On the origin of the vacuum-ultraviolet molecular band emission from high pressure helium plasmas

R. J. Carman, R. Ganesan

Research output: Contribution to conferenceAbstractResearch

Abstract

The vacuum-ultraviolet (VUV) emission band from the He₂* excimer between 60-120nm (the well-known Hopfield continuum) is of topical interest as potential source of high energy photons (10-20eV) for many emerging applications in materials processing and surface treatment. Previous time-resolved spectroscopic studies of the He₂* excimer emission bands in medium pressure pulsed-excited plasmas reported by Bartell et-al [1] have indicated the existence of a relatively weak but rapidly evolving fast component superimposed on a slower pulse. The slower pulse typically decays with a duration of several microseconds. However, the fast component has not been extensively studied to date, and its characteristics and precise origin are not well understood. In particular, its prompt appearance (within a few 10’s of nanoseconds) following plasma excitation appears to suggest a new production mechanism that is substantially faster than that attributed to known processes for forming the low-lying He₂* molecular states e.g. three-body conversion of He*(n=2) species. Interestingly, in LIF studies of a low pressure (~10mb) helium plasma by Frost et-al [2], unexplained He₂** molecular emissions were observed as a direct result of He(31,3P) + He(1¹S) collisions. Based on their results, they proposed the existence of a “neglected channel” to He₂** production.

To further investigate these observations, a comprehensive set of time and wavelength resolved VUV emission curves from a windowless dielectric barrier discharge (DBD) in helium (100mb-1000mb) utilising short voltage pulse excitation have been measured to clearly resolve the fast and slow temporal components of the Hopfield continuum over the wavelength range 60-120nm. Experimental results, together with results from computer modeling, suggest that both temporal components of the VUV emission must originate from the same molecular state He₂*(A¹Su+), and that two distinct pumping mechanisms must populate this state. The time signature of the fast component suggests a new channel for producing low-lying He₂*(A¹Su+) molecules from He* atomic excited states, and involving a rapid radiative cascade process from higher He₂** molecular states.

Conference

ConferenceGaseous Electronics Meeting
Abbreviated titleGEM
CountryAustralia
CityAdelaide
Period9/02/1412/02/14

Fingerprint

helium plasma
ultraviolet emission
vacuum
excimers
pulses
continuums
excitation
frost
surface treatment
wavelengths
laser induced fluorescence
emerging
cascades
pumping
low pressure
helium
signatures
collisions
photons
electric potential

Keywords

  • plasma physics
  • Atomic processes

Cite this

Carman, R. J., & Ganesan, R. (2014). On the origin of the vacuum-ultraviolet molecular band emission from high pressure helium plasmas. Abstract from Gaseous Electronics Meeting, Adelaide, Australia.
Carman, R. J. ; Ganesan, R. / On the origin of the vacuum-ultraviolet molecular band emission from high pressure helium plasmas. Abstract from Gaseous Electronics Meeting, Adelaide, Australia.1 p.
@conference{249339cd79d04dff846729d2e7997fcb,
title = "On the origin of the vacuum-ultraviolet molecular band emission from high pressure helium plasmas",
abstract = "The vacuum-ultraviolet (VUV) emission band from the He₂* excimer between 60-120nm (the well-known Hopfield continuum) is of topical interest as potential source of high energy photons (10-20eV) for many emerging applications in materials processing and surface treatment. Previous time-resolved spectroscopic studies of the He₂* excimer emission bands in medium pressure pulsed-excited plasmas reported by Bartell et-al [1] have indicated the existence of a relatively weak but rapidly evolving fast component superimposed on a slower pulse. The slower pulse typically decays with a duration of several microseconds. However, the fast component has not been extensively studied to date, and its characteristics and precise origin are not well understood. In particular, its prompt appearance (within a few 10’s of nanoseconds) following plasma excitation appears to suggest a new production mechanism that is substantially faster than that attributed to known processes for forming the low-lying He₂* molecular states e.g. three-body conversion of He*(n=2) species. Interestingly, in LIF studies of a low pressure (~10mb) helium plasma by Frost et-al [2], unexplained He₂** molecular emissions were observed as a direct result of He(31,3P) + He(1¹S) collisions. Based on their results, they proposed the existence of a “neglected channel” to He₂** production.To further investigate these observations, a comprehensive set of time and wavelength resolved VUV emission curves from a windowless dielectric barrier discharge (DBD) in helium (100mb-1000mb) utilising short voltage pulse excitation have been measured to clearly resolve the fast and slow temporal components of the Hopfield continuum over the wavelength range 60-120nm. Experimental results, together with results from computer modeling, suggest that both temporal components of the VUV emission must originate from the same molecular state He₂*(A¹Su+), and that two distinct pumping mechanisms must populate this state. The time signature of the fast component suggests a new channel for producing low-lying He₂*(A¹Su+) molecules from He* atomic excited states, and involving a rapid radiative cascade process from higher He₂** molecular states.",
keywords = "plasma physics, Atomic processes",
author = "Carman, {R. J.} and R. Ganesan",
year = "2014",
month = "2",
day = "12",
language = "English",
note = "Gaseous Electronics Meeting, GEM ; Conference date: 09-02-2014 Through 12-02-2014",

}

Carman, RJ & Ganesan, R 2014, 'On the origin of the vacuum-ultraviolet molecular band emission from high pressure helium plasmas' Gaseous Electronics Meeting, Adelaide, Australia, 9/02/14 - 12/02/14, .

