W. Ubachs
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View article: Letokhov-Chebotayev intracavity trapping spectroscopy of H$_2$
Letokhov-Chebotayev intracavity trapping spectroscopy of H$_2$ Open
In the early days of laser spectroscopy Letokhov and Chebotayev proposed a scheme for measuring narrow spectral lines where the resolution is not restricted to Doppler effects because the molecules are entrained in a standing-wave light fi…
View article: Precise Frequencies of H<sub>2</sub> <sup>16</sup>O Lines Protected for Radio Astronomy
Precise Frequencies of H<sub>2</sub> <sup>16</sup>O Lines Protected for Radio Astronomy Open
Precise frequency values have been determined for radio lines appearing in protected line lists of the International Astronomical Union and the Panel on Frequency Allocations of the US National Academy of Sciences. The improved …
View article: Harold Linnartz: A Life in the Molecular Universe
Harold Linnartz: A Life in the Molecular Universe Open
View article: 2D transverse laser cooling of a hexapole focused beam of cold BaF molecules
2D transverse laser cooling of a hexapole focused beam of cold BaF molecules Open
A cryogenic buffer gas beam, an electrostatic hexapole lens, and 2D transverse Doppler laser cooling are combined to produce a bright beam of barium monofluoride ($^{138}$Ba$^{19}$F) molecules. Experimental results and trajectory simulatio…
View article: Arbitrary pulse shaping in a mid-infrared optical parametric oscillator source
Arbitrary pulse shaping in a mid-infrared optical parametric oscillator source Open
We present a coherent mid-infrared (mid-IR) light source based on a periodically poled lithium niobate optical parametric oscillator (OPO) that is capable of producing arbitrary pulse shapes in the nanosecond regime. By controlling the sha…
View article: Precision measurement of the last bound states in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi mathvariant="normal">H</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:math> and determination of the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi mathvariant="normal">H</mml:mi><mml:mo>+</mml:mo><mml:mi mathvariant="normal">H</mml:mi></mml:mrow></mml:math> scattering length
Precision measurement of the last bound states in and determination of the scattering length Open
The binding energies of the five bound rotational levels J=0-4 in the highest vibrational level v=14 in the X1ςg+ ground electronic state of H2 were measured in a three-step ultraviolet-laser experiment. Two-photon UV photolysis of H2S pro…
View article: Precision measurement of the last bound states in H$_2$ and determination of the H + H scattering length
Precision measurement of the last bound states in H$_2$ and determination of the H + H scattering length Open
The binding energies of the five bound rotational levels $J=0-4$ in the highest vibrational level $v=14$ in the X$^1Σ_g^+$ ground electronic state of H$_2$ were measured in a three-step ultraviolet-laser experiment. Two-photon UV-photolysi…
View article: A method to determine the phase-space distribution of a pulsed molecular beam
A method to determine the phase-space distribution of a pulsed molecular beam Open
We demonstrate a method to determine the longitudinal phase-space distribution of a cryogenic buffer gas cooled beam of barium-fluoride molecules based on a two-step laser excitation scheme. Temporal resolution is achieved by a transversel…
View article: Pressure control of tritiated hydrogen isotopologues in hermetically sealed vessels by non-evaporable getters for sub-Doppler-resolution spectroscopy
Pressure control of tritiated hydrogen isotopologues in hermetically sealed vessels by non-evaporable getters for sub-Doppler-resolution spectroscopy Open
Small molecules serve as valuable benchmarks for testing quantum chemical theories. Ultra-high-resolution spectroscopy currently offers the capability of measuring molecular hydrogen energy levels with a relative accuracy on the order of 1…
View article: A Network Approach for the Accurate Characterization of Water Lines Observable in Astronomical Masers and Extragalactic Environments
A Network Approach for the Accurate Characterization of Water Lines Observable in Astronomical Masers and Extragalactic Environments Open
