Joseph Ganem

A 7-/spl mu/m praseodymium-based solid-state laser

We report the first demonstration of laser emission from the /sup 3/F/sub 3/ to /sup 3/F/sub 2/ transition in the rare earth praseodymium. This new 7-/spl mu/m solid-state laser operates with an optical efficiency of 2.3% at 293 K and 10% at 150 K using an upconversion pumping mechanism. A discussion of the dynamics in this new laser material is included.

Spectroscopic characterization of Er-doped KPb2Cl5 laser crystals

Abstract A discussion of the spectroscopic properties of the low-phonon energy laser host material potassium lead chloride, KPb 2 Cl 5 , doped with trivalent erbium is presented. In this paper we present room temperature spectroscopic measurements and subsequent analysis based on the Judd–Ofelt model. Additionally, Stark level energies of the Er 3+ ions in the crystal were determined from spectroscopic measurements performed at cryogenic temperatures.

Mid-infrared spectroscopy of erbium doped chloride laser crystals.

We report on a spectroscopic analysis of ErCl3 and 1% Er 3+:YCl3 to determine their potential as possible laser sources at 3.5 and 4.5 mm. Concentration quenching of the low lying excited states is reported to be surprisingly very weak in this system. Although some shortening of the lifetimes is measured in the fully concentrated system, they retain lifetimes that are of order several milliseconds or more. A Judd-Ofelt analysis is performed and the projected gains for the 3.5 and 4.5 mm transitions are calculated. Successful growth techniques of erbium doped chlorides are also described.

CROSS RELAXATION AND UPCONVERSION COEFFICIENTS OF THE MID-INFRARED TRANSITIONS OF PR3+ :LACL3

Short pulse laser-induced fluorescence experiments on the lowest-energy electronic states (υ<10−4 cm−1) of trivalent praseodymium ions are reported. Crystals of lanthanum trichloride with a range of Pr3+ concentrations were examined. We compute cross relaxation and upconversion coefficients for the metastable energy levels using a standard rate equation analysis. The limitations of the rate equation approach are examined with a focus on the underlying dynamics of this rare-earth system. The implications of these results for laser emission in the 1.3–7.2 μm spectral range are discussed.

Radiative and multiphonon relaxation of the mid-IR transitions of Pr/sup 3+/ in LaCl/sub 3/

Electric and magnetic dipole transition probabilities, fluorescence branching ratios, integrated emission coefficients, fluorescence efficiencies, and fluorescence lifetimes are determined for the lower lying states of Pr:LaCl/sub 3/ using the Judd-Ofelt theory and calculated multiphonon emission probabilities. The results are used to characterize demonstrated mid-IR laser transitions and predict new potential mid-IR laser transitions in Pr:LaCl/sub 3/.

Optically-pumped mid-IR phosphor using Tm 3+ -sensitized Pr 3+ -doped KPb 2 Cl 5

Efficient energy transfer at room temperature from Tm3+ to Pr3+ has been demonstrated in co-doped KPb2Cl5. Because of the low phonon energies in KPb2Cl5, the energy transfer processes result in the conversion of 805 nm laser diode pump energy to a broad band of mid-IR radiation between 3500to5500 nm. Energy transfer pathways, rates, and quantum efficiencies are evaluated. Results show that the material is suitable as a phosphor for the 4to5⁢ μm spectral range that can be optically pumped with low-cost 0.8⁢ μm laser diodes.

Growth and characterization of direct mid-IR laser materials (Invited Paper)

Rare earth doped ternary lead salts are being studied for use as mid-IR laser materials. We summarize progress at the Naval Research Labs on the production and evaluation of this important class of solid-state laser.

Optical cooling in multi-level systems

A theoretical model for optical cooling is developed, which yields the overall efficiency of a single endpumped cooling system. This model includes the effects of background absorption and pump saturation, while in multi-level systems, the model accounts for the important energy transfer processes. Two-level efficiency is evaluated for the case of Yb:YAG and compared with a hypothetical three-level material with identical spectral properties. This model is readily modified to include more levels and different materials.

Diode pumped room temperature 4.6 µm erbium laser

We report first operation of a 4.6 µm laser for trivalent erbium. Efficient, broadband, room temperature operation was obtained pumping with a 0.80 µm laser diode.

Data-Driven Education Reform: A New Pseudoscience

The underlying logic and assumptions behind the testing and assessment craze that has swept through education is examined, and the erroneous chain of reasoning based on tests and related metrics that leads to dangerous education policy decisions is uncovered. Many of the “data-driven” education policies and reforms are shown to resemble pseudoscience more than real science because they are missing one or more of the essential elements of science identified in Chapter 1. Examples discussed are value-added models for teacher effectiveness, measurements of adequate yearly progress in schools, college admissions based on SAT scores, and assessment practices in higher education. It is shown that all of these practices fail to provide causal explanations for student learning. The underlying reasons for why some teachers are more effective than others, why some schools succeed while others fail, why some students succeed in college while others drop out, why some college programs achieve their learning outcomes while others do not, are left unexamined. Instead these metrics provide tautologies—successful programs, teachers, schools, and students have successful outcomes.