Non-thermal Doppler-broadened Lyman-α line shape in resonant dissociation of H₂

Abstract

The detailed Lyman-α emission line shape after resonant dissociation and excitation of H2 via collisions with Ne excimer molecules has been determined (Ne*2 + H2 → 2Ne + H + H*(n = 2)). Pressure effects due to the high Ne pressure, required for efficient excimer formation, decrease the effective lifetime of the hydrogen excited state. The reduced effective lifetime significantly reduces the average number of elastic collisions experienced by the excited hydrogen atom before radiative decay. Excess energy imparted to the excited-state hydrogen atom by the Ne excimer, in the dissociative excitation collision, produces a non-thermal Doppler-broadened emission line shape. The full width at half maximum (FWHM) is 3.85 pm and the effective lifetime of the n = 2 state is estimated to be 14 ps at a Ne pressure of 1 atm. Results are obtained from pressure-dependent measurements of the Balmer-α absorption line shape using laser spectroscopy.

Electron beam induced light emission

“…Also different emission characteristics such as narrow atomic line radiation or specific molecular bands can be observed. A process which has been studied in detail is energy transfer from Ne to H 2 leading to selective and narrow-band emission of the Lyman-α line at 121.6 nm in atomic hydrogen [8,9]. Another light source uses a mixture of argon and water vapour radiating on a molecular band of OH * around 310 nm [10].…”

VUV Spectral Irradiance Measurements in H2/He/Ar Microwave Plasmas and Comparison with Solar Data

“…Low-temperature plasmas based on H 2 mixed with noble gases have been developed for a long time as a continuous Lyα source, where the corresponding intense line emission between the first excited and the ground state of the (2p 2 P 0 )→(1s 2 S) transition can be produced by electrical discharges. Microwave, low-radiofrequency (rf), micro-hollow cathode, and dielectric barrier plasmas have been commonly used as convenient Lyα sources (Davis & Braun 1968;Bergonzo et al 1992;Hollander & Wertheimer 1994;Fozza et al 1998;El-Dakrouri et al 2002;Yan et al 2002;Rahman et al 2004;McCarthy et al 2005). Microwave plasmas are often preferred because they exhibit low gas temperatures and require only simple and nonexpensive equipment.…”

Optical design and system characterization of an imaging microscope at 121.6 nm

“…4,6 The vacuum ultraviolet (VUV) Lyman-α line (λ ¼ 121.6 nm) emission from atomic hydrogen is a promising short wavelength for microscopy, as it coincides with a transparent window in the air absorption spectrum. [7][8][9] The transmission window provides flexibility in imaging samples and potentially eases system operation, as the object to be imaged can be outside the vacuum chamber. In this paper, we present the optical design and construction of a numerical aperture ðNAÞ ¼ 0.3 imaging microscope at λ ¼ 121.6 nm.…”