160,893 research outputs found
A CENTURY AFTER LYMAN
No full textT. Lyman, Astroph. J. E. Reinhold, W. Hogervorst, and W. Ubachs, Phys. Rev. Lett. A. de Lange E. Reinhold, and W. Ubachs, Phys. Rev. Lett. A. de Lange, E. Reinhold, and W. Ubachs, Int. Rev. Phys. Chem. E. Reinhold and W. Ubachs, Phys. Rev. Lett. W. Ubachs and E. Reinhold, Phys. Rev. Lett. accepted (2004).Author Institution: Laser Centre, Department of Physics and Astronomy, Vrije UniversiteitExactly a century ago Lyman reported on the first spectroscopic identification of the hydrogen . Over the years past many spectroscopists have searched for spectral signatures of the smallest neutral molecule, which has become the fundamental test system for quantum chemical ab initio calculations. Experimental work on and its isotopomers is more difficult than in other systems because electronic absorption occurs only at wavelengths ; the vibrational spectrum is extremely weak due to the inversion symmetry; due to the low nuclear mass spectra are not organized in bands as bands but rather occur as randomly organized lines; isotopic substitution is not helpful because it gives rise to another set of randomly appearing lines. In the past decade we have employed laser based techniques to unravel new spectral structures in hydrogen and measure at high resolution. Specific breakthroughs are the use of a narrowband tunable laser in the extreme ultraviolet domain and of multiple-resonance techniques involving XUV photons. These studies have led to: the observation of high-lying double-well structures of gerade ; the observation of a double-well structures of ungerade ; the observation of strong u-g symmetry ; the observation of heavy Rydberg states of the . From a comparison of extremely accurate calibration of Lyman and Werner transitions, and by comparing the laboratory results with absorptions in spectra of quasars that have occured 12 Billion years ago, a rather strict constraint can be set om a possible variation of the proton-to-electron mass
A magic wavelength optical dipole trap for high-precision spectroscopy of utracold metastable helium
Full text linkVassen, W. [Promotor]Ubachs, W.M.G. [Copromotor
Precision spectroscopy of molecular hydrogen and the search for new physics
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Previous issue date: 6The hydrogen molecule is the smallest neutral chemical entity and a benchmark system of molecular spectroscopy. The comparison between highly accurate measurements of transition frequencies and level energies with quantum calculations including all known phenomena (relativistic, vacuum polarization and self energy) provides a tool to search for physical phenomena in the realm of the unknown: are there forces beyond the three included in the Standard Model of physics plus gravity [1], are there extra dimensions beyond the 3+1 describing space time [2] ? Comparison of laboratory wavelengths of transitions in hydrogen may be compared with the lines observed during the epoch of the early Universe to verify whether fundamental constants of Nature have varied over cosmological time [3]. These concepts, as well as the precision laboratory experiments and the astronomical observations used for such searches of new physics [4] will be discussed._x000d_
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[1] E.J. Salumbides, J.C.J. Koelemeij, J. Komasa, K. Pachucki, K.S.E. Eikema, W. Ubachs, emph{Bounds on fifth forces from precision measurements on molecules}, Phys. Rev. D87, 112008 (2013)._x000d_
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[2] E.J. Salumbides, A.N. Schellekens, B. Gato-Rivera, W. Ubachs_x000d_
emph{Constraints on extra dimensions from molecular spectroscopy},_x000d_
New. J. Phys. 17, 033015 (2015)._x000d_
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[3] W. Ubachs, J. Bagdonaite, E.J. Salumbides, M.T. Murphy, L. Kaper,_x000d_
emph{Search for a drifting proton-electron mass ratio from H},_x000d_
Rev. Mod. Phys. 88, 021003 (2016)._x000d_
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[4] W. Ubachs, J.C.J. Koelemeij, K.S.E. Eikema, E.J. Salumbides,_x000d_
emph{Physics beyond the Standard Model from hydrogen spectroscopy},_x000d_
J. Mol. Spectr. 320, 1 (2016)
Rotational Level Intervals In Hd From Cryo-cooled Sub-doppler Rovibrational Spectroscopy
Full text linkThe spectroscopic investigation of the hydrogen molecule and its isotopologues has played a crucial role in the advancement of quantum mechanics in the molecular domain. Particularly, highly accurate measurements of rovibrational transitions allow for various tests of fundamental physics including searches for physics beyond the Standard Model\footnote{W. Ubachs, J.C.J. Koelemeij, K.S.E. Eikema, E.J. Salumbides, J. Mol. Spectr. 320, 1-12 (2016)}.
