Magnetic Field Effects on the 1083 nm Atomic Line of Helium. Optical Pumping of Helium and Optical Polarisation Measurement in High Magnetic Field

The structure of the excited $2^{3}$S and $2^{3}$P triplet states of $^{3}$He and $^{4}$He in an applied magnetic field B is studied using different approximations of the atomic Hamiltonian. All optical transitions (line positions and intensities) of the 1083 nm $2^{3}$S-$2^{3}$P transition are computed as a function of B. The effect of metastability exchange collisions between atoms in the ground state and in the $2^{3}$S metastable state is studied, and rate equations are derived, for the populations these states in the general case of an isotopic mixture in an arbitrary field B. It is shown that the usual spin-temperature description remains valid. A simple optical pumping model based on these rate equations is used to study the B-dependence of the population couplings which result from the exchange collisions. Simple spectroscopy measurements are performed using a single-frequency laser diode on the 1083 nm transition. The accuracy of frequency scans and of measurements of transition intensities is studied. Systematic experimental verifications are made for B=0 to 1.5 T. Optical pumping effects resulting from hyperfine decoupling in high field are observed to be in good agreement with the predictions of the simple model. Based on adequately chosen absorption measurements at 1083 nm, a general optical method to measure the nuclear polarisation of the atoms in the ground state in an arbitrary field is described. It is demonstrated at $B\sim$0.1 T, a field for which the usual optical methods could not operate.Comment: 33 pages, 31 figures, 17 tables, 61 references. Revised version (typos corrected, figure 11 replaced by the proper one) Accepted for publication in EPJ

Alfred Kastler's inspiration of the optical pumping studies in Poland

Optical pumping activity in Poland is reviewed with particular emphasis on Professor Kastler's inspiration in its development. The reviewed activity concerns studies of relaxation, modulation effects, level crossing and anticrossing effects, dressed atom model and of the forward scattering of resonance radiation

Flexible Optical Dipole Mirror for Cold Atoms

A flexible and relatively simple and cheap optical dipole mirror for cold rubidium atoms from magneto-optical trap is described, being a very modern and efficient tool for atomic physicists. Emphasis is put on physical processes responsible for the mirror parameters and their optimization. Promising perspectives are provided for evanescent wave properties investigation and atom-surface interaction measurements

Zeeman Effect Observed in the Evanescent Wave

We have observed a Zeeman effect in an evanescent wave absorption in Rb vapor with a single-mode tunable diode laser. The spectra are obtained for several magnetic field- and laser light-configurations enabling the observation of different pi and sigma Zeeman split lines contribution. The relative amplitudes and relative frequencies of all Zeeman components were calculated theoretically and compared with measured spectra. The analysis of the data can lead to the determination of the polarization state of the evanescent wave

Zeeman Effect Observed in the Evanescent Wave

We have observed a Zeeman effect in an evanescent wave absorption in Rb vapor with a single-mode tunable diode laser. The spectra are obtained for several magnetic field- and laser light-configurations enabling the observation of different pi and sigma Zeeman split lines contribution. The relative amplitudes and relative frequencies of all Zeeman components were calculated theoretically and compared with measured spectra. The analysis of the data can lead to the determination of the polarization state of the evanescent wave

Magnetic Resonance Imaging at Low Magnetic Field Using Hyperpolarized 3

A low magnetic field magnetic resonance imaging system for small animal lung imaging using hyperpolarized $\text{}^{3}$He gas is presented. The hyperpolarized $\text{}^{3}$He gas at 1 mbar pressure and 30% polarization is obtained by the metastability exchange optical pumping technique. The magnetic resonance imaging unit is based on a permanent magnet of open geometry, built from a new generation Nd-B-Fe magnetic material. It produces the magnetic field of 88 mT with homogeneity better than 50 ppm in the 10 cm diameter sphere, after application of passive shimming. The magnetic field gradients of 30 mT/m are generated by a set of biplanar, actively shielded gradient coils. The first $\text{}^{1}$H images of various biological objects, as well as $\text{}^{3}$He images of the rat lung in vivo obtained in the described system are shown. In terms of sensitivity and resolution, the technique is superior to conventional $\text{}^{1}$H magnetic resonance imaging, and offers great possibilities in early diagnosis of lung diseases

Spectroscopic issues in optical polarization of

The Magnetic Resonance Imaging (MRI) of human lungs for diagnostic purposes became possible by using nuclear spin hyperpolarized noble gases, such as 3He. One of the methods to polarize 3He is the Metastability Exchange Optical Pumping (MEOP), which up to now has been performed at low pressure of about 1 mbar and in low magnetic field below 0.1 T (standard conditions). The equilibrium nuclear polarization can reach up to 80%, but it is dramatically reduced during the subsequent gas compression to the atmospheric pressure that is necessary for the lungs examination. Further polarization losses occur during the transportation of the gas to the hospital scanner. It was shown recently that up to 50% polarization can be obtained at elevated pressure exceeding 20 mbar, by using magnetic field higher than 0.1 T (nonstandard conditions). Therefore, following the construction of the low-field MEOP polarizer located in the lab, a dedicated portable unit was developed, which uses the magnetic field of the 1.5 T MR medical scanner and works in the continuous-flow regime. The first in Poland MRI images of human lungs in vivo were obtained on the upgraded to 3He resonance frequency Siemens Sonata medical scanner. An evident improvement in the image quality was achieved when using the new technique. The paper shows how spectroscopic measurements of 3He carried out in various experimental conditions led both to useful practical results and to significant progress in understanding fundamental processes taking place during MEOP

Magnetic Resonance Imaging at Low Magnetic Field Using Hyperpolarized 3\text{}^{3}He Gas

A low magnetic field magnetic resonance imaging system for small animal lung imaging using hyperpolarized $\text{}^{3}$He gas is presented. The hyperpolarized $\text{}^{3}$He gas at 1 mbar pressure and 30% polarization is obtained by the metastability exchange optical pumping technique. The magnetic resonance imaging unit is based on a permanent magnet of open geometry, built from a new generation Nd-B-Fe magnetic material. It produces the magnetic field of 88 mT with homogeneity better than 50 ppm in the 10 cm diameter sphere, after application of passive shimming. The magnetic field gradients of 30 mT/m are generated by a set of biplanar, actively shielded gradient coils. The first $\text{}^{1}$H images of various biological objects, as well as $\text{}^{3}$He images of the rat lung in vivo obtained in the described system are shown. In terms of sensitivity and resolution, the technique is superior to conventional $\text{}^{1}$H magnetic resonance imaging, and offers great possibilities in early diagnosis of lung diseases

Flattening of the spatial laser beam profile with low losses and minimal beam divergence

International audienceA new type of Nd:YAG laser is described that uses two spatial filters that are placed against the mirrors in the focal planes of a converging lens (Fourier planes). With the appropriate filters, we experimentally obtained a uniphase beam with a flat spatial profile and minimal beam divergence in the free-running regime