Exchange currents in electric transitions and the rôle of siegert's theorem: A case study in deuteron photodisintegration

The hyperfine structure (hfs) splittings of the metastable 1s2s ³ S ₁ state of⁷Li⁺ have been measured with combined laser optical pumping and microwave resonance. A lowenergy Li⁺ ion beam, optically excited by an intersecting laser beam, passed a waveguide where radio frequency transitions were induced. The resulting population transfer among the hfs levels of the³ S ₁ was detected via the change in intensity of the fluorescence light from a second crossing region of laser light and ion beam located past the waveguide. The magnetic hfs constantA(⁷Li⁺, 1s2s ³S₁) was measured and compared with theory. A deviation of the two transition frequenciesν(F=3/2?F=5/2) andν(F=1/2?F=3/2) from the interval rule is due to a depression of theF=3/2 hfs sublevel, caused by mixing of the 2³ S ₁ and 2¹ S ₀ states via hyperfine interaction. This shift was never observed so far in a two-electron spectrum, because of absence ofI>1/2 isotopes in He, the only two-electron atom investigated spectroscopically with high precision. The size of the shift is in fair agreement with a theoretical estimate.     

Investigation of the hyperfine structure of electronic levels in chromium atom

Measurements of the hyperfine structure (hfs) of electronic levels of the chromium atom were performed using two spectroscopic methods. For 7 energy levels (3 even parity and 4 odd parity) the magnetic dipole and electric quadrupole hyperfine interaction constants A and B were determined for the first time. In this case the method of laser induced fluorescence (LIF) on an atomic beam was used. The low lying metastable levels belonging to the term 3d⁴4s² a⁵D were remeasured by the method of laser-rf double resonance on an atomic beam (ABMR-LIRF). To improve the accuracy of hyperfine splittings measurements, the stability of the radio frequnecy (rf) generator was increased by the use of a frequency standard synchronized by a GPS signal. The values of the hfs intervals for these levels were determined with the accuracy of a few kHz. The improvement in accuracy enabled an estimation of the octupole-coupling constant C.     

Zur Rumpfpolarisation des Rb-Atoms: Hyperfeinstruktur des 72 P 1/2-Terms von Rb85

The hyperfine structure splitting of the 7² P _1/2 state of Rb⁸⁵ has been investigated with optical double resonance spectroscopy. The results are:v _F=3?F=2=52.95(6) Mc/s,A _J=1/2=17.65(2) Mc/s,g _J (7² P _1/2, Rb)=0.6668(1). From the hfs interaction constants of the 7² P multiplett a 12% core polarization contribution to the magnetic hfs of the 7² P _3/2 state can be deduced. Comparison is made between the values of 〈r ^?3〉 calculated from either the magnetic hfs or the² P fine structure separation.     

Collinear laser spectroscopy on108g, 108m In using an ion source with bunched beam release

The hyperfine structure and isotope shift of^108gIn and^108mIn have been investigated by means of collinear fast-beam laser spectroscopy in the resonance line atλ=451 nm. The indium isotopes were prepared at the GSI on-line mass separator following a fusion evaporation reaction. For the first time, a FEBIAD ion source with bunched release of indium was used. Magnetic dipole moments, electric quadrupole moments and isotope shifts were determined. The present results lead us to assign the spinI=2 to the¹⁰⁸In (T _1/2=40 min) state. Spins and moments are discussed in the framework of thejj-coupling model.     

ABMR-Ramsey patterns of strongly field dependent transitions of lithium at high magnetic fields

Using the atomic beam magnetic resonance method we observed Ramsey patterns of strongly field dependent transitions of Li, Na and Rb at high magnetic fields. The structures were of high symmetry, with half widths of the central minimums between 20 kHz and 6 kHz. In a first experiment we determined theg _J -factor ratiog _J (⁶Li)/g _J (⁷Li)=1+3(70)·10^?10.     