Recent Doppler-free measurements performed at room temperature\footnote{F.M.J. Cozijn, P. Dupre, K.S.E. Eikema, E.J. Salumbides, W. Ubachs,, Phys. Rev. Lett. 120, 153002 (2018)}\footnote{M.L. Diouf , F.M.J. Cozijn, B. Darquie, E.J. Salumbides, W. Ubachs, Opt. Lett. 44, 4733 (2019)}\footnote{M.L. Diouf, F.M.J. Cozijn, K.F. Lai, E.J. Salumbides, W. Ubachs , Phys. Rev. Res. 2, 023209 (2020)}, in the (2,0) overtone band of the hydrogen deuteride molecule spurred a stimulating debate on the interpretation of the spectra which significantly differ from typical Lamb-dips. New measurements were performed in a cryogenically cooled cavity with the hope of resolving the underlying hyperfine structure. However the resulted spectra observed shared the same unusual lineshapes which still hinder the extraction of the absolute rovibrational positions. With the goal of extracting the rotational interval with a better accuracy, pairs of P and R transitions were considered. This leads to accurate values for rotational energy intervals and to a precise test of molecular QED theory\footnote{P. Czachorowski, M. Puchalski, J. Komasa, K. Pachucki, Phys. Rev. A 98, 052506 (2018)}
Advances in cavity-enhanced methods for high precision molecular spectroscopy and test of fundamental physics
No full textCavity-enhanced spectroscopic techniques are highly sensitive laser-based methods for interrogating the atomic and molecular constituents of any gaseous medium that is confined into an optical resonator. A first advantage over conventional absorption spectroscopy comes from the extremely long path length of the laser radiation inside the stable, high-finesse, optical cavity, which allows the sample to be probed over several tens of kilometers. After more than 30 years of research and development, techniques like cavity ring-down spectroscopy, cavity-enhanced absorption spectroscopy, and noise-immune cavity-enhanced optical-heterodyne molecular spectroscopy, have reached extraordinary levels of detection sensitivity, such that it is possible to measure light absorption from molecules in trace amounts or extremely weak spectral lines of more abundant species. A second advantage of the use of high-finesse cavities lies in the power amplification achieved inside the optical resonator, making it possible to saturate even weak transitions, thus reducing the width of spectral lines by some three orders of magnitude. Combining these methods with frequency comb technologies has further enhanced their capabilities, adding metrology-grade qualities to spectroscopic determinations such as transition frequencies of molecular resonances, which can be measured with sub-kHz accuracy. In this review article, we discuss the current status of highly precise and highly sensitive laser spectroscopy for fundamental tests and measurements. We describe state-of-the-art molecular spectroscopy methods and their application to a few selected molecules of fundamental importance in understanding quantum chemistry theories or testing quantum electrodynamics.</p
Spectral redshift in harmonic generation from plasma dynamics in the laser focus
Full text linkHigh-precision spectral measurements on the 9th harmonic generated in xenon gas are compared with calculations of the plasma dynamics resulting from multiphoton ionization in the laser focus. For the regime of 300 ps pulses and above-saturation intensities a novel mechanism producing redshifts in the harmonics is uncovered and explained. Ions play a double role: the nonlinear susceptibility of the ions is decisive for the harmonic intensity, while their mutual repulsion and the associated increase of the index of refraction is identified as the cause of the redshift
Plasma dynamically induced frequency shifts in high-order harmonic generation in nitrogen
