from the air we breathe
Optical pumping
Spin-Exchange Optical Pumping (SEOP) is a two stage process using lasers to polarize noble gas nuclei that requires the vapor of an alkali metal as an intermediary. Alkali metals like lithium, sodium, potassium, rubidium, and cesium are characterized by a single outer electron that is easily manipulated by lasers. In the first step of SEOP, laser light is absorbed on rubidium atoms causing them to become magnetized (the outer electron is aligned). In the second step, the electrons in the rubidium atom exert a torque on the noble gas nuclei causing them to become magnetized. The process originates with a laser beam tuned to the precise wavelength that is absorbed by a rubidium atom. By passing the laser through a crystal with its axis oriented at an angle, the laser light can be made to be circularly polarized. The electric field in the laser beam circulates in a helical pattern like a corkscrew. When rubidium vapor absorbs this light, the atoms become magnetized.
Rubidium atoms can transfer magnetization to xenon in two ways. When the rubidium and xenon gas atoms collide there is a small chance that the xenon atom becomes aligned. If the rubidium and xenon atoms temporarily form a molecule, the chance of magnetization is greater. (Helium is always polarized by the first process, collisions.)
Previous technology operated in a regime with the gas flowing through a comparatively short glass tube at high pressure, low temperature, slow flow rates, high xenon concentration. The high pressure maximized the absorption of the laser light on the rubidium vapor in the short interaction region. The low temperature maintained the rubidium density at low values, preventing it from exhausting the laser light, slow flow allowed the process to reach equilibrium, and the high xenon concentration maximized throughput. The high pressure, however, prevented molecules from living long enough to assist in the process.Our xenon technology capitalizes on the formation of molecules by operating at much lower pressure. As a consequence, we discovered that greater efficiencies could be achieved as long as the temperature was high, the xenon concentration was low, and the interaction region was long. We accomplish greater throughput by flowing at much higher velocity. This regime had previously been dismissed as inaccessible due to technical obstacles. Our patented technology overcame those obstacles and demonstrated an improvement of a factor of twenty in production rate. We recently demonstrated the next generation of the technology that allows our products to become several hundred times more productive than other methods.
