Thermal Properties of Polymer Hole-Transport Layers Influence the Efficiency Roll-off and Stability of Perovskite Light-Emitting Diodes.

While the performance of metal halide perovskite light-emitting diodes (PeLEDs) has rapidly improved in recent years, their stability remains a bottleneck to commercial realization. Here, we show that the thermal stability of polymer hole-transport layers (HTLs) used in PeLEDs represents an important factor influencing the external quantum efficiency (EQE) roll-off and device lifetime. We demonstrate a reduced EQE roll-off, a higher breakdown current density of approximately 6 A cm, a maximum radiance of 760 W sr m, and a longer device lifetime for PeLEDs using polymer HTLs with high glass-transition temperatures.

Unidirectional mode selection in bistable quantum cascade ring lasers.

Ideal ring resonators are characterized by travelling-wave counter-propagating modes, but in practice travelling waves can only be realized under unidirectional operation, which has proved elusive. Here, we have designed and fabricated a monolithic quantum cascade ring laser coupled to an active waveguide that allows for robust, deterministic and controllable unidirectional operation. Spontaneous emission injection through the active waveguide enables dynamical switching between the clockwise and counterclockwise states of the ring laser with as little as 1.

Nanosecond-Pulsed Perovskite Light-Emitting Diodes at High Current Density.

While metal-halide perovskite light-emitting diodes (PeLEDs) hold the potential for a new generation of display and lighting technology, their slow operation speed and response time limit their application scope. Here, high-speed PeLEDs driven by nanosecond electrical pulses with a rise time of 1.2 ns are reported with a maximum radiance of approximately 480 kW sr  m at 8.

Mid-Infrared Scattering in γ-AlO Catalytic Powders.

The energy efficiency of heterogeneous catalytic processes may be improved by using mid-infrared light to excite gas-phase reactants during the reaction, since vibrational excitation of molecules has been shown to increase their reactivity at the gas-catalyst interface. A primary challenge for such light-enabled catalysis is the need to ensure close coupling between light-excited molecules and the catalyst throughout the reactor. Thus, it is imperative to understand how to couple infrared light efficiently to molecules near and inside catalytic material.

Thermal Management Enables Bright and Stable Perovskite Light-Emitting Diodes.

The performance of lead-halide perovskite light-emitting diodes (LEDs) has increased rapidly in recent years. However, most reports feature devices operated at relatively small current densities (<500 mA cm ) with moderate radiance (<400 W sr m ). Here, Joule heating and inefficient thermal dissipation are shown to be major obstacles toward high radiance and long lifetime.

II-VI Quantum Cascade emitters in the 6-8μm range.

We present the growth and characterization of ZnCdSe/ZnCdMgSe quantum cascade (QC) heterostructures grown by molecular beam epitaxy (MBE) and designed to operate at 6-8μm. These structures utilize the better-understood ZnCdMgSe with InP lattice matched compositions yielding a bandgap of 2.80 eV as compared to previous work which used ZnCdMgSe compositions with bandgaps at 3.

Wavelength independent normal incident quantum cascade detectors.

We demonstrate a novel technique for normal-incident absorption in intersubband infrared detectors by taking advantage of light scattering from the side-walls of a wet-etched mesa. We fabricate 'spiral' and 'hairpin' shaped quantum cascade detector at a peak wavelength of 6.6 μm, and compare their performance with a standard rectangular mesa.

High power spiral cavity quantum cascade superluminescent emitter.

Quantum Cascade devices with an emission wavelength centered around 5 μm have been shaped into compact, yet long (8 mm and 12 mm) spiral cavities to increase mid-infrared superluminescence (SL) power. Up to ~57 mW of SL power at 250 K is obtained with a Gaussian emission spectrum with a full width at half maximum of 56 cm(-1) and a coherence length of ~107 μm.

Noninvasive in vivo glucose sensing on human subjects using mid-infrared light.

Mid-infrared quantum cascade laser spectroscopy is used to noninvasively predict blood glucose concentrations of three healthy human subjects in vivo. We utilize a hollow-core fiber based optical setup for light delivery and collection along with a broadly tunable quantum cascade laser to obtain spectra from human subjects and use standard chemo-metric techniques (namely partial least squares regression) for prediction analysis. Throughout a glucose concentration range of 80-160 mg/dL, we achieve clinically accurate predictions 84% of the time, on average.

Non-uniform lateral current distribution in quantum cascade lasers.

Non-uniform lateral current distribution in quantum cascade (QC) lasers is investigated, as a result of stimulated-optical-emission-assisted electron transport, the rate of which depends on the local photon density and is comparable to the longitudinal optical (LO) phonon scattering rate. A microscopic model based on rate equations is built to study the self-consistent process of interaction between local electrons and photons in QC lasers. The non-uniform distribution of lateral current and the corresponding spatial hole burning are simulated from this model.

Wavelength selection and spectral narrowing of Distributed Bragg Reflector quantum cascade lasers up to peak optical power.

We investigate the impact of Distributed Bragg Reflectors (DBR), ion-milled directly on top of Fabry-Perot type Quantum Cascade (QC) laser ridges, following fabrication and processing of the devices and observe a more than 10-fold reduction in spectral full-width-half-maximum (FWHM) and a maximum of 20dB side-mode suppression ratio (SMSR), maintained to peak optical power. As predicted by our model, and experimentally verified, there is a "sweet-spot" in terms of grating length, ~200 µm on a 3 mm long laser ridge, and a trade-off between spectral narrowing and output power, set by the grating depth, varied from 1.8 to 2.

