Abstract: Systems and methods are provided for filtering coherent infrared light from a thermal background for protection of infrared (IR) imaging arrays and detection systems. A Michelson interferometer is used for coherent light filtering. In an implementation, a system includes a fixed mirror, a beam splitter, and a moving mirror which can be controlled translationally, as well as tip/tilt. The Michelson interferometer may be used as an imaging system. For imaging applications, a system may comprise a tunable array of micro-electromechanical systems (MEMS) mirrors. A mid-wave IR interferometer with electronic feedback and MEMS mirror array is provided.

Abstract: A reusable, protective face mask has two detachable filter trays that attach on each side of the mask, a soft elastomeric face seal, and straps to go around the user's head. Exhalations and inhalations can pass through the same filter material. The filter trays can accept arbitrary filter media. A forward-facing port can be used to increase speech intelligibility by transmitting sound through a diaphragm without a prohibitive amount of distortion. Manufacture of the mask is facilitated because the mask body and the other mask components can be produced by injection molding. Decontamination and sterilization are facilitated because the mask can be fully disassembled.

Abstract: A time-resolved microwave reflectance apparatus comprises a pulsed or modulated optical source that irradiates a semiconductor sample with an excitation pump beam, a microwave oscillator that irradiates the sample with a continuous beam of microwaves, and a microwave detector that detects the microwaves reflected by the sample. Therefore, charge detection, rather than conventional absorption measurements (that detect the loss of photons), can be used to extract the absorption coefficient and band edge of a semiconductor material.

Abstract: Systems and methods are provided for filtering coherent infrared light from a thermal background for protection of infrared (IR) imaging arrays and detection systems. A Michelson interferometer is used for coherent light filtering. In an implementation, a system includes a fixed mirror, a beam splitter, and a moving mirror which can be controlled translationally, as well as tip/tilt. The Michelson interferometer may be used as an imaging system. For imaging applications, a system may comprise a tunable array of micro-electromechanical systems (MEMS) mirrors. A mid-wave IR interferometer with electronic feedback and MEMS mirror array is provided.

Abstract: A time-resolved microwave reflectance apparatus comprises a pulsed or modulated optical source that irradiates a semiconductor sample with an excitation pump beam, a microwave oscillator that irradiates the sample with a continuous beam of microwaves, and a microwave detector that detects the microwaves reflected by the sample. Therefore, charge detection, rather than conventional absorption measurements (that detect the loss of photons), can be used to extract the absorption coefficient and band edge of a semiconductor material.

Abstract: In a superlattice (SL) photodetector, each period of the SL includes first and second semiconductor layers having different compositions, at least one of which comprises indium arsenide (InAs). At least one of these two semiconductor layers has a graded composition. In embodiments, the first semiconductor layer comprises InAs and the second semiconductor layer is a graded layer comprising indium arsenide antimonide (InAsSb), wherein the antimony (Sb) concentration is varied. In examples, the Sb concentration in the second layer gradually increases from the top and bottom toward the middle of the layer.

Abstract: A mid-infrared tunable metamaterial comprises an array of resonators on a semiconductor substrate having a large dependence of dielectric function on carrier concentration and a semiconductor plasma resonance that lies below the operating range, such as indium antimonide. Voltage biasing of the substrate generates a resonance shift in the metamaterial response that is tunable over a broad operating range. The mid-infrared tunable metamaterials have the potential to become the building blocks of chip based active optical devices in mid-infrared ranges, which can be used for many applications, such as thermal imaging, remote sensing, and environmental monitoring.

Abstract: The present invention enables elective emission from a heterogeneous metasurface that can survive repeated temperature cycling at high temperatures (e.g., greater than 1300 K). Simulations, fabrication and characterization were performed for an exemplary cross-over-a-backplane metasurface consisting of platinum and alumina layers on a sapphire substrate. The structure was stabilized for high temperature operation by an encapsulating alumina layer. The geometry was optimized for integration into a thermophotovoltaic (TPV) system and was designed to have its emissivity matched to the external quantum efficiency spectrum of 0.6 eV InGaAs TPV material. Spectral measurements of the metasurface resulted in a predicted 32% optical-to-electrical power conversion efficiency. The broadly adaptable selective emitter design can be easily scaled for integration with TPV systems.

Abstract: An interdigitated nanoelectrode grating functions both as an absorption-enhancing sub-wavelength antenna and to minimize the distance between electron-hole creation and current collection so as to enhance photodetection schemes based upon active layers comprising two-dimensional semiconducting materials.

Abstract: An electrically tunable terahertz two-path plasmonic interferometer with an integrated detection element can down convert a terahertz field to a rectified DC signal. The integrated detector utilizes a resonant plasmonic homodyne mixing mechanism that measures the component of the plasma waves in-phase with an excitation field that functions as the local oscillator in the mixer. The plasmonic interferometer comprises two independently tuned electrical paths. The plasmonic interferometer enables a spectrometer-on-a-chip where the tuning of electrical path length plays an analogous role to that of physical path length in macroscopic Fourier transform interferometers.

Abstract: An electrically tunable terahertz two-path plasmonic interferometer with an integrated detection element can down convert a terahertz field to a rectified DC signal. The integrated detector utilizes a resonant plasmonic homodyne mixing mechanism that measures the component of the plasma waves in-phase with an excitation field that functions as the local oscillator in the mixer. The plasmonic interferometer comprises two independently tuned electrical paths. The plasmonic interferometer enables a spectrometer-on-a-chip where the tuning of electrical path length plays an analogous role to that of physical path length in macroscopic Fourier transform interferometers.

