石川 潔

The pseudopotentials and dispersion potentials are applied to a theoretical study of the hyperfine splitting frequencies of the ground-state paramagnetic hydrogen (H) and alkali-metal (Li, Na, K, Rb, and Cs) atoms in noble gases (He, Ne, Ar, Kr, and Xe). Using classical turning points for statistical averages, we find that numerical calculations based on second-order perturbation theory fit the measured frequency shifts well over a wide temperature range. The characteristic energy, pseudopotential height, and electric-dipole polarizability allow us to consistently determine the van der Waals radii and electron scattering lengths of noble-gas atoms. This study shows that the hyperfine splitting frequency of alkali-metal atoms is a good measure for investigating colliding partners.

Theoretical pseudopotentials and dispersion potentials are used to study ground-state hyperfine splitting frequencies of alkali-metal atoms (Li, Na, K, Rb, and Cs) in noble gases (He, Ne, Ar, Kr, and Xe) in all combinations. With a single fitting parameter, calculations based on first-order perturbation theory qualitatively present each temperature dependence of the measured frequency shift. With this parameter and excitation energies of alkali-metal and noble-gas atoms, the hyperfine splitting frequency of alkali-metal atoms is suitable for investigating the properties of noble-gas atoms, such as the s-wave scattering length of electrons, the electric-dipole polarizability, and the van der Waals radius. This study suggests the possibility of improving excitation energies and van der Waals potentials of colliding pairs.

<jats:p> We report an experimental and theoretical study on the shift of the hyperfine splitting frequency of ground-state Li atoms in noble gases, He, Ne, Ar, and Xe. The frequency shift is due to the change in the electron-spin density at the Li nuclei induced by collisions to the noble-gas atoms. The electron density is calculated along the interatomic distance in a pseudopotential and a dispersion potential. Based on the measured and the calculated frequency shifts, we find the importance of attractive force in collisions to helium as well as heavy noble-gas atoms. Taking advantage of the simple energy structure of the Li atom, we obtain the s wave scattering length for free electrons on noble-gas atoms by using the hyperfine splitting frequency as a precise measure. </jats:p>

Characteristics of a diffusion-bonded sapphire cell for optical experiments with hot metal vapors were investigated. The sapphire cell consisted of sapphire-crystal plates and a borosilicate-glass tube, which were bonded to each other by diffusion bonding without any binders or glues. The glass tube was attached to a vacuum manifold using the standard method applied in glass processing, filled with a small amount of Rb metal by chasing with a torch, and then sealed. The cell was baked at high temperatures, and optical experiments were then performed using rubidium atoms at room temperature. The sapphire cell was found to be vacuum tight, at least up to 350°C, and the sapphire walls remained clear over all temperatures. From the optical experiments, the generation of a background gas was indicated after baking at 200°C. The background gas pressure was low enough to avoid pressure broadening of absorption lines but high enough to cause velocity-changing collisions of Rb atoms. The generated gas pressure decreased at higher temperatures, probably due to chemical reactions.

The alkali partial pressures of composite alkali-metal vapor are crucial in atomic-physics optical experiments. The vapor pressures of alkali-metal binary alloys can be calculated by using the activity and the mixing enthalpy for homogeneous alloys from early measurements. We show that the results of sodium-containing alloys deviate appreciably from the prediction of Raoult's law. Experimentally, the phase and the mixing ratio of binary alloys are non-destructively measured by nuclear-magnetic-resonance spectroscopy in glass cells. We find that many droplets of the sodium-rubidium alloy exist on the cell walls, and they have different mixing ratios. Therefore, the vapor density varies microscopically around the glass cells. To achieve precision optical measurements, we should take account of the pressure change due to the equilibrium process and further sodium contamination over the lifetime of glass cells.

