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The transition wave numbers from selected rovibrational levels of the EF 1Σg+(v=0) state to selected np Rydberg states of ortho- and para-D2 located below the adiabatic ionization threshold have been measured at a precision better than 10-3 cm-1. Adding these wave numbers to the previously determined transition wave numbers from the X 1Σg+(v=0, N=0,1) states to the EF 1Σg+(v=0, N=0,1) states of D2 and to the binding energies of the Rydberg states calculated by multichannel quantum defect theory, the ionization energies of ortho- and para-D2 are determined to be 124 745.394 07(58) cm-1 and 124 715.003 77(75) cm-1, respectively. After re-evaluation of the dissociation energy of D2+ and using the known ionization energy of D, the dissociation energy of D2 is determined to be 36 748.362 86(68) cm-1. This result is more precise than previous experimental results by more than one order of magnitude and is in excellent agreement with the most recent theoretical value 36 748.3633(9) cm-1 [K. Piszczatowski, G. Łach, M. Przybytek et al., J. Chem. Theory Comput. 5, 3039 (2009)]. The ortho-para separation of D2, i.e., the energy difference between the N=0 and N=1 rotational levels of the X 1Σg+(v=0) ground state, has been determined to be 59.781 30(95) cm-1. [ABSTRACT FROM AUTHOR]

[Display omitted] • 11 bands of 13C18O were obtained by two complementary FT-VIS and FT-VUV methods. • Deperturbation analysis of 13C18O A1Π(1) based on 598 lines was performed. • The indirect a3Π(v = 12) ∼ A1Π(v = 1) interaction were detected and analysed. • 112 terms of B1Σ+(v = 0) J max = 50 and C1Σ+(v = 0) J max = 60 were calculated. • 23 parameters for A(1), I(2), d(6), e(3), D(1), a(12) and couplings were determined. Ro-vibronic spectra of the 13C18O carbon monoxide isotopologue were obtained with (i) emission spectroscopy in the visible region using a Bruker IFS 125HR spectrometer (University of Rzeszów) and (ii) vacuum-ultraviolet absorption spectroscopy using the wave-front-division spectrometer on the DESIRS beamline of the SOLEIL synchrotron. A deperturbation analysis of the 13C18O A1Π(v = 1) level was conducted from 598 observed transitions from the B1Σ+ - A1Π(0, 1), C1Σ+ - A1Π(0, 1), A1Π - X1Σ+(1, 0), B1Σ+ - X1Σ+(0, 0), C1Σ+ - X1Σ+(0, 0), I1Σ– - X1Σ+(2, 0) bands and five further nominally forbidden bands. An effective Hamiltonian and term-value fitting analysis was implemented. Consequently, 135 parameters were floated: 23 molecular parameters, including molecular constants for A1Π(v = 1), I1Σ–(v = 2), d3Δ(v = 6), e3Σ–(v = 3) and D1Δ(v = 1); rotation-electronic ( L -uncoupling) mixing of A1Π(v = 1) ∼ [D1Δ(v = 1), I1Σ–(v = 1), I1Σ–(v = 2)] and spin–orbit interaction parameters for A1Π(v = 1) ∼ [d3Δ(v = 6), e3Σ–(v = 3), aʹ3Σ+(v = 11)]; the spin–orbit/spin-electronic/ L -uncoupling a3Π(v = 12) ∼ d3Δ(v = 5) and spin–orbit a3Π(v = 12) ∼ [D1Δ(v = 1), I1Σ–(v = 2)] perturbation parameters; as well as 112 ro-vibronic term values of B1Σ+(v = 0) up to J = 50 and C1Σ+(v = 0) up to J = 60. The significant, indirect a3Π(v = 12) ∼ [e3Σ–(v = 2, 3), d3Δ(v = 5, 6)] ∼ A1Π(v = 1) spin–orbit/spin-electronic/ L -uncoupling interaction and a3Π(v = 12) ∼ [I1Σ–(v = 2), D1Δ(v = 1)] ∼ A1Π(v = 1) spin–orbit/ L -uncoupling interaction were detected and analysed. Thus, this study, using modern experimental methods and deperturbation analysis, leads to a much improved description in terms of molecular constants and interaction parameters, compared to previous studies of the A1Π(v = 1) energy region in the 13C18O isotopologue. This research is a continuation of the studies on the A1Π state and its numerous perturbers in the CO isotopologues made by our team. [ABSTRACT FROM AUTHOR]

