Research Terms
, National Science Foundation
Researchers at the University of Central Florida have developed a method of stabilizing external cavity QCL system alignment by exploiting changes in QCL impedance that occur with changes in alignment and optical feedback. An electrical error signal determined by the changes in QCL impedance can correct a loss of optical alignment, from changes in cavity length and mirror orientation, caused by temperature changes and vibrational or environmental noise sources.
Rapid and accurate detection of trace gases and vapors at parts-per-billion mixing ratios is critical in applications from environmental monitoring to military objectives and homeland security. Conventional analytical instruments tend to be bulky, expensive, limited to the detection of a single analyte?or require advanced training to distinguish and identify the characteristic signals of multiple analytes?are sensitive to vibrations, and have high power requirements.
The new technology for gas sensing is capable of detecting multiple analytes under the same technical principle with low power requirements and at low cost, based on intracavity laser absorption spectroscopy (ICLAS), and applicable to any chemical vapor except homopolar diatomic molecules and noble gases.
Dynamic alignment of QCL-based external cavity systems can improve the process and quality of results in applications including remote gas leak detection, pollution monitoring, medical diagnostics, industrial process controls, petrochemicals, automotive, real-time combustion control, homeland security, military applications, explosives detection, and chemical warfare agent detection.
Technical Details
By analyzing changes in optical feedback, observed as changes in QCL impedance, the UCF technology produces an error signal that can be used to stabilize the QCL system alignment. A measurement of the QCL's compliance voltage is used to determine the QCL's impedance in real time and produce a signal, conditioned and analyzed with signal processing techniques to become an error signal. The error signal is sent to electromechanical and electro-optical controls and devices (for example, galvanometer-mounted and/or piezo-controlled mirror mounts and supports), which are adjusted using known noise cancelling techniques to ensure optimized alignment for improved QCL system performance.
Researchers at the University of Central Florida have developed ring-cavity surface-emitting quantum cascade lasers (RCSE-QCLs) that are concentrically nested to combine power, coupled to ensure coherent emission, and phase controlled with integrated optical delays to engineer the beam profile. This novel method obtains high-power continuous-wave coherent laser radiation at wavelengths from 4 to 20 micrometers and provides a new design approach of a power-scalable, chip-based, high-power, single aperture RSCE-QCL with outstanding beam quality (M2 < 1.2) at infrared wavelengths. This device's output power is over 15W continuous-waves through a single aperture.
RSCE-QCLs provide large exit apertures with low power densities and stabilized emission wavelengths via second-order distributed feedback, from surface gratings that double as output couplers. Generally, RSCE-QCLs enable wafer-level fabrication and testing, which reduces piece work and handling, which in turn lowers manufacturing costs. Unlike RSCE-QCLs that emit non-Gaussian beams, nested concentric RSCE-QCLs emit more uniform radiation patterns.
Technical Details
This RSCE-QCL comprises a ring-shaped active region with first and second opposing facets, with at least one of the facets defining a radiation-emitting facet and is aligned with a ring-shaped phase shifter with a spiraled surface. A substrate is located adjacent to the ring-shaped active region and opposite of the emitting facet, and a ring-shaped phase shifter is located on the radiation emitting facet the ring-shaped active region.
Researchers at the University of Central Florida have invented a device that can intercept electromagnetic radiation in the terahertz (THz) frequency range more effectively without the costly components that other detection methods require. A key aspect of THz radiation is its ability to penetrate a wide range of materials without damaging target objects. Example materials include plastics, foams, clothing, wood, masonry and ceramics. Thus, the invention is applicable in many areas, such as security screening for illicit substances (like the narcotic, fentanyl), counterfeit currency, and hazardous items, including explosives. THz waves penetrate deeper than infrared (IR) waves, provide better resolution than radio and microwaves, and exhibit lower scattering than IR and visible light.
Devices used for electromagnetic radiation in the mid- and long-wave infrared spectral regions are not designed for detecting THz wavelengths and cannot be easily adapted. Other alternatives require multiple optical components (like bolometers that require liquid helium cooling) to achieve similar parameters with lower effectiveness. As a solution, the UCF device is specifically designed to detect THz wavelengths and eliminates the need for alternative methods and devices. Additionally, the invention keeps personnel safe by being contact-free and accurately provides results in seconds. It is simple to operate and interpret, requiring only minimal training.
Technical Details
The UCF invention comprises a pyroelectric detection device and methods for using it to receive and identify electromagnetic radiation in the THz frequency range (0.1 - 5) with ultra-narrow channel widths (0.06 THz) FWHM. Depending on its configuration, the device may either act as a large area resonator to collect weak/diffuse signals or as a constituent of an array able to take pictures within the spectrum for which it is sensitive. The device can include a pyroelectric element for generating reflectance spectra.
