Sub-Doppler molecular-iodine transitions near the dissociation limit (523-498 nm)

A widely tunable and high-resolution spectrometer based on a frequency-doubled Ti:sapphire laser was used to explore sub-Doppler transitions of iodine molecules in the wavelength range 523-498 nm. The wavelength dependence of the hyperfine transition linewidth of iodine was mapped out in this region, and the narrowest linewidth was ~4 kHz near 508 nm. The hyperfine-resolved patterns were found to be largely modified toward the dissociation limit. The observed excellent signal-to-noise ratio should lead to high-quality optical frequency standards that are better than those of the popular 532-nm system.     

Bound-free transitions and the dissociation limit

Following a sequential two-photon excitation, fluorescence is observed from several selectively excited single rotational-vibrational energy levels of theE ³ π0 _g ⁺ state of molecular iodine. The re-emittedE →B fluorescence spectrum from each of the populated rovibrational level of theE state consists of a series of sharp lines terminating on the various discrete ro-vibrational levels of theB state and a few broad lines due to transitions taking place on to the continuum of theB state. The point of transition from sharp lines to broad features in the fluorescence spectrum has been utilized to determine theB state dissociation limit. This method of obtaining the dissociation limit of the molecular electronic states appears to be quite simple and straightforward.     

Spin-orbit coupling in oxygen near the dissociation limit

By using the method of configuration interactions in the valence basis with triple exponentials, the spectrum of the oxygen molecule is calculated in a range of internuclear distances from 1.2 to 2.45 Å, with the matrix of configuration interactions being diagonalized with regard to the spin-orbit coupling. The matrix elements of the spin-orbit coupling are presented, along with the spin splittings of triplet and quintet states. Particular attention is given to the intermediate range for the breaking of the O=O bond (1.8–2.45 Å), where the strong mixing of multiplets and rearrangement of the valence bonding to the atomic limit O(³ P)+O(³ P) occur. Other dissociation limits up to O(¹ D)+O(¹ D) are also taken into account. The results obtained are discussed in the context of the theory of the chemical bond, catalysis, radiation collisions, and the theory of spectral bands for high vibrational quantum numbers.     

1240 nm diamond Raman laser operating near the quantum limit

An external-cavity diamond Raman laser generating up to 2.0 W at 1240 nm from 3.3 W of 1064 nm pump power is investigated as a function of pump polarization direction. The maximum conversion efficiency was 61%, and the slope efficiency of 84% closely approaches the quantum limit of 85.8%. The lowest threshold for Raman lasing is achieved for pump polarization parallel to the <111> axis, which we show is consistent with theory.     

Infrared wave guiding in Si(1)-(x)-(y)Ge(x)C(y) upon silicon: errata

In a previous Letter,(1) I was incorrectly listed by middle and last name in the aff iliation line. The name should have been listed as given above.     

Generation of tunable 187.9-196-nm radiation in beta-BaB(2)O(4): errata

In Ref. 1, the first full sentence in the right-hand column of p. 1608 should read as: 'Although BBO is phase matchable down to 187 nm and shorter in this configuration without a very large (2-4 degrees ) change in theta (and hence in d(eff)), and B2 is also suitable to accommodate the phase matching, tunability below 187.9 nm becomes limited by the exponential increase in crystal absorption.'     

New TEA-lasers based onD′→A′ transitions in halogen monofluoride compounds: ClF (284.4 nm), BrF (354.5 nm), IF (490.8 nm)

As an outcome of a systematic study of excitation kinetics and fluorescence spectra concerning theD′(3π_2u )→A′(3π_2g ) transitions in homonuclear diatomic halogens and corresponding transitions in interhalogen molecules [1], this paper describes, for the first time, TEA laser action in the three halogen monofluorides ClF, BrF, and IF. Output energies in the mJ range were demonstrated in a fast TEA discharge arrangement at the wavelengths of 284.4, 354.5, and 490.8 nm for ClF, BrF, and IF, respectively. The results suggest parameter scalability and wavelength tunability.     

Sub-Doppler Infrared Spectra of the OH-Stretch Fundamental of (13)C-Methanol

High-resolution infrared spectra of the (13)C-methanol OH stretching band, nu(1), were obtained by slit-jet absorption spectroscopy at a rotational temperature of 12-15 K. Twenty-eight subbands were assigned within the range of upper state quantum numbers, K' = 0 to 2 and J' = 0 to 10. The upper state energy levels are heavily perturbed; about half of the assigned subbands were found to be split by perturbations with matrix elements in the range 1-3 cm(-1). The doubled lines were deperturbed and together with the "unperturbed" lines were fitted to a global torsion-rotation Hamiltonian with root-mean-square deviation of 0.41 cm(-1) to yield a torsional barrier height of approximately 405 cm(-1) in the vibrationally excited state. Copyright 2000 Academic Press.     

Extension of the A1Σ+-X1Σ+ system of7LiH near the dissociation limit

The absorption spectra of⁷LiH have been photographed in the 3,500?2,900 Å region using the second order of a 3.4 M Ebert spectrograph. Observations comprise previously observedA ¹ Σ ⁺-X ¹ Σ ⁺ transitions and several new vibrational bands of this system near the ionisation limit. Rotational and vibrational analysis of these bands (16≦V′≦20) have been carried out and the rotational constants for the upper states have been determined.     

