Doppler-free Two-photon Spectroscopy Research Articles

Observation of quantum interference of optical transition pathways in Doppler-free two-photon spectroscopy and implications for precision measurements

Observation of quantum interference of optical transition pathways in Doppler-free two-photon spectroscopy and implications for precision measurements

Two-photon absorption laser induced fluorescence (TALIF) detection of atomic iodine in low-temperature plasmas and a revision of the energy levels of I I

In order to perfect the use of iodine, instead of xenon, in plasma thrusters, an experiment has been set up to investigate the feasibility of two-photon absorption laser induced fluorescence (TALIF) diagnostics in iodine plasmas. Levels and of atomic iodine were found qualified for that purpose, with a radiative lifetime of the former found equal to , which appears consistent with the predicted by the most recent calculations. Doppler-free two-photon spectroscopy has confirmed that the relative intensities of the hyperfine components follow well-known general formulas, which makes it possible to disentangle the hyperfine structure of from Doppler broadening. Accurate temperature measurements are shown to be possible, even though the relatively heavy mass of the iodine atom does not make it the most favorable gauge for measurements based on Doppler effect. Using an injection seeded pulsed laser as the primary laser source, the frequency-tripling of which has provided the ca 300 nm radiation used for excitation, absolute energy measurements of the two-photon excited levels revealed that all upper energy levels of I I have to be revised down, by , which pulls every energy level off its presently tabulated value by more than thirty times the currently admitted uncertainty bar.

High-precision measurement of the hyperfine splitting and ac Stark shift of the 7d D3/22 state in atomic cesium

We report the measurement of hyperfine splitting in the $7d$ $^{2}D_{3/2}$ state of $^{133}\mathrm{Cs}$ using high-resolution Doppler-free two-photon spectroscopy in a Cs vapor cell. We determine the hyperfine coupling constants $A=7.3509(9)$ MHz and $B=\ensuremath{-}0.041(8)$ MHz, which represent an order of magnitude improvement in the precision. We also obtain bounds on the magnitude of the nuclear magnetic octupole coupling constant $C$. Additionally, we measure the ac Stark shift of the $6s\phantom{\rule{0.16em}{0ex}}^{2}\mathrm{S}_{1/2}\ensuremath{\rightarrow}7d$ $^{2}D_{3/2}$ transition at 767.8 nm to be $\ensuremath{-}49\ifmmode\pm\else\textpm\fi{}5\phantom{\rule{0.16em}{0ex}}\mathrm{Hz}/(\mathrm{W}/\mathrm{c}{\mathrm{m}}^{2})$, in agreement with theoretical calculations. We further report the measurement of collisional shift (\ensuremath{-}32.6 \ifmmode\pm\else\textpm\fi{} 2.0 kHz/mTorr) and pressure broadening for the individual hyperfine levels of the $6s\phantom{\rule{0.16em}{0ex}}^{2}\mathrm{S}_{1/2}\ensuremath{\rightarrow}7d$ $^{2}D_{3/2}$ transition. These measurements provide valuable inputs for analysis of systematic effects in optical frequency standards based on the cesium $6s\phantom{\rule{0.16em}{0ex}}^{2}\mathrm{S}_{1/2}\ensuremath{\rightarrow}7d$ $^{2}D_{3/2}$ two-photon transition.

Hyperfine coupling constants of the cesium 7D5/2 state measured up to the octupole term.

We report the measurement of hyperfine splitting (HFS) in the 7D5/2 state of 133Cs using high-resolution Doppler-free two-photon spectroscopy enabled by precise frequency scans using an acousto-optic modulator (AOM). All six hyperfine levels are resolved in our spectra. We determine the hyperfine coupling constants A = -1.70867(62) MHz and B = 0.050(14) MHz which represent an over 20-times improvement in the precision of both A and B. Moreover, our measurement is sufficiently precise to put bounds on the value of the magnetic octupole coupling constant C = 0.4(1.4) kHz for the 7D5/2 state. We additionally report the measurement of the ac Stark shift [-46 ± 4 Hz/(W/cm2)], collisional shift, and pressure broadening which are important for optical frequency standards based on the 6S1/2 → 7D5/2 two-photon transition.

