Laser spectroscopy and optical pumping of alkali atoms in superfluid helium

In this paper, our recent works on the alkali atoms in superfluid helim (HeII) are reported. At first we mentions the laser-sputtering method for implantation, which is simple but is very efficient to produce various kinds of neutral atoms and molecules in HeII. Secondly, we report on the laser spectroscopy of alkali atoms in HeII. Optical excitation and emission spectra are found to be roughly explained by a spherical atomic bubble model, but the spectra corresponding to the D₂ lines indicate the quadrupole oscillation of the bubble shape. Optical pumping by a circularly polarized laser beam is found to produce perfect polarization, for both electron and nuclear spins. Using the rf-optical double resonance techniques, the magnetic and hyperfine resonances are observed. It is discussed also about the phenomena which have observed in the experiments done so far but have not been fully explained.     

High-resolution spectroscopy with and frequency stabilization of a cw dye laser

The hyperfine splittings of the Na D₁ and D₂ lines were investigated using a single mode cw dye laser. The light of the laser was scattered by the atoms of an atomic beam and the fluorescent light was observed as the frequency of the laser was tuned across the D lines. The Doppler width of the atomic beam was reduced to about 2.5 MHz so that the absorption width of the atoms of the beam was essentially determined by the natural width of the 3²P_1/2 and 3²P_3/2 levels, which is about 10 MHz. Since the linewidth observed for the hyperfine transitions was 30 MHz, most of the hyperfine components of the D₁ and D₂ lines could be resolved. In another experiment the frequency of the dye laser was locked to a hyperfine transition of the D₁ line. The observed variation of the output frequency of the dye laser was less than ±1.5 MHz. In addition, the intensity of the dye laser was controlled to about 10⁻³, using an electro-optically variable transmission filter.     

Eine Quelle für polarisierte Lithiumkerne

A source for nuclear polarized lithium-6 and -7 ions was built following the method of separation of the atomic hyperfine states in a strong inhomogeneous magnetic sextupole field and ionisation of the selected atoms by electron bombardment in a weak homogeneous field. The velocity distribution of the atomic beam formed by a Laval nozzle and the focussing properties of the sextupole magnet were determined using a mechanical velocity selector. After separation of the two isotopes the ion beam has an intensity of 10^?9 ampere. As no background of unpolarized lithium ions was found, a vector polarisation of (32±1)% and (24±1)% for lithium-6 and -7 and a tensor polarisation of (?32±1)% for lithium-6 can be expected.     

PRODUCTION OF POLARIZED 7Li ATOMIC BEAM IN STRONG MAGNETIC FIELD BY OPTICAL PUMPING

The production of a polarized ⁷Li atomic beam in a strong magnetic field was experimentally studied by laser optical pumping of a single ground hyperfine F level. It was shown that nearly complete negative and partial positive polarizations of ⁷Li atoms could be realized under appropriate conditions by this pumping scheme, which was in agreement with the rate equation calculations. Based on the analyses of transition probabilities, the maximum polarizations for various transitions and light polarizations were given.     

Theory of the polarization of highly charged ions in storage rings: Production, preservation, observation and application to the search for a violation of the fundamental symmetries

Theoretical concepts for the production, preservation and control of polarized highly charged ion beams in storage rings are investigated. It is argued that hydrogen-like ions can be polarized efficiently by optical pumping of the Zeeman sublevels of ground state hyperfine levels and that the maximum achievable nuclear polarization exceeds 90%. In order to study the preservation of the polarization during the ion motion through the magnetic system of the ring, the concept of the instantaneous quantization axis is introduced. It is suggested that the employment of “Siberian snakes” may help to preserve the ion beam polarization in the ring. The control of the beam polarization can be achieved by different methods: by measuring the Stokes parameters for the emitted photons or by observing the angular dependence of the transition rates for polarized ions. The important motivation for the production of polarized ion beams is the possibility to observe parity nonconservation effects in the hyperfine-quenched transitions in helium-like highly charged ions, where these effects can reach an unprecedented high value for atomic physics. The possible observation of parity nonconservation effects connected with the nuclear anapole moment is also discussed. A method for the observation of the electric dipole moment of an electron in a storage ring with a polarized highly charged ion beam is proposed. This method allows, in principle, to improve the existing boundaries for the electric dipole moment of an electron. However, the requirements of the corresponding experiment are very stringent.     

