Two-photon Laser Spectroscopy Research Articles

Ac polarizability and photoionization-cross-section measurements in an optical lattice

We use double-resonant two-photon laser spectroscopy to measure the dynamic scalar polarizability of the rubidium $5{D}_{3/2}$ level, ${\ensuremath{\alpha}}_{5{D}_{3/2}}^{S}$, at a wavelength of $\ensuremath{\lambda}=1064$ nm. Since $\ensuremath{\lambda}$ is shorter than the photoionization (PI) limit of the Rb $5{D}_{3/2}$ level, this state undergoes significant broadening due to PI. The 1064-nm field is applied in the form of a deep optical lattice ($\ensuremath{\sim}{10}^{5}$ photon recoils) generated by an in-vacuum field-enhancement cavity. In our spectroscopic method, we use known dynamic polarizabilities to eliminate the need to measure the light intensity. Our method yields, in atomic units, ${\ensuremath{\alpha}}_{5{D}_{3/2}}^{S}=\ensuremath{-}524(17)$, in agreement with estimates. Additionally, we extract the $5{D}_{3/2}$ photoionization cross section $\ensuremath{\sigma}$ at 1064 nm from spectral linewidths; we find $\ensuremath{\sigma}=44(1)$ Mb.

Comparison of high-resolution electric field measurements in a hollow cathode glow-discharge operated in hydrogen and deuterium

High-resolution measurements of the electric field strength in a hollow cathode discharge operated with deuterium gas are presented. The electric field strength is determined via Stark effect splitting of the 2S level of deuterium atoms using Doppler-free two-photon laser spectroscopy. The results are compared with equivalent measurements when the discharge was operated in hydrogen. The measured electric fields are analyzed using two classical models to obtain valuable parameters about the discharge dynamics, such as the energy of the ions and their mean free path in the cathode region. This information is compared with previous results for hydrogen and allows insight into the differences when gas discharges are operated with one of the isotopes.

Two-photon Doppler-free ultraviolet laser spectroscopy on sulphur atoms

The 3p43PJ–3p34p3PJ transition in the sulphur atom is investigated in a precision two-photon excitation scheme under Doppler-free and collision-free circumstances yielding an absolute accuracy of 0.0009 cm−1, using a narrowband pulsed laser. This verifies and improves the level separations between amply studied odd parity levels with even parity levels in S I. An improved value for the 3P2–3P1 ground state fine structure splitting is determined at 396.0564 (7) cm−1. A 34S–32S atomic isotope shift was measured from combining time-of-flight mass spectrometry with laser spectroscopy.

Spectroscopy and perturbation analysis of the A1π (v=0) state of 13 C16 O

ABSTRACTThe lowest v = 0 level of the A1Π state of the 13C16O isotopologue of carbon monoxide has been reinvestigated with a variety of high-resolution spectroscopic techniques. The A1Π −X1Σ+(0, 0) band has been studied by vacuum-ultraviolet Fourier-transform absorption spectroscopy, using the SOLEIL synchrotron as a radiation source. Spectra were obtained under quasi-static gas conditions at liquid-nitrogen temperature, room temperature and at an elevated temperature of 900 K, with absolute accuracies of 0.01−0.03 cm−1. Two-photon Doppler-free laser spectroscopy has been applied to a limited number of transitions in the A1Π −X1Σ+(0, 0) band, under collision-free circumstances of a molecular beam, yielding an absolute accuracy of 0.002 cm−1. The third technique is high-resolution Fourier-transform emission spectroscopy in the visible region applied to the B1Σ+ −A1Π(0, 0) band in a gas discharge, at an absolute accuracy of up to 0.003 cm−1. With these methods, rotational levels of A1Π (0) could be studied in both parity components up to a rotational quantum number of J = 46. The frequencies of 397 transitions were used to analyse the perturbations between the A1Π(0) level by vibrational levels of the D1Δ, e3Σ−, d3Δ, and a′3Σ+ states.

