Optical Pumping Experiments Research Articles

Observation of 201Hg NMR spectra for solid K2Hg(CN)4

AbstractThe first observation of 201Hg NMR signals in the solid state is reported for potassium tetracyanomercurate(II), K2Hg(CN)4. NMR measurements of 201Hg and 199Hg were carried out at 4.70, 7.05 and 9.40 T. The ratio between the observed NMR frequency for 201Hg and 119Hg yields an accurate value for the ratio of their magnetogyric ratios, |γ(201Hg)/γ(199Hg) | = 0.369 1389(9). This value agrees well with that obtained from optical pumping experiments on mercury vapor in the gas phase. The 201Hg NMR line shapes observed for solid K2Hg(CN)4 are Lorentzian owing to efficient relaxation via the quadrupolar mechanism. In contrast, the corresponding 199Hg NMR line shapes are Gaussian and much narrower.

Two- and three-grating resonators for high-power pulsed CO_2 lasers

Development of broadly tunable narrow-linewidth CO(2) lasers is critical to the continued development of tunable far-infrared Raman lasers and could also improve many other optical pumping experiments. Here we extend the use of multiple intracavity gratings, a widely used dye laser technique, to multiatmosphere continuously tunable CO(2) lasers. We analyze the angular dispersion, wavelength tuning performance, and grating size requirements for several different grating configurations. Experimentally, by double passing each of two gratings worked near grazing incidence in a three-mirror 10-atm laser resonator, we have produced approximately 200-mJ pulses with < 600-MHz linewidth, and our analysis shows that operation in a single longitudinal mode (SLM) should be possible at somewhat reduced output levels. The simpler experimental task of producing SLM operation in a two-grating CO(2) transversely excited atmospheric laser has also been accomplished.

4He optical pumping with polarization modulated light

In optical pumping experiments using a laser, beam polarization can be changed easily with the help of an electro-optic device. High frequency modulation of a LNA laser beam polarization has been used to pump 4He (2 3S 1) metastable atoms. New resonances, never observed before, have been studied theoretically and experimentally, and application to high sensitivity magnetometers is suggested.

Picosecond photoluminescence excitation spectroscopy of GaAs/AlGaAs quantum wells

A synchronous pair of pulsed dye lasers is used to obtain continuous photoexcitation energy spectra of quantum well luminescence at fixed time delays following carrier generation, with picosecond time resolution. A measurement of the energy-dependent initial luminescence polarization of photoexcited carriers in GaAs/AlGaAs quantum wells, from a pulsed optical pumping experiment, is presented as an illustration of the technique.

Optical properties of CdTe/ Cd1- xZnxTe quantum wells and superlattices

MBE growth of high-quality CdTe/ Cd 1- x Zn x Te single quantum wells and superlattices with x=0.08−0.15, on Cd 0.96 Zn 0.04 Te substrates, is described. Due to lattice-parameter mismatch, the different layers are strained, and these strains predominate in determining the valence-band discontinuity at the CdTe/ Cd 1- x Zn x Te interfaces. Deformation potentials for CdTe are determined from optical spectra of strained CdTe layers. Optical properties of excitons in single quantum wells are described, emphasizing methods for identifying the different transitions (optical pumping experiments) and the nature of the quantized exciton states observed (centre-of-mass quantization versus separate-carrier quantization). Oscillator strengths for excitons in CdTe layers and quantum wells are determined as a function of layer thickness from transmission measurements. A high quality superlattice shows both direct (Type I) heavy-hole and indirect (Type II) light-hole exciton transitions; for this sample the 2s excited state of the heavy exciton is identified by its diamagnetic shift and the band offsets are deduced directly from the energies of direct and indirect transitions.

Optically driven spin nutations in the ground state of atomic sodium.

We report detailed studies of the dynamic response of spin coherence to a step input of optically resonant narrow-band laser radiation in the presence of a static transverse magnetic field. The evolution of the spins is observed with a cw optical probe beam using polarization-selective detection of the transmitted light. In extension of previous optical-pumping experiments, the dynamics of the system are studied systematically as a function of optical-resonance detuning and intensity. Our experiments are performed on the 3s $^{2}S_{1/2}$ ground state of sodium, using the ${D}_{1}$ line for optical excitation. The experimental data are compared with theoretical predictions based on a Bloch-type equation of motion for an optically driven spin system in a J=(1/2 ground state.

