The hyperfine and isotope structure of the Cd intercombination line – revisited

Careful analysis of the intercombination 5¹S₀–5³P₁ line of the ¹¹³Cd isotope with two hfs components and was carried out. The hyperfine splitting of this line was determined to uncertainty less than 10^-3 cm^-1 using neon-perturbed Doppler limited spectra.     

Probing spin-orbit quenching in Cl (2P) + H2 via crossed molecular beam scattering

In our previous work we investigated electronically non-adiabatic effects in using crossed molecular beam scattering coupled with velocity mapped ion imaging. The prior experiments placed limits on the cross-section for electronically non-adiabatic spin-orbit excitation and electronically non-adiabatic spin-orbit quenching . In the present work, we investigate electronically non-adiabatic spin-orbit quenching for which is the required first step for the reaction of Cl^* to produce ground state HCl+H products. In these experiments we collide Cl (²P) with H₂ at a series of fixed collision energies using a crossed molecular beam machine with velocity mapped ion imaging detection. Through an analysis of our ion images, we determine the fraction of electronically adiabatic scattering in Cl^* +H₂, which allows us to place limits on the cross-section for electronically non-adiabatic scattering or quenching. We determine the following quenching cross-sections σ _quench(2.1 kcal/mol) = 26 ± 21 ?², σ _quench(4.0 kcal/mol) = 21 ± 49 ?², and σ _quench(5.6 kcal/mol) = 14 ± 41 ?².     

Temporal coherent control induced by wave packet interferences in one and two photon atomic transitions

The interaction of a sequence of two identical ultrashort laser pulses with an atomic system results in quantum interferences as in Ramsey fringes experiments. These interferences allow achievement of temporal coherent control of the excitation probability. We present the results of a temporal coherent control experiment on two different atomic systems: one-photon absorption in K (4s-4p) and two-photon absorption in Cs (6s-7d). In K, the quantum interferences between the two excitation paths associated with the laser pulses are revealed through rapid oscillations of the excitation probability as a function of the time delay between the two pulses. These oscillations take place at the transition frequency (period T = 2.56 fs). The interferences are modulated by beats (at about 580 fs) resulting from the doublet structure of the excited state (4p (² P _1/2 , ² P _3/2 )). Three complementary interpretations of this experiment are presented: in terms of beats of quantum interferences, of variation in the spectrum intensity, and of wave packet interferences. Whenever the two laser pulses are temporally overlapped, optical interferences are superimposed on to the quantum interferences. The distinction between these two types of interference is clearly revealed in the two-photon excitation scheme performed on Cs (6s-7d (² D _3/2 , ² D _5/2 )) because quantum interferences occur at twice the frequency of the optical interferences. Received: 30 December 1997 / Revised: 28 February 1998 / Accepted: 4 March 1998     

Features of the Formation of the Spin Polarization of an Alkali Metal at the Resolution of Hyperfine Sublevels in the <Superscript>2</Superscript><Emphasis Type="Italic">S</Emphasis><Subscript>1/2</Subscript> State

The optical orientation of the angular momenta of alkali atoms in the presence of a buffer gas (molecular nitrogen) has been studied experimentally. It has been shown that, even at a low concentration of molecular nitrogen in the cell, the excitation of ¹³³Cs atoms from the lower hyperfine level with F = 3, which belongs to the ground ²S_1/2 state, results in a larger amplitude of the magnetic resonance than the excitation from the hyperfine level with F = 4. This result has been theoretically explained under the assumption that the spin state of the alkali atomic nucleus does not change at collision with a nitrogen molecule, which is accompanied by a nonradiative transition of the alkali atom from the excited ²P_1/2 state to the ground ²S_1/2 state.     

Two-step laser excitation of the highly excited even-parity states of atomic mercury

We report term energies and quantum defects of highly excited even-parity states of mercury in the 83 876–84 140 cm^-1 energy range, employing a two-step laser excitation scheme via the S₀↦6s6p³P₁ inter-combination transition. Two dye lasers, pumped by a common Nd:YAG laser, were frequency doubled by BBO crystals and used to record the spectra in conjunction with a thermionic diode ion detector. Our new observations include the much extended D₂ (22 ≤n ≤52) series and a few members of the S₁ (24 ≤n ≤30) Rydberg series. Members of the D₂ Rydberg series with such a high n value are reported for the first time. The relative intensities of the D₂ and S₁ transitions (m = 4, 5 and 6) of group II-B elements excited from the P₁ inter-combination states are also discussed.     

