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Annual Meeting Optical Society of America

Record nuclear polarization in optically pumped 3He gas using a high power LNA laser

N. P. Bigelow, Christian Larat, Pierre-Jean Nacher, Michèle Leduc

Published Jan 1, 1992• 0 citations

Abstract

Optical pumping is an efficient method for creating nuclear polarization M in a gas of 3He. M is first achieved in the metastable 23S state and then transfered to the ground state. Polarized 3He has numerous applications: quantum fluids, precision magnetometry, nuclear targets, etc. Much progress in achieving high values of M has resulted from the development of efficient IR lasers capable of exciting the 23S–23P3He transition at 1.08 μm. Using a novel lamp pumped LNA laser delivering 5 W cw, we have achieved M >85% for samples in the torr pressure range. To measure M we have developed an accurate technique based on the change as a function of M of the ratio between σ and π polarized light absorbed from a weak; probe beam by the 23S metastable atoms. The probe was delivered by a single mode tunable diode pumped LNA laser that was frequency modulated by using an étalon mounted on a galvoplate. M was also measured by monitoring the circular polarization of the 668 nm line emitted by the dis charge. Experimental and theoretical results on the optimization of the pumping will be presented, and the laser systems will be discussed.

DOI: 10.1364/oam.1992.tul5

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Optical pumping is an efficient method for creating nuclear polarization M in a gas of 3He. M is first achieved in the metastable 23S state and then transfered to the ground state. Polarized 3He has numerous applications: quantum fluids, precision magnetometry, nuclear targets, etc. Much progress in achieving high values of M has resulted from the development of efficient IR lasers capable of exciting the 23S–23P3He transition at 1.08 μm. Using a novel lamp pumped LNA laser delivering 5 W cw, we have achieved M >85% for samples in the torr pressure range. To measure M we have developed an accurate technique based on the change as a function of M of the ratio between σ and π polarized light absorbed from a weak; probe beam by the 23S metastable atoms. The probe was delivered by a single mode tunable diode pumped LNA laser that was frequency modulated by using an étalon mounted on a galvoplate. M was also measured by monitoring the circular polarization of the 668 nm line emitted by the dis charge. Experimental and theoretical results on the optimization of the pumping will be presented, and the laser systems will be discussed.

Diode laser optical pumping to produce a highly spin-polarized metastable He beam to be used in a spin-polarized metastable atom deexcitation spectroscopy experiment on magnetized surfaces is described. Efficient pumping of the beam is performed by means of an SDL-6702 distributed Bragg reflector diode laser which yields 50 mW of output power in a single longitudinal mode at 1083 nm, the resonance wavelength for the 23 S→23 P0,1,2 (D0, D1, and D2) transitions of He*. The light is circularly polarized by a quarter-wave plate, allowing easy change of the sense of atomic polarization. The laser frequency can be locked to the atomic transition for several hours by phase-sensitive detection of the saturated absorption signal in a He discharge cell. Any of the three transitions of the triplet system can be pumped with the laser but the maximum level of atomic polarization of 98.5% is found pumping the D2 line.

A study of the physics of a nuclear magnetic resonance gyroscope is described. Experimental results in nuclear polarization and relaxation in 3He are obtained using an optical pumping apparatus and a high resolution rf spectroscopic technique. Polarization in the metastable states of the heavy noble gases (20, 21 Ne, 129, 132 Xe) was observed using a similar optical pumping apparatus. A sensitive detection method based on optical polarization of an excited state transition is developed and compared with the conventional method of monitoring optical transmission through the optical pumping cell. A new concept for the optical pumping of odd-mass-numbered heavy noble was isotopes to provide for ground-state nuclear polarization is discussed. Significant polarization in excited state neon was observed via collisional transfer from optically pumped helium in a cell filled with a mixture of helium and neon isotopes. The measured polarization was essentially independent of the isotopic composition. (Author)

^4

He (2

^3

S

_1

) metastable atoms are optically pumped with intensity modulated light. The use of a single mode diode-pumped LNA laser as the pumping source, allows the study of resonance signals predicted by the optical pumping theory but not yet observed. Resonances are detected on the transmitted pumping beam at the modulation frequency and its harmonics. Application of this method to high sensitivity magnetometers is suggested.

The use of high-power ${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$

{\mathrm{Al}}_{\mathit{x}}

As diode laser arrays for optical pumping of Rb vapor has been examined both theoretically and experimentally. Our studies show that large atomic polarizations can be obtained using the broad spectral output of a diode laser array if the Rb resonance line is collisionally broadened by several atmospheres of a buffer gas. The objective was to study the effectiveness of diode laser arrays as light sources for optically pumped spin-exchange polarized

^{3}\mathrm{He}

targets. The average Rb polarization was deduced at three different Rb vapor pressures using the polarization induced in the

^{3}\mathrm{He}

buffer gas. The largest

^{3}\mathrm{He}

polarization observed was 53% using a 20-W diode array with 1.9-nm full width at half maximum spectral width in 10.5 amagat of

^{3}\mathrm{He}

. This result compares favorably with other light sources for this target. The measured average Rb polarizations are compared to theoretical calculations.

A polarized He{sup +} ion source based on spin conservation in Penning ionization reactions involving polarized He(2{sup 3}S) atoms contained in an optically-pumped, rf-excited helium discharge is being developed for surface studies. To optimize source performance, the He(2{sup 3}S) polarization must be determined. The authors have devised a technique for doing this that involves measuring the attenuation of a circularly-polarized probe beam provided by a 1.083 {mu}m DBR diode laser whose output frequency is scanned by varying the drive current to allow separate measurements on the 2{sup 3}S{sub 1}-2{sup 3}P{sub 0}, 2{sup 3}P{sub 1} and 2{sup 3}P{sub 2} transitions. As will be discussed, several independent expressions for the polarization (and alignment) can be derived from the experimental data thus providing valuable internal consistency checks. The technique is simple to implement and reliable in operation.