Enhanced Coherent Emission from Ionized Nitrogen Molecules by Femtosecond Laser Pulses
journal contributionposted on 15.10.2019, 17:04 by Wei Zheng, Zhiming Miao, Linlin Zhang, Yang Wang, Chen Dai, An Zhang, Hongbing Jiang, Qihuang Gong, Chengyin Wu
The forward emission spectra were experimentally measured for ionized nitrogen molecules by an 800 nm pump laser and a delayed seed laser. It was found that emission lines around both 428 and 391 nm are greatly enhanced upon use of a 391 or 428 nm seed laser. The emission lines around 391 and 428 nm can be assigned to the rotational transitions of N2+ [B2Σu+(v′ = 0) → X2Σg+(v = 0)] and N2+ [B2Σu+(v′ = 0) → X2Σg+(v = 1)], respectively. They originate from seed-induced superfluorescence and resonant stimulated Raman scattering. The genetic algorithm was utilized to simulate the experimental observations and determine the relative population of B2Σu+(v′ = 0), X2Σg+(v = 1), and X2Σg+(v = 0). The result verifies that vibrational population inversion is achieved between B2Σu+(v′ = 0) and X2Σg+(v = 0) by the 800 nm pump laser. Our finding provides new insights into controlling the coherent emission of ionized nitrogen molecules, which has promising application in filamentation-based remote atmospheric sensing.