PRODUCTION OF POLARIZED 7Li ATOMIC BEAM IN STRONG MAGNETIC FIELD BY OPTICAL PUMPING

The production of a polarized ⁷Li atomic beam in a strong magnetic field was experimentally studied by laser optical pumping of a single ground hyperfine F level. It was shown that nearly complete negative and partial positive polarizations of ⁷Li atoms could be realized under appropriate conditions by this pumping scheme, which was in agreement with the rate equation calculations. Based on the analyses of transition probabilities, the maximum polarizations for various transitions and light polarizations were given.     

Studying the regime of complete decoupling of the bond between the electron and nuclear moments at the <Emphasis Type="Italic">D</Emphasis><Subscript>1</Subscript>-line of the <Superscript>39</Superscript>K potassium isotope using a spectroscopic microcell

Atomic transitions of the ³⁹K potassium isotope in strong (up to 1 kG) longitudinal and transverse magnetic fields have been studied with a high spectral resolution. It has been shown that crossover resonances are almost absent in the saturated absorption spectrum of potassium vapors in a 30-μm-thick microcell. This, together with the small spectral width of atomic transitions (~30 MHz), allows one to use the saturated absorption spectrum for determining frequencies and probabilities of individual transitions. Among the alkali metals, potassium atoms have the smallest magnitude of the hyperfine splitting of the lower level. This allows one to observe the break of the coupling between the electronic and nuclear angular momentums at comparatively low magnetic fields B > 500 G, i.e., to implement the hyperfine Paschen–Back regime (HPB). In the HPB regime, four equidistantly positioned transitions with the same amplitude are detected in circularly polarized light (σ⁺). In linearly polarized light (π) at the transverse orientation of the magnetic field, the spectrum consists of eight lines which are grouped in two groups each of which consists of four lines. Each group has a special distinguished G-transition and the transition that is forbidden in the zero magnetic field. In the HPB regime, the probabilities of transitions in a group and derivatives of their frequency shifts with respect to the magnetic field asymptotically tend to magnitudes that are typical for the aforesaid distinguished G-transition. Some practical applications for the used microcell are mentioned.     

铯原子7S1/2态磁偶极超精细常数的测量

在室温下的原子气室中, 基于铯原子6S_1/2-6P_3/2-7S_1/2(852.3 nm+1469.9 nm) 阶梯型能级系统, 利用电光调制器的主频和±1级边带分别产生的三套双共振吸收光谱, 当驱动电光调制器的信号源频率严格等于7S_1/2态超精细分裂的能级间隔时, 三套谱线中的一些超精细跃迁谱线重叠且线宽最窄, 利用这一现象很好地避免了激光器频率扫描时非线性效应的影响, 测量出了7S_1/2 态超精细分裂能级间隔: 2183.72 MHz±0.23 MHz, 并计算出该态的磁偶极超精细常数: A_hfs= 545.93 m MHz±0.06 MHz, 与文献中报道的测量结果一致.     

Irreducible spin precession theory applied to some topics in atomic and nuclear radio-frequency spectroscopy

Several problems from radio-frequency spectroscopy of atoms and nuclei are treated with irreducible spin precession theory. In the first part, effective field techniques are used to derive analytically single and multiple quantum double resonance lineshapes for atoms with a hyperfine structure in a high magnetic field. In the second part (as an extension to previous work), nuclear resonance signals are calculated for oriented nuclei subject to an electric hexadecapole interaction. Lineshapes of acoustically driven hexadecapole transitions are derived in closed form and compared to experiment. Further, multiple quantum NMR transitions within a hexadecapole shifted nuclear Zeeman structure are calculated, and some distinct features of hexadecapole effects on NMR lineshapes are pointed out. This last case is of current interest due to recent progress in NMR-line narrowing techniques. — In the Appendix, we give lineshape equations for single and double quantum NMR transitions on oriented (I=1)-nuclei subject to an electric quadrupole interaction; these equations are also being used in the atomic rf-spectroscopy calculations. The equations are exact to all orders of the interaction with the external fields.     

