Production of narrowband tunable extreme-ultraviolet radiation by noncollinear resonance-enhanced four-wave mixing

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...

Section: H 2 Spectroscopy In the Laboratorymentioning

confidence: 99%

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

“…In addition, this krypton transition was employed in a resonance enhanced sumfrequency mixing scheme, for efficient upconversion of the narrow-band output at = 212 nm to the XUV range near 90 nm; at these wavelengths, high-resolution spectroscopy was performed on narrow resonances in the H 2 and N 2 molecules. 34 In this resonance enhanced sum-frequency mixing experiment, a cw laser diode operating at wavelengths about 850 nm was implemented, 34 showing that a system of diode lasers, covering the wavelength range of Ti:sapphire lasers, can be used alternatively as seed light source.…”

Section: Spectroscopic Applications Of the Ti:sapphire Source In mentioning

confidence: 99%

A narrow-band injection-seeded pulsed titanium:sapphire oscillator-amplifier system with on-line chirp analysis for high-resolution spectroscopy

Hannemann

Duijn

Review of Scientific Instruments

2007

Self Cite

A narrow-band tunable injection-seeded pulsed titanium:sapphire laser system has been developed for application in high-resolution spectroscopic studies at the fundamental wavelengths in the near infrared as well as in the ultraviolet, deep ultraviolet, and extreme ultraviolet after upconversion. Special focus is on the quantitative assessment of the frequency characteristics of the oscillator-amplifier system on a pulse-to-pulse basis. Frequency offsets between continuous-wave seed light and the pulsed output are measured as well as linear chirps attributed mainly to mode pulling effects in the oscillator cavity. Operational conditions of the laser are found in which these offset and chirp effects are minimal. Absolute frequency calibration at the megahertz level of accuracy is demonstrated on various atomic and molecular resonance lines.

“…If some of the beams have transverse components relative to the propagation direction, the true vectorial properties of the wave vectors k i have to be taken into account. These properties can be beneficially applied in a noncollinear phase-matching geometry configuration of input beams, as displayed in Figure 5 (Hannemann et al 2005). Experimentally, a small angle between incident beams wave vectors at k 1 (λ 1 = 212 nm) and k 2 (at a tunable wavelength in the visible range) was chosen in a sum-frequency process, yielding ω 4 = 2ω 1 + ω 2 .…”

Section: Coherently Propagating Beams and Noncollinear Phase Matchingmentioning

confidence: 99%

“…The advantage of this method is that the direction of k 4 is not along any of the incident wave vectors, or of the third harmonic (which is along k 1 ), or along the difference-frequency beam. As was demonstrated by placing a slit, selecting the angle along the sum-frequency direction, a pure monochromatic XUV beam was produced, which could be applied online for spectroscopic studies (Hannemann et al 2005). The phase-matching geometry then intrinsically operates as a monochromator.…”

Section: Coherently Propagating Beams and Noncollinear Phase Matchingmentioning

confidence: 99%

Precision Laser Spectroscopy in the Extreme Ultraviolet

Eikema

Handbook of High‐resolution Spectroscopy

2011

Techniques for the production of short wavelengths in the extreme ultraviolet wavelength range are described, spanning low‐order harmonic generation in the perturbative regime for narrow bandwidth XUV production to the plateau‐regime with the three‐step collisional model for the generation of high harmonics with broadband ultrafast pulses. In addition, the intermediate regime is discussed for pulses of 300 ps duration, as well as the regime of harmonic conversion based on continuous wave lasers aiming at the production of coherent Lyman‐α radiation. Applications of XUV sources in the frequency domain typically rely on the production of XUV‐light from narrowband Fourier‐transform‐limited pulses for recording high‐resolution spectra. Alternatively, harmonically upconverted pulses of ultrashort duration (with inter‐pulse coherence) can be used for spectroscopic studies in the time and frequency domain (such as direct frequency comb spectroscopy techniques). Examples of both approaches for atomic and molecular spectroscopy are discussed at some length. For precision metrology on atomic systems, a focus is put on the Lamb shift determination in the He ground state. In the realm of molecular spectroscopy, predissociation phenomena in the nitrogen molecule are highlighted, with relevance for dissociation processes occurring in the upper layers of the Earth atmosphere. Similar predissociation phenomena in carbon monoxide are also treated in some detail, in this case with relevance for the chemistry in interstellar clouds. Precision XUV spectroscopy of molecular hydrogen is discussed as well, as it relates to the possibility of detecting a variation of the proton–electron mass ratio on a cosmological time scale. In the last section, applications of direct frequency comb spectroscopic techniques at short wavelengths are explained and prospects are given for using these techniques at extreme ultraviolet wavelengths.