We use nuclear magnetic resonance spectroscopy of alkali metals sealed in glass vapor cells to perform in situ identification of chemical contaminants. The alkali Knight shift varies with the concentration of the impurity, which in turn varies with temperature as the alloy composition changes along the liquidus curve. Intentional addition of a known impurity validates this approach and reveals that sodium is often an intrinsic contaminant in cells filled with distilled, high-purity rubidium or cesium. Measurements of the Knight shift of the binary Rb-Na alloy confirm prior measurements of the shift's linear dependence on Na concentration, but similar measurements for the Cs-Na system demonstrate an unexpected nonlinear dependence of the Knight shift on the molar ratio. This non-destructive approach allows monitoring and quantification of ongoing chemical processes within the kind of vapor cells which form the basis for precise sensors and atomic frequency standards. Published by AIP Publishing.

We report diffusion coefficients of optically pumped lithium atoms in helium buffer gas. The free-induction decay and the spin-echo signals of ground-state atoms were optically detected in an external magnetic field with the addition of field gradient. Lithium hot vapor was produced in a borosilicate-glass cell at a temperature between 290 and 360 degrees C. The simple setup using the glass cells enabled lithium atomic spectroscopy in a similar way to other alkali-metal atoms and study of the collisional properties of lithium atoms in a hot-vapor phase.

The diamagnetic Faraday rotation of broadband vacuum ultraviolet light was investigated for the xenon gas of thermal nuclear-spin polarization. The smaller and blue-shifted signals were observed due to the molecular absorption at the high xenon-gas pressure. For a dilute xenon gas, the rotation signals were measured in the buffer gas up to 30 kPa. The pressure broadening of atomic line was obtained from the measurements and the calculations of signal amplitude with various pressures of helium gas. Based on the observed diamagnetic rotation, the nuclear paramagnetic Faraday rotation was estimated for spin polarized xenon gas. (C) 2015 Elsevier B.V. All rights reserved.

ガラス容器内の熱い気体原子を分光する際,容器内壁における原子のスピン状態の緩和が,分光計測の精度や感度を低下させる.そのため,壁で電子や核のスピンダイナミクスを妨げずに原子を反射するような緩和防止膜が研究されている.一方,表面において原子の状態が変化するので,反作用として,衝突相手である壁のスピン状態も変化するはずだ.しかし,壁はマクロな環境であり,その反作用を調べるのは難しい.これまでは,反射した偏極原子の状態を観測し,表面をうかがい知るのみだった.最近,表面膜材料の核磁気共鳴により,原子がスピン偏極を表面に移す現象を発見した.以来,表面におけるスピン偏極の注入を調べ,超偏極物質の生成を試みている.一般に,核磁気共鳴では熱平衡状態にある非常に小さなスピン偏極率の核スピン集団を観測する.その微弱な信号を飛躍的に増大させるため,物質を核スピン偏極させる手法が数多く開発されている.その中でも,光の角運動量を使う方法は低温を必要とせず,熱い物質をスピン偏極できる.光ポンピングの難しい物質には,あらかじめ光でスピン偏極した物質から,スピン相互作用により角運動量を移すことも可能だ.このスピン交換光ポンピングの例として,超偏極希ガスがある.核スピン偏極率が高いので,偏極標的として基礎物理実験に供され,磁気共鳴画像診断の造影剤や磁力計に応用される.本稿では,これに類似の,原子が物体表面に接触したときのスピン偏極の移行を紹介する.レーザー光により希薄な原子気体をスピン偏極し,液体や固体と接触させると,表面をとおし,これら凝縮体がスピン偏極する.圧倒的な数差にも関わらず,凝縮体の核スピン集団が偏極するのは,スピン源となる気体原子集団に,常に光から角運動量が供給されるからである.実験では,電子のゼーマン分裂が原子内のスピン結合(電子と核の超微細相互作用)より大きくなる磁場で,ガラス容器中のセシウム原子を光励起する.スピン偏極原子は,気体中を拡散運動しながら,セシウム塩表面に達し,価電子を放出,イオンになる.表面では,結晶のイオンと入れ替わるか,同種核間のスピン交換で偏極を結晶に移すことにより,角運動量を注入する.数秒間光を照射すれば,セシウム塩にスピン角運動量が蓄積(セシウム核がスピン偏極)するので,その核磁気共鳴信号を観測する.結晶だけでなく,溶融塩やガラスにもスピン注入できる.知る人ぞ知る,とても単純な実験だ.重要な要素は,原子の高磁場光ポンピング,表面におけるスピン偏極注入,物質内のスピン拡散である.残念なことに,原子の偏極電子がスピン注入に関与しない.そのため,異種核へ偏極移行するような汎用性はなく,気体原子と凝縮系イオンは同種核でなければならない.特徴は,スピン注入するので,表面強調の磁気共鳴計測が可能なことである.その結果,表面でも核スピン偏極が長生きすることがわかった.これまで仮定してきた気体に対するスピンの境界条件(壁において熱平衡状態)を見直す必要がある.さらに,角運動量を担うイオン自身が,核スピン偏極を失わずに埋め込まれるのにも驚いた-四重極緩和につながる電子軌道の歪は生じないのか?スピン緩和時間の短い液体の方が,偏極率が高くなる-結晶表面の液体薄膜の存在がスピン注入に重要か?このように,新たな知見が得られるほど,疑問が湧きあがる.結晶中のスピン偏極イオンが角運動量を輸送するので,イオンの移動度の大きな超イオン伝導体を使えば,スピン輸送という応用が期待できる.