Hyperfine splitting constants in the optical transition \boldsymbol{{4{f}^{7}} {6{s}^{2}} \;{^{8}{\rm S}_{7/2}} \to {4{f}^{7}} {6{s}6{p}}\; {^{6}{\rm P}_{5/2}} \ {\rm of} \ {^{151-155}{\rm Eu}}} isotopes and hyperfine anomaly

Using the method of laser-induced fluorescence in an atomic beam we have measured the hyperfine splitting constants, A and B, of the ground and excited states of the optical transition 4f ⁷6s ^{2 8}S $_{1/2}\to 4f^{7}$ 6s6p ⁶P_5/2 (564.58 nm) for ^151???155Eu isotopes. For all isotopes, the magnetic dipole constants of the ⁶P_5/2 atomic level are determined to a precision better than 0.04%. The A and B constants for the ground state ⁸S_7/2 of the radioactive ^152,154,155Eu were obtained for the first time with a precision better than 0.5%. Our data along with previous ground state hyperfine structure measurements for the stable europium isotopes allow us to determine the hyperfine anomaly for mentioned Eu isotopes.     

Interaction of frequency modulated light pulses with rubidium atoms in a magneto-optical trap

The spatial displacement of the ⁸⁵Rb atoms in a Magneto-Optical Trap (MOT) under the influence of series of frequency modulated light pulse pairs propagating opposite to each other is measured as a function of the time elapsed after the start of the pulse train, and compared with the results of simulations. Adiabatic excitation and consecutive de-excitation take place between the ground 5²S_1/2 (F=3) and the 5²P_3/2 (F'=2, 3, 4) excited levels as the result of the interaction. The displacement of the ⁸⁵Rb atoms is calculated as the solution of simple equation of motion where the expelling force is that arising from the action of the frequency modulated light pulses. The restoring and friction forces of the MOT are taken into account also. The system of Bloch equations for the density matrix elements is solved numerically for transitions between six working hyperfine levels of the atom interacting with the sequence of the frequency modulated laser pulses. According to these simulations, the momentum transferred by one pulse pair is always smaller than the expected 2ħk, (1) where ħ is the Plank constant and k=2π/λ where λ is the wavelength, (2) having a maximum value in a restricted region of variation of the laser pulse peak intensity and the chirp.     

Orientation of Cs 6p 2P3/2 atomic photofragments in a magnetic field: interference in the photodissociation of diatomic molecules

In a magnetic field, Cs₂ molecules were excited from the ground X¹Σ⁺_g(v_X=0,J_X=55) level to the D ¹Σ⁺_u(v=46,J=54) level by dissociation laser light linearly polarized parallel to the field, for which the magnetic sublevels were degenerated and thus all the transitions between them were simultaneously stimulated. Probe laser light excited the dissociated Cs 6p²P_3/2 atomic fragments to 6p²D_3/2 level and the resultant 6p²P_1/2 - 6d²D_3/2 emission was detected as the function of the wavelength of the probe light. The populations of the 6p²P_3/2,mj magnetic sublevels were determined from the relative strengths of the 6p²P_3/2,mj - 6d²D_3/2,m'j transitions induced by the probe light. Non-zero orientation O₀ was found in the ensemble of dissociated Cs 6p²P_3/2 atomic fragments. The orientation O₀ increased as the magnetic field strength increased. It was demonstrated both experimentally and theoretically that the orientation O₀ was induced through the interference in the excitation and dissociation paths in the presence of an external magnetic field, even when all degenerated transitions between the magnetic sublevels of the molecules are simultaneously excited by the light linearly polarized parallel to the field.     

