sub-Doppler Laser Spectroscopy Research Articles

Testing the limits of the Maxwell distribution of velocities for atoms flying nearly parallel to the walls of a thin cell.

For a gas at thermal equilibrium, it is usually assumed that the velocity distribution follows an isotropic 3-dimensional Maxwell-Boltzmann (M-B) law. This assumption classically implies the assumption of a "cos θ" law for the flux of atoms leaving the surface. Actually, such a law has no grounds in surface physics, and experimental tests of this assumption have remained very few. In a variety of recently developed sub-Doppler laser spectroscopy techniques for gases one-dimensionally confined in a thin cell, the specific contribution of atoms moving nearly parallel to the boundary of the vapor container becomes essential. We report here on the implementation of an experiment to probe effectively the distribution of atomic velocities parallel to the windows for a thin (60 μm) Cs vapor cell. The principle of the setup relies on a spatially separated pump-probe experiment, where the variations of the signal amplitude with the pump-probe separation provide the information on the velocity distribution. The experiment is performed in a sapphire cell on the Cs resonance line, which benefits from a long-lived hyperfine optical pumping. Presently, we can analyze specifically the density of atoms with slow normal velocities ∼5-20 m/s, already corresponding to unusual grazing flight-at ∼85°-88.5° from the normal to the surface-and no deviation from the M-B law is found within the limits of our elementary setup. Finally we suggest tracks to explore more parallel velocities, when surface details-roughness or structure-and the atom-surface interaction should play a key role to restrict the applicability of an M-B-type distribution.

Cs 5D5/2–6F 728 nm Laser Spectroscopy with Single Pumping Laser**Supported by the National Natural Science Foundation of China under Grant No 91436210.

The sub-Doppler absorption laser spectroscopy at 728 nm transition from the 5 state to the state of cesium with linewidth near 10 MHz is first experimentally performed with indirect pumping from the ground state 6 to the state by a 455.5 nm diode laser. Using a 455.5 nm diode laser as an indirect pump laser, several excited states will be populated due to spontaneous decay from the state. We first implement the sub-Doppler absorption laser spectroscopy at 728 nm from the 5 state to the state when Cs atoms within thermal glass cell decay to the 5 state. Due to velocity transfer effect, the hyperfine structure of 5 shows a mixed and complicated pattern but very clear structure when the 455.5 nm pumping laser is counter-propagating (or co-propagating) with the 728 nm probing laser.

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

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

Sub-Doppler laser spectroscopy on relativistic beams and tests of Lorentz invariance

We demonstrate sub-Doppler laser spectroscopy with a beam of ${^{7}\text{L}\text{i}}^{+}$ ions stored at 33.8% of the speed of light in the experimental storage ring at GSI. Using two lasers, the one copropagating and the other counterpropagating, with respect to the ion beam, a fluorescence line is observed via optical-optical double-resonance spectroscopy on a $\ensuremath{\Lambda}$-type level configuration. A linewidth of $\ensuremath{\approx}114\text{ }\text{MHz}$ is found, which is 12 times narrower than the Doppler broadening due to the momentum spread of the ion beam. Interpreted as a test of Lorentz invariance, we find $|{\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{\ensuremath{\alpha}}}_{2}|l1.2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$, a $25\ifmmode\times\else\texttimes\fi{}$ tighter limit on $O\mathbf{(}{(v/c)}^{4}\mathbf{)}$ deviations from time dilation than any other experiment.

On the possible analysis of the sub-Doppler spectrum structure of atoms in a gas using the anisotropy of photoion flows

We propose the new highly sensitive method of sub-Doppler laser spectroscopy based on the selective record of anisotropic flows of ions, which are formed as a consequence of the photoionization of atoms (molecules) of a rarefied gas in a cell after their resonance excitation by running monochromatic radiation. This method of photoionization spectroscopy may be used for the receipt of spectroscopic data on atoms (molecules), for the detection of individual atoms, and for isotope (isomer) separation in a gas cell.

