A simulation on quasi-phase-matched high-harmonic generation in gas-filled hollow core waveguide

Coherent Extreme Ultraviolet (EUV) and x-ray sources have many applications in industry and fundamental research. Although these sources are available in the large facility centres such as synchrotrons and free electron lasers, high-harmonic generation (HHG) can provide us a tabletop approach. However, coherent EUV and X-ray sources based on HHG normally suffer a very low photon flux. Quasi-phase-matching (QPM) techniques can be applied to enhance the HHG photon flux. Here, we apply multimode quasi-phase-matching for HHG in gas-filled hollow core waveguide in the simulation. The quasi-phase-matching is achieved by inducing mode beating between two waveguide modes. A pair of pulses with adjustable relative time delay is coupled into the hollow core waveguide. The mode beating happens exactly at the end of the hollow core waveguide by controlling the intermodal delay. The simulation shows that the photon flux of HHG is much enhanced by intermodal delay controlled QPM. These simulation results are very important for developing the HHG based coherent EUV and x-ray sources with higher photon flux.