We have designed a microfabricated planar absolute radiometer based on a vertically aligned carbon nanotube (VACNT) absorber and an electrical power substitution method. The radiometer is designed to operate at room temperature and to be capable of measuring laser powers up to 300 mW from 300 nm to 2300 nm with an expected expanded uncertainty of 0.06% (k = 2). The electrical power substitution capability makes the radiometer absolute and traceable to the international system (SI) of units. The new bolometer is currently under construction and will replace NIST's 50 year old detector standard for free-space CW laser power measurements. We also study the possibility of reducing background temperature sensitivity by optimizing the spectral selectivity of the VACNT forest with a photonic crystal structure.
The long-term balance between Earth’s absorption of solar energy and emission of radiation to space is a fundamental climate measurement. Total solar irradiance (TSI) has been measured from space, uninterrupted, for the past 40 years via a series of instruments. The Compact Total Irradiance Monitor (CTIM) is a CubeSat instrument that will demonstrate next-generation technology for monitoring total solar irradiance. It includes novel silicon-substrate room temperature vertically aligned carbon nanotube (VACNT) bolometers. The CTIM, an eight-channel 6U CubeSat instrument, is being built for a target launch date in late 2020. The basic design is similar to the SORCE, TCTE and TSIS Total Irradiance Monitors (TIM). Like TSIS TIM, it will measure the total irradiance of the Sun with an uncertainty of 0.0097% and a stability of <0.001%/year. The underlying technology, including the silicon substrate VACNT bolometers, has been demonstrated at the prototype-level. During 2019 we will build and test an engineering model of the detector subsystem. Following the testing of the engineering detector subsystem, we will build a flight detector unit and integrate it with a 6U CubeSat bus during late 2019 and 2020, in preparation for an on-orbit demonstration in 2021.
Currently at NIST, there is an effort to develop a black array of broadband absolute radiometers (BABAR) for far infrared sensing. The linear array of radiometer elements is based on uncooled vanadium oxide (VOx) microbolometer pixel technology but with the addition of two elements: vertically aligned carbon nanotubes (VACNTs) and an electrical substitution heater. Traditional microbolometer pixels use a thermistor film as an absorber, which is placed a quarter wavelength above a reflector, typically limiting absorption to a narrow band from 8 μm to 15 μm. To extend the sensing range of the imaging array into the far infrared (20 μm to 100 μm), we are replacing the cavity with a single absorber of VACNTs. In addition, each pixel has an electrical substitution heater which can be used to determine equivalent incident optical power when the device is non-illuminated. This device forms the basis of an absolute radiometer eliminating the need for an external reference (e.g. blackbody source).
The application of THz plasmonics in imaging dielectric objects embedded in the metallic media is presented.
Signatures of the embedded object was detected when the time domain information of the transmitted pulse was
analyzed by THz time domain spectroscopy. The resolution of the acquired images was enhanced by using a super-resolution
image processing technique. It is further shown that the images acquired from the pulse arrival time and
phase magnitude reveal more details of the embedded object compared to the pulse power information.
We demonstrate the potential utilization of a Schottky barrier in the plasmonic regime at terahertz (THz)
frequencies. Experimental evidence of local THz plasmonic field enhancement via radiation from the space-charge
distribution at a Schottky interface is shown. A 12% increase in the plasmonic-mediated transmission of THz radiation
through random, dense ensembles of Cu particles is observed when a CuxO/Au structure is introduced to the surface of
the particles. The THz electric field induces oscillations of the local charge density at the Schottky interface leading to
emission of high frequency radiation as the charges settle back into equilibrium. The non-linear THz response of the
Schottky interface introduces the physical groundwork for the implementation of plasmonic circuits that have operational
frequencies exceeding the limits of traditional semiconductor electronics.