Direct resonant pumping of the 4Z1 I /z upper state of the 2.8 pm Er" : YLF laser at 0.97 pm is shown to be more efficient than other pumping schemes which have been used for this transition. Upper-state pumping avoids nonradiative losses arising from phonon and self-quenching decays inherent in other pumping schemes. Efficient performance of the 2.8 pm laser is maintained on condition that extremely shallow pump absorption is avoided. Reduced efficiency for shallow pump absorption is attributed to upconversion loss arising from high pumping rates. 4 l9/2

The performance of the Rice source of spin polarized electrons, which is based on an optically pumped flowing helium afterglow, has been substantially improved. He(23S) metastable atoms contained in the afterglow are optically pumped using 1.08 μm 23S1↔23P1 radiation from an LNA laser. Spin conservation in subsequent chemi-ionization reactions with CO2 results in the production of free polarized electrons that are extracted from the afterglow. At low currents, ≲1 μA, polarizations of 80%–90% are achieved. This decreases to ∼75% at 10 μA and to ∼50% near 100 μA. The polarization can be simply reversed (P→−P). The energy spread in the extracted beam is <0.4 eV, and the beam emittance is <4 mrad cm−1 at 270 eV. This source is suitable for use in a wide variety of applications, and is particularly attractive for use with the new generation of high-duty factor electron accelerators that are currently being developed.

We have investigated high-peak- and high-average-power operation of diode-pumped, thulium-sensitized, holmium 2.1-microm lasers. Free-running laser powers of 14 W at 29 Hz have been demonstrated with 2.6% electrical efficiency. Q-switched operation produced average powers in excess of 11 W in a burst of short pulses. Preliminary optical parametric oscillator frequency conversion of the holmium laser to 4 microm is also reported.

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Efficient, stable optical pumping of a collimated beam of Ar((3)P(2)) metastable atoms is obtained using a low-power, frequency-modulated multimode dye laser. The advantages provided by frequency modulation are discussed. The technique is suitable for use in optically pumping a wide variety of atomic species.