Implementation and commissioning of an experimental system towards sub-eV axion-like particle searches with 0.1 PW laser at ELI-NP
We have developed and commissioned an experimental system at ELI-NP towards searches for axion-like particles (ALPs) in the worldwide 10~PW-class laser facility. The search principle is based on the Four-Wave Mixing (FWM) process at a focal region of coaxially combined two laser beams. The subsystems to control vacuum pressure, area size, spatiotemporal overlap and trigger-event pattern, are integrated into the experimental area for 0.1 PW laser output at ELI-NP. The integrated system is dedicated to identifying the possible background sources originated from the residual atoms and the optical elements. The performance and functionality of the subsystems were validated through the evaluations of laser characteristics, their stability and the FWM signal detections. Furthermore commissioning results for the background studies were demonstrated with 20 mJ-level laser pulses at the vacuum pressure of $1.3 \times 10^{-7}$ mbar. In conclusion, the integrated experimental system is fully functional as designed and provides a suitable platform for the background studies towards the ALP searches, enabling a stepwise scale-up of the laser pulse energies from 20 mJ to the maximum energy of 2.5 J in the 0.1 PW experimental area.