M.C. Delong

Tunable, Gap-State Lasing in Switchable Directions for Opal Photonic Crystals

A photonic crystal laser that is tunable throughout the visible in three-dimensionally switchable directions is demonstrated. This photo-pumped laser utilizes a dye-infiltrated, single-crystal SiO2 opal having incomplete bandgaps. Our results support a gap-state-enhanced distributed feedback mechanism for lasing. Three different types of wavelength tunability are demonstrated, each applicable over a different frequency range and involving either single or multiple bandgaps. The many independent laser cavities that exist in one photonic crystal are demonstrated by simultaneously obtaining lasing in various colors and directions from an opal crystal. The observation of characteristic laser emission lines provides a new spectroscopy for characterizing intra-gap photonic states, which may be useful for developing the photonic crystal analogues of electronic circuitry.

Structual and optical studies of distyrylbenzene single crystals

High quality single crystals of distyrylbenzene (DSB) have been grown from the vapor phase, and their structural and optical properties studied. The crystal structure has been determined to be orthorhombic. A rich vibronic structure is observed in the photoluminescence (PL) emission at low temperature. At room temperature, we found a high PL quantum yield and self-waveguiding that leads to laser action.

Photonic versus random lasing in opal single crystals

We demonstrate a photopumped photonic crystal laser based on synthetic opal single crystal infiltrated with various laser dye solutions. The optical feedback in these lasers is provided via Bragg scattering of light from crystallographic planes in the opal. Localization of the laser modes within the stop band is assigned to defect states caused by crystal structure faults. We distinguish this photonic lasing mechanism from another regime of stimulated emission associated with random lasing what could be also observed in dye-infiltrated opals, but at higher excitation intensities.

Optical studies of distyrylbenzene single crystals

Abstract The optical properties of high quality single crystals of distyrylbenzene (DSB) have been studied. At room temperature the photoluminescence (PL) spectrum is quite broad with quantum yield of 65%. At low temperature the PL spectrum shows many narrow vibrational side bands with QE of 68%, where the 0–0 band shows different polarization properties from the other phonon bands. We used the Spano ‘pinwheel’ model of strong vibration–exciton coupling in herringbone lattice to explain the appearance of the ‘forbidden’ 0–0 transition at low temperature and its unusual polarization properties. This model also predicts a strong temperature dependence for the 0–0 band relative to the 0– n transitions, as verified experimentally.

Synthesis and processing of conducting polymer microlasers and microsize light emitting diodes

Conducting polymers show interesting optical and electrical properties, but have proven difficult to form into devices. We have synthesized improved poly-p-phenylene vinylene and its derivatives, and substituted polyacetylenes. From these polymers devices were fabricated in films and on fibers. The polymers show quantum efficiencies as high as 62%, with colors ranging from red to yellow green to blue green. The devices were built using typical silicon chip fabrication technology. Light emitting diodes and lasers have been fabricated as small as four microns in diameter.

Optical spectroscopies of excited states in poly(para phenylene vinyleae)

Abstract We have applied a multitude of continuous wave and pulsed optical spectroscopies to thin films of unsubstituted poly (para-phenylene vinylene) (PPV) with photoluminescence quantum efficiency ≥30%. Laser action in thin films, microdisks and microrings has been demonstrated. The threshold for lasing is comparable to other PPV derivatives Electroabsorption unambiguosly shows that the mA g state is located at 3.4 eV. At higher photon energies no large polarizability of excited states could be found. The photoinduced absorption spectrum which contains both polaron and triplet excitations is very weak, showing a relatively defect free polymer.