The water molecule, crucial to the chemical composition and dynamics of the universe, is typically identified in its gas phase via radio and submillimeter transitions, with frequencies up to a few THz. To understand the physicochemical beh…
View article: Hyperfine structure of the methanol molecule as traced by Class I methanol masers
Hyperfine structure of the methanol molecule as traced by Class I methanol masers Open
We present results on simultaneous observations of Class I methanol masers at 25, 36, and 44 GHz towards 22 Galactic targets carried out with the Effelsberg 100-m telescope. The study investigates relations between the hyperfine (HF) struc…
View article: Hyperfine structure of the methanol molecule as traced by Class I methanol masers
Hyperfine structure of the methanol molecule as traced by Class I methanol masers Open
We present results on simultaneous observations of Class~I methanol masers at 25, 36, and 44 GHz towards 22 Galactic targets carried out with the Effelsberg 100-m telescope. The study investigates relations between the hyperfine (HF) struc…
View article: Spin-precession method for sensitive electric dipole moment searches
Spin-precession method for sensitive electric dipole moment searches Open
We demonstrate a spin-precession method to observe and analyze multilevel coherence between all hyperfine levels in the X2ς+,N=0 ground state of barium monofluoride (Ba138F19). The signal is sensitive to the state-preparation Rabi frequenc…
View article: Manipulating a beam of barium fluoride molecules using an electrostatic hexapole
Manipulating a beam of barium fluoride molecules using an electrostatic hexapole Open
An electrostatic hexapole lens is used to manipulate the transverse properties of a beam of barium fluoride molecules from a cryogenic buffer gas source. The spatial distribution of the beam is measured by recording state-selective laser-i…
View article: Influence of source parameters on the longitudinal phase-space distribution of a pulsed cryogenic beam of barium fluoride molecules
Influence of source parameters on the longitudinal phase-space distribution of a pulsed cryogenic beam of barium fluoride molecules Open
Recently, we have demonstrated a method to record the longitudinal phase-space distribution of a pulsed cryogenic buffer gas cooled beam of barium fluoride molecules with high resolution. In this paper, we use this method to determine the …
View article: Advances in cavity-enhanced methods for high precision molecular spectroscopy and test of fundamental physics
Advances in cavity-enhanced methods for high precision molecular spectroscopy and test of fundamental physics Open
Cavity-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…
View article: All paths lead to hubs in the spectroscopic networks of water isotopologues H216O and H218O
All paths lead to hubs in the spectroscopic networks of water isotopologues H216O and H218O Open
View article: Manipulating a beam of barium fluoride molecules using an electrostatic hexapole
Manipulating a beam of barium fluoride molecules using an electrostatic hexapole Open
An electrostatic hexapole lens is used to manipulate the transverse properties of a beam of barium fluoride molecules from a cryogenic buffer gas source. The spatial distribution of the beam is measured by recording state-selective laser-i…
View article: FT-spectroscopy of the 12C18O rare isotopologue and deperturbation analysis of the A1Π(v = 3) level
FT-spectroscopy of the 12C18O rare isotopologue and deperturbation analysis of the A1Π(v = 3) level Open
View article: A novel method to determine the phase-space distribution of a pulsed molecular beam
A novel method to determine the phase-space distribution of a pulsed molecular beam Open
We demonstrate a novel method to determine the longitudinal phase-space distribution of a cryogenic buffer gas beam of barium-fluoride molecules based on a two-step laser excitation scheme. The spatial resolution is achieved by a transvers…
View article: Influence of source parameters on the longitudinal phase-space distribution of a pulsed cryogenic beam of barium fluoride molecules
Influence of source parameters on the longitudinal phase-space distribution of a pulsed cryogenic beam of barium fluoride molecules Open