On the origin of the vacuum-ultraviolet molecular band emission from high pressure helium plasmas. / Carman, R. J.; Ganesan, R.

2014. Abstract from Gaseous Electronics Meeting, Adelaide, Australia.

Research output: Contribution to conferenceAbstractResearch

TY - CONF

T1 - On the origin of the vacuum-ultraviolet molecular band emission from high pressure helium plasmas

AU - Carman, R. J.

AU - Ganesan, R.

PY - 2014/2/12

Y1 - 2014/2/12

N2 - The vacuum-ultraviolet (VUV) emission band from the He₂* excimer between 60-120nm (the well-known Hopfield continuum) is of topical interest as potential source of high energy photons (10-20eV) for many emerging applications in materials processing and surface treatment. Previous time-resolved spectroscopic studies of the He₂* excimer emission bands in medium pressure pulsed-excited plasmas reported by Bartell et-al [1] have indicated the existence of a relatively weak but rapidly evolving fast component superimposed on a slower pulse. The slower pulse typically decays with a duration of several microseconds. However, the fast component has not been extensively studied to date, and its characteristics and precise origin are not well understood. In particular, its prompt appearance (within a few 10’s of nanoseconds) following plasma excitation appears to suggest a new production mechanism that is substantially faster than that attributed to known processes for forming the low-lying He₂* molecular states e.g. three-body conversion of He*(n=2) species. Interestingly, in LIF studies of a low pressure (~10mb) helium plasma by Frost et-al [2], unexplained He₂** molecular emissions were observed as a direct result of He(31,3P) + He(1¹S) collisions. Based on their results, they proposed the existence of a “neglected channel” to He₂** production.To further investigate these observations, a comprehensive set of time and wavelength resolved VUV emission curves from a windowless dielectric barrier discharge (DBD) in helium (100mb-1000mb) utilising short voltage pulse excitation have been measured to clearly resolve the fast and slow temporal components of the Hopfield continuum over the wavelength range 60-120nm. Experimental results, together with results from computer modeling, suggest that both temporal components of the VUV emission must originate from the same molecular state He₂*(A¹Su+), and that two distinct pumping mechanisms must populate this state. The time signature of the fast component suggests a new channel for producing low-lying He₂*(A¹Su+) molecules from He* atomic excited states, and involving a rapid radiative cascade process from higher He₂** molecular states.

AB - The vacuum-ultraviolet (VUV) emission band from the He₂* excimer between 60-120nm (the well-known Hopfield continuum) is of topical interest as potential source of high energy photons (10-20eV) for many emerging applications in materials processing and surface treatment. Previous time-resolved spectroscopic studies of the He₂* excimer emission bands in medium pressure pulsed-excited plasmas reported by Bartell et-al [1] have indicated the existence of a relatively weak but rapidly evolving fast component superimposed on a slower pulse. The slower pulse typically decays with a duration of several microseconds. However, the fast component has not been extensively studied to date, and its characteristics and precise origin are not well understood. In particular, its prompt appearance (within a few 10’s of nanoseconds) following plasma excitation appears to suggest a new production mechanism that is substantially faster than that attributed to known processes for forming the low-lying He₂* molecular states e.g. three-body conversion of He*(n=2) species. Interestingly, in LIF studies of a low pressure (~10mb) helium plasma by Frost et-al [2], unexplained He₂** molecular emissions were observed as a direct result of He(31,3P) + He(1¹S) collisions. Based on their results, they proposed the existence of a “neglected channel” to He₂** production.To further investigate these observations, a comprehensive set of time and wavelength resolved VUV emission curves from a windowless dielectric barrier discharge (DBD) in helium (100mb-1000mb) utilising short voltage pulse excitation have been measured to clearly resolve the fast and slow temporal components of the Hopfield continuum over the wavelength range 60-120nm. Experimental results, together with results from computer modeling, suggest that both temporal components of the VUV emission must originate from the same molecular state He₂*(A¹Su+), and that two distinct pumping mechanisms must populate this state. The time signature of the fast component suggests a new channel for producing low-lying He₂*(A¹Su+) molecules from He* atomic excited states, and involving a rapid radiative cascade process from higher He₂** molecular states.

KW - plasma physics

KW - Atomic processes

UR - https://www.conferenceonline.com/abstract/alogin/?clear=1&warehouse_id=296

M3 - Abstract

ER -

Carman RJ, Ganesan R. On the origin of the vacuum-ultraviolet molecular band emission from high pressure helium plasmas. 2014. Abstract from Gaseous Electronics Meeting, Adelaide, Australia.