Elizabeth D. Filer

Ho:Tm lasers. I. Theoretical

Energy transfer dynamics pertinent to Ho:Tm lasers are modeled in two steps: a calculation of the parameters controlling the energy transfer process and a calculation of the population densities of all manifolds influencing the laser process. Energy transfer parameters are modeled with the classical dipole-dipole approximation, but several important changes are implemented to better describe laser materials such as Ho:Tm laser materials. This approach was used to calculate energy transfer parameters using measured energy levels coupled with quantum mechanical calculations although spectroscopically measured parameters could be used in principle. Given the energy transfer parameters, a rate equation approach is used with the eight manifolds required for an accurate description of the Ho:Tm laser. Population densities of all eight manifolds can be predicted as a function of time whether or not lasing occurs. Results of the modeling process are compared with experimental results for both Ho:Tm:YAG and Ho:Tm:YLF with different concentration and a variety of different mirror reflectivities and different pump pulse lengths in a companion paper.

Spectroscopic and lasing properties of Ho:Tm:LuAG

Ho:Tm:LuAG has been grown, examined spectroscopically, and lased at 2.1 microm. Ho:Tm:LuAG was selected for this experimental investigation when quantum-mechanical modeling predicted that it would be a good laser material for Ho laser operation on one of the (5)I(7) to (5)I(8) transitions. Lasing was achieved at 2.100 microm, one of the three wavelengths predicted to be most probable for laser action.

Optical spectra, energy levels and branching ratios of trivalent dysprosium-doped yttrium scandium gallium garnet

Abstract Absorption spectra of trivalent dysprosium ions in yttrium scandium gallium garnet are reported between 2.9 and 0.4 μn at 4K. Laser-excited fluorescence was observed at 4 K for transitions between the 4 F 9 2 manifold and several of the lower-lying 6HJ and 6FJ manifolds. A crystal-field splitting calculation was carried out in which a parametrized Hamiltonian (including Coulombic, spin-orbit, and crystal field terms in D2 symmetry) was diagonalized for selected manifolds of the Dy3+ (4f9) configuration. The RMS deviation between 69 experimental and calculated Stark levels was 8 cm−1. Calculations were carried out to predict branching ratios for emission from the 4 F 9 2 manifold.

YLF Isomorphs for Ho and Tm Laser Applications

A quantum mechanical model describing the energy levels and transition probabilities of lanthanide series elements in laser materials was used to assess the laser possibilities of Ho and Tm in YLF isomorphs. Known X-ray parameters of YLF and its isomorphs as well as known energy levels of Ho and Tm in YLF were used to determine the energy levels and transition probabilities in YLF isomorphs. With this, a figure of merit can be defined to select the best candidate laser material for both Ho and Tm.

OPTICAL SPECTRA, ENERGY LEVELS, AND EMISSION INTENSITY CALCULATIONS OF TRIVALENT THULIUM IONS IN GADOLINIUM SCANDIUM GALLIUM GARNET

Absorption spectra of trivalent thulium ions in gadolinium scandium gallium garnet are reported between 1.9 and 0.25 μm at 4 K. Laser‐induced fluorescence was observed at 4 K from the 1D2, 1G4, and 3H4 (4 and 300 K) manifolds. Site‐selective excitation experiments reveal large fractions of thulium ions in both regular D2 sites and alternate sites. A crystal‐field splitting calculation was carried out in which a parameterized Hamiltonian (including Coulombic, spin‐orbit, and crystal‐field terms in D2 symmetry) was diagonalized for all multiplet manifolds of the Tm3+ (4f12) configuration. The rms deviation between 56 experimental and calculated Stark levels was 10 cm−1. Calculations were carried out to predict branching ratios for emission from the 3H4 manifold to the 3H5, 3F4, and 3H6 manifolds, as well as line‐to‐line transition probabilities for transitions between the 3H4 manifold and the 3H5 manifold.

Theoretical Temperature-Dependent Branching Ratios and Laser Thresholds of the 3F4 to 3H6 Levels of Tm3+ in Ten Garnets

A prediction of laser performance of Tm transitions from the 3F4 to 3H6 manifolds in 10 garnets has been made using a quantum mechanical model. Theoretical energy levels, branching ratios, and population inversion percentages were calculated to determine threshold as a function of temperature.

Self Quenching of the Nd 4F3/2 Manifold

An alternate approach to describe self quenching of the Nd 4F3/2 manifold is developed using computed self quenching and diffusion parameters. Two general regimes exist, one associated with slow diffusion and another associated with fast diffusion. Disparate results are obtained for Nd:YLF, Nd:YAG, as well as Nd:LaSc3(BO3)4 and are compared with experimental results. Calculated results are in general agreement with the experimental results.

Spectroscopy and Lasing in Ho:Tm:Lu3Al5O12

Crystal growth and spectroscopy of Ho:Tm:LuAG has been accomplished and lasing has been achieved using Ti:Al2O3 pumping at 0.781 μm to simulate laser diode pumping. Lasing was observed at 2.10 μm, a wavelength previously predicted to have a low threshold for lasing.

Software system for laser design and analysis

The unique demands of space-based lasers for atmospheric remote sensing require the development of high efficiency, narrow line width lasers throughout the .280 pm to 10.0 μm region. The combination of laser performance requirements, large number of candidate laser materials, and complex mathematical models necessitates the development of an integrated, computerized software system consisting of a database, laser models, and a user-friendly software interface. Such a three part software system for laser design is under development. The three parts include: a database of laser, optical, and nonlinear materials; laser component, amplifier, resonator, and oscillator models; and a menu-driven interface.

1.75 µm Pumped Ho:Tm:LuAG High Efficiency Laser

Large improvements in the slope efficiencies and thresholds of Ho:Tm:LuAG with small changes in temperature are investigated. The temperature relation between the upper laser level storage time, upconversion, and slope efficiencies is observed.