Abstract: Deep-UV spectra of 15N18O have been recorded using cavity ring-down spectroscopy in the 205–216nm region. The rotationally resolved spectra have been assigned for a first time as originating from the v″=0 X2Π r states toward v′=1 and 2 vibrationally excited levels in the upper A2Σ+ state. Nearly 400 individual line positions have been identified and included in a fit using an effective Hamiltonian method. Accurate ground state values as available from literature were used to derive rovibronic parameters for the A2 and A2 levels. This results in the following values: T 1 =46427.21(2)cm−1, B 1 =1.79635(7)cm−1, D 1 =4.14(6)×10−6 cm−1 and T 2 =48636.04(2)cm−1, B 2 =1.78055(18)cm−1, D 2 =5.8(3)×10−6 cm−1. [Copyright &y& Elsevier]

The standard model of physics is built on the fundamental constants of nature, but it does not provide an explanation for their values, nor require their constancy over space and time. Here we set a limit on a possible cosmological variation of the proton-to-electron mass ratio by comparing transitions in methanol observed in the early universe with those measured in the laboratory. From radio-astronomical observations of PKS1830-211, we deduced a constraint of Δμ/μ = (0.0 ± 1.0) x 10-7 at redshift z = 0.89, corresponding to a look-back time of 7 billion years. This is consistent with a null result. [ABSTRACT FROM AUTHOR]

The resolution of any spectroscopic or interferometric experiment is ultimately limited by the total time a particle is interrogated. Here we demonstrate the first molecular fountain, a development which permits hitherto unattainably long interrogation times with molecules. In our experiments, ammonia molecules are decelerated and cooled using electric fields, launched upwards with a velocity between 1.4 and 1.9 m/s and observed as they fall back under gravity. A combination of quadrupole lenses and bunching elements is used to shape the beam such that it has a large position spread and a small velocity spread (corresponding to a transverse temperature of < 10 μK and a longitudinal temperature of < 1 μK) when the molecules are in free fall, while being strongly focused at the detection region. The molecules are in free fall for up to 266 ms, making it possible, in principle, to perform sub-Hz measurements in molecular systems and paving the way for stringent tests of fundamental physics theories. [ABSTRACT FROM AUTHOR]

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 behavior of astronomical objects, accurate transition frequencies are required for these lines. From a set of 26 new and 564 previous Lamb dip measurements, utilizing our ultrasensitive laser-based spectrometers in the near-infrared region, ultrahigh-precision spectroscopic networks were set up for H 2 16 O and H 2 18 O, augmented with 40 extremely accurate frequencies taken from the literature. Based on kHz-accuracy paths of these networks, considerably improved line-center frequencies have been obtained for 35 observed or predicted maser lines of H 2 16 O, as well as for 14 transitions of astronomical significance of H 2 18 O. These reference frequencies, attached with 5-25 kHz uncertainties, may help future studies in various fields of astrochemistry and astrophysics, in particular when precise information is demanded about Doppler-velocity components, including the gas flows of galactic cores, the kinematics of planetary nebulae, or the motion in exoplanetary atmospheres., Competing Interests: The authors declare no competing financial interest., (© 2024 The Authors. Published by American Chemical Society.)

Network theory has fundamentally transformed our comprehension of complex systems, catalyzing significant advances across various domains of science and technology. In spectroscopic networks, hubs are the quantum states involved in the largest number of transitions. Here, utilizing network paths probed via precision metrology, absolute energies have been deduced, with at least 10-digit accuracy, for almost 200 hubs in the experimental spectroscopic networks of H 2 16 O and H 2 18 O. These hubs, lying on the ground vibrational states of both species and the bending fundamental of H 2 16 O, are involved in tens of thousands of observed transitions. Relying on the same hubs and other states, benchmark-quality line lists have been assembled, which supersede and improve, by three orders of magnitude, the accuracy of the massive amount of data reported in hundreds of papers dealing with Doppler-limited spectroscopy. Due to the omnipresence of water, these ultraprecise line lists could be applied to calibrate high-resolution spectra and serve ongoing and upcoming space missions., (© 2024. The Author(s).)

We present simultaneous 1D imaging and broadband spectroscopy of a laser-produced plasma (LPP) source of extreme ultraviolet light, using a tapered zone plate that is matched to the dispersion of a transmission grating. We describe the design and fabrication of the zone plates in the 5-80 nm wavelength regime with designed spatial resolution of ∼10 µm and spectral resolution of ∼0.8 nm. Subsequently, we benchmark the imaging spectrometer with a solid tin target LPP. Plane wave propagation simulations qualitatively match the experimental results and confirm the device performance.

