The first component of the SYLOS laser system, SYLOS 1, was designed by the Lithuanian companies EKSPLA and Light Conversion in collaboration with ELI ALPS. This device was a 4.5 TW peak intensity laser with a pulse duration of less than 10 femtoseconds and a repetition rate of 1 kHz with outstanding stability values. In the second phase of development (SYLOS 2A), the two above-mentioned companies and ELI ALPS launched a joint R&D programme, which led to a 30 percent reduction in the pulse length down to 6.5 femtoseconds, while maintaining the peak intensity, repetition rate and other stability and operational parameters of the laser pulses. This improvement was achieved by further developing the original laser system. This required the redesign and rearrangement of several components, which took until March 2019. The laser system was eventually delivered and installed in May 2019.
However, the reduction of the pulse length resulted in a decrease in output energy. The plan for SYLOS 2B was to maintain the pulse duration but increase the output energy to 120 millijoules (which would have exceeded the output energy of SYLOS 2A by nearly fourfold). Furthermore, due to changing circumstances and needs, the decision was made that we should not concentrate our energy on SYLOS 2B, but keep SYLOS 2A and develop a new, stand-alone laser. This is SYLOS 3, the laser which has been operational since summer 2023. It currently serves four target areas, including MTA0, which hosts one of the experiments selected for support under the third joint user call. This proposal was submitted by laser physicists at ELI ALPS.
“’Our goal is to build an experimental device that further broadens the spectral range of the pulse by using a nonlinear process. To this end, we shoot the laser beam through very thin glass plates of different compositions, which results in the appearance of other spectral components too. As result of the dispersion, we can achieve even shorter pulse lengths,” János Csontos said, explaining the direction of research development at the institute.
During the first commissioning experiment, the National Laser-Initiated Transmutation Laboratory (NLTL), led by Károly Osvay, focused the SYLOS 3 laser pulse onto a very thin layer, and the deuteron ions that were ejected from this layer then hit a secondary target, producing neutrons. With the SYLOS 3 laser system, researchers fired pulse energies over 100 millijoules of energy compared to the 20–30 millijoule range used previously, and shot 1,000 pulses per second instead of 10. As this was a commissioning experiment, researchers also faced problems. For example, we had to overcome the heat load on the optics, which changes the parameters of the laser pulses. We had to wait for the devices to thermalize and the actual work could begin after fine-tuning the laser parameters. According to János Csontos, it was necessary to find out how long this process would take and what parameters might need to be changed for optimal operation.
Csontos János
We have used the SYLOS 3 laser on other workstations too. In the eSYLOS, i.e. electron acceleration beamline, laser pulses are focused into a gas target and the resulting electrons are accelerated. This laser has also been applied on the SHHG-SYLOS beamline. One of the exciting developments of our research centre is the construction of a beam delivery system to the LTA1 target area, the design phase of which has been completed. The components of the vacuum system have been delivered and the optical elements are expected to arrive in September. This means that, when completed, SYLOS 3 will serve a total of five beamlines, and brainstorming has started about a sixth beamline. It is important to note that SYLOS 3 delivers a laser beam to one workstation at a time.
Experience shows that SYLOS 3 is becoming more and more reputed and popular among physicists. ELI ERIC’s fourth joint user call, which closed at the end of April this year, attracted eight user proposals. It seems that numerous laser physicists intend to use a high energy beam.
“A user typically experiments with the laser for one to four weeks. But this does not mean that a user arrives at ELI on a Monday and starts his measurements on the very same day. We conduct long preliminary discussions to identify what exactly the researcher needs. We set up the workstation based on his needs so that he can spend his time at ELI ALPS as efficiently as possible,” János Csontos says.