In vitro measurements of physiological glucose concentrations in biological fluids using mid-infrared light.

Mid-infrared transmission spectroscopy using broadband mid-infrared or Quantum Cascade laser sources is used to predict glucose concentrations of aqueous and serum solutions containing physiologically relevant amounts of glucose (50-400 mg/dL). We employ partial least squares regression to generate a calibration model using a subset of the spectra taken and to predict concentrations from new spectra. Clinically accurate measurements with respect to a Clarke error grid were made for concentrations as low as 30 mg/dL, regardless of background solvent.

In vivo measurement of mid-infrared light scattering from human skin.

Two mid-infrared light sources, a broadband source from a Fourier Transform Infrared Spectrometer (FTIR) and a pulsed Quantum Cascade (QC) Laser, are used to measure angle-resolved backscattering in vivo from human skin across a broad spectral range. Scattering profiles measured using the FTIR suggest limited penetration of the light into the skin, with most of the light interacting with the stratum corneum layer of the epidermis. Scattering profiles from the QC laser show modulation patterns with angle suggesting interaction with scattering centers in the skin.

ZnCdSe/ZnCdMgSe quantum well infrared photodetector.

We report the design, fabrication and characterization of a II-VI Zn(0.51)Cd(0.49)Se / Zn_0.

Ridge-width dependence of the threshold of long wavelength (λ ≈ 14 µm) Quantum Cascade lasers with sloped and vertical sidewalls.

We investigate the ridge-width dependence of the threshold of Quantum Cascade lasers fabricated by wet and dry etching, respectively. The sloped sidewalls resulting from wet etching affect the threshold in two ways as the ridge gets narrower. First, the transverse modes are deeper in the substrate, hence reducing the optical confinement factor.

Enhanced bandwidth and reduced dispersion through stacking multiple optical metamaterials.

All-semiconductor, highly anisotropic metamaterials provide a straightforward path to negative refraction in the mid-infrared. However, their usefulness in applications is restricted by strong frequency dispersion and limited spectral bandwidth. In this work, we show that by stacking multiple metamaterials of varying thickness and doping into one compound metamaterial, bandwidth is increased by 27% over a single-stack metamaterial, and dispersion is reduced.

Temperature-insensitive long-wavelength (λ ≈14 µm) Quantum Cascade lasers with low threshold.

We demonstrate high-performance, long-wavelength (λ ≈14 µm) Quantum Cascade (QC) lasers based on a diagonal optical transition and a "two-phonon-continuum" depletion scheme in which the lower laser level is depopulated by resonant longitudinal optical phonon scattering followed by scattering to a lower energy level continuum. A 2.8 mm long QC laser shows a low threshold current density of 2.

Chalcogenide glass waveguides integrated with quantum cascade lasers for on-chip mid-IR photonic circuits.

We demonstrate on-chip hybrid integration of chalcogenide glass waveguides and quantum cascade lasers (QCLs). Integration is achieved using an additive solution-casting and molding method to directly form As(2)S(3) strip waveguides on an existing QCL chip. Integrated As(2)S(3) strip waveguides constructed in this manner display strong optical confinement and guiding around 90° bends, with a NA of 0.

Continuous-wave subwavelength microdisk lasers at λ = 1.53 µm.

Subwavelength InGaAs/AlInAs microdisk lasers are demonstrated under continuous-wave optical pumping at a heat-sink temperature of 45 K. A 1.49 µm diameter, 209 nm thick microdisk lases in single-mode at a wavelength of 1.

Mid-infrared characterization of solution-processed As2S3 chalcogenide glass waveguides.

An etch-free and cost-effective deposition and patterning method to fabricate mid-infrared chalcogenide glass waveguides for chemical sensing applications is introduced. As(2)S(3) raised strip optical waveguides are produced by casting a liquid solution of As(2)S(3) glass in capillary channel molds formed by soft lithography. Mid-IR transmission is characterized by coupling the output of a quantum cascade (QC) laser (lambda = 4.

A quantum cascade laser cw cavity ringdown spectrometer coupled to a supersonic expansion source.

A new instrument has been constructed that couples a supersonic expansion source to a continuous wave cavity ringdown spectrometer using a Fabry-Perot quantum cascade laser (QCL). The purpose of the instrument is to enable the acquisition of a cold, rotationally resolved gas phase spectrum of buckminsterfullerene (C(60)). As a first test of the system, high resolution spectra of the nu(8) vibrational band of CH(2)Br(2) have been acquired at approximately 1197 cm(-1).

Sub-diffraction negative and positive index modes in mid-infrared waveguides.

We characterize a strongly anisotropic waveguide consisting of alternating 80 nm layers of n(+)-InGaAs and i-AlInAs on InP substrate. A strong increase in the transverse magnetic (TM) reflection at lambda = 8.4 microm corresponds to a characteristic low-order mode cutoff for the left-handed waveguide.

Low voltage-defect quantum cascade laser with heterogeneous injector regions.

We demonstrate an In(0.635)Al(0.356)As/In(0.