Microcavity Device Research Articles

Redox cycling measurements of a model compound and dopamine in ultrasmall volumes with a self-contained microcavity device

A ∼13 μm diameter×8 μm deep cavity with integrated electrodes was used for redox cycling in ultrasmall volumes (∼1 nl) to selectively detect species that undergo reversible electron transfer reactions at electrodes in the presence of species that do not. Better sensitivities were obtained when the gold recessed microdisk (RMD), located at the bottom of the cavity, served as generator electrode and the gold tubular nanoband (TNB), located 4 μm away from the RMD and circling the cavity's wall, served as collector electrode, than for the reverse assignment. A gold electrode at the rim was the pseudoreference/auxiliary electrode. The signal at the collector electrode gave better detection limits than the amplified signal at the generator electrode for solutions of hexaamineruthenium(III) chloride and of dopamine, because charging current and faradaic current from interferents (e.g. oxygen and ascorbic acid) that undergo irreversible reactions were eliminated. The present work contrasts with other electrochemical detection methods for dopamine that require fast scan electronics or anionic coatings. It also contrasts with previously reported dopamine measurements that used redox cycling with larger working electrodes, external reference and auxiliary electrodes, and larger volumes. The detection limit for dopamine in the microcavity was 2 μM. By changing generator-collector spacings, the required performance at physiological concentrations should be possible.

P‐78: Design and Characterization of Organic Light Emitting Diodes with Microcavity Structure

AbstractAn organic light emitting diode with a microcavity structure has been fabricated. The intensity enhancement at the resonance wavelength is 2.3 compared to a non‐cavity device. The emission color is also modified from a yellow‐green of non‐cavity device to a primary green for the microcavity device. The experimental results compared well to theoretically calculations.

Performance of integrated optical microcavities for refractive index and fluorescence sensing

The performance of a novel sensor based on an integrated optical (IO) disk microcavity (MC) is theoretically studied. The MC is a resonant waveguide structure in which multiple interference of a guided mode occurs. At resonance, the MC is extremely sensitive to refractive index changes and it sustains locally enhanced optical field. Therefore, the MC is naturally suitable as an extremely responsive sensor for measuring minute changes in refractive index and/or fluorescence of an analyte. Combination of multiple interference and extremely small sampling volume (few femtoliters) provides unique sensitivity of the MC device. A factor of 9 increase in fluorescence sensitivity versus waveguide sensor is anticipated. Provided shot-noise limited detection, the refractive index resolution down to 10 −9 is feasible with the MC sensor, which exceeds that of the straight waveguide interferometer by the order of magnitude. MC-sensors can be combined into arrays providing high throughput detection of both labeled and non-fluorescent biological species.

Low-threshold lasing in a microcavity of fluorene-based liquid-crystalline polymer blends

We report the lasing characteristics of a microcavity device made of fluorene-based luminescent polymer blends with liquid crystallinity. Poly(2,7-bis(p-stiryl)-9,9′-di-n-hexylfluorene sebacate) (PBSDHFS) and poly(9,9′-di-n-hexyl fluorenediylvinylene-alt-1,4-phenylenevinylene) (PDHFPPV) were used to comprise a binary blend system. We employed the Förster-type energy transfer from a liquid crystalline donor to a non-liquid-crystalline acceptor to obtain a low lasing threshold. The binary blend film of PBSDHFS/PDHFPPV (98/2 by wt) demonstrated a very low-threshold energy (∼3 nJ/cm2/pulse) for microcavity lasing, which is lower than any other values previously reported on the organic or polymeric microcavity devices with metal or dielectric mirrors. This result implies that the liquid crystalline polymer blends could be a good candidate for the gain material of photo and electrically pumped lasing devices.

Room-temperature polariton lasers based on GaN microcavities

The critical temperature for Bose condensation of exciton polaritons in an AlGaN microcavity containing 9 GaN quantum wells is calculated to be T=460 K. We have modeled the kinetics of polaritons in such a microcavity device using the two-dimensional Boltzmann equation. Room-temperature lasing is found with a threshold as small as 100 mW. The kinetic blocking of polariton relaxation that prevents formation of the Bose-condensed phase of polaritons at low temperatures disappears at high temperatures, especially in n-doped samples. Thus, GaN microcavities are excellent candidates for realization of room-temperature polariton lasers.