Sub-Doppler Laser Spectroscopy of Na2 in a Cold Molecular Beams

Sub-Doppler Laser Spectroscopy of Na2 in a Cold Molecular Beams

Sub-Doppler Laser Spectroscopy of SO2 Molecule of 30548.0 cm-1 and 31770.0 cm-1 Bands

Sub-Doppler Laser Spectroscopy of SO2 Molecule of 30548.0 cm-1 and 31770.0 cm-1 Bands

Tuneable, stabilised diode lasers for compact atomic frequency standards and precision wavelength references

We describe the ongoing activities in Observatoire Cantonal de Neuchâtel in the fields of precision laser spectroscopy and metrology of Rb atomic vapours. The work is motivated by the potentials of highly stable and narrowband laser light sources for a variety of technical and scientific applications. We describe the use of extended-cavity diode lasers for the realisation of such narrowband light sources and the basic schemes under study for their stabilisation, with focus on Doppler and sub-Doppler laser spectroscopy. The resulting laser systems offer good frequency stabilities and can be effectively miniaturised. This makes them interesting for direct applications of these techniques, as well as the presently developed precision instruments: compact atomic frequency standards for ground and space applications (GALILEO satellite positioning system), secondary optical frequency standards, transportable extended cavity diode lasers as seeding lasers, and others.

The hyperfine structure in the electronic A 2E″←X 2E′ system of the pseudorotating lithium trimer

Sub-Doppler laser spectroscopy of the A 2E″←X 2E′ band of Li3 shows well-resolved and characteristic hyperfine structures of rovibronic transitions which can be explained in all detail by the interplay between the underlying Fermi-contact interaction, the symmetry species of the rovibronic states and the Coriolis coupling of rotational and pseudorotational motions. Ab initio calculated electron spin densities reproduce the observed line splittings to within 3%. In this Jahn–Teller distorted molecule magnetic equivalence of identical nuclei is strictly valid only for rovibronic states of A symmetry. However, it also holds for rovibronic states of E symmetry if they are of pure A vibronic origin, and it is enforced for many E states of pure E vibronic origin by Coriolis coupling. In contrast, those transitions which involve states with dominant Kc=0 rotation functions and/or with strong vibronic E/A mixing show significant changes in the hyperfine patterns due to magnetic inequivalence, sometimes called “hyperfine doubling.”

Nomenclature, Symbols, Units, and Their Usage in Spectrochemical Analysis - Part XVII; Laser-Based Molecular Spectrometry For Chemical Analysis: Absorption

Abstract This report is the 17th in a series on spectrochemical methods of analysis issued by IUPAC commission V.4. It is concerned with the principles of laser absorption spectroscopy and its application in the optical wavelength region. The present report has four main sections: fundamentals of laser absorption spectroscopy, Doppler-limited spectroscopy; sub-Doppler laser spectroscopy, and time-resolved laser spectroscopy.

Sub-Doppler laser spectroscopy of ZrN

The (1,1) band of the A 2Π-X 2Σ + transition of ZrN has been studied using intermodulated laser induced fluorescence spectroscopy. The sub-Doppler spectrum obtained was at a resolution of about 150 MHz. The magnetic hyperfine structure caused by the 91ZrN nuclear (I=5/2) is partially resolved, and the coupling of the nuclear spin angular momentum with X 2Σ + state conforms to case b βs scheme. This hyperfine interaction splits a rotational line into 12 hyperfine components which are divided into two groups with G=2 (5 components) and G=3 (7 components). The ground state molecular constants needed for explaining the observed hyperfine structures are: B=0.479809 cm −1, D=4.515x10 −7 cm −1. γ=−0.002445 cm −1, b=−0.0645 cm −1, c=−0.0045 cm −1.

Sub-Doppler laser spectroscopy of H2 and D2 in the range 91–98 nm

The absorption spectra of hydrogen and deuterium have been measured in the range 91–98 nm. A narrowband extreme ultraviolet laser source is employed in combination with a molecular beam, allowing for sub-Doppler resolution and yielding linewidths of 0.23 cm−1. Transition frequencies of 291 lines of the Lyman and Werner bands are determined with an average absolute accuracy of 0.03 cm−1. The data are analyzed in a semi-empirical perturbation model, involving heterogeneous couplings between nearby lying levels of B1Σu+ and C1Πu states. This model is found to be accurate on the level of accuracy of the data obtained.

Sub-Doppler laser spectroscopy of the 1B2(1Δu) state of CS2 in a cold molecular beam

Sub-Doppler excitation spectra of CS2 in the spectral range 30200−32300 cm−1 have been extensively measured with a frequency-doubled single mode cw dye laser in a cold collimated argon beam, seeded with CS2. From the rotational analysis of the measured spectra, the geometry and the position of the barrier to linearity of the CS2 molecule in the excited 1B2(1Δu) state has been determined. The observed bands are heavily perturbed and cluster around some intense vibrational transitions. A statistical analysis of the distribution of these bands showed that no chaotic behavior is present in the considered energy region and therefore a non-linear interaction with highly excited vibrational levels of the ground state cannot be responsible for this irregular vibronic structure, although chaotic regions for vibrational energies E≳12000 cm−1 in the electronic ground state have been reported in the literature. Different coupling mechanisms causing the observed perturbations of the rotational and vibrational structure are also discussed.