Recently, we have demonstrated a method to record the longitudinal phase-space distribution of a pulsed cryogenic buffer gas cooled beam of barium fluoride molecules. In this paper, we use this method to determine the influence of various …
View article: Precision Measurement of Vibrational Quanta in Tritium Hydride (HT)
Precision Measurement of Vibrational Quanta in Tritium Hydride (HT) Open
Saturated absorption measurements of transitions in the (2-0) band of radioactive tritium hydride (HT) are performed with the ultra-sensitive NICE-OHMS intracavity absorption technique in the range 1460-1510 nm. The hyperfine structure of …
View article: Hyperfine structure in a vibrational quadrupole transition of ortho-H <sub>2</sub>
Hyperfine structure in a vibrational quadrupole transition of ortho-H <sub>2</sub> Open
A Lamb dip spectroscopic measurement of the Q(1) transition in the (2-0) overtone band of ortho- (Formula presented.) is performed with the ultra-sensitive NICE-OHMS intracavity absorption technique at (Formula presented.). For the first t…
View article: New constraint on cosmological variation of the proton-to-electron mass ratio from Q0528−250
New constraint on cosmological variation of the proton-to-electron mass ratio from Q0528−250 Open
Molecular hydrogen transitions in quasar spectra can be used to constrain variation in the proton-to-electron mass ratio, μ≡ mp/me, at high redshifts (z ≳ 2). We present here an analysis of a new spectrum of the quasar Q0528−250, obtained …
View article: A high-velocity narrow absorption line outflow in the quasar J212329.46 - 005052.9
A high-velocity narrow absorption line outflow in the quasar J212329.46 - 005052.9 Open
We report on the discovery of a high-velocity narrow absorption line outflow in the redshift 2.3 quasar J212329.46 − 005052.9. Five distinct outflow systems are detected with velocity shifts from −9710 to −14 050 km s−1 and C iv λλ1548, 15…
View article: Analysis of molecular hydrogen absorption toward QSO B0642-5038 for a varying proton-to-electron mass ratio
Analysis of molecular hydrogen absorption toward QSO B0642-5038 for a varying proton-to-electron mass ratio Open
Rovibronic molecular hydrogen (H-2) transitions at redshift z(abs) similar or equal to 2.659 toward the background quasar B0642-5038 are examined for a possible cosmological variation in the proton-to-electron mass ratio mu. We utilize an …
View article: High-resolution spectroscopic imaging of atoms and nanoparticles in thin film vaporization
High-resolution spectroscopic imaging of atoms and nanoparticles in thin film vaporization Open
We introduce a spectroscopic absorption imaging method in the UV regime (225–400 nm) to study tin vapor created by irradiating a thin film with a low intensity 108 W cm−2 nanosecond laser pulse, a case inspired by current developments arou…
View article: Production of 13.5 nm light with 5% conversion efficiency from 2 <b> <i>μ</i> </b>m laser-driven tin microdroplet plasma
Production of 13.5 nm light with 5% conversion efficiency from 2 <b> <i>μ</i> </b>m laser-driven tin microdroplet plasma Open
We demonstrate the efficient generation of extreme ultraviolet (EUV) light from laser-produced plasma (LPP) driven by 2 μm wavelength laser light as an alternative for 10 μm CO2 gas LPP currently employed in EUV lithography machines for hi…
View article: Ionization and dissociation energies of HD and dipole-induced <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>g</mml:mi><mml:mo>/</mml:mo><mml:mi>u</mml:mi></mml:mrow></mml:math>-symmetry breaking
Ionization and dissociation energies of HD and dipole-induced -symmetry breaking Open
The ionization energy of HD has been determined to be EI(HD)=124568.48466(7)cm-1 by two-photon Doppler-free vacuum-ultraviolet pulsed laser spectroscopy, near-infrared continuous-wave laser spectroscopy, and Rydberg-series extrapolation by…
View article: Lamb Dip of a Quadrupole Transition in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">H</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>
Lamb Dip of a Quadrupole Transition in Open
The saturated absorption spectrum of the hyperfineless S(0) quadrupole line in the (2-0) band of H_{2} is measured at λ=1189 nm, using the NICE-OHMS technique under cryogenic conditions (72 K). It is the first time that a Lamb dip of a mol…