21 research outputs found
Wavelength calibration of the CI line at 94.5 nm for comparison with quasar data
With the use of an ultra-narrow-band extreme ultraviolet laser source, tunable near 94 nm, transition wavelengths are determined for lines connecting the 1s(2)2s(2)2p(2) P-3(0,1,2) ground-term levels to the 1s(2)2s2p(3) S-3(1) excited level in neutral carbon at an absolute accuracy of 4x10(-8). With the determination of the zero-velocity rest-frame wavelengths these lines can be included in an analysis of a possible temporal variation of the fine-structure constant alpha from a comparison with quasar data. A value for the C-12/C-13 transition isotope shift was also obtained yielding 0.5107(13) cm(-1), in average over the three fine-structure lines. The latter measurement will allow to study isotopic evolution in the universe and test models of nuclear processes in stars
Atomic transition frequencies, isotope shifts, and sensitivity to variation of the fine structure constant for studies of quasar absorption spectra
Theories unifying gravity with other interactions suggest spatial and
temporal variation of fundamental "constants" in the Universe. A change in the
fine structure constant, alpha, could be detected via shifts in the frequencies
of atomic transitions in quasar absorption systems. Recent studies using 140
absorption systems from the Keck telescope and 153 from the Very Large
Telescope, suggest that alpha varies spatially. That is, in one direction on
the sky alpha seems to have been smaller at the time of absorption, while in
the opposite direction it seems to have been larger.
To continue this study we need accurate laboratory measurements of atomic
transition frequencies. The aim of this paper is to provide a compilation of
transitions of importance to the search for alpha variation. They are E1
transitions to the ground state in several different atoms and ions, with
wavelengths ranging from around 900 - 6000 A, and require an accuracy of better
than 10^{-4} A. We discuss isotope shift measurements that are needed in order
to resolve systematic effects in the study. The coefficients of sensitivity to
alpha-variation (q) are also presented.Comment: Includes updated version of the "alpha line" lis
Extreme-ultraviolet laser metrology of OI transitions
Some 16 transitions in atomic oxygen originating from its P-3 ground state were measured using a tunable narrow-band extreme-ultraviolet laser source, with an unprecedented accuracy of Delta lambda/lambda= 8 x 10(-8). The results are relevant for comparisons with spectral absorption features observed in the line of sight of quasars, in order to test a possible variation of the fine-structure constant alpha on a cosmological time-scale
Lithium vapour excitation at 2S→3D two-photon resonance
We report study of processes which occur in lithium vapour under two-photon
excitation of the Li(3D) state at 639.1 nm. A time-resolved technique has
been used to measure the fluorescence from the Li(3D), Li(2P) and Li(3P)
states. We have determined radiation rates for lithium atom densities in
the range 1013-1014 cm-3 and laser powers (105-106
Wcm-2). The ground-state lithium atom density was determined by
knowing temperature and vapour pressure in a modified heat-pipe oven. The
contribution to radiation rates from different processes and prospect for
cross-section determination of homonuclear reverse energy-pooling are
discussed
Study of Mn laser ablation in methane atmosphere
Laser ablation of Mn target in vacuum and in the presence of CH4 was
studied under 308Â nm laser irradiation. Time-resolved emission using gated
detection and scanning monochromator and absorption using the cavity ring-down
spectroscopy were used to study vaporized plume. In the CH4 atmosphere we
observed transitions identified as C2 and MnH bands, while these spectral
features were not detected in emission spectra. This is a clear evidence of
importance in combining both spectroscopic techniques in laser vaporized plume study