Optical pumping of helium-3 with a frequency electromodulated laser

We have operated an electrooptical modulator to generate sidebands to the laser used for optical pumping of a helium-3 gas. Spreading the laser power over the Doppler absorption profile of the metastable helium atoms can enhance the efficiency of the optical pumping process. This improvement is discussed in terms of velocity changing collisions and compared to the result of a velocity selective optical pumping experiment.

Optical study of residual strains in CdTe and ZnTe layers grown by molecular beam epitaxy on GaAs

Residual strains in (001) and (111) thick layers of CdTe and ZnTe grown by molecular beam epitaxy on nominal or slightly tilted (001) GaAs have been investigated by reflectance, photoluminescence, and optical pumping experiments at low temperature. Strains are found to be independent of both layer orientations and thicknesses in the range 2–6 μm. They are compressive ≊−0.5×10−3 in CdTe and tensile ≊10−3 in ZnTe. Estimates of thermal expansion effects show that they are the dominant cause of residual strains in these heterostructures.

Electron-polarised photon coincidence experiments on the 32P state in sodium

Components of the Stokes vector have been measured using an electron-photon coincidence technique for radiation emitted normal to the scattering plane in the electron excitation of the 32P state in sodium at several energies from 5.1 to 30 eV. The coherence of the excitation process is probed through the concept of the reduced polarisation. The data are compared with those derived from optical pumping experiments, which are the time-reversed equivalent of the present experiments. In general, very good agreement is found with the data from the two techniques. Scattering amplitudes derived from the components of the Stokes vector are compared with theoretical predictions. It is observed that there is only moderate agreement between theory and experiment.

Far-infrared studies of doped AlGaAs/GaAs multiple-quantum-well structures

Far infrared spectroscopic studies of MBE-grown, selectively Si-doped multiple-quantum-well (MQW) structures have been carried out between 4.2K and 70K in magnetic fields up to 9T. Magnetotransmission measurements on a sample doped both in the centers of the barriers and the centers of the wells show strong features attributed to electrons in the wells bound to their parent donor ions in the barriers. Samples doped at the edges of the wells at the two different interfaces exhibit dramatically different absorption line profiles. This provides evidence for redistribution of impurities along the growth direction on a scale of 30 – 40 A°. Optical pumping experiments on center-doped MQW samples show large excess free electron concentrations at modest pump intensities while the density of neutral donors remains unchanged. These results are interpreted in terms of the existence of substantial densities of compensating acceptor-like states. Experiments on a center-doped 450 A° well-width sample with the magnetic field in the plane of the sample (Voigt geometry) have permitted measurements of the 2p state associated with the first excited confinement subband.

The Autler-Townes effect in an optical pumping experiment

Using a laser RF double-resonance technique optical Autler-Townes splitting was observed for 23Na atoms. Despite the complicated level structure of the optical pumping scheme the main features of the data can be understood in terms of a three-level system. The interpretation of the experiment is useful in the production of highly nuclear-spin-polarised alkali-metal atomic beams by optical pumping.

Relaxation of sodium hyperfine populations in wall collisions

We report on the population relaxation of the Na ground state hyperfine levels due to Na-wall collisions. An optical pumping experiment has been performed in the Knudsen regime, monitoring the velocity distributions in both ground state hyperfine levels. It is found that the surface thermalization probability for the Na hyperfine population is 75±5% per collision of a Na atom with an uncoated pyrex surface.

Observation of quadrupole and dipole diamagnetic shifts in atomic ground-state hyperfine structure.

A high-precision laser optical-pumping experiment on the $^{2}S_{\frac{1}{2}}$ ground state of atomic rubidium in magnetic fields of up to 8 T has led to the first observation of a magnetically induced quadrupole hyperfine interaction, in both $^{85}\mathrm{Rb}$ and $^{87}\mathrm{Rb}$. The quadrupole coupling constant was measured to be 7.0(6) \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}4}$ Hz ${\mathrm{T}}^{\ensuremath{-}2}$ in $^{85}\mathrm{Rb}$. The diamagnetic shift in dipole hyperfine structure was also measured in both $^{85}\mathrm{Rb}$ and $^{87}\mathrm{Rb}$. The fractional dipole shift was found to be independent of isotope with a value $\frac{\ensuremath{\delta}a}{a}=5.2(2)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10}$ ${\mathrm{T}}^{\ensuremath{-}2}$, confirming and extending previous results for $^{85}\mathrm{Rb}$ only.

