Almost all sodium laser guide star (LGS) systems in the world are based on pulsed lasers. We review the relevant
sodium physics and compare different laser pulse formats. Selected formats are discussed on the basis of numerical
simulation results. One of the key findings is that the brightness of most existing LGS facilities could be boosted at, as
we argue, reasonable expense. Recommendations are presented to enhance the LGS return flux and to design future LGS
lasers, including those suitable for spot tracking in the mesosphere to mitigate the spot elongation problem.
We extend previous sodium LGS models by integrating the return flux across the mesosphere, taking into account
variable mesospheric gas density, temperature, and local sodium density. This method allows us to produce accurate
predictions of the actual return flux on the ground, relevant for determining the performance of adaptive-opticsassisted
instruments. We find that the flux distribution across the sky depends strongly on geographic location and
laser parameters. Almost independent of location, future sodium LGS will be about three times brighter at zenith
than at the observing horizon.
A self-oscillating magnetometer based on nonlinear magneto-optical rotation using amplitude-modulated pump light and unmodulated probe light (AM-NMOR) in 87Rb has been constructed and tested towards a goal of airborne detection of magnetic anomalies. In AM-NMOR, stroboscopic optical pumping via amplitude modulation of the pump beam creates alignment of the ground electronic state of the rubidium atoms. The Larmor precession causes an ac rotation of the
polarization of a separate probe beam; the polarization rotation frequency provides a measure of the magnetic field. An anti-relaxation coating on the walls of the atomic vapor cell results in a long lifetime of 56 ms for the alignment, which enables precise measurement of the precession frequency. Light is delivered to the magnetometer by polarization-maintaining optical fibers. Tests of the sensitivity include directly measuring the beat frequency between the magnetometer and a commercial instrument and measurements of Earth's field under magnetically quiet conditions, indicating a sensitivity of at least 5 pT/νHz. Rotating the sensor indicates a heading error of less than 1 nT, limited in part by residual magnetism of the sensor.
We demonstrate a magnetometric technique based on nonlinear magneto-optical rotation using amplitude modulated
light. The magnetometers can be operated in either open-loop (typical nonlinear magneto-optical rotation with
amplitude-modulated light) or closed-loop (self-oscillating) modes. The latter mode is particularly well suited for
conditions where the magnetic field is changing by large amounts over a relatively short timescale.