Isotope shifts and hyperfine structure in the transitions of gadolinium

High-resolution resonance ionization mass spectrometry has been used to measure isotope shifts and hyperfine structure in all (J = 2-6) and the transitions of gadolinium (Gd I). Gadolinium atoms in an atomic beam were excited with a tunable single-frequency laser in the wavelength range of 422-429 nm. Resonant excitation was followed by photoionization with the 363.8 nm line of an argon ion laser and resulting ions were mass separated and detected with a quadrupole mass spectrometer. Isotope shifts for all stable gadolinium isotopes in these transitions have been measured for the first time. Additionally, the hyperfine structure constants of the upper states have been derived for the isotopes ^{155, 157} Gd and are compared with previous work. Using prior experimental values for the mean nuclear charge radii, derived from the combination of muonic atoms and electron scattering data, field shift and specific mass shift coefficients for the investigated transitions have been determined and nuclear charge parameters for the minor isotopes ^{152, 154} Gd have been calculated. Received 18 November 1999     

Atomic beam,optogalvanic and stored ion spectroscopy for radioactive isotopes

Systematic studies of the optical isotope shift and the hyperfine splitting of long chains of stable and radioactive isotopes were performed. The method applied was laser induced resonance absorption; the experimental techniques were the atomic beam method with fluorescence detection and the optogalvanic method. The theory of hyperfine splitting and isotope shift of atoms is reviewed in short with emphasis on the aspects interesting for nuclear physics and on the evaluation problem. The experimental methods are described and their key parameters sensitivity and resolution are discussed. Preliminary results on stored thorium ions are given. Sample results for the nuclear quantity δ<r ²> derived from atomic beam experiments with tin and strontium are presented.     

Precision spectroscopy of metastable hydrogen and antihydrogen with a Lamb-shift polarimeter

A spinfilter, the most important component of a Lamb-shift polarimeter, can be used to produce a beam of metastable hydrogen (deuterium) atoms in one hyperfine state (α1, α2 and together with the Sona transition β3). As function of a magnetic field separated transitions between the 2S _1/2 metastable hyperfine states seem to be observable as well as single transitions into the short-lived 2P _1/2 and 2P _3/2 states. The Breit-Rabi diagrams for these states can be measured with good precision. Furthermore, the hyperfine splittings and the Lamb shift can be observed as well. Application of this method to anti-hydrogen atoms are suggested.     

Nuclear orientation by anisotropic collisions

The anisotropic interaction of fast ions with atoms or a solid results in an orientation of the spatial distribution of the orbital angular momenta of excited electronic levels. This orientation of the electronic shell is transfered via hyperfine (hf) interaction to the nuclei and a vector polarization of the nuclear spins is observed. Since this kind of fast beam interaction generates an anisotropy in a rather general way, this technique seems to provide a universal source for polarized ions. General concepts of this type of interaction are discussed, and the applications to produce nuclear spin polarized ions and future developments in this field are outlined.     

Antihydrogen atom formation in a CUSP trap towards spin polarized beams

The ASACUSA collaboration has been making a path to realize high precision microwave spectroscopy of ground-state hyperfine transitions of antihydrogen atom in flight for stringent test of the CPT symmetry. For this purpose, an efficient extraction of a spin polarized antihydrogen beam is essential. In 2010, we have succeeded in synthesizing our first cold antihydrogen atoms employing a CUSP trap. The CUSP trap confines antiprotons and positrons simultaneously with its axially symmetric magnetic field to form antihydrogen atoms. It is expected that antihydrogen atoms in the low-field-seeking states are preferentially focused along the cusp magnetic field axis whereas those in the high-field-seeking states are defocused, resulting in the formation of a spin-polarized antihydrogen beam.     

