The synthesis of 2-amino-7-(β-D-ribofuranosyl)pyrrolo[2,3-d]-pyrimidin-4-one (7-deazaguanosine), a nucleoside Q and Q* analog

The synthesis of 2-amino-7-(β-D-riholuranosyl)pyrrolo[2,3-d ]pyrimidin-4-one (7-deazaguanos-ine, a nucleoside Q and Q* analog, has been accomplished hy two independcnl routes.     

Interferometric, modulation-free laser stabilization

We demonstrate novel modulation-free frequency locking of a diode laser, utilizing a simple Sagnac interferometer to create an error signal from saturated-absorption spectroscopy. The interference condition at the output of the Sagnac is strongly affected by the sharp dispersion feature near an atomic resonance. Slight misalignment of the interferometer and subsequent spatially selective, or tilt, detection allows this phase change to be converted into an error signal. Tilt locking has significant advantages over previously described methods, as it requires only a small number of low-cost optical components and a detector. In addition, the system has the potential to be constructed as a plug-and-play fiber-coupled monolithic device to provide submegahertz stability for lasers in the commercial market.     

Stability of continuously pumped atom lasers

A multimode model of a continuously pumped atom laser is shown to be unstable below a critical value of the scattering length. Above the critical scattering length, the atom laser reaches a steady state, the stability of which increases with pumping. Below this limit the laser does not reach a steady state. This instability results from the competition between gain and loss for the excited states of the lasing mode. It will determine a fundamental limit for the linewidth of an atom laser beam.