The high resolution infrared spectrum and laser Stark spectroscopy of thev 8 band of propyne

The perpendicularv8 band lying in the 1000–1100 cm−1 region has been studied from infrared and laser Stark, spectra. We were interested in the part of spectrum corresponding to the spectral range of the 9 μm CO2 laser lines. Assignments of rovibrational lines with J'<40 and K'<6 have been made. About 100 Stark resonances have been assigned to 12 rovibrational transitions. Effective molecular constants and dipole moment have been determined with high accuracy. A list of close resonances with CO2 laser lines is given and may be used for optical pumping experiments.

A NEW SENSITIVE METHOD FOR DETECTING R. F. RESONANCE IN OPTICAL PUMPING EXPERIMENT

By making use the influence of microwave-r.f. multi-quantum transition on the spectral line intensity of single quantum microwave transition, a new sensitive method for detecting r.f. resonance in optical pumping experiment is found.

Collisional relaxation of excited-state Zeeman coherences in atomic ytterbium vapor.

We present the results of an experiment designed to probe the collision-induced relaxation of excited-state Yb Zeeman coherences. Our experiment is sensitive not only to the depolarization-type relaxation mechanisms often observed in optical-pumping experiments, but also to the effects of collisionally induced velocity changes. Our measurements were performed in the 6s6p /sup 3/P/sub 1/ excited state of the even (I = 0) isotopes of gas-phase atomic Yb by means of a trilevel photon-echo technique. Depolarization rates, velocity-change spectra, and total scattering cross sections of Yb-He (Yb-Ar) collisions were measured (deduced). Both rank-1 and rank-2 spherical tensor components of the /sup 3/P/sub 1/ state play a role in our experiment, and our results represent averages of potentially different relaxation rates attributable to these quantities. Comparison of our results with rank-0 results obtained elsewhere reveals interesting similarities as well as differences.

Spectroscopy of positively charged multiple acceptors

Experimental results from far-infrared photoconductive spectroscopy of positively charged multiple acceptors in germanium, i.e. those with three or four bound holes, will be explained in terms of a theoretical model. The fundamental concept is that of the pseudo-atom, making use of pseudo-electrons with spin quantum number s= 3 2 . This allows up to four-fold occupation of the (1s)-like ground state spatial envelope function. Optical pumping and stress experiments for the case of Ge:Be demonstrate the qualitative features of the model. Satisfactory agreement is obtained for the energy levels of the positively charged double acceptors using an effective Rydberg approach. A new physical system which does not exist in isolated atoms has been studied for the first time, for which the binding of a third (or fourth) particle for Z=2 (or 3) becomes possible.

Optical pumping of stored atomic ions

Optical pumping experiments on atomic ions which are stored in ekG tromagnetic (( traps )) are discussed. Weak relaxation and extremely small energy shifts of the stored ions lead to very high resolution and accuracy in optical pumping- double resonance experiments. In the same spirit of Kastler's proposal for (( lumino refrigeration )) (1950), the kinetic energy levels of stored ions can be optically pumped. This technique, which has been called laser cooling significantly reduces Doppler frequency shifts in the spectra.

Optically pumped helium - a spin dependent probe

In the 25 years since the first optical pumping experiments in helium were reported, there have been an astonishing variety of applications. We describe briefly the use of spin-polarized helium to measure interplanetary magnetic fields, to probe spin-dependent nuclear and atomic collisions, to investigate surface properties of materials, and to study the quantum properties of a spin-polarized Fermi system.

THE MICROWAVE-RADIO FREQUENCY MULTI-QUANTUM TRANSITION IN OPTICAL PUMPING EXPERIMENT (CONTINUED)

The microwave-radio frequency multi-quantum transition in optical pumping experiment is studied for different r.f. power. The microwave-r.f. subharmonic multi-quantum trasition has also been observed.