We study polarization spectroscopy of Rb vapour. A weak probe beam analyses the birefringence induced in a room temperature vapour by a strong counterpropagating circularly polarized pump beam. In contrast to most other work on polarization spectroscopy, we use a polarization beam splitting cube and two detectors (rather than a polarizer and one detector) to analyse the probe beam. The signal is in the form of a derivative of a Lorentzian. For theoretical analysis we study the closed atomic transition 5 2 S 1/2 (F = 3) → 5 2 P 3/2 (F = 4) in the D2 line of 85 Rb. We study the time needed to redistribute population among the m F states, derive an expression for the expected lineshape and present experimental data in excellent agreement with theory. The polarization spectrum provides an ideal error signal for frequency stabilization of a laser. We describe the geometry and parameters for optimizing the error signal.
Collinear laser-beam/ion-beam spectroscopy provides a collision-free environment in which to study atomic and molecular ions. Ion-beam spectroscopy has particular advantages over other methods: spectra are relatively simple due to mass selection; kinematics allow sub-Doppler resolution of the whole velocity distribution; and the Doppler effect can be used to tune ions into resonance with fixed frequency light sources. We consider methods by which spectra have been obtained and review important results of ion-beam spectroscopy in fields from nuclear physics to astrophysical chemistry.
We have obtained hyperfine-resolved infrared spectra of a P Q 23 (N) branch line in the vϭ2-1 band of the X 3 ⌺ Ϫ state of the molecular dication D 35 Cl 2ϩ . Analysis of the hyperfine structure allows us to estimate the magnitude of the Fermi contact interaction for the chlorine nucleus; b F ͑Cl͒ϭ167 ͑25͒ MHz.PACS number͑s͒: 33.15. PW, 31.30.Gs, 33.20.Ea, 42.62.Fi Introduction. Molecular dications are of interest as minority constituents in laboratory plasmas, astrophysical environments, and the ionosphere ͓1͔. The calculation of dication properties has proven to be far more demanding than molecular structure calculations for similar neutral species ͓2,3͔. The characteristic feature of dication potential-energy curves that have ''volcanic ground states'' ͓4͔ is that the molecules are thermodynamically unstable: the long-range part of the potential corresponds to Coulomb repulsion, and only at short range does the potential have a minimum. As shown in Fig. 1, even the minimum of the well is above the asymptote, and all vibration-rotation levels are quasibound. The lifetimes of the resonant levels can vary between years ͑at the bottom of the well͒ to one of the order of a vibrational period at, or above, the top of the potential barrier. Thermodynamically stable molecular dications also exist ͓5͔, but are not of interest here.The only molecular dications for which rotationally resolved spectra are known are N 2 2ϩ ͓6͔,NO 2ϩ ͓7͔, and DCl 2ϩ ͓8͔. The spectra of N 2 2ϩ and NO 2ϩ were first obtained in emission from discharges; many spectra of N 2 2ϩ were subsequently obtained with fast-ion beam techniques ͓2͔. Such measurements were reviewed by Larsson ͓9͔. Abusen et al. ͓8͔ recently reported a rotationally resolved infrared spectrum of DCl 2ϩ , which was obtained using our fast-ion beam/ laser beam spectrometer. The deuterium isotopomer was chosen because the calculated vibrational spacings were suitable for interrogation with the CO 2 laser that was available. The preliminary measurements indicate that the spectrum is almost certainly the vϭ2←1 band of DCl 2ϩ in its X 3 ⌺ Ϫ ground electronic state. We now report the observation of well-resolved hyperfine structures in an observed transition.The hyperfine-resolved measurements of DCl 2ϩ represent the most detailed information on the structure of molecular dications that has yet been obtained. A comparison of the measured values of the hyperfine constants with values calculated from first principles shows satisfactory agreement.
We report the first measurement of effective electron g-factors in a doubly positively charged molecule (molecular dication); the measurements were made using a fast-ion-beam/laser-beam spectrometer. We measured Zeeman splittings of a rotational line within the v = 2←1 vibrational band of the X3Σ- electronic ground state of D35Cl2+. The Zeeman splittings allowed us to assign the line as a PQ23(6) fine structure transition and to measure the effective upper and lower state effective electron g-factors as g(v' = 2, N' = 5, J' = 5) = 1.0 ± 0.4 and g(v'' = 1, N'' = 6, J'' = 5) = 1.85 ± 0.05. The large differences in the g-factors arise from vibrationally dependent spin-orbit coupling with a repulsive A3Π state.
We have developed a removable and bakeable viewport for UHV applications. The viewport consists of a modified blank Conflat flange; a ring of flux-free solder to form a vacuum seal; a viewport window; a clamping flange, and conical disk springs. We have cyclically baked viewports up to 240 °C and have achieved an ultimate pressure of 1.2×10−10 Torr (limited by our pumping station), with no leak detected at the 10−10 atm cm3/s level. Both BK7 and zinc selenide windows have been used successfully.
A 3D lattice based on a high-power CO2 laser is considered in the context of laser cooling and trapping of atomic calcium. We expect to be able to realize a system with >10 000 lattice sites each with more than 100 atoms, and the facility to laser cool all the atoms into the vibrational ground state using the intercombination line. The configuration allows the production of an array of small Bose–Einstein condensates, enabling an investigation of the build-up of phase coherence as a function of atom number.
We have constructed an apparatus for studying the infrared spectra of molecules with a doubly positive charge (molecular dications). The spectroscopic transitions were recorded indirectly by means of observing a change in the fragmentation rate of the molecular dication when a transition was in resonance. The design and performance of the spectrometer are described, with particular emphasis on the sensitivity achieved for detecting infrared spectra and Zeeman split infrared spectra. The operation and calibration of the spectrometer are discussed and sample results for DCl2+ are presented. It is shown that we achieve the maximum possible signal/noise ratio that could be achieved in this type of experiment.
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