EXPERIMENTS ON NONLINEAR SPIN OSCILLATIONS IN A RAREFIED QUANTUM GAS: SPIN POLARIZED ATOMIC HYDROGEN.

The results are presented of studies on spin polarized atomic hydrogen in the fully nonlinear regime and, in particular, on the evolution of the pulsed magnetic resonance frequency spectrum which results as the system is disturbed increasingly far from equilibrium. Numerical simulations of reduced dimensionality based on the fully nonlinear equations are compared with the experimental results and show good qualitative agreement. The spectra indicate the presence of at least one mode which is not observed in the linear spectrum in addition to a tipping angle dependence of the frequency and damping of all observed modes. Here the tipping angle is a measure of the nonlinearity of the disturbance. This system is both novel and unique from a variety of viewpoints: the gas remains in kinetic equilibrium throughout the experiment, having a typical kinetic temperature of 0. 4 K. Most nonlinear phenomena are associated with highly correlated and often very dense systems, whereas the system is very dilute, having typical densities of 10**1**6 atoms/cc and a mean free path of 0. 2 mm. The nonlinearity arises from purely quantum mechanical single-particle exchange effects which induce correlated behavior in the gas through collisions even though the relevant Hamiltonian is spin-independent.

EXPERIMENTS ON NONLINEAR SPIN OSCILLATIONS IN A RAREFIED QUANTUM GAS: SPIN POLARIZED ATOMIC HYDROGEN. Conference Paper