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our laboratory we have developed a tunable narrow bandwidth laser
source in the vacuum ultraviolet (VUV) region (100-200 nm) for
spectroscopic applications. Visible light provided by two pulsed dye
lasers is converted to VUV light by a nonlinear optical process,
four-wave sum-frequency generation, in a medium of magnesium vapour and
krypton gas prepared inside a heat pipe oven. This source can provide
tunable coherent VUV light in the region 140-160 nm. The spectral
bandwidth of the VUV light is approximately 0.2 pm in this region. The
development of a second source using zink vapour as medium to provide
VUV wavelengths down to 106 nm is in progress. A VUV spectrometer with
a Deuterium lamp is also available for broadband measurements. We are applying the tunable VUV light to
selectively excite individual rovibronic transitions of molecules. The
total fluorescence is detected as function of wavelength to yield laser
induced fluorescence (LIF) spectra with a high spectral resolution and
an excellent signal to noise ratio. The molecules are flow-cooled in a
supersonic jet facilitating the detection of molecules in low
concentration such as rare isotopomers. The method has been applied to
study 4 stable isotopopmers of carbon monoxide (CO). CO is the second
most abundant molecule in outer space and therefore it spectral
features are important in astrophysics. We have recently measured
wavelengths of 29 transitions of the rare isotopomer 12-C 17-O (0.04 %
in nature) for which wavelength values were previously unavailable. We
are currently investigating forbidden singlet-triplet excitations of
12-C 16-O for which wavelength values have not been measured before.
We
are currently investigating the use of the VUV source and LIF setup to
excite and detect fluorescence and self-trapped excitons in large
bandgap materials such as CaF 2 .
This project is supported by the CSIR National Laser Centre under the Rental Pool programme. |
VUV Lab
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Heat Pipe Oven |
The group:
- Researchers: Prof. EG Rohwer, Dr. CM Steenkamp
- Collaborators: Prof. H Stafast, IPHT, Jena , Germany .
- Current students: Mr. AC Nortje (MSc), Mr. M Franke (PhD exchange student from Jena , Germany)
- Graduated students: Dr. CM Steenkamp (PhD, 2003), Dr. A du Plessis (PhD, 2006), Me. P Huang (MSc 2005),
Mr. GD Dickenson (MSc 2008)
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Selected publications:
(for complete list of publications see Publications)
Papers
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C.M.
Steinmann and E.G. Rohwer (US), H. Stafast (Institut für physikalische
Hochtechnologie in Jena , Germany ). "Accurate laboratory wavelengths
of the vacuum ultraviolet A(v'=3)-X(v"=0) band of 12 C 17 O and 12 C 18
O", Astrophysical Journal 590, L123-L126, 2003.
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C.M.
Steinmann, A. du Plessis, E.G. Rohwer, "High-resolution vacuum
ultraviolet laser spectroscopy of molecules in a free supersonic jet:
in search of rare CO isotopomers and CO-Ar van der Waals molecules", S.
Afr. J. Sci. 101, 87-88, 2005
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A.
du Plessis , C.M. Steinmann, E.G. Rohwer, "Experimental conditions for
vacuum ultraviolet laser spectroscopy", S. Afr. J. Sci. 101, 93-94,
2005.
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C.M.
Steenkamp, Anton du Plessis , Erich G. Rohwer, " An improved
experimental setup for high resolution vacuum ultraviolet laser
spectroscopy", S. Afr. J. Sci. 101, 272-275, 2005.
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A.
du Plessis, E.G. Rohwer, C.M. Steenkamp, "Accurate laboratory
wavelengths of the A 1 P ( u ' = 0 - 5) - X 1 Sigma + ( u '' = 0)
vibronic bands of 12 C 17 O and 12 C 18 O", Astrophysical Journal
Supplement Series 165, 432, 2006.
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A.
du Plessis, E.G. Rohwer, C.M. Steenkamp, "Investigation of four Carbon
Mo no xide isotopomers in natural abundance by laser induced
fluorescence in a supersonic jet", Journal of Molecular Spectroscopy
243, 124-133, 2007.
Theses/dissertations
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C.M.
Steinmann. "Development and characterisation of a tunable laser source
in the vacuum ultraviolet", M.Sc. thesis, University of Stellenbosch ,
December 1999. Supervisors: E .G. Rohwer (US) and P. E . Walters (US).
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C.M.Steinmann.
"Vacuum ultraviolet laser spectroscopy of CO molecules in a supersonic
jet", Ph.D. dissertation, University of Stellenbosch , December 2003.
Promoters: E .G. Rohwer (US) and H. Stafast (Institut für Physikalische
Hochtechnologie and Friedrich-Schiller University , Jena , Germany)
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A.
du Plessis. "Laser spectroscopy of the fourth positive system of carbon
monoxide isotopomers", Ph.D. dissertation, University of Stellenbosch ,
April 2006. Promoters: E.G. Rohwer (US) and C.M. Steenkamp (US).
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G.D. Dickenson. “Development of a Tuneable Laser Source in the Vacuum
Ultraviolet and its Applications to Spectroscopy” MSc thesis,
University of Stellenbosch , December 2008. Promoters: C.M. Steenkamp
(US) and E.G. Rohwer (US).
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