R. E. Slusher

Laser action from two-dimensional distributed feedback in photonic crystals

We report an analysis of the operation of a new type of laser resonator with two-dimensional distributed feedback from a photonic crystal. The gain medium consists of a 2-(4-biphenylyl)-5(4-tert-butylphenyl)-1,3,4-oxadiazole host doped with Coumarin 490 and DCM and is deposited on lithographically patterned Si/SiO2 structures. Bragg reflections caused by the grating diminish the group velocity of photons along some directions of crystallographic symmetry to zero, and the resulting feedback gives rise to laser oscillations. Dispersion relations for photons were calculated analytically and are used to interpret the laser emission spectra.

Large Raman gain and nonlinear phase shifts in high-purity As 2 Se 3 chalcogenide fibers

Third-order Kerr nonlinearities and Raman gain are studied experimentally in high-purity As2Se3 optical fibers for wavelengths near 1.55 μm. Kerr nonlinear coefficients are measured to be nearly 1000 times higher than those for silica fibers. In pulsed mode, nonlinear phase shifts near 1.2-π rad are measured in fibers only 85 cm long with peak pulse powers near 3 W. However, there are nonlinear losses near 20% for nonlinear phase shifts near π. By use of a cw optical pump, large Raman gains nearly 800 times that of silica were measured. In the cw case there were losses in the form of index gratings formed from standing waves at the exit face of the fiber. Discrete Raman amplifiers and optical regenerators are discussed as possible applications.

Time‐resolved reflectivity of ion‐implanted silicon during laser annealing

The time‐resolved reflectivity at 0.63 μm from arsenic‐implanted silicon crystals has been measured during annealing by a 1.06‐μm laser pulse of 50‐ns duration. The reflectivity was observed to change abruptly to the value consistent with liquid silicon and to remain at that value for a period of time which ranged from a few tens of nanoseconds to several hundreds of nanoseconds, depending on the annealing pulse intensity. Concurrently, the transmission of the primary annealing beam dropped abruptly. These observations confirm the formation of a metallic liquid phase at the crystal surface during the annealing process.

Light amplification in organic thin films using cascade energy transfer

There is currently renewed interest in the development of lasers using solid-state organic and polymeric materials as the gain media. These materials have a number of properties that make them good candidates for such applications — for example, emission bands that are displaced (via a Stokes shift) from absorption bands, and the ease with which the emitting species can be embedded in a suitable host material. But despite these advantages, the threshold power densities required for light amplification that have been reported so far have been high. Here we describe an approach, based on energy transfer between molecular species, that can lower the threshold for stimulated emission and laser action while improving markedly the waveguiding properties of the active material. In our materials, an initial molecular excited state is generated in the host compound by absorption of light; this state is then resonantly and non-radiatively transferred down in energy (through one or more steps) between suitably matched dye molecules dispersed in the host, so ensuring that the absorption losses at the final emission wavelengths are very small. Such composite gain media provide provide broad tunability of the emission wavelength, and also decouple the optical emission properties from the transport properties, so providing greater flexibility for the design of future electrically driven device structures.

Large Kerr effect in bulk Se-based chalcogenide glasses

High-speed optical communication requires ultrafast all-optical processing and switching capabilities. The Kerr nonlinearity, an ultrafast optical nonlinearity, is often used as the basic switching mechanism. A practical, small device that can be switched with ~1-pJ energies requires a large Kerr effect with minimal losses (both linear and nonlinear). We have investigated theoretically and experimentally a number of Se-based chalcogenide glasses. We have found a number of compounds with a Kerr nonlinearity hundreds of times larger than silica, making them excellent candidates for ultrafast all-optical devices.

EFFICIENCY ENHANCEMENT OF MICROCAVITY ORGANIC LIGHT EMITTING DIODES

We report microcavity efficiency enhancement of organic electroluminescent devices based on the hole transporter bis(triphenyl) diamine and the electron transporter and light emitter tris(8‐hydroxyquinoline) aluminum. Microcavity organic light emitting diodes are described that emit four times the light measured in the forward direction (spectrally integrated), or almost twice the total light (spectrally and spatially integrated) of a noncavity organic light‐emitting diode for identical electrical drive conditions.

Physics and applications of organic microcavity light emitting diodes

The important changes produced on the electroluminescence characteristics of organic materials due to planar microcavity effects are examined in detail. The photon density of states is redistributed such that only certain wavelengths, which correspond to allowed cavity modes, are emitted in a given direction. This enables us to realize color selectivity over a large wavelength (and color coordinate) range with broadband emitters such as 8‐hydroxyquinoline aluminum (Alq), and intensity enhancement in narrow band emitters. The intensity enhancement in Alq‐based cavity light emitting diodes (LEDs) is extensively evaluated both experimentally and theoretically. The design considerations for and device characteristics of a novel multiple emissive layer LED are also described.

Stimulated emission and lasing in dye-doped organic thin films with Forster transfer

Optically pumped stimulated emission and lasing in thin films of an absorbing host 8-hydroxyquinolinato aluminum(Alq) doped with small amounts of the laser dye DCM II is observed. Forster transfer of the excitation from the Alq molecules to the DCM II molecules results in a high absorption coefficient at pump wavelength (337 nm) as well as low absorption loss at the emission wavelengths (610–650 nm).

Organic solid-state lasers with imprinted gratings on plastic substrates

Optically pumped laser emission has been observed from thin films of 8-hydroxyquinolinato aluminum (Alq) doped with a DCM dye deposited on a diffraction,orating formed by imprinting a film of BCB w ...

Polymer microdisk and microring lasers

Dye-doped polymer microlasers have been fabricated by photolithography and self-assembly. Microdisk lasers 5 to 30 microm in diameter were photolithographically patterned on thin planar polymer waveguides. We formed polymer microring lasers on thinned silica fibers by dipping the fibers in polymers and allowing the polymer droplets to cure.