Precision Determination of Isotope Shifts in Ytterbium and Implications for New Physics.

We report measurements of isotope shifts for the five spinless Yb isotopes on the 6s^{2} ^{1}S_{0}→5d6s ^{1}D_{2} transition using Doppler-free two-photon spectroscopy. We combine these data with existing measurements on two transitions in Yb^{+} [Counts etal. Phys. Rev. Lett. 125, 123002 (2020)PRLTAO0031-900710.1103/PhysRevLett.125.123002], where deviation from King-plot linearity showed hints of a new bosonic force carrier at the 3σ level. The combined data strongly reduce the significance of the new-physics signal. We show that the observed nonlinearity in the joint Yb/Yb^{+} King-plot analysis can be accounted for by the deformation of the Yb nuclei.

Analysis of nonresonant effects in the two-photon spectroscopy of helium

In the present paper, we study nonresonant corrections for experimental measurements of the transition frequencies in the helium atom. Having attracted more attention, such effects can make a significant contribution to experiments based on one- and two-photon atomic spectroscopy. The quantum interference effects in the measurements of n 3 S 1 − 33 D 1 (n = 3, 4, 5) transition frequencies based on Doppler-free two-photon spectroscopy, are considered as a possible source of current discrepancy between the experimental and theoretical data. We demonstrate that line profile asymmetry caused by the quantum interference of fine sub-levels of the state can reach tenths of a megahertz for different experimental conditions. Thus, previously unaccounted nonresonant corrections should be taken in next-generation experimental measurements of transitions frequencies in helium. However, they could not completely eliminate the current imbalance in the study of helium spectra and the question is still open.

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.

The first decades of Doppler-free two-photon spectroscopy

Abstract This paper gives a review of the Doppler-free two-photon experiments performed since the beginning of the 1970s until the end of the 1990s. The Doppler-free two-photon method was first tested on the sodium atom, then used extensively to study the hydrogen atom and measure the Rydberg constant and the Lamb shifts.

Dissociation Energy of the Hydrogen Molecule at 10^{-9} Accuracy.

The ionization energy of ortho-H_{2} has been determined to be E_{I}^{o}(H_{2})/(hc)=124 357.238 062(25) cm^{-1} from measurements of the GK(1,1)-X(0,1) interval by Doppler-free, two-photon spectroscopy using a narrow band 179-nm laser source and the ionization energy of the GK(1,1) state by continuous-wave, near-infrared laser spectroscopy. E_{I}^{o}(H_{2}) was used to derive the dissociation energy of H_{2}, D_{0}^{N=1}(H_{2}), at 35 999.582 894(25) cm^{-1} with a precision that is more than one order of magnitude better than all previous results. The new result challenges calculations of this quantity and represents a benchmark value for future relativistic and QED calculations of molecular energies.

Precise and highly-sensitive Doppler-free two-photon absorption dual-comb spectroscopy using pulse shaping and coherent averaging for fluorescence signal detection.

We demonstrated Doppler-free two-photon absorption dual-comb spectroscopy of 5S1/2 - 5D5/2 and 5D3/2 transitions of Rb. We employed simple pulse-shaping of the dual-comb source and eliminated Doppler-broadening backgrounds, which cause fitting errors of the Doppler-free signals. Moreover, to improve sensitivity, we investigated the coherence in dual-comb fluorescence signals and the coherent averaging method was applied to fluorescence dual-comb detection for the first time. The detection sensitivity was significantly improved by coherent averaging to reduce the noise floor. Observed Doppler-free spectra was fitted to Voigt profiles and we performed absolute frequency determination with a precision of about 100 kHz.

