27 research outputs found
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 S and P triplet states of He
and 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 S-P transition are
computed as a function of B. The effect of metastability exchange collisions
between atoms in the ground state and in the 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 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
Metastability exchange optical pumping of 3He gas up to hundreds of millibars at 4.7 Tesla
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 He gas is presented. The hyperpolarized 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 H images of various biological objects, as well as 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 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 He Gas
A low magnetic field magnetic resonance imaging system for small animal lung imaging using hyperpolarized He gas is presented. The hyperpolarized 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 H images of various biological objects, as well as 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 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