Milan R. Kokta

Judd-ofelt analysis of the Er3+ (4f11) absorption intensities in Er3+-doped garnets

Spectroscopic and laser properties of three different Er3+−doped garnet systems are characterized by employing the Judd–Ofelt (JO) analysis. The three garnet hosts are Y3Al5O12 (YAG), Y3Sc2Ga3O12 (YSGG), and Gd3Ga5O12 (GGG). The JO model has been applied to the room temperature absorption intensities of Er3+ (4f11) transitions to establish the so-called JO intensity parameters: Ω2, Ω4, and Ω6 in the three garnet hosts. The intensity parameters are used to determine the radiative decay rates (emission probabilities of transitions) and branching ratios of the Er3+ transitions from the excited state J manifolds to the lower-lying J′ manifolds. The predicted decay rates and branching ratios of these Er3+ transitions in YAG, YSGG, and GGG hosts are compared. From the radiative decay rates, the radiative lifetimes of the Er3+ excited states are determined in the three garnets and are also compared. We also report the spectroscopic quality factors, Ω4/Ω6, obtained for the three garnets. The quantum efficiencies ...

Spectral dynamics of laser-pumped Y3Al5O12:Tm,Ho lasers

Abstract The spectroscopic properties and energy transfer rates of Tm3+ and Ho3+ ions in Y3Al5O12:Tm,Ho (Tm,Ho:YAG) have been investigated. The dynamics of optical pumping in both the visible and near infra-red spectral regions were studied to establish rates for the various processes involved in laser-pumped Tm,Ho:YAG laser systems. Infrared to visible upconversion processes were investigated using dual wavelength excitation. The results of these experiments were used in a rate equation model to simulate laser operation.

Spectroscopic properties of Co2+ in related spinels

We report the absorption and fluorescence spectra of divalent cobalt (Co2+) in a series of related spinels Mg(1−x)CoxAlBOC, where B=2, 4, 6, C=4, 7, 10, and x represents the amount of Co2+ that substitutes for Mg2+ in tetrahedral sites of Td symmetry. The spectra support the assumption that both Mg2+ and Co2+ prefer the tetrahedral cation sites during the growth of these crystalline materials. These observations also support earlier conclusions obtained from crystallographic and thermodynamic studies of the MgO and Al2O3 phase diagram. The observed spectra are analyzed and compared to calculated electronic levels derived from lattice-sum models using crystallographic data determined from the crystals grown in the present studies. Comments are made in relevance to the use of these crystals as saturable absorbers for near infrared Q-switched lasers.

Comparison of Laser-Pumped Tm, Ho Laser Systems

We report on a comparison of various host materials for Tm,Ho based laser systems. A pulsed alexandrite laser has been used as a pump source to investigate the lasing properties of Tm,Ho in yttrium aluminum garnet (Y3Al5012 ), yttrium lithium fluoride (YLF4), and fguoro-zircoaluminate glass (ZSAi) These results are compared to the predictions of a computer simulation of the Tm,Ho optical pumping dynamics using a rate equation model.