A laser system generating high-energy pulses at 2-µm wavelength with pulse widths tunable from 10-24 ns is described. It comprises an optical parametric oscillator that generates mJ-level signal seed radiation and an optical parametric amplifier that boosts the output to 800 mJ of combined signal and idler when pumped with 2 J pulses of 1064-nm laser light. The system operated with KTP crystals and running at 10 Hz repetition rate is characterized in the spatial, temporal, and spectral domains. The effect of saturation leads to an output pulse approaching flat-top spatial and box-shaped temporal profiles, as desired in various applications. The amplified pulses can be imaged down to sub-100 µm diameters, making this laser system a suitable driver for plasma sources of extreme ultraviolet light.

A non-linear spectroscopic study of the HDO molecule is performed in the wavelength range of 1.36-1.42 μ m using noise-immune cavity-enhanced optical-heterodyne molecular spectroscopy (NICE-OHMS). More than 100 rovibrational Lamb dips are recorded, with an experimental precision of 2-20 kHz, related to the first overtone of the O-H stretch fundamental of HD 16 O and HD 18 O. Significant perturbations, including distortions, shifts, and splittings, have been observed for a number of Lamb dips. These spectral perturbations are traced back to an AC-Stark effect, arising due to the strong laser field applied in all saturation-spectroscopy experiments. The AC-Stark effect mixes parity pairs, that is pairs of rovibrational states whose assignment differs solely in the K c quantum number, where K c is part of the standard J K a , K c asymmetric-top rotational label. Parity-pair mixing seems to be especially large for parity pairs with K a  ≥ 3, whereby their energy splittings become as small as a few MHz, resulting in multi-component asymmetric Lamb-dip profiles of gradually increasing complexity. These complex profiles often include crossover resonances. This effect is well known in saturation spectroscopy, but has not been reported in combination with parity-pair mixing. Parity-pair mixing is not seen in H2 16O and H2 18O, because their parity pairs correspond to ortho and para nuclear-spin isomers, whose interaction is prohibited. Despite the frequency shifts observed for HD 16 O and HD 18 O, the absolute accuracy of the detected transitions still exceeds that achievable by Doppler-limited techniques.

Huge efforts have recently been taken in the derivation of accurate compilations of rovibrational energies of water, one of the most important reference systems in spectroscopy. Such precision is desirable for all water isotopologues, although their investigation is challenged by hyperfine effects in their spectra. Frequency-comb locked noise-immune cavity-enhanced optical-heterodyne molecular spectroscopy (NICE-OHMS) allows for achieving high sensitivity, resolution, and accuracy. This technique has been employed to resolve the subtle hyperfine splittings of rovibrational transitions of H 2 17 O in the near-infrared region. Simulation and interpretation of the H 2 17 O saturation spectra have been supported by coupled-cluster calculations performed with large basis sets and accounting for high-level corrections. Experimental 17 O hyperfine parameters are found in excellent agreement with the corresponding computed values. The need of including small hyperfine effects in the analysis of H 2 17 O spectra has been demonstrated together with the ability of the computational strategy employed for providing quantitative predictions of the corresponding parameters.

The spectral distribution of light scattered by microscopic thermal fluctuations in binary mixture gases was investigated experimentally and theoretically. Measurements of Rayleigh-Brillouin spectral profiles were performed at a wavelength of 532 nm and at room temperature, for mixtures of SF&#95;{6}-He,SF&#95;{6}-D&#95;{2}, and SF&#95;{6}-H&#95;{2}. In these measurements, the pressure of the gases with heavy molecular mass (SF&#95;{6}) is set at 1 bar, while the pressure of the lighter collision partner was varied. In view of the large polarizability of SF&#95;{6} and the very small polarizabilities of He, H&#95;{2}, and D&#95;{2}, under the chosen pressure conditions these low mass species act as spectators and do not contribute to the light scattering spectrum, while they influence the motion and relaxation of the heavy SF&#95;{6} molecules. A generalized hydrodynamic model was developed that should be applicable for the particular case of molecules with heavy and light disparate masses, as is the case for the heavy SF&#95;{6} molecule, and the lighter collision partners. Based on the kinetic theory of gases, our model replaces the classical Navier-Stokes-Fourier relations with constitutive equations having an exponential memory kernel. The energy exchange between translational and internal modes of motion is included and quantified with a single parameter z that characterizes the ratio between the mean elastic and inelastic molecular collision frequencies. The model is compared with the experimental Rayleigh-Brillouin scattering data, where the value of the parameter z is determined in a least-squares procedure. Where very good agreement is found between experiment and the generalized hydrodynamic model, the computations in the framework of classical hydrodynamics strongly deviate. Only in the hydrodynamic regime both models are shown to converge.

