Vacuum-ultraviolet stimulated emission from two-photon-excited molecular hydrogen

1 August 1983

journal article
research article
Published by American Physical Society (APS) in Physical Review A

Vol. 28 (2) , 795-801
https://doi.org/10.1103/physreva.28.795

Abstract

Intense vacuum-ultraviolet stimulated emission in molecular hydrogen, on both the Lyman and Werner bands, following excitation by two-quantum absorption at 193 nm on the

X {}^{1}Σ_{g}^{+} \to E

F {}^{1}Σ_{g}^{+}

transition, has been observed. The shortest wavelength seen in the stimulated-emission spectrum was 117.6 nm corresponding to the

C {}^{1}Π_{u} \to X {}^{1}Σ_{g}^{+} (2 - 5)

Q (2)

transition. The

C {}^{1}Π_{u}

state appears to be populated with a mechanism involving electron collisions. The radiative cascade mechanism found to lead to the vacuum-ultraviolet emissions on the Lyman band also causes strong infrared stimulated emission to occur on the

E

F {}^{1}Σ_{g}^{+} \to B {}^{1}Σ_{u}^{+}

band. Two entirely separate radiative excitation channels are observed to play important roles in the state-selective molecular population of the

E

F {}^{1}Σ_{g}^{+}

level. One involves two 193-nm quanta in the

X \leftarrow E

F

amplitude while the other process combines a 193-nm quantum with a first Stokes-shifted photon in

H_{2}

. The optical Stark effect was seen to play a significant role in the excitation process with shifts of molecular resonances as large as ∼45

{cm}^{- 1}

. Substantial deviations from Born-Oppenheimer behavior, resulting in a dramatic shift of the stimulated spectrum depending upon the excited-state rotational quantum number, were clearly observed for molecular levels close to the potential maximum separating the inner and outer wells of the

E

F {}^{1}Σ_{g}^{+}

state. The maximum energy observed in the strongest stimulated line was ∼ 100 μJ, a value corresponding to an energy conversion efficiency of ∼ 0.5%. The pulse duration of the stimulated emission is estimated from collisional data to be ∼ 10 ps, a figure indicating a maximum converted vacuum-ultraviolet power of ∼ 10 MW.

Keywords

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