Nuclear spin polarization of cesium ions in the salt was enhanced during optical pumping of cesium vapor at high magnetic field. Significant motional narrowing and frequency shift of NMR signals were observed by intense laser heating of the salt. When the hyperpolarized salt was cooled by blocking the heating laser, the signal width and frequency changed during cooling and presented the phase transition from liquid to solid. Hence, we find that the signal enhancement is mostly due to the molten salt and nuclear spin polarization is injected into the salt efficiently in the liquid phase. We also show that optical pumping similarly induces line narrowing in the solid phase. The use of powdered salt provided an increase in effective surface area and signal amplitude without glass wool in the glass cells. (C) 2015 Author(s).

Hyperpolarized (HP) Cs-133 nuclear magnetic resonance signals were measured from borosilicate glass cell walls during optical pumping of cesium vapor at high magnetic field (9.4 T). Significant signal enhancements were observed when additional heating of the cell wall was provided by intense but non-resonant laser irradiation, with integrated HP Cs-133 NMR signals and line widths varying as a function of heating laser power (and hence glass temperature). Given that virtually no Cs ions would originally be present in the glass, absorbed HP Cs atoms rarely met thermally-polarized Cs ions already at the surface; thus, spinex-change via nuclear dipole interaction cannot be the primary mechanism for injecting spin polarization into the glass. Instead, it is concluded that the absorption and transport of HP atoms into the glass material itself is the dominant mechanism of nuclear spin injection at high temperatures-the first reported experimental demonstration of such a mechanism. (C) 2014 Elsevier Inc. All rights reserved.

We report the hyperpolarisation of caesium salts by spin transfer of atomic nuclear polarisation. Glass wool is used in our experiments for increasing the surface area of the salt which is in contact with the atomic vapour. In spite of being randomly scattered in the wool, the pumping of light using a narrow-band laser tuned to a single atomic transition in high magnetic field helped polarise the atoms. The heating due to the intense laser irradiation increased the ion mobility leading to better transport of the polarised caesium ions. The diffusive motion of the caesium ions transported the spin angular momentum, greatly enhancing the nuclear polarisation in the salt. As a result of using both pumping and heating lasers, we succeeded in polarising the bulk and not just the surface. These experiments show that the glass wool which served as a test bed for hybrid experiments using laser excitation and NMR detection was useful for the NMR study of a solid and its surface in a random scattering medium. (C) 2013 Elsevier Inc. All rights reserved.

Hyperpolarization of Cs-133 nuclei in CsCl salt is achieved through spin transfer from an optically pumped Cs vapor, with maximum polarizations of 0.1% demonstrated. Motional narrowing of the enhanced NMR line indicates that ion movement facilitates this process by transporting spin-polarized ions from the interface into the salt. The resulting NMR enhancement allows measurement of the polarization and its dynamics in real time. Based upon the NMR frequency and the longitudinal spin relaxation time, we find no evidence that the salt is contaminated by Cs metal or paramagnetic impurities. The Cs nuclear polarization reported here could be improved several orders of magnitude by intense laser heating of the entire sample.