Absolute frequency and isotope shift measurements of the cooling transition in singly ionized indium

We report greater than two orders of magnitude improvements in the absolute frequency and isotope shift measurements of the In⁺ 5s^{2 1}S₀ (F = 9/2)–5s5p ³P₁ (F = 11/2) transition near 230.6 nm. The laser-induced fluorescence from a single In⁺ in a radio-frequency trap is detected. The fourth-harmonic of a semiconductor laser is used as the light source. The absolute frequency is measured with the help of a frequency comb referenced to a Cs atomic clock. The resulting transition frequencies for isotopes ¹¹⁵In⁺ and ¹¹³In⁺ are measured to be 1 299 648 954.54(10) MHz and 1 299 649 585.36(16) MHz, respectively. The deduced cooling transition frequency difference is 630.82(19) MHz. By taking into account of the hyperfine interaction, the isotope shift is calculated to be 695.76(1.68) MHz.     

A rubidium-stabilized ring-cavity resonator for optical frequency metrology: precise measurement of the D1 line in 133Cs

We have developed a ring-cavity resonator that can be used to measure the absolute frequencies of optical transitions with an uncertainty below 40 kHz. The length of the resonator is calibrated against a reference laser locked to the D₂ line of ⁸⁷Rb, the frequency of which is known with 6 kHz accuracy. We demonstrate the power of this technique by measuring the absolute frequencies of various hyperfine transitions in the D₁ line of ¹³³Cs. Our results agree with earlier measurements using the frequency-comb technique, and have similar accuracy. Measurement of the D₁-line frequency could lead to a more precise determination of the fine-structure constant. We also report a precise value of A=291.918(8) MHz for the hyperfine constant in the 6P_1/2 state.     

Photodissociation dynamics of CF3I investigated by two-color femtosecond laser pulses

We report an experimental study of the multiphoton dissociation dynamics of CF₃I performed on a home-built femtosecond laser pump-probe system, with time-of-flight mass spectrometer. The first repulsive A band and the 5pπ³7sσ υ₂=1 Rydberg state of CF₃I were accessed by one- and two-photon transitions at 267 nm, respectively, with the latter two-photon absorption followed by a further two-photon probe transition at 401 nm to the state of the parent ion. The observed signals from the CF₃ ⁺ and I⁺ fragments show similar multi-component exponential decay patterns but the former is 4 times stronger than the latter. However, the parent CF₃I⁺ signal was observed to evolve in a very different manner, decreasing sharply when probed in the first 289 fs following excitation and subsequently rising again after 860 fs to a constant level below that measured at negative pump-probe delay times when the pump and probe pulses exchange roles. This dip observed in the parent ion profile, is very different from that previously reported at shorter pump wavelengths of 264 nm or 265 nm, and is interpreted as the competition between two different ionization channels. One from the vibrationally excited υ₂=1 of the irradiated Rydberg state and the other from the dissociative vibrational origin of the same electronic state which is populated by internal vibrational relaxation.     

Efficient long-term laser excitation of a collimated beam of potassium atoms on the D2 line

With the aim to provide a reliable scheme for efficient laser excitation of the potassium D2 line over long periods of time, we have developed a robust stabilization of a single mode laser of frequency f ₀ = (f ₁₂ + f ₂₃)/2 onto a crossover peak in the saturation spectrum of the ³⁹K(D2) line (4s ²S P . The two hyperfine transitions (frequency f ₁₂) and (frequency f ₂₃) are simultaneously excited by the first order sidebands of the laser beam (f ₀), generated by its electro-optical modulation at the frequency f _EOM = (f ₁₂-f ₂₃)/2. In this way stable excitation of the two transitions on their proper frequencies is achieved and hyperfine pumping compensated.Received: 10 March 2004, Published online: 29 June 2004PACS: 39.30. + w Spectroscopic techniques - 32.80.Bx Level crossing and optical pumping - 42.60.Fc Modulation, tuning, and mode locking     

Investigation of highly excited states of calcium by three-photon ionization

The three-photon ionization in Ca from S₀ ground state is studied. The two-photon process is a near -- resonance process with one of the following bound states: 4s4d ¹D₂, 4p P₂, 4s6s ¹S₀, 4 D₂ and 4 S₀ while the third photon reach either directly the continuum or one of the autoionizing states. The succession of bound states as well as the transitions above the ionization limit are discussed. The dynamics of the multiphoton excitation processes is also discussed and radiative decay of 4 S₀ Ca state with two-photon excitation as well as (the measured) decay times of the Ca autoionizing states using the proper line profiles for different quantum numbers has been determined.Received: 29 September 2003, Published online: 18 May 2004PACS: 32.70.-n Intensities and shapes of atomic spectral lines - 32.70.Cs Oscillator strengths, lifetimes, transition moments - 32.80.Fb Photoionization of atoms and ions - 32.80.Rm Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)     

