While the energy levels in Ho:YLF have been measured previously, they have not been as thoroughly investigated in the isomorphs, Ho:LuLF and Ho:GdLF. We report here the measurement of the energy levels of the trivalent lanthanide Ho3+ in GdLiF4 (GdLF), YLiF4 (YLF), and LuLiF4 (LuLF). The measurement of the energy levels of Ho:YLF, although they have been measured before, are repeated here for self-consistent comparison to Ho:LuLF and Ho:GdLF. The Stark split levels for the first ten Ho manifolds in these materials have been measured, and the results have been fitted to a free-ion plus crystal-field Hamiltonian to generate a theoretical set of energy levels. Crystal-field parameters were varied to determine the best fit between experimental and theoretical energy levels. The energy levels of Ho:GdLF and Ho:LuLF are seen to be very similar to those in Ho:YLF. However, subtle changes resulting from replacing Y3+ with Gd3+ or Lu3+ in the fluoride crystal YLiF4 result in shorter transition wavelengths in GdLF and longer transition wavelengths in LuLF. This has implications for Ho lasers operating at ∼2.0 µm. The energy levels for Ho:GdLF and Ho:LuLF determined here indicate that Ho:GdLF will have a larger lower laser level thermal population than Ho:YLF, while Ho:LuLF lasers will have a smaller lower laser level thermal population than Ho:YLF. This is consistent with the larger Stark splitting associated with the larger host ions that Ho substitutes for in these lithium fluoride materials. The intensity parameters are also determined from a Judd–Ofelt analysis and used to calculate radiative lifetimes and branching ratios for the first ten manifolds in Ho:GdLF, Ho:YLF and Ho:LuLF.

No abstract

The meteoroid experiments by five Lunar Orbiters have provided direct measurements in the near-lunar environment of the rate of penetration of 0.025-millimeter beryllium copper by meteoroids. Each experiment used 20 pressurized-cell detectors having a total effective exposed area of 0.186 square meter. The spacecraft carrying the cells were in both equatorial and polar orbits; altitudes ranged between 30 and 6200 kilometers. Data collected continuously for 17 months indicate that the rate of penetration in the lunar environment is approximately half the rate in the near-Earth environment as measured by detectors of the same type aboard Explorers 16 and 23.

No abstract