Precision measurement of the hyperfine structure of Lu175 with the atomic beam magnetic resonance method

The hyperfine structure separations of both doublet states² D _3/2 and² D _5/2 of the ground state configuration 6s ² 5d of Lu¹⁷⁵ have been remeasured with high precision using the atomic beam magnetic resonance method. Magnetic dipole transitions between Zeeman components of the hfs levels were induced applying Ramsey's technique of separated oscillatory fields whenever the field dependence of the resonances was small enough. The hfs intervals at zero field and hfs interaction constants were derived from the measurements. The constants were then corrected for hfs perturbations between the two levels of the doublet. Configuration interaction has been taken into account for the calculation of the dipole matrix elements. The corrected hfs constants are:J=3/2:A=194.332921 (300) MHzB=1511.396 267 (320) MHzC=?70 (19) HzJ=5/2:A=146.776 472 (138) MHzB=1860.656132 (840) MHzC=913 (162) HzD=?16 (24) Hz A quadrupole hfs anomaly between Lu¹⁷⁵ and Lu^176m was not found when comparing the following two ratios: Lu¹⁷⁵:B(5/2)/B(3/2)=1.2310850 (16) Lu^176m :B(5/2)/B(3/2)=1.2310818 (30). So far we have not succeeded in computing an octopole moment from the twoC-factors for the terms² D _3/2,5/2 because the influence of higher configurations could not sufficiently be considered.     

Precision measurement of two iodine lines at 585 nm and 549 nm

The transition frequencies of thei-component of the R(99)15-1 and thew-component of the R(85)26-0 transition in the B-X system of molecular¹²⁷I₂ have been determined with an overall relative standard uncertainty of 1.3 · 10^?10. For this purpose a commercial linear dye laser has been modified and stabilized to the corresponding iodine line. This dye laser serves as a transportable frequency standard which is compared with the wavelength standards of the PTB. The evaluation of an experiment for testing special relativity at the test storage ring (TSR) in Heidelberg is based on the precision of the reported interferometric wavelength comparison.     

Formation of periodic surface nanostructures on Ti:Al2O3 crystals using femtosecond laser pulses

Periodic surface nanostructures are observed on Ti³⁺:Al₂O₃ single crystals that have been irradiated by a single focused beam from a femtosecond pulsed laser (wavelength: 800 nm; pulse duration: 130 and 152 fs). Atomic force microscopy images of single-ablated zones and modified structures created by fixing and translating samples through the focal region of a linearly polarized laser beam reveal self-organized periodic surface nanostructures (ripples) with a subwavelength spacing, which are oriented perpendicular to the electric-field vector of the laser beam. The period of the subwavelength ripples obtained by linearly polarized laser irradiation varies from ∼λ/5 to 2λ/5 (λ: incident laser wavelength) depending on the laser pulse energy. This phenomenon can be explained by assuming that the incident light field interferes with the electric field of electron plasma waves propagating inside the material; this interference periodically modulates the electron plasma density and modifies the surface ablation. In addition, for the first time, we observe screw-shaped nanostructures in the focal spot of circularly polarized beam irradiation. The morphology of these nanostructures appears to reflect the circular polarization of the laser light.     

Application of the light-shift effect to laser frequency stabilization with reference to a microwave frequency standard

A new method allowing laser frequency stabilization with reference to a microwave oscillator, independently of the laser intensity, is described. The method makes use of the dependence of the ground-state hfs transition frequency on the optical radiation frequency in alkali atoms irradiated by quasi-resonant light. Preliminary experimental investigations are reported in the case of a cw GaAs diode laser tuned to the D₂ absorption line in a cesium gas cell. The absolute laser frequency exhibited variations of 1.4 MHz r.m.s. around an average value determined to within 2 parts in 10¹⁰ for a period of 5 minutes. The possibility of defining a cesium beam, reference wavelength connected with the time standard is discussed.     

