Abstract: In order to extend harmonic cutoff energy and enhance harmonic radiation intensity, a method using the combined field of chirped laser and ultraviolet laser to drive He atoms to regulate the harmonic radiation process is proposed. Results show that driven by the single-color field, the harmonic cutoff energy is extended with the introduction of negative chirp. Moreover, as the laser pulse width increases, the harmonic cut-off energy further extends. When the second laser field is introduced, the harmonic cutoff energy extends slightly. At the same time, the harmonic radiation intensity is enhanced by three orders of magnitude. When the third beam ultraviolet laser field is introduced, the harmonic radiation intensity is enhanced by two orders of magnitude compared with that of the two-color field. As the intensity of ultraviolet laser is increased, the intensity of harmonic radiation is further enhanced. Finally, an isolated attosecond pulse with a pulse width of 38 as can be obtained by superposing the harmonics of the spectral continuum region. 

Key words: laser physics, high-order harmonic generation, isolated attosecond pulse, chirped pulse, ultraviolet pulse