Strategies for the noninvasive diagnosis of melanoma

The diagnosis of advanced cutaneous melanoma may easily be made by the unaided eye, followed by excisional biopsy and histopathological examination. However, in the setting of melanoma screening examinations in high-risk patients with many nevi, dermatologists are challenged with the differentiation of atypical but benign nevi and early invasive or in situ melanomas. In this situation, there is areal need for additional, noninvasive examination techniques that may serve as an aide to decide for or against an excisional biopsy. Conventional dermoscopy is awell-established examination procedure and an increase in sensitivity was confirmed by two independent meta-analyses. Moreover, dynamic changes or newly developed pigmented lesions may be detected by sequential digital dermoscopy or (automated) total body photography, respectively. Over the past years, anumber of medicinal products gained market access after licensing by American and European agencies for the noninvasive diagnosis of cutaneous neoplasms. These devices are based on technologies including in vivo reflectance confocal microscopy, multispectral analysis, electrical impedance spectroscopy, or Raman spectroscopy. Other technologies are still on the verge of becoming less experimental but more clinically applicable for diagnosing melanoma (invivo multiphoton tomography, stepwise two-photon laser spectroscopy, infrared thermal image analysis, epidermal genetic information retrieval). This review provides aconcise overview of general principles and sheds light on indication and added value for dermatologists.

Two photon laser spectroscopy of antiprotonic helium atoms at CERN’s AD

The ASACUSA collaboration of CERN has carried out two-photon laser spectroscopy of antiprotonic helium atoms using counter-propagating ultraviolet laser beams. This excited some non-linear transitions of the antiproton at the wavelengths λ = 139.8–197.0 nm, in a way that reduced the thermal Doppler broadening of the observed resonances. The resulting narrow spectral lines allowed the measurement of three transition frequencies with fractional precisions of 2.3–5 parts in 109. By comparing these values with three-body QED calculations, the antiproton-to-electron mass ratio was derived as 1836.1526736(23). We briefly review these results.

Antiproton–to–electron mass ratio determined by two-photon laser spectroscopy of antiprotonic helium atoms

The ASACUSA collaboration of CERN has recently carried out two-photon laser spectroscopy of antiprotonic helium atoms. Three transition frequencies were de- termined with fractional precisions of 2.3-5 parts in 10 9 . By comparing the results with three-body QED calculations, the antiproton-to-electron mass ratio was determined as 1836.1526736(23).

Two-photon laser spectroscopy of antiprotonic helium atoms, and the antiproton-to-electron mass ratio

Some two-photon transitions in antiprotonic helium atoms at the deep UV wavelengths λ = 139.8–197.0 nm were recently studied by laser spectroscopy. The thermal Doppler broadening of the observed antiprotonic resonances were reduced by exciting the atoms with two counterpropagating laser beams of wavelengths λ = 265–417 nm. The resulting narrow spectral lines allowed the measurement of three transition frequencies in antiprotonic helium-3 and helium-4 isotopes with fractional precisions of 2.3–5 parts in 109. By comparing the results with three-body QED calculations, the antiproton-to-electron mass ratio was derived as 1836.1526736(23). We briefly review these experimental results that were presented in Ref. [1].

TWO-PHOTON LASER SPECTROSCOPY OF ANTIPROTONIC HELIUM

The ASACUSA collaboration of CERN has recently carried out two-photon laser spectroscopy of antiprotonic helium atoms. Some nonlinear two-photon transitions of the antiproton at the deep UV wavelengths λ = 139.8–197.0 nm were excited by irradiating the atom with two counterpropagating laser beams. This reduced the thermal Doppler broadening in the observed spectral lines. Three transition frequencies were thus determined with fractional precisions of 2.3–5 parts in 109. By comparing the results with three-body quantum electrodynamics calculations, the antiproton-to-electron mass ratio was derived as 1836.1526736(23). In this paper, we briefly review these recent experimental results.

High resolution spectroscopy and perturbation analysis of the CO A1Π −X1Σ+ (0,0) and (1,0) bands

The two lowest-v′ (0,0) and (1,0) bands of the A1Π −X1Σ+ system of 12C16O have been investigated by two high-resolution spectroscopic methods. A vacuum ultraviolet Fourier-transform spectrometer, illuminated by synchrotron radiation, was applied to record a jet-cooled spectrum and a room temperature static gas spectrum, resulting in absolute accuracies of 0.01−0.02 cm−1. In addition two-photon Doppler-free laser spectroscopy has been applied to a limited number of rotational lines, resulting in an accuracy of 0.002 cm−1. The data were used to perform an improved analysis of the perturbations in the A1Π, v = 0 and v = 1 levels by vibrational levels in the D1Δ, I1Σ−, e3Σ−, d3Δ. and a′3Σ+ states.

