title: Generation of an air laser at extended distances by femtosecond laser filamentation with telescope optics.
abstract: We present the generation of self-induced-white-light-seeded lasing action of nitrogen molecules in air by a Ti:sapphire femtosecond laser (800 nm, 5.5 mJ) and demonstrate that such lasing action is strongly influenced by external focusing conditions. It is found that the self-seeded lasing signal of N(2)(+) at ~391 nm decreases dramatically by orders of magnitude and ultimately disappears when the focal length of an external lens increases from 0.5 m to 1 m. By using a telescope, it is shown that such limitation can be overcome and the 391 nm lasing can be controlled to occur at remotely designated distance, providing a possibility for practical applications in standoff spectroscopy.
authors.forename: Chenrui
authors.initials: C
authors.lastname: Jing
authors.forename: Haisu
authors.initials: H
authors.lastname: Zhang
authors.forename: Wei
authors.initials: W
authors.lastname: Chu
authors.forename: Hongqiang
authors.initials: H
authors.lastname: Xie
authors.forename: Jielei
authors.initials: J
authors.lastname: Ni
authors.forename: Bin
authors.initials: B
authors.lastname: Zeng
authors.forename: Guihua
authors.initials: G
authors.lastname: Li
authors.forename: Jinping
authors.initials: J
authors.lastname: Yao
authors.forename: Huailiang
authors.initials: H
authors.lastname: Xu
authors.forename: Ya
authors.initials: Y
authors.lastname: Cheng
authors.forename: Zhizhan
authors.initials: Z
authors.lastname: Xu