Photolysis of NO2 at multiple wavelengths in the spectral region 200–205 nm

A study of the photodissociation dynamics of NO₂ in the 200–205 nm region using resonance enhanced multiphoton ionization (REMPI) in conjunction with the velocity map imaging technique is presented. We chose this region because it allowed the use of a single laser to photodissociate the NO₂ molecule and probe both the O(¹D₂) fragment using (2+1) REMPI via the 3p'¹P₁ state at 2 ×205.47 nm and the 3p'¹F₃ state at 2 ×203.5 nm, and the O(³P_J) fragments using (2+1) REMPI via the P_J states around 2 ×∼200 nm. Translational energy and angular distributions are extracted from the O(¹D) and O(³P) product images. A growth in the population of highly excited vibrational levels of the NO X(²Π) co-fragment is found as the dissociation wavelength decreases. These are compared with similar trends observed previously for other triatomic O-atom containing molecules. Detailed information on the electronic angular momentum alignment of the ¹D₂ state is obtained from analysis of the polarization sensitivity of the O(¹D) images using the two resonant intermediate states. The angular dependence of the potential energy in the exit channels is examined using long-range quadrupole-dipole and quadrupole-quadrupole interaction terms, from which molecular-frame multipole moments of the total angular momentum of the recoiling O atoms have been calculated. Comparison with the experimentally derived multipole moments is used to help provide insight into the dissociation mechanism.     

Anomalous linewidths and peak-height ratios in137Ba hyperfine lines

We have investigated several effects of optical pumping in the hyperfine spectrum of the6s6p ¹ P ₁6s ^{2 1} S ₀ transition in¹³⁷Ba. Most of these effects are explained by absorption strength changes which occur because of redistribution of population among magnetic substates. At very low laser intensities, no redistribution effects are observed. At higher intensities, it is possible to either empty the magnetic substates that are accessible to optical excitation, or to redistribute the population among these states until a steady-state condition is achieved. The first case results in the familiar disappearance of a hyperfine line. The less familiar second case can result in peak-height ratios in the Ba¹ P ₁¹ S ₀ hyperfine spectrum that differ by almost a factor of three from the low-intensity case. In this second case, the observed linewidth can either broaden or narrow, depending on whether redistribution decreases or increases absorption strength. At high intensities, saturation effects dominate and branching to intermediateD states becomes apparent. We report here the result of a numerically integrated rate equation model which shows good agreement with our experiments.     

Radio-frequency laser double-resonance spectroscopy of trapped171Yb ions and determination of line shifts of the ground-state hyperfine resonance

The paper reports on radio-frequency laser double-resonance experiments on¹⁷¹Yb ions confined in a cylindrically symmetric electrodynamic trap in the presence of helium buffer gas. The optical-excitation scheme relies on the selective excitation of a cycling hyperfine component of the = 370 nm resonance transition. Additional excitation of a transition at = 935 nm prevents population trapping of ions in the metastable² F _7/2 level. Using a maser reference, the ground-state hyperfine resonance frequency is measured under conditions of a systematic variation of confinement conditions. Kinetic temperatures and the resulting relativistic resonance shifts are inferred from the inhomogeneous broadening of the optical resonance transition. Shifts of the hyperfine resonance frequency due to quadratic Stark effect and collisions are determined. By extrapolation, the unperturbed transition frequency is determined as 12 642 812 118.471 (9) Hz.     