Precision spectroscopy of high rotational states in H2investigated by Doppler-free two-photon laser spectroscopy in theEF 1Σg+–X 1Σg+system

Recently a high precision spectroscopic investigation of the EF^1\Sigma_g^+ - X^1\Sigma_g^+ system of molecular hydrogen was reported yielding information on QED and relativistic effects in a sequence of rotational quantum states in the X^1\Sigma^+_g$ ground state of the H_2 molecule [E.J. Salumbides et al., Phys. Rev. Lett. 107, 043005 (2011)]. The present paper presents a more detailed description of the methods and results. Furthermore, the paper serves as a stepping stone towards a continuation of the previous study by extending the known level structure of the EF^1\Sigma^+_g state to highly excited rovibrational levels through Doppler-free two photon spectroscopy. Based on combination differences between vibrational levels in the ground state, and between three rotational branches (O, Q and S branches) assignments of excited EF^1\Sigma^+_g levels, involving high vibrational and rotational quantum numbers, can be unambiguously made. For the higher EF^1\Sigma^+_g levels, where no combination differences are available, calculations were performed using the multi-channel quantum defect method, for a broad class of vibrational and rotational levels up to J=19. These predictions were used for assigning high-J EF-levels and are found to be accurate within 5 cm^-1.

COA−Xsystem for constraining cosmological drift of the proton-electron mass ratio

The $\textrm{A}^1\Pi-\textrm{X}^1\Sigma^+$ band system of carbon monoxide, which has been detected in six highly redshifted galaxies ($z=1.6-2.7$), is identified as a novel probe method to search for possible variations of the proton-electron mass ratio ($\mu$) on cosmological time scales. Laboratory wavelengths of the spectral lines of the A-X ($v$,0) bands for $v=0-9$ have been determined at an accuracy of $\Delta\lambda/\lambda=1.5 \times 10^{-7}$ through VUV Fourier-transform absorption spectroscopy, providing a comprehensive and accurate zero-redshift data set. For the (0,0) and (1,0) bands, two-photon Doppler-free laser spectroscopy has been applied at the $3 \times 10^{-8}$ accuracy level, verifying the absorption data. Sensitivity coefficients $K_{\mu}$ for a varying $\mu$ have been calculated for the CO A-X bands, so that an operational method results to search for $\mu$-variation.

Sub-Doppler Two-Photon Laser Spectroscopy of Antiprotonic Helium(Current Topics)

Sub-Doppler Two-Photon Laser Spectroscopy of Antiprotonic Helium(Current Topics)

Two-photon laser spectroscopy of antiprotonic helium and the antiproton-to-electron mass ratio

Physical laws are believed to be invariant under the combined transformations of charge, parity and time reversal (CPT symmetry). This implies that an antimatter particle has exactly the same mass and absolute value of charge as its particle counterpart. Metastable antiprotonic helium (pHe(+)) is a three-body atom consisting of a normal helium nucleus, an electron in its ground state and an antiproton (p) occupying a Rydberg state with high principal and angular momentum quantum numbers, respectively n and l, such that n ≈ l + 1 ≈ 38. These atoms are amenable to precision laser spectroscopy, the results of which can in principle be used to determine the antiproton-to-electron mass ratio and to constrain the equality between the antiproton and proton charges and masses. Here we report two-photon spectroscopy of antiprotonic helium, in which p(3)He(+) and p(4)He(+) isotopes are irradiated by two counter-propagating laser beams. This excites nonlinear, two-photon transitions of the antiproton of the type (n, l) → (n - 2, l - 2) at deep-ultraviolet wavelengths (λ = 139.8, 193.0 and 197.0 nm), which partly cancel the Doppler broadening of the laser resonance caused by the thermal motion of the atoms. The resulting narrow spectral lines allowed us to measure three transition frequencies with fractional precisions of 2.3-5 parts in 10(9). By comparing the results with three-body quantum electrodynamics calculations, we derived an antiproton-to-electron mass ratio of 1,836.1526736(23), where the parenthetical error represents one standard deviation. This agrees with the proton-to-electron value known to a similar precision.

Development of pulsed UV lasers and their application in laser spectroscopy

The application of two-photon laser spectroscopy to plasma diagnostics requires tuneable UV-laser spectrometers providing: some mJ pulse energy at ns time scale with spectral quality close to Fourier Transform Limit, good pulse to pulse reproducibility and tuning linearity. We report about two different systems, a first laser specially optimized for the radiation at 243 nm, which is required for the 1S-2S two photon transition of atomic hydrogen, and a second one generating 205 nm suited for the transition 1S – 3S/3D.