Abstract: A system and method for identifying objects possessing minute but significant details is described. At its core, the system includes a user interface, means for comparatively identifying the object and means for displaying results. Notably, because the system does not rely upon highly specialized or complex equipment, the invention is expected to have particular applicability in a wide variety of every-day situations. Moreover, the system is explicitly designed for user friendliness, so as to eliminate that need for extensive training for any prospective user of the system. The system should have particular applicability in key blank identification and key duplication processes.

Abstract: A tunable plasmonic crystal comprises several periods in a two-dimensional electron or hole gas plasmonic medium that is both extremely subwavelength (˜?/100) and tunable through the application of voltages to metal electrodes. Tuning of the plasmonic crystal band edges can be realized in materials such as semiconductors and graphene to actively control the plasmonic crystal dispersion in the terahertz and infrared spectral regions. The tunable plasmonic crystal provides a useful degree of freedom for applications in slow light devices, voltage-tunable waveguides, filters, ultra-sensitive direct and heterodyne THz detectors, and THz oscillators.

Abstract: A mid-infrared tunable metamaterial comprises an array of resonators on a semiconductor substrate having a large dependence of dielectric function on carrier concentration and a semiconductor plasma resonance that lies below the operating range, such as indium antimonide. Voltage biasing of the substrate generates a resonance shift in the metamaterial response that is tunable over a broad operating range. The mid-infrared tunable metamaterials have the potential to become the building blocks of chip based active optical devices in mid-infrared ranges, which can be used for many applications, such as thermal imaging, remote sensing, and environmental monitoring.

Abstract: A highly directional thermal emitter device comprises a two-dimensional periodic array of heavily doped semiconductor structures on a surface of a substrate. The array provides a highly directional thermal emission at a peak wavelength between 3 and 15 microns when the array is heated. For example, highly doped silicon (HDSi) with a plasma frequency in the mid-wave infrared was used to fabricate nearly perfect absorbing two-dimensional gratings structures that function as highly directional thermal radiators. The absorption and emission characteristics of the HDSi devices possessed a high degree of angular dependence for infrared absorption in the 10-12 micron range, while maintaining high reflectivity of solar radiation (˜64%) at large incidence angles.

Abstract: A heterodyne photomixer spectrometer comprises a receiver photomixer that is driven at a different frequency than the source photomixer, thereby maintaining the coherent nature of the detection, eliminating etalon effects, and providing not only the amplitude but also the phase of the received signal. The heterodyne technique can be applied where the source and receiver elements are components of a waveguide thereby forming an on-chip heterodyne spectrometer.

Abstract: An apparatus and method are disclosed for detecting terahertz radiation at room temperature. A detecting pixel includes a sub-wavelength split-ring resonator, and is mechanically coupled to (but thermally decoupled from) a substrate via a cantilever formed from two materials that have a significant mismatch in their thermal expansion coefficients. Incident radiation causes the split-ring resonator to resonate, thereby generating heat that is transferred to the cantilever, causing the cantilever to flex. An optical readout system includes a secondary light source, such as a laser, that shines on a reflective surface on the pixel, whereby a photodiode detects the reflected light and permits calculation of a relative deflection of the pixel in the nanometer range. An exemplary detector has a noise equivalent power rating of approximately 60 pW/?Hz.

Abstract: An apparatus and method are disclosed for detecting terahertz radiation at room temperature. A detecting pixel includes a sub-wavelength split-ring resonator, and is mechanically coupled to (but thermally decoupled from) a substrate via a cantilever formed from two materials that have a significant mismatch in their thermal expansion coefficients. Incident radiation causes the split-ring resonator to resonate, thereby generating heat that is transferred to the cantilever, causing the cantilever to flex. An optical readout system includes a secondary light source, such as a laser, that shines on a reflective surface on the pixel, whereby a photodiode detects the reflected light and permits calculation of a relative deflection of the pixel in the nanometer range. An exemplary detector has a noise equivalent power rating of approximately 60 pW/?Hz.

Abstract: A tunable extraordinary optical transmission (EOT) device wherein the tunability derives from controlled variation of the dielectric constant of a semiconducting material (semiconductor) in evanescent-field contact with a metallic array of sub-wavelength apertures. The surface plasmon resonance wavelength can be changed by changing the dielectric constant of the dielectric material. In embodiments of this invention, the dielectric material is a semiconducting material. The dielectric constant of the semiconducting material in the metal/semiconductor interfacial region is controllably adjusted by adjusting one or more of the semiconductor plasma frequency, the concentration and effective mass of free carriers, and the background high-frequency dielectric constant in the interfacial region. Thermal heating and/or voltage-gated carrier-concentration changes may be used to variably adjust the value of the semiconductor dielectric constant.

Abstract: A direct detector for terahertz radiation comprises a grating-gated field-effect transistor with one or more quantum wells that provide a two-dimensional electron gas in the channel region. The grating gate can be a split-grating gate having at least one finger that can be individually biased. Biasing an individual finger of the split-grating gate to near pinch-off greatly increases the detector's resonant response magnitude over prior QW FET detectors while maintaining frequency selectivity. The split-grating-gated QW FET shows a tunable resonant plasmon response to FIR radiation that makes possible an electrically sweepable spectrometer-on-a-chip with no moving mechanical optical parts. Further, the narrow spectral response and signal-to-noise are adequate for use of the split-grating-gated QW FET in a passive, multispectral terahertz imaging system. The detector can be operated in a photoconductive or a photovoltaic mode.