Single pulse near field study on a Co(3 nm)/Cu(6 nm)/Co(20 nm) multilayer structure by using a femtosecond laser

Single pulse near field study on a Co(3 nm)/Cu(6 nm)/Co(20 nm) multilayer structure was experimentally investigated with a laser pulse width of 200 fs at a wavelength of 775 nm. For the near field experiments, we have used polystyrene colloidal particles of 700 nm diameter deposited by spin coating on top of the multilayer structure, as well on top of Co (50 nm) and Cu (50 nm) thin films. The diameter and the morphologies of the holes were investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM). We have estimated the fluence thresholds values for the near field and discuss their values in respect with the enhancement factor of the intensity of the electromagnetic field due to the use of the colloidal particles. We compare the depths and the widths of the holes obtained at the same peak laser fluence for the Co thin film (50 nm), Cu thin film (50 nm) and Co(3 nm)/Cu(6 nm)/Co(20 nm) multilayer structure. Depending on the laser fluence, the ablation depth can reach the first, the second, or the third layer. Theoretical estimations of the intensity enhancement were done using the finite-difference time-domain (FDTD) by using the RSoft software. This type of a selective distribution of the ablation depth, in the near field regime, of a planar metal/dielectric interface can open new perspective in the excitation of propagating surface plasmons.     

Low-power Lamb-dip spectroscopy of very weak CO(2) transitions near 4.25 mum

We report saturated-absorption spectra recorded by use of 5 muW of infrared radiation coupled into a build-up cavity. Single-pass generation of difference-frequency radiation tunable near 4.25 mum in a periodically poled LiNbO(3) crystal was used. Lamb dips of weak transitions of the fundamental rovibrational band of CO(2) were observed, for what is believed to be the first time, up to the J=82 level. Application of these results to the extension of frequency-comb-based metrology in the infrared is discussed.     

Surface phase transitions and defect-phonon interactions: The Si(111)-(2 × 1) to (7 × 7) to (1 × 1) transitions

A thermodynamic equation is derived, showing the relation between defect-phonon interactions, the free energy of formation of defects and surface disordering or melting. When applied to Si(111), the theory shows that the (2 × 1) to (7 × 7) transition temperature is deduced from the (7 × 7) to (1 × 1) temperature via the relative concentrations of dangling bonds on the (2 × 1) and (7 × 7) surfaces.     

Phase transitions in lattice 2D O(N)σ-model with mixed action in the largeN limit

We study the exactN→∞ solution of the two-dimensional latticeo(N) σ-model, described by a two parameter action that mixes Wilson (quadratic) andRP ^N?1 ≈O(N)/Z ₂ (quartic) actions. A rich phase structure emerges, with a first order transition line crossing, in the two-dimensional parameter space theRP ^N?1 axis. At the end of this line the specific-heat diverges while the correlation length remains finite.     

Coherent population trapping resonances in thermal (85)Rb vapor: D(1) versus D(2) line excitation: errata

In our recent Letter,(1) Ref. 12 was printed incorrectly. The correct reference is M. Zhu, Coherent population trapping-based frequency standard and method for generating a frequency standard incorporating a quantum absorber that genrates the CPT state with high frequency, U.S. patent 6,359,916 (March 19, 2002).     

Absolute frequency measurements of the 2(3)S1-->2(3)P 0,1,2 atomic helium transitions around 1083 nm

We measure the frequency of the 2(3)S1-->2(3)P(0,1,2) transitions of helium in a metastable beam using an optical frequency comb synthesizer. The relative uncertainty of these measurements ranging from 5x10(-11) to 7x10(-12) is, to our knowledge, the most precise result for any optical helium transition. Considering existing accurate values of the 2(3)P fine structure, we measure a centroid value of the 2(3)S-2(3)P frequency of 276 736 495 624.6(2.4) kHz, improving the previous interferometric measurement by 30 times. New accurate values of the 2(3)S-2(3)P and 2(3)P Lamb-shift energies are obtained.     

Hall effect plateaus and giant Shubnikov-de Haas oscillations in (BiSb)Telayered single crystals near the quantum limit

On bulk layered single crystals (Bi_0.25Sb_0.75)₂Te₃ with a hole concentration cm^-3 and a mobility cm²/Vs magnetoresistance and Hall effect investigations were performed in the temperature range T = 1.4 K ... 20 K in magnetic fields up to 18 T. For the magnetic field perpendicular to the layered structure giant Shubnikov-de Haas oscillations are measured; the positions of the maxima are triplets in the reciprocally scaled magnetic field. From the damping of the amplitudes with increasing temperature the cyclotron mass m _c = 0.12m ₀ is evaluated. Correlated with the SdH oscillations doublets of Hall effect plateaus (or kinks in low fields) are found. The weak well known Shubnikov-de Haas oscillations from the generally accepted multivallied highest valence band can be detected as a modulation on the giant oscillation. The high anisotropy of the SdH oscillations and their triplet structure in connection with the layered crystal structure lead us to suggest that the effects are caused by hole carrier pairing (mediated by the bipolaron mechanism) in quasi 2D sheets parallel to the crystal layer stacks. The measured Hall plateau resistances coincide with the quantum Hall effect values considering the number of layer stacks and the valley degeneracy of the 3D hole carrier reservoir. The ratio of spin splitting to Landau (cyclotron) splitting is observed to be . Received: 12 September 1997 / Revised: 8 January 1998 / Accepted: 22 January 1998     

Sub-Doppler Laser Cooling of ~(23)Na in Gray Molasses on the D_2 Line

We report on the efficient gray molasses cooling of sodium atoms using the D_2 optical transition at 589.1 nm.Thanks to the hyperfine split about 6Γ between |F' = 2 and |F' = 3 in the excited state 3~2 P_(3/2), this atomic transition is effective for the gray molasses cooling mechanism. Using this cooling technique, the atomic sample in F = 2 ground manifold is cooled from 700 μK to 56 μK in 3.5 ms. We observe that the loading efficiency into magnetic trap is increased due to the lower temperature and high phase space density of atomic cloud after gray molasses. This technique offers a promising route for the fast cooling of the sodium atoms in the F = 2 state.