Modeling the population lens effect in thermal lens spectrometry.

We report a theoretical model and experimental results for laser-induced lensing in solids. The model distinguishes and quantifies the contributions from population and thermal effects. Laser-induced lensing in ytterbium-doped fluorozirconate glass ZBLAN:Yb(3+) is measured, and the thermal and optical properties obtained from analyzing the data with the proposed model agree well with published values. Photothermal techniques are used extensively for the investigation of laser and laser-cooling materials, and the model developed here enables the interpretation of convoluted laser-induced lensing signals that have contributions from different sources.

Light yield measurement method for milled nanosize inorganic crystals.

Composite scintillators consisting of nanosize inorganic crystals embedded in an organic matrix have been actively pursued in recent years. One method of producing nanosize crystals is through wet milling; however, since milling is known to introduce defects, the light yield of the milled crystals must be characterized. In this work, a new method of characterizing the light yield of milled inorganic crystals will be explored and discussed; this method will take into account explicitly the concentration of the inorganic crystals and the difference in stopping power between the crystals and the solvent.

Constraining the evolution of the fundamental constants with a solid-state optical frequency reference based on the 229Th nucleus.

We describe a novel approach to directly measure the energy of the narrow, low-lying isomeric state in 229Th. Since nuclear transitions are far less sensitive to environmental conditions than atomic transitions, we argue that the 229Th optical nuclear transition may be driven inside a host crystal with a high transition Q. This technique might also allow for the construction of a solid-state optical frequency reference that surpasses the short-term stability of current optical clocks, as well as improved limits on the variability of fundamental constants. Based on analysis of the crystal lattice environment, we argue that a precision (short-term stability) of 3×10(-17)<Δf/f<1×10(-15) after 1 s of photon collection may be achieved with a systematic-limited accuracy (long-term stability) of Δf/f∼2×10(-16). Improvement by 10(2)-10(3) of the constraints on the variability of several important fundamental constants also appears possible.

Local lattice dynamics and the origin of the relaxor ferroelectric behavior.

Relaxor ferroelectricity is observed in many strongly disordered ferroelectric solids. However, the atomistic mechanism of the phenomenon, particularly at high temperatures, is not well understood. In this Letter we show the local lattice dynamics as the origin of relaxor ferroelectricity through the first use of the dynamic pair-density function determined by pulsed neutron inelastic scattering. For a prototypical relaxor ferroelectric, Pb(Mg(1/3)Nb(2/3))O(3), we demonstrate that the dynamic local polarization sets in around the so-called Burns temperature through the interaction of off-centered Pb ions with soft phonons, and the slowing down of local polarization with decreasing temperature produces the polar nanoregions and the relaxor behavior below room temperature.

Damping of antiferromagnetic spin waves by valence fluctuations in the double layer perovskite YBaFe2O5.

Inelastic neutron scattering experiments show that spin dynamics in the charge-ordered insulating ground state of the double layer perovskite YBaFe(2)O(5) is well described in terms of e(g) superexchange interactions. Above the Verwey transition at T(V)=308 K, t(2g) double exchange-type conduction proceeds within antiferromagnetic FeO(2)-BaO-FeO(2) double layers by an electron hopping process that requires a spin flip of the five-coordinated Fe ions, costing an energy of 5S(2) approximately 0.1 eV. The hopping process disrupts near-neighbor spin correlations, leading to massive damping of zone-boundary spin waves.

Stabilization of charge ordering in La1/3Sr2/3FeO3-delta by magnetic exchange.

The magnetic exchange energies in charge ordered La1/3Sr2/3FeO3-delta (LSFO) and its parent compound LaFeO3 (LFO) have been determined by inelastic neutron scattering. In LSFO, the measured ratio of ferromagnetic exchange between Fe3+-Fe5+ pairs (JF) and antiferromagnetic exchange between Fe3+-Fe3+ pairs (JAF) fulfills the criterion for charge ordering driven by magnetic interactions (|JF/JAF|>1). The 30% reduction of JAF as compared to LFO indicates that doped holes are delocalized, and charge ordering occurs without a dominant influence from Coulomb interactions.

Ultrafast, cross-correlated harmonic imaging through scattering media.

A simple upconversion scheme utilizing 40-fs pulses is shown to permit high-contrast imaging of objects obscured by a highly scattering medium when no ballistic component is evident in the scattered light and imaging is performed with any portion of the scattered light pulse. We present a time-gated, inherently low-pass spatially filtered imaging method that minimizes signal-averaging requirements and greatly facilitates imaging under severe scattering (turbid) conditions.

Uniform upconversion in high-concentration Er(3+)-doped soda lime silicate and aluminosilicate glasses.

Uniform upconversion in erbium-doped silicate glasses is investigated as a function of glass composition, concentration, and fabrication method. Comparisons of upconversion coefficients are made among soda lime silicate and aluminosilicate bulk glasses and soda lime silicate waveguides. Comparisons are also made with studies performed by other researchers. The results indicate that both the composition and the preparation method of the glass affect the value of the upconversion coefficient, with as much as a factor-of-4 variation observed at fixed Er(3+) concentration. Values of the upconversion coefficient are found to be consistent with the Förster-Dexter microscopic model.