Two-photon spectroscopy of mercury and velocity-selective double resonances

Two-photon laser spectroscopy of the $6\text{ }{^{1}S}_{0}\ensuremath{-}7\text{ }{^{1}S}_{0}$ transition in mercury has been performed using two copropagating continuous-wave laser beams. One laser beam is at 254 nm wavelength and can be tuned to the $6\text{ }{^{1}S}_{0}\ensuremath{-}6\text{ }{^{3}P}_{1}$ resonance. The other laser beam is at 408 nm. Two very different regimes can be distinguished, one far off resonance and one near resonance with the one-photon resonance. A resonance which is not Doppler broadened has been observed for low Rabi frequencies. This velocity-selective double resonance in a three-level ladder system is analogous to the dark resonance in three-level $\ensuremath{\Lambda}$ systems.

One- and two-photon laser spectroscopy of silica gel-doped fluorescent nanoparticles

One- and two-photon laser spectroscopy of Rhodamine 6G (Rh6G) and Coumarin 153 (C153) dyes embedded in silica nanoparticles with and without TiO2 scatters was investigated. Silica gel samples with different dye-doped nanoparticle concentrations were prepared as homogeneous bulk disks by the sol–gel method. Fluorescence and lifetime measurements were performed in the bulk matrices as well as in the resulting ground powders under one- and two-photon excitation. The effect of nanoparticles and TiO2 scatters concentration on the lifetime quenching was evaluated. The results show a reduction of the fluorescence lifetime for increasing concentrations of both dye-doped nanoparticles and TiO2 scatters. The fluorescence degradation under infrared ultrashort laser pulses was also explored as a function of irradiation time.

Fluorine substitution and nonconventional OH⋯π intramolecular bond: high-resolution UV spectroscopy and ab initio calculations of 2-(p-fluorophenyl)ethanol

The para-fluorinated flexible neurotransmitter analogue 2-phenylethanol has been investigated by highly resolved resonance-enhanced two-photon ionisation two-colour UV laser spectroscopy with mass resolution and ab initio structural optimisations and energy calculations. Two stable conformations, gauche and anti, separated by a high potential barrier have been identified in the cold molecular beam by rotational analysis of the vibronic band structures. The theoretically predicted higher-lying conformations most likely relax to these two structures during the adiabatic expansion. The lowest-energy gauche conformer is stabilised by an intramolecular nonconventional OH...pi-type hydrogen bond between the terminal OH group of the side chain and the pi electrons of the phenyl ring. The good agreement between the experimental and theoretical results demonstrates that even the substitution with a strongly electronegative atom of 2-phenylethanol at the para position has no noticeable effect on the strength and orientation of the OH...pi bond.

Observation by two-photon laser spectroscopy of the4d105sS1∕22→4d95s2D5∕22clock transition in atomic silver

We report the observation of the very narrow $4{d}^{10}5s\phantom{\rule{0.2em}{0ex}}^{2}S_{1∕2}\ensuremath{\rightarrow}4{d}^{9}5{s}^{2}\phantom{\rule{0.2em}{0ex}}^{2}D_{5∕2}$ transition in atomic silver. The frequencies of the hyperfine components in $^{107}\mathrm{Ag}$ and $^{109}\mathrm{Ag}$ have been measured using Doppler-free two-photon laser spectroscopy of a thermal beam and heterodyne calibration with respect to the ${a}_{1}$ component of the $62P(4\text{\ensuremath{-}}5)$ line in molecular iodine near $661\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$. For the center of gravity of a mixture of natural abundance, we deduce the value $906\phantom{\rule{0.2em}{0ex}}641\phantom{\rule{0.2em}{0ex}}295.77(19)\phantom{\rule{0.3em}{0ex}}\mathrm{MHz}$. For the isotope shift, we obtain $\ensuremath{\nu}(^{109}\mathrm{Ag})\ensuremath{-}\ensuremath{\nu}(^{107}\mathrm{Ag})=564.15(37)\phantom{\rule{0.3em}{0ex}}\mathrm{MHz}$, from which we deduce the frequency and isotope shift of the $4{d}^{10}5s\phantom{\rule{0.2em}{0ex}}^{2}S_{1∕2}\ensuremath{\rightarrow}4{d}^{10}6p\phantom{\rule{0.2em}{0ex}}^{2}P_{3∕2}$ transition at $206\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$.

Optical observation of the 3sσgFΠu3 Rydberg state of N2

Using ultrahigh-resolution 1XUV+1UV two-photon ionization laser spectroscopy, the FΠu3←XΣg+1(0,0) transition of N2 has been optically observed for the first time, and the 3sσgFΠu3(υ=0) Rydberg level fully characterized with rotational resolution. The experimental spectroscopic parameters and predissociation level widths suggest strong interactions between the F state and the 3pπuGΠu3 Rydberg and C′Πu3 valence states, analogous to those well known in the case of the isoconfigurational Πu1 states.