Coherent signal beam amplification in two-wave mixing experiments with photorefractive Bi12SiO20 crystals

The amplification of the input signal beam in two-wave mixing experiments with photorefractive Bi₁₂SiO₂₀ crystals is achieved when an additional phase shift is established between the photoinduced index modulation (phase volume hologram) and the incident fringe pattern. This stationary phase shift is introduced by either moving the crystal or the interference fringes at a constant speed. The transferred intensity is measured versus the applied electric field, fringe spacing and crystal velocity. The crystallographic orientation and the relative displacement with respect to the applied electric field polarity determine the amplitude of the energy transfer. For the first time in this crystal, signal beam amplification is reached for an applied field E₀ > 8 kV cm^?1 and a crystal or fringe displacement speed around 5 μm s^?1 at the green line (λ = 514 nm) of an argon laser.     

High resolution Zeeman spectroscopy on the neon levels 2s 2 and 2p 4 by mode crossing at high magnetic fields

Mode crossing signals in laser intensity occur if the Zeeman splitting of one laser level equals the frequency separation between two laser modes. This kind of experiment using two optical frequencies for double resonance yields high resolution in Zeeman spectroscopy and allows very accurate determination ofg _J -values. Mode crossing dips of the 0.633μ, 1.152μ and 1.523μ transitions of the He-Ne-laser in an axial magnetic field were measured by tuning the field strength up to 0.17 Tesla. At this field strength the Zeeman splitting of the Dopplerbroadenedσ-lines corresponds to approximately 6 Gcps. The frequency separation between resonant modes was controlled by means of a scanning high resolution Fabry-Perot. The experimental results for theg _J -values areg _J =1.2211±0.002 for the Ne 2s ₂ level andg _J =1.3008±0.002 for the Ne 2p ₄ level. A pressure inducedg _J -shift of aboutΔg _J /(g _J ×p _He)=?1.6×10^?3/Torr for the 2p ₄ level has been observed. The influence of helium collisions disturbing the Zeeman splitting of the 2p ₄ state is discussed.     

Iodine hyperfine structure and absolute frequency measurements at 565, 576, and 585 nm

The hyperfine structure splittings of the P(10)14-1, R(15)14-1, and R(99)15-1 transitions at 585 nm, P(62)17-1 at 576 nm, and P(80)21-1 at 565 nm in ¹²⁷I₂ are measured by heterodyne spectroscopy using two dye lasers. In addition, the absolute frequencies of the hyperfine components P(10)14-1 a₁₅ and P(80)21-1 a₁₀ are determined using a self-referenced frequency comb. These frequencies are used in an experiment testing relativistic time dilation by laser spectroscopy on a fast ion beam.     

Hyperfine structure in optical spectra of LiYF4-Ho

We report high resolution infrared absorption spectra of LiYF₄-Ho exhibiting well resolved nuclear hyperfine structure (hfs). The halfwidths of some hfs components do not exceed 0.03 cm^?1. Magnetic field at the nucleus is evaluated. Non-radiative relaxation rates due to phonon emission are estimated. With the help of experimentally found 〈Γ₃|J_z|Γ₃〉 matrix elements g-factors of the excited crystal field levels are calculated. Some hfs peculiarities are discussed.     

Bestimmung derg J-Faktoren in den Zuständen 62 P 3/2 und 82 P 3/2 von133Cs

The hyperfine structures of the 6² P _3/2- and 8² P _3/2-states of¹³³Cs have been investigated by optical double resonance in a strong magnetic field. The Landé-g-factors and the hfs coupling constants were found to be:g _J(6² P _3/2)=1.3340(3)g _J(8² P _3/2)=1.3342(2)a(6² P _3/2)=50.02(25) MHza(8² P _3/2)=7.644(25) MHz. Contrarily to recent measurements, theg _J-factors agree well with the value calculated from the Landé formula.     

