Quasi-monochromatic radiation from a circularly polarized laser pulse cross colliding with a relativistic electron

The utilization of X-rays produced by interaction between relativistic electrons and laser pulses finds profound application in domains such as photoelectron spectroscopy. Through numerical simulation, the influence of the laser pulse delay time ${\tau }_0$ and the initial Lorentz factor ${\gamma }_0$ on the spatial and spectral properties of radiation produced by electron cross collision with a circularly polarized laser pulse is investigated. Also, the optimal parameters for generating quasi-monochromatic pulses and high-order harmonic radiation are discussed. The results reveal that when $|{\tau }_0|$ is large, the electron collides with the leading or trailing edge of the laser pulse, resulting in superior quasi-monochromatic radiation pulses. However, when ${\tau }_0$=0, the electron collides with the center of the laser pulse, which is most favorable for the generation of high-order harmonics. Furthermore, ${\gamma }_0$ has a negligible impact on the monochromaticity of the fundamental harmonic but plays a detrimental role in forming a single quasi-monochromatic pulse at higher values. Instead, higher ${\gamma }_0$ promotes the broadening of high-order harmonics. These results are important for obtaining radiating X-rays with different properties according to practical requirements.