Nuclear spin relaxation of $^{131}\mathrm{Xe}$ produced by collisions of the xenon atoms with the walls of the experimental cell has been studied. The xenon nuclear ensemble is polarized through spin-exchange collisions with an optically oriented rubidium vapor. Depolarization of the $^{131}\mathrm{Xe}$ ensemble in the wall collisions is assumed to be due to the quadrupole coupling between the $^{131}\mathrm{Xe}$ nucleus and the electric field gradients which appear at the nucleus during collisions of the atoms with the cell walls. Model equations describing the nuclear relaxation are derived and estimates of the electric field gradients are given.Nuclear spin relaxation of $^{131}\mathrm{Xe}$ produced by collisions of the xenon atoms with the walls of the experimental cell has been studied. The xenon nuclear ensemble is polarized through spin-exchange collisions with an optically oriented rubidium vapor. Depolarization of the $^{131}\mathrm{Xe}$ ensemble in the wall collisions is assumed to be due to the quadrupole coupling between the $^{131}\mathrm{Xe}$ nucleus and the electric field gradients which appear at the nucleus during collisions of the atoms with the cell walls. Model equations describing the nuclear relaxation are derived and estimates of the electric field gradients are given.

Physical Review AOct 1, 198160 citations

Analytic Expressions for Transient Signals in the Optical Pumping of Alkali-Metal Vapors

F. A. Franz, C. E. Sooriamoorthi

Rate equations for the optical pumping of alkali-metal vapors simultaneously subject to pumping, relaxation in the excited state, and relaxation in the ground state are shown to yield analytic solutions for the alkali-metal electronic and nuclear-spin polarizations in the limit of weak pumping. Nuclear-spin and hyperfine-interaction effects are properly included. Analysis of the double-exponential form of the pumping transient of the ground-state electronic-spin polarization is shown to yield new methods for the measurement of cross sections for collisional relaxation in both the ground and excited states. Formulas are derived that relate relaxation cross sections to experimentally measurable parameters. Formulas describing the influence of nuclear spin on signals obtained from standard depolarization of resonance-radiation experiments also are provided. Ambiguities in earlier optical-pumping experiments and calculations arising from oversimplified descriptions of relaxation processes are discussed.Rate equations for the optical pumping of alkali-metal vapors simultaneously subject to pumping, relaxation in the excited state, and relaxation in the ground state are shown to yield analytic solutions for the alkali-metal electronic and nuclear-spin polarizations in the limit of weak pumping. Nuclear-spin and hyperfine-interaction effects are properly included. Analysis of the double-exponential form of the pumping transient of the ground-state electronic-spin polarization is shown to yield new methods for the measurement of cross sections for collisional relaxation in both the ground and excited states. Formulas are derived that relate relaxation cross sections to experimentally measurable parameters. Formulas describing the influence of nuclear spin on signals obtained from standard depolarization of resonance-radiation experiments also are provided. Ambiguities in earlier optical-pumping experiments and calculations arising from oversimplified descriptions of relaxation processes are discussed.

Physical Review ANov 1, 197330 citations

Ruby NMR laser: A phenomenon of spontaneous self-organization of a nuclear spin system