Frequency combs and cavity-enhanced optical techniques have revolutionized molecular spectroscopy: their combination allows recording saturated Doppler-free lines with ultrahigh precision. Network theory, based on the generalized Ritz principle, offers a powerful tool for the intelligent design and validation of such precision-spectroscopy experiments and the subsequent derivation of accurate energy differences. As a proof of concept, 156 carefully-selected near-infrared transitions are detected for H 2 16 O, a benchmark system of molecular spectroscopy, at kHz accuracy. These measurements, augmented with 28 extremely-accurate literature lines to ensure overall connectivity, allow the precise determination of the lowest ortho-H 2 16 O energy, now set at 23.794 361 22(25) cm -1 , and 160 energy levels with similarly high accuracy. Based on the limited number of observed transitions, 1219 calibration-quality lines are obtained in a wide wavenumber interval, which can be used to improve spectroscopic databases and applied to frequency metrology, astrophysics, atmospheric sensing, and combustion chemistry.

Rayleigh-Brillouin scattering spectra of CO 2 were measured at pressures ranging from 0.5 to 4 bars and temperatures from 257 to 355 K using green laser light (wavelength 532 nm, scattering angle of 55.7°). These spectra were compared to two line shape models, which take the bulk viscosity as a parameter. One model applies to the kinetic regime, i.e., low pressures, while the second model uses the continuum, hydrodynamic approach and takes the rotational relaxation time as a parameter, which translates into the bulk viscosity. We do not find a significant dependence of the bulk viscosity with pressure or temperature. At pressures where both models apply, we find a consistent value of the ratio of bulk viscosity over shear viscosity η b /η s = 0.41 ± 0.10. This value is four orders of magnitude smaller than the common value that is based on the damping of ultrasound and signifies that in light scattering only relaxation of rotational modes matters, while vibrational modes remain "frozen."

We demonstrate direct frequency-comb (FC) spectroscopy of the dipole-forbidden 4s(2)S(1/2)-3d(2)D(5/2) transition in trapped (40)Ca(+) ions using an unamplified FC laser. The excitation is detected with nearly 100% efficiency using a shelving scheme in combination with single-ion imaging. The method demonstrated here has the potential to reach hertz-level accuracy, if a hertz-level linewidth FC is used in combination with confinement in the Lamb-Dicke regime.

We present a novel setup that allows the observation of the geometric phase that accompanies polarization changes in monochromatic light beams for which the initial and final states are different (so-called non-cyclic changes). This Pancharatnam-Berry phase can depend in a linear or in a nonlinear fashion on the orientation of the optical elements, and sometimes the dependence is singular. Experimental results that confirm these three types of behavior are presented. The observed singular behavior may be applied in the design of optical switches., ((c) 2010 Optical Society of America.)

For the first time a detailed study of hybrid mode-locking in two-section InAs/InP quantum dot Fabry-Pérot-type lasers is presented. The output pulses have a typical upchirp of approximately 8 ps/nm, leading to very elongated pulses. The mechanism leading to this typical pulse shape and the phase noise is investigated by detailed radio-frequency and optical spectral studies as well as time-domain studies. The pulse shaping mechanism in these lasers is found to be fundamentally different than the mechanism observed in conventional mode-locked laser diodes, based on quantum well gain or bulk material.

Both laser-induced fluorescence and cavity ring-down spectral observations were made in the Schumann-Runge band system of oxygen, using a novel-type ultranarrow deep-UV pulsed laser source. From measurements on the very weak (0,0) band pressure broadening, pressure shift, and predissociation line-broadening parameters were determined for the B 3sigma(u)-, v = 0,F(i) fine-structure components for various rotational levels in O2. The information content from these studies was combined with that of entirely independent measurements probing the much stronger (0,10), (0,19), and (0,20) Schumann-Runge bands involving preparation of vibrationally excited O2 molecules via photolysis of ozone. The investigations result in a consistent set of predissociation widths for the B 3sigma(u)-, v = 0 state of oxygen.