Radiative decay ofJ/ψ into γ π+ π−

The radiative decayJ/ψ → γ π⁺ π^? has been studied using the 8.6 millionJ/ψ produced in the DM2 experiment at the DCIe ⁺e^? storage rings at Orsay. The π⁺ π^? mass spectrum shows a cleanf ₂ (1270) signal, and the possible presence of two other states at thef ₂ (1720) andf ₄ (2030) masses. For thef ₂ (1270), the branching ratio BR(J/ψ →γf)xBR(f→π⁺ π^?) is measured to be (7.50±0.30±1.12)×10^?4, and the spin analysis prefers theJ=2 assignment, with helicity parametersx=0.83±0.06 andy=0.01±0.06. The existence of higher mass states is discussed.     

Beat frequency intercomparisons of127I2 stabilized ion lasers at 514.5 nm

International comparisons of I₂ stabilized ion lasers operated at 514.5 nm have shown a laser frequency reproducibility of 2·10⁻¹⁰ v to 5·10⁻¹² v. These results encouraged the international acceptance of the wavelength value λ_vac=514.673467 for thea ₃ hyperfine component of the¹²⁷I₂ line 43-0P(13).     

A multichannel Raman spectrometry study of polyacetylene isomerization induced by laser irradiation

The multichannel Raman spectrometry has been used in the study of the isomerization reaction of an 80% cis PA film into a trans PA, using a laser beam for a double purpose. It is employed simultaneously as an activation agent inducing the isomerization reaction and the Raman diffusion. In each experience, the power of the laser beam Pⁱ(λ) was equivalent to the temperature. Twelve spectra have been recorded at different time periods tj = j·dt. The integrations of the Raman intensities related to two selected bands were numerically calculated.We also proposed an original method for the determination of the isomeric composition. A quantitative relationship between the equilibrium temperature and the laser beam power (in the range of laser power: 30 < Pⁱ(λ) < 300 mW) has been found. An estimate number of isomerized molecules N₀ and then a correction factors f_cis and f_trans were also obtained.     

Method to investigate the symmetry of saturated absorption signals by means of laser frequency locking techniques

It is shown that the line shape of a saturated absorption signal — especially its symmetry — can be investigated by combining laser frequency locking methods. The laser frequencyv, modulated with a frequencyf, is stabilized alternatively to the zero crossings of the synchronously detected 2f and 3f absorption signals. In addition, almost any other part of the profile can be tested by locking the laser frequency to neighboruing points of the zero crossings by using an offset technique. With two prestabilized Ar⁺ lasers atv=582 THz the symmetry of different¹²⁷ I ₂ hfs signals was investigated with an uncertainty of typically 2×10^–12 v or 10^–3 halfwidths.     

Hyperfeinstrukturuntersuchungen mit einem sphärischen Fabry-Perot-Interferometer mit internem Absorptionsatomstrahl im Tm I- und Eu I-Spektrum

A spherical Fabry-Perot spectrometer with an absorbing atomic beam passing the interior of the interferometer is described. By use of the internal beam it is possible to reduce the amount of material needed for the atomic beam source to a few milligrams per hour. The set-up is especially suitable for hyperfine structure and isotope shift investigations. For the photoelectric recording of the signal the geometrical distance between the spherical mirrors was changed using the piezoelectric effect. In order to reduce the influence of the intensity distribution of the light sourceI ₀(λ) the ratio [I ₀(λ)-I(λ)]/I ₀(λ) was measured, whereI ₀(λ)=I ₀(λ) exp (—V·k(λ)·d) is the observed intensity with absorbing atoms between the mirrors, andV the increase of the absorption signal due to the multiple reflections of the light through the atomic beam (V≈75). For an accurate and easy evaluation of the data this ratio was measured by a digital voltmeter and punched into paper tape. The small line width of the absorption profile obtained in the experiments with Tm and Eu enabled us to measure hyperfine distances of the order of 5 · 10^?3 cm^?1 to 20 · 10^?3 cm^?1 with an error not exceeding 0.1 · 10^?3 cm^?1 in some cases. From the measurements theA-factors for five levels of the configurations 4f ¹³6s 6p and 4f ¹²5d 6s ² in Tm I and theA- andB-factors of the stable Eu isotopes of the 4f ⁷ 6s 6p y ⁸ P _5/2level in Eu I were determined.