Full text linkExperiments and theoretical calculations on high-harmonic generation in nitrogen are presented in the regime of laser pulses of a 300-ps duration, where the plasma dynamics following the ionization of the medium plays a decisive role. The experiments are performed with similar to 4-GW Ti:sapphire laser pulses, giving rise to fully saturated ionization. The shifts between the exact harmonic frequency in the extreme ultraviolet and the integer multiple of the fundamental frequency are caused by the self-phase modulation of the laser pulse due to the time-dependent free-electron density in the plasma generated in the focal zone. Well-calibrated atomic resonances in the extreme ultraviolet measured through absorption in a secondary gas jet are used as frequency markers in the extreme ultraviolet for the accurate determination of the sign and magnitude of the frequency shifts. A theoretical model including both plasma dynamics and harmonic generation from atoms and ions has previously been developed, and successfully applied to explain the frequency red shift observed in xenon [Phys. Rev. Lett. 96, 123904 (2006)]. The plasma-dynamical model is extended and applied to the results of the harmonic generation in nitrogen, fully explaining the observed harmonic frequency shifts in the 9th and 13th harmonic
Measurements of chirp-induced frequency shift in high-order harmonic generation in xenon RID F-5649-2011
No full textA precise metrology experiment on the ninth harmonic generated in the nonperturbative regime in xenon is presented. Harmonic generation is performed with a 300-ps 4-GW narrowband tunable laser, and well-calibrated atomic resonances are used as a frequency markers in the extreme ultraviolet, enabling an absolute frequency calibration at the 10(-6)-10(-7) level. A harmonic frequency is observed that deviates from the expected integer multiple of the fundamental frequency. This frequency shift is found to increase with gas density starting from negative values, i.e., redshift, at a low gas density. Possible sources of the observed frequency shift are critically discussed. The increase of the frequency shift toward high gas densities is consistent with self-phase modulation of the fundamental beam due to the presence of free electrons in the interaction region that are generated via multiphoton ionization, while the observed redshift toward lower gas densities may be attributable to plasma-dynamics effects
Spectroscopy of highly charged tin ions for an extreme ultraviolet light source for lithography
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Previous issue date: 6Laser-produced tin plasmas are the prime candidates for the generation of extreme ultraviolet (EUV) light around 13.5 nm in nanolithographic applications. This light is generated primarily by atomic transitions in highly charged tin ions: Sn-Sn. Due to the electronic configurations of these charge states, thousands of atomic lines emit around 13.5 nm, clustered in a so-called unresolved transition array. As a result, accurate line identification becomes difficult in this regime. Nevertheless, this issue can be circumvented if one turns to the optical: with far fewer atomic states, only tens of transitions take place and the spectra can be resolved with far more ease. We have investigated optical emission lines in an electron-beam-ion-trap (EBIT), where we managed to charge-state resolve the spectra. Based on this technique and on a number of different emph{ab initio} techniques for calculating the level structure, the optical spectra could be assigned [1,2]. As a conclusion the assignments of EUV transitions in the literature require corrections. The EUV and optical spectra are measured simultaneously in the controlled conditions of the EBIT as well as in a droplet-based laser-produced plasma source providing information on the contribution of Sn charge states to the EUV emission._x000d_
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[1] A. Windberger, F. Torretti, A. Borschevsky, A. Ryabtsev, S. Dobrodey, H. Bekker, E. Eliav, U. Kaldor, W. Ubachs, R. Hoekstra, J.R. Crespo Lopez-Urrutia, O.O. Versolato, Analysis of the fine structure of Sn - Sn ions by optical spectroscopy in an electron beam ion trap, Phys. Rev. A 94, 012506 (2016)._x000d_
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[2] F. Torretti, A. Windberger, A. Ryabtsev, S. Dobrodey, H. Bekker, W. Ubachs, R. Hoekstra, E.V. Kahl, J.C. Berengut, J.R. Crespo Lopez-Urrutia, O.O. Versolato, Optical spectroscopy of complex open 4d-shell ions Sn - Sn, arXiv:1612.0074
Prof. Th. W. Adorno and the author Hans Erich Nossack.
No full textProf. Th. W. Adorno and the author Hans Erich Nossack at a reception of Insel Verlag, Buchmesse Frankfurt 1966LB
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