Frequency-mixing scheme for the production of tunable narrowband XUV radiation (91–95 nm): application to precision spectroscopy and predissociation in diatomic molecules

The Journal of Chemical Physics

2014

114

Precision measurement of the rotational energy-level structure of the three-electron molecule He 2 + Transitions in atoms and molecules provide an ideal test ground for constraining or detecting a possible variation of the fundamental constants of nature. In this perspective, we review molecular species that are of specific interest in the search for a drifting proton-to-electron mass ratio μ.In particular, we outline the procedures that are used to calculate the sensitivity coefficients for transitions in these molecules and discuss current searches. These methods have led to a rate of change in μ bounded to 6 × 10 −14 /yr from a laboratory experiment performed in the present epoch. On a cosmological time scale, the variation is limited to | μ/μ| < 10 −5 for look-back times of 10-12 × 10 9 years and to | μ/μ| < 10 −7 for look-back times of 7× 10 9 years. The last result, obtained from high-redshift observation of methanol, translates intoμ/μ = (1.4 ± 1.4) × 10 −17 /yr if a linear rate of change is assumed.

Section: A Transitions In Molecular Hydrogen and Carbon Monoxidementioning

confidence: 92%

Perspective: Tipping the scales: Search for drifting constants from molecular spectra

Jansen

Bethlem

The Journal of Chemical Physics

2014

114

“…A 99.40% isotopically enriched gas sample (Euriso-top) was used for the 15 N 2 measurements. Philip et al [10] deduced a XUV source bandwidth of 300 MHz at full width at half maximum (FWHM) (all further widths and bandwidths in this paper are FWHM) by measuring a long-lived krypton resonance at a nozzleskimmer distance of 150 mm. This is the same bandwidth determined from measurements applying the third harmonic of the frequency-doubled output of the PDA corresponding to x XUV = 6x PDA [4].…”

Section: Methodsmentioning

confidence: 99%

“…Now the system has been modified to produce XUV radiation at energies exceeding 106 000 cm À1 . The extension has been documented before [10] and will only be briefly described here. The output of a narrow-band tunable cw ring dye laser, pumped by a 532-nm Millennia-V laser, was amplified in a pulsed dye amplifier (PDA), which was in turn pumped with the second harmonic of a pulsed Nd:YAG laser.…”

Section: Methodsmentioning

confidence: 99%

Lifetimes and transition frequencies of several singlet ungerade states in N2 between 106000 and 109000cm−1

Sprengers

Journal of Molecular Spectroscopy

2006

Self Cite

Using a narrow-band tunable XUV source, ultra-high resolution 1 XUV + 1 UV two-photon ionisation spectra were recorded of transitions to several singlet ungerade states in 14 N 2 and 15 N 2 in the range 106 000-109 000 cm À1 . The natural linewidths of the individual rotational spectral lines were determined and the resulting lifetimes were found to depend on vibrational level and for the c 3 1 P u (v = 1) level also on isotope. Furthermore, accurate transition frequencies were determined and for several bands, lines near bandhead regions were resolved for the first time.

“…Shorter wavelengths in the range 92-95 nm were produced by mixing the fixed 532 nm output of an injectionseeded pulsed Nd:YAG laser with that of the output of the PDA [89]; in this specific range the resulting spectral resolution is similar to that at longer wavelengths, but the accuracy is limited to 0.011 cm À1 . This is due to the fact that two lasers need to be calibrated on-line during the measurements, where one is at fixed wavelength, but subject to slow drifts.…”

Section: H 2 Spectroscopy In the Laboratorymentioning

confidence: 99%

“…This is the generic setup. As discussed in the text some variations on this scheme are used to perform measurements on some wavelength regions, involving mixing with the 532 nm output of a Nd:YAG laser [89], addition of a short wavelength ionization laser [90], and using a sum-frequency mixing scheme for the production of XUV light [92]. PBS: polarizing beam splitter; PD: photodiode.…”

Section: H 2 Spectroscopy In the Laboratorymentioning

confidence: 99%

On a possible variation of the proton-to-electron mass ratio: H2 spectra in the line of sight of high-redshift quasars and in the laboratory

Journal of Molecular Spectroscopy

Buning

Eikema

et al. 2007

Self Cite

124

Recently the finding of an indication for a decrease of the proton-to-electron mass ratio l = m p /m e by 0.002% in the past 12 billion years was reported in the form of a Letter [E. Reinhold, R. Buning, U. Hollenstein, P. Petitjean, A. Ivanchik, W. Ubachs, Phys. Rev. Lett. 96 (2006) 151101]. Here we will further detail the methods that led to that result and put it in perspective. Laser spectroscopy on molecular hydrogen, using a narrow-band and tunable extreme ultraviolet laser system at the Laser Centre Vrije Universiteit Amsterdam, results in transition wavelengths of spectral lines in theWerner band systems at an accuracy of (4-11) · 10 À8, depending on the wavelength region. This corresponds to an absolute accuracy of 0.000004-0.000010 nm. A database of 233 accurately calibrated H 2 lines is presented here for future reference and comparison with astronomical observations. Recent observations of the same spectroscopic features in cold hydrogen clouds at redshifts z = 2.5947325 and z = 3.0248970 in the line of sight of two quasar light sources (Q 0405À443 and Q 0347À383) resulted in 76 reliably determined transition wavelengths of H 2 lines at accuracies in the range 2 · 10 À7 to 1 · 10 À6 . Those observations were performed with the Ultraviolet and Visible Echelle Spectrograph at the Very Large Telescope of the European Southern Observatory at Paranal, Chile. A third ingredient in the analysis is the calculation of an improved set of sensitivity coefficients K i , a parameter associated with each spectral line, representing the dependence of the transition wavelength on a possible variation of the proton-to-electron mass ratio l. The new model for calculation of the K i sensitivity coefficients is based on a Dunham representation of ground state and excited state level energies, derived from the most accurate data available in literature for the X 1 R þ g ground electronic state and the presently determined level energies in the B 1 R þ u and C 1 P u states. Moreover, the model includes adiabatic corrections to electronic energies as well as local perturbation effects between B and C levels. The full analysis and a tabulation of the resulting K i coefficients is given in this paper. A statistical analysis of the data yields an indication for a variation of the proton-to-electron mass ratio of Dl/l = (2.45 ± 0.59) · 10 À5 for a weighted fit and Dl/l = (1.99 ± 0.58) · 10 À5 for an unweighted fit. This result, indicating the decrease of l, has a statistical significance of 3.5r. Mass-variations as discussed relate to inertial or kinematic masses, rather than gravitational masses. Separate treatment of the data gives a similar positive result for each of the quasars Q 0405À443 and Q 0347À383. The statistical analysis is further documented and possible systematic shifts underlying the data, with the possibility of mimicking a non-zero Dl/l value, are discussed. The observed decrease in l corresponds to a rate of change of d lnl/dt = À2 · 10 À15 per year, if a linear variation with time is assumed. Expe...