High-resolution two-photon spectroscopy of a 5p56p←5p6 transition of xenon

We report high-resolution Doppler-free two-photon excitation spectroscopy of Xe from the ground state to the $5{p}^{5}(^{2}P_{3/2})6p\phantom{\rule{0.16em}{0ex}}\phantom{\rule{0.16em}{0ex}}^{2}[3/2]_{2}$ electronic excited state. This is a first step to developing a comagnetometer using polarized $^{129}\mathrm{Xe}$ atoms for planned neutron electric dipole moment measurements at TRIUMF. Narrow linewidth radiation at 252.5 nm produced by a continuous wave laser was built up in an optical cavity to excite the two-photon transition, and the near-infrared emission from the $5{p}^{5}6p$ excited state to the $5{p}^{5}6s$ intermediate electronic state was used to detect the two-photon transition. Hyperfine constants and isotope shift parameters were evaluated and compared with previously reported values. In addition, the detected photon count rate was estimated from the observed intensities.

Precision measurements and test of molecular theory in highly excited vibrational states of H2 (v=11).

Accurate EF^1varSigma ^+_g{-}X^1varSigma ^+_g transition energies in molecular hydrogen were determined for transitions originating from levels with highly excited vibrational quantum number, v = 11, in the ground electronic state. Doppler-free two-photon spectroscopy was applied on vibrationally excited hbox {H}_2^*, produced via the photodissociation of H2S, yielding transition frequencies with accuracies of 45 MHz or 0.0015 cm−1. An important improvement is the enhanced detection efficiency by resonant excitation to autoionizing 7ppi electronic Rydberg states, resulting in narrow transitions due to reduced ac-Stark effects. Using known EF level energies, the level energies of X(v = 11, J = 1, 3–5) states are derived with accuracies of typically 0.002 cm−1. These experimental values are in excellent agreement with and are more accurate than the results obtained from the most advanced ab initio molecular theory calculations including relativistic and QED contributions.

Hydrogen molecular ions for improved determination of fundamental constants

The possible use of high-resolution rovibrational spectroscopy of the hydrogen molecular ions H + 2 and HD + for an independent determination of several fundamental constants is analyzed. While these molecules had been proposed for metrology of nuclear-to-electron mass ratios, we show that they are also sensitive to the radii of the proton and deuteron and to the Rydberg constant at the level of the current discrepancies colloquially known as the proton size puzzle. The required level of accuracy, in the 10 --12 range, can be reached both by experiments, using Doppler-free two-photon spectroscopy schemes, and by theoretical predictions. It is shown how the measurement of several well-chosen rovibrational transitions may shed new light on the proton-radius puzzle, provide an alternative accurate determination of the Rydberg constant, and yield new values of the proton-to-electron and deuteron-to-proton mass ratios with one order of magnitude higher precision.

Hydrogen molecular ions: new schemes for metrology and fundamental physics tests

High-accuracy spectroscopy of hydrogen molecular ions has important applications for the metrology of fundamental constants and tests of fundamental theories. Up to now, the experimental resolution has not surpassed the part-per-billion range. We discuss two methods by which it could be improved by a huge factor. Firstly, the feasibility of Doppler-free quasidegenerate two-photon spectroscopy of trapped and sympathetically cooled ensembles of HD+ ions is discussed, and it is shown that rovibrational transitions may be detected with a good signal-to-noise ratio. Secondly, the performance of a molecular quantum-logic ion clock based on a single Be+-H2+ ion pair is analyzed in detail. Such a clock could allow testing the constancy of the proton-to-electron mass ratio at the 10-17/yr level.

Doppler-free two-photon absorption spectroscopy of rovibronic transition of naphthalene calibrated with an optical frequency comb

We performed Doppler-free two-photon absorption spectroscopy of naphthalene using an optical frequency comb as a frequency reference. Rotationally resolved rovibronic spectra were observed, and absolute frequencies of the rovibronic transitions were determined with an uncertainty of several tens of kHz. The resolution and precision of our system are finer than the natural width of naphthalene. We assigned 1466 lines of the Q(Ka)Q(J) transition and calculated molecular constants. We attribute systematic spectral line shifts to the Coriolis interaction, and discuss the origin of the spectral linewidths.