Optically pumped alkali-metal atomic magnetometers are expected to be used not only for biomagnetic field measurements but also for magnetic resonance imaging because of their potential ultrahigh sensitivity. Here, we studied magnetic field mapping and biaxial vector operation using atomic magnetometers. A potassium atomic magnetometer was used in these measurements. First, we obtained sensor output signals by solving the Bloch equation. Next, we measured magnetic field distributions generated by a current dipole electrode that was placed in a spherical phantom, which simulated a group of simultaneously activated neurons in the human brain.We obtained vector contour maps of the magnetic field distributions from the dipoles oriented parallel and orthogonal to the pump laser beam and have found good agreement with theoretical magnetic field distributions. These results demonstrate practical applications of magnetic field mapping and biaxial vector operation using optically pumped atomic magnetometers. © 2011 The Japan Society of Applied Physics.

The spin angular momentum accumulates in the Cs nuclei of salt on contact with optically pumped Cs vapor. The spin polarization in stable chloride as well as dissociative hydride indicates that nuclear dipole interaction works in spin transferring with a lesser role of atom exchange. In the solid film, not only the spin buildup but also the decay of enhanced polarization is faster than the thermal recovery rate for the bulk salt. Eliminating the signal of thick salt, we find that the nuclear spin polarization in the chloride film reaches over 100 times the thermal equilibrium.

The nuclear spin polarization of optically pumped Cs atoms flows to the surface of Cs hydride in a vapor cell. A fine glass wool lightly coated with the salt helps greatly increase the surface area in contact with the pumped atoms and enhance the spin polarization of the salt nuclei. Even though the glass wool randomly scatters the pump light, the atomic vapor can be polarized with unpolarized light in a magnetic field. The measured enhancement in the salt enables study of the polarizations of light and atomic nuclei very near the salt surface.

Optical pumping of alkali-metal atoms in vapor cells causes spin currents to flow to the cell walls where excess angular momentum accumulates in the wall nuclei. Experiments reported here indicate that the substantial enhancement of the nuclear-spin polarization of salts at the cell walls is primarily due to the nuclear-spin current, with a lesser contribution from the electron-spin current of the vapor.

We developed a highly sensitive optically pumped atomic magnetometer for measuring biomagnetic fields from the human body noninvasively. The sensor head was a cubic Pyrex glass cell containing potassium metal and buffer gases. A pump laser beam for spin-polarizing potassium atoms and a probe laser beam for detecting magneto-optical rotation crossed at right angles in the cell, which was heated in an oven to vaporize potassium atoms. The sensitivity of the magnetometer reached to 10100 $\\hbox{fT/Hz}^{1/2}$ at frequencies below several hundred hertz. To test system performance, we made a phantom which models the human brain, taking into account the contribution of distributed electric currents. First, we tested the phantom by a 306-channel whole-head MEG system and confirmed good agreement of the measured field distributions with theoretical calculations. Subsequently, we measured magnetic field distribution with the phantom scanning two-dimensionally above the oven. The signal source location was estimated by least squares fitting to the measured distribution. The goodness of fit value between the measured and the theoretical distributions was 97.9%. © 2006 IEEE.

We report NMR measurements of metallic Cs-133 in glass cells. The solid-liquid phase transition was studied by observing the NMR peaks arising from these two phases; surprisingly, many cells yielded two additional NMR peaks below the melting point. We attribute these signals to two distinct impurities which can dissolve in the liquid alkali metal and affect its chemical shift. Intentional contamination of cesium cells with O-2 confirms this hypothesis for one peak. The other contaminant remains unknown but can appear in evacuated cells. Similar effects have been seen in Rb-87 cells.

We report enhancement of the spin polarization of Cs-133 nuclei in CsH salt by spin transfer from an optically pumped cesium vapor. The nuclear polarization was 4.0 times the equilibrium polarization at 9.4 T and 137 degrees C, with larger enhancements at lower fields. This work is the first demonstration of spin transfer from a polarized alkali vapor to the nuclei of a solid, opening up new possibilities for research in hyperpolarized materials.