Self-contained microelectrochemical immunoassay for small volumes using mouse IgG as a model system.

A self-contained, microelectrochemical immunoassay on the smallest volumes reported to date (1 microL for the antigen, 1 microL for the secondary antibody-enzyme conjugate, and 200 nL for the electrochemically detected species) has been developed using mouse IgG as a model system in a sandwich-type enzyme-linked immunosorbant assay, which takes less than 30 min to both complete the assembly of immunoassay components onto the antibody-modified surface and detect enzymatically generated species (excluding time for electrochemical cleaning of electrodes). These studies demonstrate the advantage of the close proximity of electrodes to modified surfaces and their application in the analysis of small volumes. Using a 50 microm diameter x 8 microm deep cavity with individually addressable electrodes on a microfabricated chip, the primary antibody was selectively and covalently attached at a gold, recessed microdisk (RMD) at the bottom of the microcavity to the free end of SAMs of either 11-mercaptoundecanoic acid or 11-mercapto-1-undecanol using 1-ethyl-3-[3-(dimethylamino)propyl]carbodiimide hydrochloride. Nonspecific adsorption to the surrounding material, polyimide, of the microcavity device was eliminated. Electrochemical desorption was used to confine the immunoassay activity at the RMD. Enzymatic conversion of the substrate p-aminophenyl phosphate top-aminophenol is detectable in less than 30 s using cyclic voltammetry at a gold, tubular nanoband electrode, which is on the wall of the microcavity and immediately adjacent to the modified RMD. A third electrode, also within the region of the microcavity, served as the pseudoreference/auxiliary electrode. Calibration curves obtained for 1-microL solutions of 5-100 ng/mL of IgG and for 200 nL-solutions of 5 microM to 4 mM of PAPR gave detection limits of 4.4 nM (6.4 ng/mL) or 880 fmol (129 pg) for PAPR and 56 fM (9 pg/mL) or 56 zmol (9 fg) for IgG. It is expected that the device may be suitable for analysis with volumes down to tens of picoliters.

Instantaneous optical modulation in bulk GaAs semiconductor microcavities

Picosecond pump–probe experiments at room temperature on a bulk GaAs microcavity are presented. The microcavity device is designed to adjust the cavity mode energy 15 meV below the band gap energy of the intracavity bulk GaAs material. For low pump-energy densities (∼μJ/cm2), ultrafast modulation of the reflectivity is demonstrated due to the purely coherent refractive index change. A 5:1 contrast ratio is achieved and shows the potential of the semiconductor microcavities for implementation in ultrafast all optical switching.

Optical properties of luminescent PPV copolymers

Copolymers derived from poly( p-phenylenevinylene) PPV were synthesized and their optical properties are studied for lasing applications. Poly(octanedioxy-co-PPV) and methoxy group substituted derivatives consist of emitting conjugated polymer unit and non-conjugated alkyl chain. Methoxy substitutions to the phenyl ring increases the degree of alignments and orientation of the polymer chain, while its electronic effect is appeared to be small. The dMPPV copolymer is highly oriented and the molecular character of PPV unit is preserved and well isolated in copolymer. Microcavity device based on dMPPV copolymer exhibits excellent lasing characteristics and durability.

Investigation on anisotropy of vertical-cavity surface-emitting lasers

We have studied the spontaneous emission of polarized excitons in the GaInP/AlGaInP vertical-cavity surface-emitting lasers from 50 K to room temperature. It is observed that the spontaneous emission peak enters and leaves the resonant regime. At the resonant regime, the emission intensities of the perpendicularly and horizontally polarized excitons are enhanced and their proportions are different from that in nonresonant regime. These experimental results are explained by the dressed exciton theory of the semiconductor microcavity device. Based on this theory, the intensity enhancement and the polarization dependence are understood as cooperative emission and the microcavity anisotropy.

