Among the several metals, the silver plasma plume is one of the main bases for higher-order harmonics generation (HHG). The ablating laser wavelength, pulse duration, and energy expressively affect the plasma plume characteristics.

Dr. Srinivasa Rao Konda, Dr. LAI Yuhang and Prof. LI Wei from the GPL, State Key Laboratory of Applied Optics, Changchun Institute of Optics, Fine Mechanics, and Physics (CIOMP) of Chinese Academy of Sciences (CAS), have shown the advantages of shorter pulse duration for the first time, i.e., fs pulses, to create the plasma plumes from silver, and extend the harmonics cut-off up to 65 order using 800 nm, 35fs pulses as driving laser beam. This work is published on Optics & Laser Technology.

The ns, ps, and fs laser pulses produced the silver plasma and revealed that shorter pulse duration leads to enhanced plasma density. For ns and ps pulses, the plasma extension angle could be lesser with narrower angular distribution of ions than the ns/ps LIPs. Therefore, fs LIPs have a higher density than ps and ns LIPs.

Besides, the contribution of Ag atoms was theoretically calculated, Ag⁺ and Ag²⁺ towards the generation of HHG. In the case of fs LIPs, the calculated theoretical harmonic is closely matched with experimental cut-off, which reveals the advantage of selecting fs laser pulses to create the plasma plumes.

Moreover, the harmonic spectra of silver bulk and nanoparticles were measured using negatively(-) and positively(+)chirped 135 fs driving pulses. The -ve and + ve chirp pulses lead to blueshifts and redshifts of the harmonic's spectra.

The obtained results showed that Ag is one of the projecting resources for the emission of higher-order harmonics. The intensity and cut-off of harmonics could be preciously tuned with respect to driving and heating pulse durations and intensities. Specifically, the current investigation paid attention to choosing the fs pulses as driving and ablating pulses for improving the intensity and cut-off of harmonics from silver plasma.  

Fig.1 HHG spectra of silver bulk and nanoparticles plasma plumes produced by ns, ps, and fs laser pulses(Images by Konda).

Author: Dr. Srinivasa Rao Konda

Assistant Professor

GPL, State Key Laboratory of Applied Optics, Changchun Institute of Optics, Fine Mechanics, and Physics (CIOMP), Chinese Academy of Sciences, No. 77 Ying Ku Road, Changchun, Jilin, 130033, China.

 E-mail: ksrao@ciomp.ac.cn

Article links: https://doi.org/10.1016/j.optlastec.2021.107602