We measured the spin relaxation of polarized xenon atoms dissolved in deuterated ethanol. Surface relaxation was suppressed by coating the cell walls with deuterated eicosane. From the dependence of the decay rate on temperature and static magnetic field, we obtained the correlation time of random fluctuations of the local field at the liquid-solid interface. By varying the cell volume, the wall coating, and the surface area of the eicosane, we measured the contribution of the spin-rotation interaction to the relaxation. The use of both deuterated molecules enables us to distinguish surface relaxation from the magnetic dipole-dipole and spin-rotation interactions in solution. (c) 2005 Elsevier Inc. All rights reserved.

A mode-locked laser has been introduced in combination with synchrotron radiation to establish a versatile technique for highly time-resolved correlation measurements utilizing the short-pulse and high-pulse frequency characteristics of both photon sources. Successive pulse timing delay detected by nonlinear optical mixing between the two sources yields a cross-correlation profile capable of accurate measurement of the picosecond pulse profile of the synchrotron radiation without any synchronization control. Although the experiment was performed in the visible spectral domain, the present technique opens up a methodology for time-resolved spectroscopy in femtosecond and higher-energy domains by introducing a suitable nonlinear process that informs of the pulse coincidence between the two radiation sources. © 2005 International Union of Crystallography Printed in Great Britain - all rights reserved.

A simple method for single-shot sub-picosecond optical pulse diagnostics has been demonstrated by imaging the time evolution of the optical mixing onto the beam cross section of the sum-frequency wave when the interrogating pulse passes over the tested pulse in the mixing crystal as a result of the combined effect of group-velocity difference and walk-off beam propagation. A high linearity of the time-to-space projection is deduced from the process solely dependent upon the spatial uniformity of the refractive indices. A snap profile of the accidental coincidence between asynchronous pulses from separate mode-locked lasers has been detected, which demonstrates the single-shot ability. © 2005 The Japan Society of Applied Physics.

We measured a spin relaxation of polarized xenon atoms in deuterated ethanol. The decay behavior depends on the magnetic dipole interaction and the electric quadrupole relaxation of deuterons. Though the cross-relaxation rate of deuteron with xenon was much less than that of proton, the enhancement of deuteron signal could be observed since the detection was performed at low magnetic fields. We define the figure of merit for a spin reservoir of solvent as the result of intensive investigation of the temperature dependence of decay rates and the solubility of xenon atoms in ethanol. For the long-term storage of a large number of polarized xenon atoms, it is important to take into account the viscosity of solvent which affects the translational motion as well as the decay time. By a time-resolved chemical-shift imaging, we observed the xenon atom acquiring its homogeneous distribution in viscous ethanol at low temperatures.

Impulsive optical spin orientation has been observed directly by a pick-up-coil detection in copper (II)-acetate in water, acetic acid, and solids. Difference in the dependences of the signal intensity and relaxation time on the excitation polarization, external magnetic field, and temperature reveals two origins of the optical spin orientation: one due to angular-momentum transfer from a circularly polarized light and the other from the photo-creation of a Zeeman-mixed state under the external magnetic field. © 2004 Elsevier B.V. All rights reserved.

We detect the free-induction signals of xenon atoms polarized by spin-exchange optical pumping. The temperature dependence of dissolution and spin-polarization transfer of xenon atoms to ethanol is measured by simultaneous detection of both xenon and proton signals. The polarization of proton is efficiently enhanced in the xenon-saturated solution at low magnetic fields. The large polarization and chemical shift enable us to obtain clearly the distribution image of xenon atoms near the gas-liquid and liquid-liquid boundaries. Therefore the localization of polarized xenon atoms is observed near the surface. By time-resolved magnetic resonance imaging of polarized xenon and polarization-enhanced proton, the spin dynamics is qualitatively studied for the nuclear spins interacting with each other in a dense solution. (C) 2004 American Institute of Physics.

