Abstract : Substantial improvements have been made in the performance of the optically pumped 546.1 nm Hg laser. DC-pumped operation of sealed-off laser tubes has been demonstrated with no apparent lifetime limitations. Several new pump lamp designs have been developed and tested to overcome limitations set by emission line self-reversal, cataphoresis, and single-isotope mercury fill requirements. A novel dc-excited 'diffusion-bypass' lamp has been shown to provide a particularly effective pumping source. Extensive measurements of gain, saturation intensity, and power output have been made, with both natural and single-isotope mercury. A detailed theoretical analysis of pumping and relaxation processes in the Hg laser has been developed for interpreting these experimental measurements. Laser operation with Ar-H2O-Hg and He-H2O-Hg gas mixes in addition to the previous N2-Hg gas mix has been obtained but found to be less efficient. Preliminary observations of line overlap between the mercury laser and various molecular absorbers for absolute wavelength stabilization have been made by observing mercury-laser-induced fluorescence in Br2, I2(127) and I2(129) cells, and by making preliminary observations of a saturated-absorption feature in I2(127) using a single-frequency Hg202 laser. The optically pumped mercury laser continues to appear interesting as an absolute wavelength stabilized visible laser, as a potential ring laser gyroscope medium, and as a special-purpose low-power visible green laser. (Author)