33-µm microcavity light emitter for gas detection

A room-temperature resonant-cavity light source emitting at 3.327 microm is presented. It combines a CdHgTe light-emitting layer, grown by molecular beam epitaxy, and two evaporated YF(3)-ZnS Bragg mirrors. The emitter is optically pumped by a commercial low-power GaAs laser diode. Compared with an unprocessed sample, this microcavity device shows a drastic (10-fold) linewidth reduction, a 3.3-fold intensity increase at 3.327 microm , and a 2.4-fold angular-spread decrease. The emitted optical power is 15 microW , and the device is used as a light source in a basic gas-detection setup. Measurements of a butane-propane mixture in the 1 to 5x 10(-3) bar range with a 5-cm-long single-path gas cell are demonstrated.

Microcavity device of PPV dimer based copolymer

PPV dimer based copolymers were synthesized to investigate their applicability to the microcavity device. The blue emitting copolymers consist of strictly alternating conjugated PPV dimer unit and non-conjugated alkyl group. Two microcavity devices based on distributed Bragg reflector (DBR) and the spin-coated copolymer thin film show promising lasing characteristics. The gain narrowed blue emissions at 374.5 and 428.5 nm with 3.0–4.2 nm linewidth were obtained and those are the lowest wavelength among the devices based on PPV derivatives. N 2 laser (337 nm) was used as a pulsed pump source and their lasing thresholds were around 0.3–1 microjoules. The lasing characteristics strongly depended on the microcavity structure and the copolymer film processing. Q factor of each devices were calculated to be 120 and 102, respectively. The stability of the copolymer under UV excitation was excellent that the devices have the operational lifetime of over 3×10 5 pulses at 10 μJ.

Blue Lasing in Poly(Octanedioxy-Co-DMPPV) Copolymer Microcavity

Poly[octanedioxy-co-DMPPV] copolymer was synthesized to fabricate the microcavity device. The blue emitting polymers consist of strictly alternating conjugated PPV and non-conjugated alkyl group. The microcavity based on distributed Bragg reflector (DBR) and the spin-coated copolymer thin film shows promising lasing characteristics. A strong blue emission at 437.9 nm with 6.5 nm line width was due to cavity enhancement and large gain from the copolymer layer. Third harmonic of Nd:YAG laser(355 nm) was used as a pulsed pump source and its energy threshold for lasing was around few microjoules per pulse. The lasing characteristics strongly depended on the microcavity structure and copolymer film processing. Q factor was calculated to be 67 and the operational lifetime of over 7×105 pulses was observed.

Radiation of dressed excitons in the semiconductor microcavity

In this paper, we introduced the dressed exciton model of the semiconductor micro-cavity device. In the semiconductor micro cavity of vertical-cavity surface-emission device, the excitons first coupled with the cavity through an intra-electromagnetic field and formed the dressed excitons. Then these dressed excitons decayed into the vacuum cavity optical mode, as a multiparticle process. Through the quantum electrodynamics method, the dipole emission density and system energy decayed equation were obtained. And it was predicted that the excitons decay into a very narrow mode when the exciton-cavity coupling becomes strong enough.

Lasing in substituted polythiophene between dielectric mirrors

We report photopumped lasing in a microcavity device with a polythiophene layer as emitter. The microcavity is made of a polymer film between two dielectric Bragg reflecting mirrors (DBR). The microcavity devices is built by joining two polymer coated DBR mirrors at elevated temperature. When photopumping the film, a lasing threshold is observed at 120 nJ/cm 2. Comparative studies with fast pump-probe spectroscopy of thin polythiophene films and the same polymer in photopumped lasing studies, indicate that the gain coefficient is 80±20 cm 2, and that the exciton concentration is 2x10 17 cm 2 at the lasing transition, well below the exciton-exciton recombination level.

A polythiophene microcavity laser

We report photopumped lasing in a microcavity device with a polythiophene layer as the emitter. These microcavity devices are built by joining two polymer coated dielectric mirrors at elevated temperature. When photopumping the film, a lasing threshold is observed at 120 nJ/cm 2. Comparative studies with fast pump–probe spectroscopy of thin polythiophene films and the same polymer in photopumped lasing studies, indicate that the gain coefficient is 80±20 cm −1, and that the exciton concentration is 2×10 17 cm −3 at the lasing transition, well below the exciton–exciton recombination level.