experience with long term operation of 1 kW laser are presented. In addition, depolarization effects have been detected inside the main amplifier. Details on these results along with numerical simulations are presented.
We present an overview of the cryo-amplifier concept and design utilized in the DiPOLE100 laser system built for use at the HiLASE Center, which has been successfully tested operating at an average power of 1kW. Following this we describe the alterations made to the design in the second generation system being constructed for high energy density (HED) experiments in the HED beamline at the European XFEL. These changes are predominantly geometric in nature, however also include improved mount design and improved control over the temporal shape of the output pulse. Finally, we comment on future plans for development of the DiPOLE laser amplifier architecture.
In this paper we present details of the commissioning of DiPOLE100, a kW-class nanosecond pulsed diode pumped solid
state laser (DPSSL), at the HiLASE Centre at Dolní Břežany in the Czech Republic. The laser system, built at the
Central Laser Facility (CLF), was dismantled, packaged, shipped and reassembled at HiLASE over a 12 month period by
a collaborative team from the CLF and HiLASE. First operation of the laser at the end of 2016 demonstrated
amplification of 10 ns pulses at 10 Hz pulse repetition rate to an energy of 105 J at 1029.5 nm, representing the world’s
first kW average power, high-energy, nanosecond pulsed DPSSL. To date DiPOLE100 has been operated for over
2.5 hours at energies in excess of 100 J at 10 Hz, corresponding to nearly 105 shots, and has demonstrated long term
energy stability of less than 1% RMS for continuous operation over 1 hour. This confirms the power scalability of multislab
cryogenic gas-cooled amplifier technology and demonstrates its potential as a laser driver for next generation
scientific, industrial, and medical applications.
In this paper, we review the development, at the STFC’s Central Laser Facility (CLF), of high energy, high repetition rate diode-pumped solid-state laser (DPSSL) systems based on cryogenically-cooled multi-slab ceramic Yb:YAG. Up to date, two systems have been completed, namely the DiPOLE prototype and the DiPOLE100 system. The DiPOLE prototype has demonstrated amplification of nanosecond pulses in excess of 10 J at 10 Hz repetition rate with an opticalto- optical efficiency of 22%. The larger scale DiPOLE100 system, designed to deliver 100J temporally-shaped nanosecond pulses at 10 Hz repetition rate, has been developed at the CLF for the HiLASE project in the Czech Republic. Recent experiments conducted on the DiPOLE100 system demonstrated the energy scalability of the DiPOLE concept to the 100 J pulse energy level. Furthermore, second harmonic generation experiments carried out on the DiPOLE prototype confirmed the suitability of DiPOLE-based systems for pumping high repetition rate PW-class laser systems based on Ti:sapphire or optical parametric chirped pulse amplification (OPCPA) technology.
In this paper we review the development of high energy, nanosecond pulsed diode-pumped solid state lasers within the Central Laser Facility (CLF) based on cryogenic gas cooled multi-slab ceramic Yb:YAG amplifier technology. To date two 10J-scale systems, the DiPOLE prototype amplifier and an improved DIPOLE10 system, have been developed, and most recently a larger scale system, DiPOLE100, designed to produce 100 J pulses at up to 10 Hz. These systems have demonstrated amplification of 10 ns duration pulses at 1030 nm to energies in excess of 10 J at 10 Hz pulse repetition rate, and over 100 J at 1 Hz, with optical-to-optical conversion efficiencies of up to 27%. We present an overview of the cryo-amplifier concept and compare the design features of these three systems, including details of the amplifier designs, gain media, diode pump lasers and the cryogenic gas cooling systems. The most recent performance results from the three systems are presented along with future plans for high energy DPSSL development within the CLF.