Sub-Doppler laser spectroscopy of silver dimers Ag 2 in a supersonic beam

Sub-Doppler excitation spectra of the A 1Σ u←X 1Σ g system of Ag 2 molecules in a collimated supersonic Ar/Ag 2 beam have been measured with a cw dye laser. Accurate molecular constants of both states are derived from 740 analyzed rotational lines.

Sub-Doppler laser spectroscopy of molecules and clusters in cold beams

This paper illustrates, with several examples, the spectral resolution and attainable sensitivity reached with sub-Doppler laser spectroscopy in cold argon beams, seeded with molecular or metal vapors. Linear as well as nonlinear spectroscopy has been applied. The detection techniques use either LIF or resonant two-photon ionization. Examples given include NO2, SO2 and Na3-molecules. The advantage of optical double resonance methods is illustrated.

Continuous-wave laser optical spectroscopy of the oxygen atom

Doppler-limited and sub-Doppler laser spectroscopy of atomic oxygen is performed by means of optogalvanic detection. Collisional processes determining atomic populations are studied by simultaneous investigation of the fluorescence spectra. Fine structures are resolved, and the higher-accuracy values are compared with those previously inferred from conventional optical spectra.

Nuclear hyperfine structure in sub-Doppler electronic spectra of the Swan (d 3Π g -a 3Π u ) system of 13C2

High-resolution electronic spectra of the 0–1 band of the Swan system (d 3Π g -a 3Π u ) of 13C2 have been recorded using sub-Doppler laser spectroscopy. Carbon-13 nuclear hyperfine structure is resolved in many of the rotational lines. The orbital-nuclear, Fermi contact, spin-dipolar and hyperfine lambda-doubling hyperfine parameters in both electronic states are obtained from an analysis of the spectra and their values are discussed in terms of the electronic wavefunctions for the electronic states.

Reinvestigation of the A6Σ +- X6Σ + transition of MnS: Analysis of the fine and hyperfine structures

The A 6Σ +- X 6Σ + (0−1) band of MnS has been reinvestigated using sub-Doppler laser spectroscopy. The 12 branches of the transition have been identified with the help of the pattern of the hyperfine structure. All the lines have been fitted simultaneously. It has been necessary to take into account the second-order spin-spin interaction (parameter θ) to explain the fine structure of the transition. The observation of a few extra lines in the perturbed region allowed a determination of the rotational constant of the perturbing state. The hyperfine constant b′ ( A 6Σ + state) has been determined.

High-resolution optical spectroscopy of atomic oxygen.

We report sub-Doppler laser spectroscopy of atomic oxygen. The atom is detected as a trace in a noble-gas radio-frequency discharge by means of optogalvanic effect. The fine structure of the $2{p}^{3}3p^{5}P_{1,2,3}\ensuremath{\rightarrow}2{p}^{3}(4{S}^{0})4d^{5}D_{4,3,2,1,0}$ transitions is fully resolved and preliminary values for the upper level splittings are: ${\ensuremath{\Delta}}_{4,3}=1382(20)$ MHz, ${\ensuremath{\Delta}}_{3,2}=1594(20)$ MHZ, ${\ensuremath{\Delta}}_{2,1}=1360(20)$ MHz, and ${\ensuremath{\Delta}}_{1,0}=735(20)$ MHz. The best values so far derived from conventional spectroscopy are one order of magnitude less accurate and in marginal agreement with our data.

Laser Spectroscopy of Molecules and Clusters

The advantages of collimated cold supersonic beams for sub-Doppler laser spectroscopy of molecules and small clusters are discussed and illustrated by several examples. These include sub-Doppler spectroscopy of the SO2 molecule in the ultraviolet and of NO2 in the visible region. Lifetime measurements under collision-free conditions, stepwise excitation of high lying molecular Rydberg states, and sub-Doppler double resonance spectroscopy of Na3 demonstrate the achievements possible by combining molecular beam techniques with various methods of laser spectroscopy. The relevance of the experimental results for our understanding of the dynamics of molecules in excited states and for the development of new theoretical approaches is emphasized. Some sensitive detection techniques are presented which are in particular useful when cw lasers are used for spectroscopy in cw molecular beams at low densities.