We observed the free-induction decays in the ground state of Cs atoms in a thin glass cell. The line narrowing of magnetic resonance is theoretically and experimentally presented as a function of the time interval between the pump and probe pulses. The atoms moving parallel to the windows are found to have long-lived polarization and coherence. The above phenomena are characteristic of the vacuum cell in contrast to those of the buffer gas cell.

We measured the diffusion coefficient of Rb atoms in Nz buffer gas by the constant-gradient spin-echo method. At a temperature of 60 degreesC, our measured diffusion coefficient is D-o=0.159 cm(2)/s, which is consistent with values found from polarization decay. We report also the tipping angle dependence of the phase-relaxation time of Rb atoms at high density.

We perform optical magnetic-resonance (MR) imaging of Cs atoms that are polarized by the transfer fi om the polarized Xe or Rb atoms in a glass cell, as well as by direct optical pumping. With MR images of Cs by alternate optical pumping and detection the distribution of polarized Xe or ph of low gas pressure is observed in a weak magnetic field. We also discuss the effect of the spin-relaxation and the spin-exchange collisions between Cs, Xe, and Rb atoms on the spatial resolution of MR images of the diffusing Cs atoms. (C) 2000 Optical Society of America [S0740-3224(00)01302-3].

We have succeeded in magneto-optical trapping of Yb atoms decelerated by a Zeeman slower method. The number of the trapped atoms is more than about 1.3x10(6) measured by light absorption. We have found the evidence of the branching from the P-1(1) excited state to triplet states, and determined the lower limit on the branching ratio to be 1.2x10(-7). [S1050-2947(99)51002-0].

Optical magnetic-resonance imaging (MRI) is performed to observe a density distribution of the laser-polarized Cs atoms that diffuse in helium buffer gas at roughly room temperature. Spatial resolution of optical MRI and sensitivity of optical detection are discussed for gaseous atoms in a weak magnetic field. We propose a fast method of three-dimensional optical MRI with parallel processing of signals from a photodetector array, and we discuss its application to the spin-polarized noble gas. (C) 1999 Optical Society of America. [S0740-3224(99)02001-9]. OCIS codes: 100.6950, 110.6960, 110.0180.

The excitation, emission spectra, and decay curves of the emission intensity of thulium atoms implanted in liquid and solid helium were observed in the presence and absence of an external magnetic field. The observed narrow line (width (Formula presented) nm) of the excitation spectrum at 590.60 nm is assigned as a zero-phonon transition from the electronic ground state (Formula presented), which indicates that the transition between the inner shells is weakly perturbed by surrounding helium atoms. The pressure dependence of the emission wavelength suggests that the symmetry of helium atoms distributed around a thulium atom in the solid phase is similar to that in the liquid phase. The emission intensity was stable and large in the solid phase since thulium atoms were trapped at a density of 10(Formula presented)-10(Formula presented) atoms/cm(Formula presented). The lifetime of the excited state was measured to be (Formula presented)s, which was longer than that of the (Formula presented) state of free thulium atoms. The excited state is expected to be a mixed state of the (Formula presented) and (Formula presented) configurations. The metastable state (Formula presented) is populated by a radiative transition from this excited state and relaxes to the ground state through a magnetic dipole transition. The lifetime of the metastable state of a neutral thulium atom was measured to be (Formula presented) ms. © 1997 The American Physical Society.

Applicability of the Bloch equations for describing relaxation in the saturation regime is studied experimentally and theoretically. Hole burning in the proton NMR line of water was observed, and the shape and width of the hole were investigated in a well-characterized noise field. The behavior of power broadening is remarkably different from that expected from the Bloch equations and strongly depends on the correlation time of the noise field. The hole shape is not a single Lorentzian. The experimental results are well explained by a stochastic theory of power broadening. We show that the hole burning in well-characterized noise fields is very useful for the experimental test of power-broadening theories.

An experimental approach for the verification of relaxation theories is presented. Spectral hole burning in the proton NMR line in water was observed, and the hole shape was investigated in well-characterized noise fields. Motional narrowing of the hole shape is demonstrated. Power broadening of the hole shape was observed, and a violation of the Bloch equations in the saturation regime is studied.