In this paper we provide an overview of the design of DiPOLE100, a cryogenic gas-cooled DPSSL system based on Yb:YAG multi-slab amplifier technology, designed to efficiently produce 100 J pulses, between 2 and 10 ns in duration, at up to 10 Hz repetition rate. The current system is being built at the CLF for the HiLASE project and details of the front end, intermediate 10J cryo-amplifier and main 100J cryo-amplifier are presented. To date, temporal and spatial pulse shaping from the front end has been demonstrated, with 10 ns pulses of arbitrary shape (flat-top, linear ramps, and exponentials) produced with energies up to 150 mJ at 10 Hz. The pump diodes and cryogenic gas cooling system for the 10J cryo-amplifier have been fully commissioned and laser amplification testing has begun. The 100J, 940 nm pump sources have met full specification delivering pulses with 250 kW peak power and duration up to 1.2 ms at 10 Hz, corresponding to 3 kW average power each. An intensity modulation across the 78 mm square flat-top profile of < 5 % rms was measured. The 100J gain media slabs have been supplied and their optical characteristics tested. Commissioning of the 100J amplifier will commence shortly.
Lasers generating multi-J to kJ ns-pulses are required for many types of laser-plasma interactions. Such lasers are either used directly for compressing matter to extreme densities or they serve as pump lasers for short-pulses laser chains based on large-aperture Ti:sapphire or parametric amplifiers. The thus generated high-energy fs-pulses are most useful for laser driven secondary sources of particles (electrons, protons) or photons (from THz to gamma). While proof-of-principle experiments have been carried out with flashlamp-pumped glass lasers, lasers with much higher efficiency and repetition rate are required to make this applications practically viable. We have developed a scalable new laser concept called DiPOLE (diode pumped optical laser for experiments) based on a gas-cooled ceramic Yb:YAG multi-slab architecture operating at cryogenic temperatures. While the viability of this concept has been shown earlier , we have now reached our target performance of 10 J pulse energy at 10 Hz repetition rate at an optical-to-optical efficiency of 21%. To the best of our knowledge, these are record values for average power and efficiency for lasers of this type. We have also upgraded the system by adding a fibre-based front-end system with arbitrary pulse shaping capability and by installing an image-relayed multipass system enabling up to eight passes of the main amplifier. We have then used this system to demonstrate frequency doubling with 65 % conversion efficiency and a long-term shot-to-shot stability of 0.5% rms over a total of nearly 2 million shots, achieved in runs extending over 4 to 6 hours.
Yb<sup>3+</sup> doped YAG is one of the most promising materials for high energy, high repetition rate laser systems producing
nanosecond pulses. YAG as the host medium offers good thermo-mechanical and thermo-optical properties and, if it is
used in ceramic form, it can be produced in large sizes with laser-grade optical properties. Large sized, laser-grade gain
media are pivotal for the development of high energy kJ-class laser systems. Much effort has been devoted to the
development of advanced polishing and coating techniques in order to produce optical materials able to withstand high
fluence levels at different environmental conditions. In this paper, we present experimental results for 1 on 1 laser
induced damage threshold (LIDT) tests in the nanosecond regime following ISO standards on anti-reflective coated
ceramic Yb:YAG samples. Experimental results show that, generally, Ion Beam Sputtering (IBS) coatings perform better
than Ion Assisted Deposition (IAD) coatings on low roughness substrates, while IAD and IBS coatings deposited on
substrates characterised by higher surface roughness values offer a comparable performance. Performance of IBS
coatings improves as substrate roughness decreases, whereas performance of IAD coatings improves as substrate
roughness increases. No clear correlation has been observed between LIDT values and temperature or pressure.
However, an inspection of damage sites allowed to conclude that both temperature and pressure have an impact on
High Harmonic Generation is a well established technique for generating Extreme Ultraviolet radiation. It is a promising
technique for both structure and spectroscopic imaging due to both the high flux and coherence of the source, and the
existence of multiple absorption edges at the generated wavelengths. To increase the flux, a focussing device can be
used. Here we present focussing results for a Mo/Si spherical mirror that has been used in an off-axis arrangement, and
give extensive analysis of the resulting astigmatic focus and its consequence on diffractive imaging. The astigmatic beam
exists as a vertical and horizontal focus, separated by a circle of least confusion. With the help of a theoretical model we
show that the most intense part of the beam is always the second line foci and that the phase at the focus is strongly
saddle-shaped. However, this phase distortion cannot explain the significant interference peak splitting that is
experimentally observed in our diffraction patterns. Instead we propose that the beam quality is degraded upon reflection
from the multilayer mirror and it is this asymmetric phase distortion that causes the diffraction peak splitting.