Physical Sciences

Single-Photon-Sensitive HgCdTe Avalanche Photodiode Detector

Detector provides extra dimension to lidar scene data for multi-photon returns. The purpose of this program was to develop single-photon-sensitive shortwavelength infrared (SWIR) and midwavelength infrared (MWIR) avalanche photodiode (APD) receivers based on linear-mode HgCdTe APDs, for application by NASA in light detection and ranging (lidar) sensors. Linear-mode photon-counting APDs are desired for lidar because they have a shorter pixel dead time than Geiger APDs, and can detect sequential pulse returns from multiple objects that are closely spaced in range. Linear-mode APDs can also measure photon number, which Geiger APDs cannot, adding an extra dimension to lidar scene data for multi-photon returns. High-gain APDs with low multiplication noise are required for efficient linear-mode detection of single photons because of APD gain statistics — a low-excess- noise APD will generate detectible current pulses from single photon input at a much higher rate of occurrence than will a noisy APD operated at the same average gain. MWIR and LWIR electron-avalanche HgCdTe APDs have been shown to operate in linear mode at high average avalanche gain (M > 1000) without excess multiplication noise (F = 1), and are therefore very good candidates for linear-mode photon counting. However, detectors fashioned from these narrow-bandgap alloys require aggressive cooling to control thermal dark current. Wider-bandgap SWIR HgCdTe APDs were investigated in this program as a strategy to reduce detector cooling requirements.

Posted in: Physical Sciences, Briefs

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Surface-Enhanced Raman Scattering Using Silica Whispering- Gallery Mode Resonators

Silica sphere optical resonators are used to provide surface-enhanced spectroscopic signal. The motivation of this work was to have robust spectroscopic sensors for sensitive detection and chemical analysis of organic and molecular compounds. The solution is to use silica sphere optical resonators to provide surface-enhanced spectroscopic signal.

Posted in: Physical Sciences, Briefs

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Color-Changing Sensors for Detecting the Presence of Hypergolic Fuels

Chemochromic pigment indicates the presence of hypergols, improving workers’ safety. Hypergolic fuel sensors were designed to incorporate novel chemo chromic pigments into substrates for use in various methods of leak detection. There are several embodiments to this invention that would provide specific visual indication of hypergols used during and after transfer. The ability to incorporate these pigments into various polymer matrices provides a unique opportunity to manufacture nearly any type of sensor shape that is required. The vibrant color change from yellow to black instantaneously shows the worker the presence of hypergols in the area, providing the worker the ability to immediately evacuate the area.

Posted in: Physical Sciences, Briefs

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Wind-Driven Wireless Networked System of Mobile Sensors for Mars Exploration

GOne with the Wind ON-Mars (GOWON-Mars): A mobile sensor network that could be used on any windy solar system body, such as Mars or Titan. A revolutionary way is proposed of studying the surface of Mars using a wind-driven network of mobile sensors: GOWON. GOWON would be a scalable, self-powered and autonomous distributed system that could allow in situ mapping of a wide range of environmental phenomena in a much larger portion of the surface of Mars compared to earlier missions. It could improve the possibility of finding rare phenomena such as “blueberries” or bio-signatures and mapping their occurrence, through random wind-driven search. It would explore difficult terrains that were beyond the reach of previous missions, such as regions with very steep slopes and cluttered surfaces. GOWON has a potentially long life span, as individual elements can be added to the array periodically. It could potentially provide a costeffective solution for mapping wide areas of Martian terrain, enabling leaving a long-lasting sensing and searching infrastructure on the surface of Mars.

Posted in: Physical Sciences, Briefs

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Analysis of the Effects of Streamwise Lift Distribution on Sonic Boom Signature

The objective is to find ways to reduce sonic booms. Investigation of sonic boom has been one of the major areas of study in aeronautics due to the benefits a low-boom aircraft has in both civilian and military applications. Current Federal Aviation Administration regulations prohibit supersonic flight over land due to potential effects the sonic boom may have on structures and humans.

Posted in: Physical Sciences, Briefs

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In Situ Solid Particle Generator

This system enables filter testing, and fluid and gas dynamic research, in closed-system, nonstandard, or extreme environments. Particle seeding is a key diagnostic component of filter testing and flow imaging techniques. Typical particle generators rely on pressurized air or gas sources to propel the particles into the flow field. Other techniques involve liquid droplet atomizers. These conventional techniques have drawbacks that include challenging access to the flow field, flow and pressure disturbances to the investigated flow, and they are prohibitive in high-temperature, non-standard, extreme, and closed-system flow conditions and environments.

Posted in: Physical Sciences, Briefs

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Ultra-Compact, Superconducting Spectrometer-on-a-Chip at Submillimeter Wavelengths

These spectrometer modules can be used for future astrophysics missions that require compact cryogenic spectrometers. Small size, wide spectral bandwidth, and highly multiplexed detector readout are required to develop powerful multi-beam spectrometers for high-redshift observations. Currently available spectrometers at these frequencies are large and bulky. The grating sizes for these spectrometers are prohibitive. This fundamental size issue is a key limitation for space-based spectrometers for astrophysics applications.

Posted in: Tech Briefs, Physical Sciences, Semiconductors & ICs, Photonics, Briefs

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