Quantum interference in two-photon spectroscopy for laser stabilization and cesium-cell comparison

An alternate method of two-photon spectroscopy is presented where cesium atoms interact with a phase-modulated laser beam. Doppler-free two-photon spectroscopy of the cesium atom $6S\ensuremath{\rightarrow}8S$ hyperfine transition was used to experimentally demonstrate quantum interfered two-photon spectra. We calculated the photon-atom interaction by second-order perturbation theory and assumed that the one-photon frequency is detuned far from any intermediate state. Then we calculated the relative transition rates of all spectral lines resolved by the laser carrier and sidebands. A physical picture of multipathway quantum interference in the frequency domain is given that explains the unusual line strength, based on the trick that a phase-modulated laser beam can be decomposed into a series of coherent and collinear laser modes (carrier and sidebands). For all pairs of modes in which the sum frequency of each pair was on resonance with the cesium atom $6S\ensuremath{\rightarrow}8S$ transition, the superposition of all pathways induced by the different mode pairs resulted in a destructive interference, which then leads to a lack of absorption. We have shown in this paper that our calculation agrees very well with our experimental results in terms of the relative interfered line strengths, which were functions of modulation depth. We further discuss some related issues concerning laser stabilization and we demonstrate an approach for simultaneously comparing two cesium cells.

Communication: Test of quantum chemistry in vibrationally hot hydrogen molecules.

Precision measurements are performed on highly excited vibrational quantum states of molecular hydrogen. The v = 12, J = 0 - 3 rovibrational levels of H2 (X(1)Σg (+)), lying only 2000 cm(-1) below the first dissociation limit, were populated by photodissociation of H2S and their level energies were accurately determined by two-photon Doppler-free spectroscopy. A comparison between the experimental results on v = 12 level energies with the best ab initio calculations shows a good agreement, where the present experimental accuracy of 3.5 × 10(-3) cm(-1) is more precise than theory, hence providing a gateway to further test theoretical advances in this benchmark quantum system.

Precision two-photon spectroscopy of alkali elements

In this paper, we have briefly reviewed the work on two-photon spectroscopy of alkali elements and its applications. The technique of Doppler-free two-photon spectroscopy is briefly summarized. A review of various techniques adopted for measuring absolute frequencies of the atomic transitions and precision measurements of isotope shifts and hyperfine structures (HFS) is presented. Some of the recent works on precision measurements of HFS constants of 6s 2 S 1/2 level of 39K and 41K, 9s 2 S 1/2level and 7d 2 D 3/2 level of 133Cs are also discussed.

Hyperfine structure and isotope shift in the 3s23p23P0,1,2→3s23p4p3P0,1,2transitions in silicon by Doppler-free in-source two-photon resonance-ionization spectroscopy

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Hyperfine structure of the7d2D3/2level in cesium measured by Doppler-free two-photon spectroscopy

We report the measurement of the hyperfine structure in the 7$d$ ${}^{2}{D}_{3/2}$ state of ${}^{133}$Cs isotope by Doppler-free two-photon fluorescence spectroscopy in a gas cell. The hyperfine level separations were measured using a frequency-stabilized Ti:sapphire laser locked to one of the hyperfine transitions and an acousto-optic modulator locked to another hyperfine transition. The frequency separation between various hyperfine levels has been measured with a precision of \ensuremath{\sim}100 kHz. From the measured hyperfine separations of the excited state, we have determined the magnetic dipole coupling constant ($A$) and electric quadrupole coupling constant ($B$) for the 7$d$ ${}^{2}{D}_{3/2}$ state. The determined hyperfine structure constants are $A=7.38$ (0.01) MHz and $B=\ensuremath{-}0.18$ (0.1) MHz. The values measured are found to be in good agreement with the earlier reported results using stepwise excitation process.