Nucleon form factors and the BLAST experiment

Measurements of the electric and magnetic form factors of the nucleon present a sensitive test of nucleon models and QCD-inspired theories. A precise knowledge of the neutron form factors at low Q² is also essential to reduce the systematic errors of parity violation experiments. At the MIT-Bates Linear Accelerator Center, the nucleon form factors have been measured by means of scattering of polarized electrons from vector-polarized hydrogen and deuterium. The experiment used the longitudinally polarized stored electron beam of the MIT-Bates South Hall Ring along with an isotopically pure, highly vector-polarized internal atomic hydrogen and deuterium target provided by an atomic beam source. The measurements have been carried out with the symmetric Bates Large Acceptance Spectrometer Toroid (BLAST) with enhanced neutron detection capability.     

利用原子的塞曼光谱对半导体激光器进行稳频

中性原子的超精细能级在磁场中产生塞曼分裂 ,另外 ,左旋和右旋圆偏振光激发下原子的跃迁选择定则不同 ,因此 ,原子在超精细塞曼能级间的吸收谱峰相对无磁场条件下的吸收谱峰有一定的移动。利用这一点 ,验证了一种简单、灵活的方法对半导体激光器进行稳频 ,使激光器的线宽稳到小于 1MHz。通过对实验结果的分析 ,发现由左旋和右旋圆偏振光激发引起的原子吸收谱峰移动之和与饱和吸收峰半高宽相等时 ,稳频效果最好     

Optical manipulation of nuclear spin by a two-dimensional electron gas

Conduction electrons are used to optically polarize, detect, and manipulate nuclear spin in a (110) GaAs quantum well. Using optical Larmor magnetometry, we find that nuclear spin can be polarized along or against the applied magnetic field, depending on field polarity and tilting of the sample with respect to the optical pump beam. Periodic optical excitation of the quantum-confined electron spin reveals a complete spectrum of optically induced and quadrupolar-split nuclear resonances, as well as evidence for Deltam = 2 transitions.     

On the possibility of polarizing atoms and nuclei by pulsed electromagnetic fields without using ultra-low temperatures

A method is proposed for fast and deep polarization of the system of hyperfine sublevels of the ground state of an atom having an optical excited state by means of two-component microwave pulses. The pulse of the bichromatic optical field that induces the transitions between the ground state and excited state of the atom is supposed to provide coherence among the hyperfine sublevels of the atomic ground state via the effect of coherent population trapping. The subsequent resonance microwave pulses create the polarization of equally populated ground state sublevels of the atom. The proposed polarization technique may be used for designing the new schemes of quantum computers, for the pulse transformation in optical experiments when light passes through a resonant medium containing rear-earth ions, as well as for producing polarized nuclear targets.     

Enhanced electron–ion recombination in ion storage rings

We review recent advances in the understanding of the enhanced electron–ion recombination observed in storage ring experiments. The measured recombination rates show a strong enhancement relative to what the standard radiative recombination rates predict. A transient motional electric field is induced in the merging region of an electron and an ion beam in the electron cooler. This induced field opens an additional pathway for free-bound transitions of electrons. The formed Rydberg states can be radiatively stabilized and contribute to the measured rate. We show that this “field induced recombination” (FIR) explains the gap previously observed between measurements and the standard radiative recombination rate.     

射频驱动精细结构能级跃迁引起的非线性效应

研究了射频驱动精细结构能级跃迁引起的电磁诱导透明（EIT）和电磁诱导吸收（EIA）的转化。通过采用射频场同时驱动激发态和基态精细结构能级跃迁,使系统中出现EIT和EIA。研究结果表明,调谐射频场频率从与基态精细结构能级共振到与激发态精细结构能级共振的过程中,EIT和EIA相互转化,而且射频场的拉比频率取值不同,EIT和EIA的变化规律也不同。