Peter Boesiger, Ernst Brun, D. Meier

Radio wave amplification by stimulated emission of radiation (NMR laser) was observed in ${\mathrm{Al}}_{2}$ ${\mathrm{O}}_{3}$ : ${\mathrm{Cr}}^{3+}$ (ruby) with the $^{27}\mathrm{Al}$ spin system pumped to an inverted Zeeman state by means of dynamic nuclear polarization (DNP) and with an LC circuit tuned to the NMR transitions. A theory is developed which combines standard Bloch equations with the dynamic equations of a heat-reservoir model for the spin dynamics. Experimental data concerning the relaxation and polarization mechanisms in the nonradiant state are presented, and the parameters of the reservoir model are determined. In accord with these results, dynamic NMR laser equations for different modes of operation (continuous or pulsed) are derived from which the threshold of the NMR laser, its critical behavior near threshold, and its transient response after $Q$ -switch tuning can be calculated. The agreement between theory and experiments in the superradiant state reflects unambiguously the interplay between nuclear-spin relaxation, DNP, spin fluctuations, and the self-induced ordering of the $^{27}\mathrm{Al}$ spins perpendicular to the applied field. In particular, the results highlight the decisive role of the electronic dipole-dipole system in the spin and NMR laser dynamics of ruby. Special emphasis is placed on the close relationship between the NMR laser, as a system far from thermal equilibrium which shows the phenomenon of cooperative self-organization, and a system at thermal equilibrium which undergoes a second-order phase transition. Thus, the rotating nuclear-spin magnetization is treated as an order parameter.Radio wave amplification by stimulated emission of radiation (NMR laser) was observed in ${\mathrm{Al}}_{2}$${\mathrm{O}}_{3}$: ${\mathrm{Cr}}^{3+}$ (ruby) with the $^{27}\mathrm{Al}$ spin system pumped to an inverted Zeeman state by means of dynamic nuclear polarization (DNP) and with an LC circuit tuned to the NMR transitions. A theory is developed which combines standard Bloch equations with the dynamic equations of a heat-reservoir model for the spin dynamics. Experimental data concerning the relaxation and polarization mechanisms in the nonradiant state are presented, and the parameters of the reservoir model are determined. In accord with these results, dynamic NMR laser equations for different modes of operation (continuous or pulsed) are derived from which the threshold of the NMR laser, its critical behavior near threshold, and its transient response after $Q$-switch tuning can be calculated. The agreement between theory and experiments in the superradiant state reflects unambiguously the interplay between nuclear-spin relaxation, DNP, spin fluctuations, and the self-induced ordering of the $^{27}\mathrm{Al}$ spins perpendicular to the applied field. In particular, the results highlight the decisive role of the electronic dipole-dipole system in the spin and NMR laser dynamics of ruby. Special emphasis is placed on the close relationship between the NMR laser, as a system far from thermal equilibrium which shows the phenomenon of cooperative self-organization, and a system at thermal equilibrium which undergoes a second-order phase transition. Thus, the rotating nuclear-spin magnetization is treated as an order parameter.

Physical Review AAug 1, 197846 citations

Nuclear spin relaxation of

^{131}\mathrm{Xe}

produced by collisions of the xenon atoms with the walls of the experimental cell has been studied. The xenon nuclear ensemble is polarized through spin-exchange collisions with an optically oriented rubidium vapor. Depolarization of the

^{131}\mathrm{Xe}

ensemble in the wall collisions is assumed to be due to the quadrupole coupling between the

^{131}\mathrm{Xe}

nucleus and the electric field gradients which appear at the nucleus during collisions of the atoms with the cell walls. Model equations describing the nuclear relaxation are derived and estimates of the electric field gradients are given.

Radio wave amplification by stimulated emission of radiation (NMR laser) was observed in

{\mathrm{Al}}_{2}

{\mathrm{O}}_{3}

{\mathrm{Cr}}^{3+}

(ruby) with the

^{27}\mathrm{Al}

spin system pumped to an inverted Zeeman state by means of dynamic nuclear polarization (DNP) and with an LC circuit tuned to the NMR transitions. A theory is developed which combines standard Bloch equations with the dynamic equations of a heat-reservoir model for the spin dynamics. Experimental data concerning the relaxation and polarization mechanisms in the nonradiant state are presented, and the parameters of the reservoir model are determined. In accord with these results, dynamic NMR laser equations for different modes of operation (continuous or pulsed) are derived from which the threshold of the NMR laser, its critical behavior near threshold, and its transient response after

Q

-switch tuning can be calculated. The agreement between theory and experiments in the superradiant state reflects unambiguously the interplay between nuclear-spin relaxation, DNP, spin fluctuations, and the self-induced ordering of the

^{27}\mathrm{Al}

spins perpendicular to the applied field. In particular, the results highlight the decisive role of the electronic dipole-dipole system in the spin and NMR laser dynamics of ruby. Special emphasis is placed on the close relationship between the NMR laser, as a system far from thermal equilibrium which shows the phenomenon of cooperative self-organization, and a system at thermal equilibrium which undergoes a second-order phase transition. Thus, the rotating nuclear-spin magnetization is treated as an order parameter.