Speaker
Description
High harmonic generation (HHG) has emerged as a powerful method for producing coherent femtosecond-to-attosecond light in the VUV, EUV, and X-ray regions. Since the harmonic cutoff energy and the upconversion phase matching limits increase with the driving laser wavelength, mid-infrared (MIR) drivers are uniquely advantageous for extending the emission toward soft X-ray wavelengths, and potentially even into the hard X-ray regime. In this study, we exploit MIR-FEL oscillators to investigate harmonic generation in gaseous media. We report on experiments using LEBRA-FEL at Nihon University and KU-FEL at Kyoto University, operating at wavelengths of 2 µm and 5 µm, respectively. By focusing 80-120 fs micro-pulses onto argon and oxygen targets, we observe, for the first time, harmonics up to the 7th order using advanced 20-120 µJ-class MIR-FELs and high gas pressures for phase matching. The experimental results reveal distinct spectral differences between the harmonics produced in gases and the intrinsic harmonics of the FEL. Furthermore, the measured macro-pulse temporal profiles of all harmonics exhibit significant deviations from the fundamental FEL pulse, providing clear evidence of the nonlinear dynamics inherent in the upconversion process. These results represent an essential milestone toward the realization of phase-matched HHG in the VUV, EUV, and X-ray spectral regions using MIR-FEL drivers.
Funding Agency
MEXT Q-LEAP (JPMXS0118070271), JSPS-KAKENHI 23K25135, the International Research Exchange Support Prog. of NINS. (314150403), Marie Sklodowska-Curie 101210692, UC San Diego Academic Senate Grants
| I have read and accept the Privacy Policy Statement | Yes |
|---|