Guest editorial

Includes bibliographical references.Guest editorial introducing issue of IEEE Journal of Quantum Electronics

Three-dimensional confinement in the conduction band structure of InP

Includes bibliographical references.Strong quantum confinement in InP is observed to significantly reduce the separation between the direct and indirect conduction band states. The effects of three-dimensional confinement are investigated by tailoring the initial separation between conduction band states using quantum dots (QDs) of different sizes and hydrostatic pressure. Analyses of the QD emission spectra show that the X1c states are lowest in energy at pressures of ~6 GPa, much lower than in the bulk. The transition to the X1c states can be explained by either a sequence of Γ-L and L-X crossings, or by the crossover between strongly coupled Γ and X states.The work at CSU was supported by the National Science Foundation, and that at NREL by the U.S. Department of Energy, Office of Basic Energy Sciences, Chemical Sciences Division

A method for the experimental measurement of bulk and shear loss angles in amorphous thin films

Brownian thermal noise is a limiting factor for the sensitivity of many high precision metrology applications, among other gravitational-wave detectors. The origin of Brownian noise can be traced down to internal friction in the amorphous materials that are used for the high reflection coatings. To properly characterize the internal friction in an amorphous material, one needs to consider separately the bulk and shear losses. In most of previous works the two loss angles were considered equal, although without any first principle motivation. In this work we present a method that can be used to extract the material bulk and shear loss angles, based on current state-of-the-art coating ring-down measurement systems. We also show that for titania-doped tantala, a material commonly used in gravitational-wave detector coatings, the experimental data strongly favor a model with two different and distinct loss angles, over the simpler case of one single loss angle

Investigation of laser annealing mechanisms in thin film coatings by photothermal microscopy

We study the evolution of the absorptance of amorphous metal oxide thin films when exposed to intense CW laser radiation measured using a photothermal microscope. The evolution of the absorptance is characterized by a nonexponential decay. Different models that incorporate linear and nonlinear absorption, free carrier absorption, and defect diffusion are used to fit the results, with constraints imposed on the fit parameters to scale with power and intensity. The model that best fits is that two types of interband defects are passivated independently, one by a one-photon process and the other one by a two-photon process.Fil: Zaldivar Escola, Facundo. Universidad de Buenos Aires. Facultad de Ingeniería. Departamento de Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Mingolo, Nélida. Universidad de Buenos Aires. Facultad de Ingeniería. Departamento de Física; ArgentinaFil: Martínez, Oscar E.. Universidad de Buenos Aires. Facultad de Ingeniería. Departamento de Física; ArgentinaFil: Rocca, Jorge J.. State University of Colorado - Fort Collins; Estados UnidosFil: Menoni, Carmen S.. State University of Colorado - Fort Collins; Estados Unido

Ablation of Submicrometer Holes Using an Extreme-Ultraviolet Laser

Simulations and experiments are used to study extreme-ultraviolet (EUV) laser drilling of submicrometer holes. The ablation process is studied with a 2D Eulerian hydrodynamic code that includes bound-free absorption processes relevant to the interaction of EUV lasers with a solid material. Good agreement is observed between the simulated and measured ablated depths for on-target irradiances of up to 1×1010  W cm−2. An increase in the irradiance to 1×1012  W cm−2 is predicted to ablate material to a depth of 3.8  μm from a single pulse with a hole diameter 3 to 4 times larger than the focal spot size. The model allows for the simulation of the interaction of a laser pulse with the crater created by a previous shot. Multiple-pulse lower-fluence irradiation configurations under optimized focusing conditions, i.e., approaching the diffraction limit, are shown to be advantageous for applications requiring mesoscale [(100  nm)–(1  μm)] features and a high level of control over the ablation profile

Strain-induced modifications of the band structure of InxGa1-xP–In0.5Al0.5P multiple quantum wells

Includes bibliographical references.The effect of strain on the band structure of InxGa1-xP-In0.5Al0.5P multiple quantum wells (MQW's) has been investigated from high-pressure and low-temperature photoluminescence measurements. The biaxial strain in the wells was varied between +0.6% compressive to -0.85% tensile strain by changing the well composition x from 0.57 to 0.37. Strain increases the valence band offsets in either tensile or compressively strained structures. Whereas relatively insensitive to tensile strain, the valence band offsets showed a strong dependence on the magnitude of the compressive strain. Good agreement is found between the measured valence band offsets and those predicted by the model solid theory, except for the largest compressively strained MQW's, for which the model calculations underestimate the measured valence band offset. Strain and the associated variations in composition also modified the separation among the well states associated with Γ1c, L1c, and X1c. From these results, the bandgaps of each conduction band extrema were calculated in InxGa1-xP for 0.37 < x < 0.57 and compared with the predictions of the model solid theory.This work was supported by the National Science Foundation under Grant DMR 9321422 and Grant ECS-9502888, and by the AFOSR under Contract F49620-93-1-0021

Structure and morphology of low mechanical loss TiO₂-doped Ta₂O₅

The exceptional stability required from high finesse optical cavities and high precision interferometers is fundamentally limited by Brownian motion noise in the interference coatings of the cavity mirrors. In amorphous oxide coatings these thermally driven fluctuations are dominant in the high index layer compared to those in the low index SiO₂ layer in the stack. We present a systematic study of the evolution of the structural and optical properties of ion beam sputtered TiO₂-doped Ta₂O₅ films with annealing temperature. We show that low mechanical loss in TiO₂-doped Ta₂O₅ with a Ti cation ratio = 0.27 is associated with a material that consists of a homogeneous titanium-tantalum-oxygen mixture containing a low density of nanometer sized Ar-filled voids. When the Ti cation ratio is 0.53, phase separation occurs leading to increased mechanical loss. These results suggest that amorphous mixed oxides with low mechanical loss could be identified by considering the thermodynamics of ternary phase formation

Structure and morphology of low mechanical loss TiO₂-doped Ta₂O₅

The exceptional stability required from high finesse optical cavities and high precision interferometers is fundamentally limited by Brownian motion noise in the interference coatings of the cavity mirrors. In amorphous oxide coatings these thermally driven fluctuations are dominant in the high index layer compared to those in the low index SiO₂ layer in the stack. We present a systematic study of the evolution of the structural and optical properties of ion beam sputtered TiO₂-doped Ta₂O₅ films with annealing temperature. We show that low mechanical loss in TiO₂-doped Ta₂O₅ with a Ti cation ratio = 0.27 is associated with a material that consists of a homogeneous titanium-tantalum-oxygen mixture containing a low density of nanometer sized Ar-filled voids. When the Ti cation ratio is 0.53, phase separation occurs leading to increased mechanical loss. These results suggest that amorphous mixed oxides with low mechanical loss could be identified by considering the thermodynamics of ternary phase formation