Stanley R. Rotman

Optical studies of cerium doped yttrium aluminum garnet single crystals

Single crystals of undoped and cerium‐doped yttrium aluminum garnet have been pumped with laser radiation of 220‐ and 266‐nm wavelength. A broadband defect emission at approximately 300 nm was observed, similar to that obtained with cathodoluminescence, although decreased in magnitude. Evidence of a transfer of energy from these defect states to the Ce+3 states was inferred from the photoluminescence decay time measurements. We have associated the absorption spectra from 200–300 nm with the defect excitation spectrum, including the peaks at 225 and 270 nm.

Wide-gap luminescent materials : theory and applications

1: Hosts for Solid-State Luminescent Systems.- 2: Luminescent Dopants.- 3: The Effect of Defects on Inorganic Luminescent Materials.- 4: Solid State Lasers.- 5: Inorganic Scintillators.- 6: Rare Earth-Doped Fiber Laser and Amplifiers.

Modeling human search and target acquisition performance: IV. detection probability in the cluttered environment

To model the target acquisition capability of an electro-optic system operated by a human, one should take into account how the clutter in the scene affects the human performance. We consider one global and two local clutter metrics; we compare actual target acquisition results to those predicted by our metrics.

Defect luminescence in cerium‐doped yttrium aluminum garnet

The absorption and photoluminescence of lattice defects and of the cerium ion (Ce+3) in cerium‐doped yttrium aluminum garnet have been measured after annealing single crystals of this material in various reducing atmospheres. The absorption in the 200–300‐nm wavelength range is observed to decrease as the partial pressure of oxygen (PO2) in the annealing atmosphere decreases, while both the cerium emission at 550 nm and the lattice defect luminescence at 300 nm increases. The lattice defect emission appears to be associated with electrons located on oxygen vacancies.

Improved covariance matrices for point target detection in hyperspectral data

Algorithms for point target detection in hyperspectral images use the inverse covariance matrix in order to separate a detected pixel from it surrounding noise. The inverse covariance matrix can be implemented from all the pixels or from the close surroundings of the examined pixel. We compare the different methods and conclude which method brings the best results.

Non-radiative energy transfer in non-uniform codoped laser crystals☆

Abstract A new, general treatment of Forster-Dexter non-radiative energy transfer applied to non-uniform codoped fluorescing crystals is described. Analytical expressions for excited-state donor concentrations in cases where the spherically symmetric distribution of acceptors is a function of the radial distance from the donor are presented. Two simple cases relevant to current experiments are highlighted. This work is of general interest due to the growing importance of non-radiative energy transfer in solid-state laser development.

Clutter metrics for target detection systems

The problem of calculating an effective contrast for diffused targets in visual scenery is addressed. The effect of local variations of intensity in the vicinity of the target is modeled by considering the distribution of the intensity of the edges. The effect of global clutter is discussed from the vantage point of selecting the best model for background scenery. Generalized contrast measures are described and applied to real scenes. >

Defect-property correlations in garnet crystals. VI: The electrical conductivity, defect structure, and optical properties of luminescent calcium and cerium-doped yttrium aluminum garnet

The electrical and optical properties of calcium and cerium‐doped yttrium aluminum garnet (Ca,Ce:YAG) have been studied. Ca,Ce:YAG is a mixed ionic and electronic conductor with an ionic conductivity activation energy of 4.3 eV. Evidence of cluster formation with a consequent higher‐than‐expected activation energy is presented. The cerium normally enters the crystal as Ce+4, but it may be converted to Ce+3 under reducing atmospheres at elevated temperatures.

Some optical properties of Cr4+-doped crystals

We summarize briefly some of our past studies, and report of preliminary recent new results concerning the optical properties of Cr 4+ -doped crystals that are important for utilization as passive Q-switching devices in Nd:YAG laser systems. The host crystals involved are YAG, YSGG, GGG, LuAG and forsterite. Excited-state lifetimes of 4.0, 1.0 and 1.7 μs were measured by the Cr 4+ fluorescence decay (1.3-1.7 μm) following pulsed excitation at 1064 nm in YAG, YSGG and GGG, respectively. The ground- and excited-state absorption (ESA) cross-sections at λ = 1064 nm were estimated from transmission saturation measurements. For [Cr 4+ ,Mg 2+ ]:YAG the respective results were σ gs = (3.25 ± 0.15) × 10 -18 cm 2 and σ es = (6.25 ± 0.5) × 10 -19 cm 2 . In the orthorhombic forsterite, the cross-sections were polarization dependent. We got σ gs < (3.3 ± 1) × 10 -19 cm 2 for E∥a∥, σ gs = (23 ± 2) × 10 -19 cm 2 and σ es = (9.0 ± 0.7) × 10 -19 cm 2 for E∥b, and σ gs = (16 ± 1) × 10 -19 cm 2 and σ es = (5.7 ± 0.4) × 10 -19 cm 2 for E∥c. Polarised ESA spectra were measured between 680 and 960 nm using the pulsed pump/probe technique. At 750 nm we got σ gs = (110 ± 10) × 10 - 19 cm 2 and σ es = (25 ± 3) × 10 -19 cm 2 for E∥b. Passive Q-switching performance of a flashlamp-pumped Nd:YAG laser using an intracavity [Cr 4+ ,Ca 2+ ]:GGG sample is also demonstrated.

Analysis of false alarm distributions in the development and evaluation of hyperspectral point target detection algorithms

We analyze the efficacy of various point target detection algorithms for hyperspectral data. We present a novel way to measure the discrimination capability of a target detection algorithm; we avoid being critically dependent on the particular placement of a target in the image by examining the overall ability to detect a target throughout the various backgrounds of the cube. We first demonstrate this approach by analyzing previously published algorithms from the literature; we then present two new dissimilar algorithms that are designed to eliminate false alarms on edges. Trade-offs between the probability of detection and false alarms rates are considered. We use our metrics to quantify the improved capability of the proposed algorithms over the standard algorithms.