Detection of a hexadecapole interaction in the atomic ground state3 H 6 of167Er

Using the atomic beam magnetic resonance method, precision measurements of the hyperfine structure and Zeeman interactions have been performed in the ground state 4f ¹²6s ^{2 3} H ₆ of¹⁶⁷Er. The experimental data were analyzed using an effective operator parametrized in the space of states of the ground state multiplet. It yielded eight effective hyperfine structure and Zeeman interaction constants which served to calculate the seven hyperfine separations of the ground state. The results are: $$\begin{gathered} 2F 2F' v_{FF'} (MHz) \hfill \\ 5 7 - 354.371 9409 (27) \hfill \\ 7 9 - 2{\text{78}}{\text{.231}} {\text{8263(14)}} \hfill \\ {\text{9}} 11 - 69.050 7785 (4) \hfill \\ 11 13 + 302.735 3731(12) \hfill \\ 13 15 + 866.691 3871(10) \hfill \\ 15 17 + 1,652.383 5154 (6) \hfill \\ 17 19 + 2,689.380 8050(10) \hfill \\ \end{gathered}$$ From the effective Zeeman interaction constants it was possible to determine an improvedg _I -value, uncorrected for atomic diamagnetism: $$ g_I = + 0.086 775 (19) \cdot 10^{ - 3}$$ Furthermore a hexadecapole interaction corresponding to a diagonal hexadecapole interaction constant $$A_4 = - 16 (10) Hz$$ could be established which is of the order of magnitude expected from Coulomb excitation experiments as well as theoretical calculations.     

Photoionization cross section and oscillator strength distribution in the near-threshold region of strontium

We present experimentally measured absolute values of the photoionization cross sections from the 5s5p ¹P₁ and 5s5p ³P₁ excited states of strontium at the first ionization threshold as 11.4±1.8 Mb and 10.7±1.7 Mb respectively using saturated absorption technique along with a thermionic diode ion detector in conjunction with a Nd:YAG pumped dye laser system. These threshold photoionization cross sections values have been utilized to determine the oscillator strengths of the 5s5p ¹P₁↦5snd ¹D₂ and 5s5p ³P₁↦5snd ³D₂ Rydberg transitions. The oscillator strength densities in the continuum corresponding to the 5s5p ³P₁ excited state have also been determined by measuring the photoionization cross sections at five ionizing wavelengths above the first ionization threshold. Smooth merging of the discrete f-values into the oscillator strength densities has been observed for the 5s5p ³P₁↦5snd ³D₂ series across the ionization threshold.     

Hyperfine quenching of the 4s4p <Superscript>3</Superscript>P<Subscript>0</Subscript> level in Zn-like ions

In this paper, we used the multiconfiguration Dirac-Fock method to compute with high precision the influence of the hyperfine interaction on the [Ar] P₀ level lifetime in Zn-like ions for stable and some quasi-stable isotopes of nonzero nuclear spin between Z=30 and Z=92. The influence of this interaction on the [Ar] P P₀ separation energy is also calculated for the same ions.     

Tails of the dynamical structure factor of 1D spinless fermions beyond the Tomonaga approximation

We consider one-dimensional (1D) interacting spinless fermions with a non-linear spectrum in a clean quantum wire (non-linear bosonization). We compute diagrammatically the 1D dynamical structure factor, S(ω,q), beyond the Tomonaga approximation focusing on it's tails, |ω| ≫vq, i.e. the 2-pair excitation continuum due to forward scattering. Our methodology reveals three classes of diagrams: two “chiral” classes which bring divergent contributions in the limits ω→±vq, i.e. near the single-pair excitation continuum, and a “mixed” class (so-called Aslamasov-Larkin or Altshuler-Shklovskii type diagrams) which is crucial for the f-sum rule to be satisfied. We relate our approach to the T=0 ones present in the literature. We also consider the case and show that the 2-pair excitation continuum dominates the single-pair one in the range: |q|T/k_F ≪ω±vq ≪T (substantial for q ≪k_F). As applications we first derive the small-momentum optical conductivity due to forward scattering: σ∼1/ω for T ≪ω and σ∼T/ω² for T ≫ω. Next, within the 2-pair excitation continuum, we show that the attenuation rate of a coherent mode of dispersion Ω_q crosses over from , e.g. γ_q ∼|q|³ for an acoustic mode, to , independent of Ω_q, as temperature increases. Finally, we show that the 2-pair excitation continuum yields subleading curvature corrections to the electron-electron scattering rate: , where V is the dimensionless strength of the interaction.