In one configuration, the UCF device is a portable handheld unit. The unit may include a broadband mercury source, stereoscopic detection scheme for localization, and a visible camera for overlaying images, such as an active pixel sensor. The element may consist of an aluminum nitride film and conductive layers of chromium and gold. One conductive layer contains a periodic array of plasmonic absorbers that simultaneously provide capacitive and inductive coupling of electromagnetic radiation. A non-contact THz reflectance spectroscope provides the means for identifying targets of interest. The spectroscope comprises a light source and a camera to emit far-infrared wavelength electromagnetic radiation onto a target. Measurement circuitry connected to the conductive layers measures electrical signals from the reflectance spectra. Analysis circuitry then compares the reflectance spectra to known spectra to identify various objects or substances.
Partnering Opportunity
The research team is looking for partners to develop the technology further for commercialization.
Stage of Development
Prototype available.
UCF researchers have invented a graphene phototransistor providing a narrowband photo-response that is broadly tunable over a wide frequency range. The detector can be adapted to produce tunable phototransistors operable in the spectral range from ultraviolet (UV) to mm-waves, as well as the entire infrared and THz region. This mechanism is based on resonant gating of graphene by the concentrated, dynamic electric fields of surface plasmon polaritons (SPPs) and it forms the basis for tunable, high-speed imaging arrays.
Technical Details
Within the graphene phototransistor, photodetection occurs through an innovative combination of two transduction steps. 1) Incident photons are instantly converted with high efficiency to SPPs. 2) The SPP fields produce a measurable perturbation on graphene transport, where high speed is anticipated due to graphene's high room-temperature carrier mobility and by potentially light-like speeds for information transfer via SPP propagation.
The graphene sheet is positioned at the surface of a suitable photon-to-SPP excitation coupler. The SPPs are excited at a specific angle of incidence for a given wavelength. The intense SPP fields, in turn, penetrate, gate, dynamically dope, and excite traveling waves of charge density in the graphene, causing changes in its conductance by a variety of potential mechanisms that are sensed electrically.
UCF researchers have invented a graphene phototransistor providing a narrowband photoresponse that is broadly tunable over a wide frequency range. The detector can be adapted to produce tunable phototransistors operable in the spectral range from ultraviolet (UV) to mm-waves, as well as the entire infrared and THz region. This mechanism is based on resonant gating of graphene by the concentrated, dynamic electric fields of surface plasmon polaritons (SPPs) and it forms the basis for tunable, high-speed imaging arrays.
Technical Details
Within the graphene phototransistor, photodetection occurs through an innovative combination of two transduction steps. 1) Incident photons are instantly converted with high efficiency to SPPs. 2) The SPP fields produce a measurable perturbation on graphene transport, where high speed is anticipated due to graphene's high room-temperature carrier mobility and by potentially light-like speeds for information transfer via SPP propagation.
The graphene sheet is positioned at the surface of a suitable photon-to-SPP excitation coupler. The SPPs are excited at a specific angle of incidence for a given wavelength. The intense SPP fields, in turn, penetrate, gate, dynamically dope, and excite traveling waves of charge density in the graphene, causing changes in its conductance by a variety of potential mechanisms that are sensed electrically.
The University of Central Florida invention is a method that cost-effectively restores infrared (IR) image sensors damaged by radiation. The new radiation-defect mitigation technology quickly repairs and prolongs the life of IR sensors, such as long-wavelength IR detectors deployed in near-Earth orbits. Companies can implement the method via software, without affecting the weight or volume of a detector’s electronics. Additionally, the restoration process requires only the voltages and currents of commercial off-the-shelf read-out-integrated-circuits (ROICs) used by the sensor.
Whether exposed to a single burst of radiation (such as gamma rays) or to several smaller doses, an IR detector can suffer damage that significantly degrades its photoresponse capability and performance. With the UCF invention, a detector’s photoresponse can be restored to pre-irradiation levels in seconds and stably maintain it without undue inoperative periods.
Technical Details
The invention encompasses a defect-mitigation strategy for restoring and maintaining the photoresponse of radiation-damaged IR detectors. Essentially, the strategy uses a purely electrical, in-situ radiation-hardening treatment that does not require changes to hardware or any increase in a sensor’s size or weight. The treatment only minimally affects power requirements, as well. Companies can use the strategy on a wide range of detector designs, such as InAs/GaSb Type-II SLS detectors. In one example application of the invention, a GaSb/InAs Type-II SLS sensing circuit receives treatment via software remotely and automatically during the usual dead time between image frames. The process uses only voltages and currents available from standard ROICs for the sensor.
