Pt is a suitable thermistor for use in microbolometers due to its high melting point, chemical inertness, and low 1/f noise. This work explores mechanisms of grain growth to fabricate Pt thin film thermistors for maximizing the temperature coefficient of resistance (TCR). The interplay between the microstructure and TCR is examined by varying Pt film deposition parameters, AlOX interlayer deposition technique, patterning technique, and annealing parameters. A smooth thin film morphology having giant grains of several hundreds of micrometers is achieved by abnormal grain growth, which is not attainable through normal grain growth. The fabrication of thermistor meanders is demonstrated through a combination of processes including Pt film deposition in O2/Ar environment, annealing at 1000 degrees C in Ar, and ion beam etching. Pt thermistors with a TCR (0 degrees C - 100 degrees C) of 0.371 +/- 0.001 %/ degrees C are compatible with microbolometers utilizing carbon nanotube absorbers.

We report on the demonstration of a laser-heated blackbody source fabricated from vertically aligned carbon nanotubes (VACNTs). This thermal source has potential use for performing micro- and nano- infrared spectroscopies because VACNTs have an extremely high melting point >3000 K, near unity emissivity across the infrared, and are compatible with lithographic microfabrication that can be exploited to maximize etendue of thermal emission.

Thermal emitters are an important component for performing broadband infrared spectroscopy for critical applications. We report on the development and demonstration of a laser-heated thermal emitter source based on vertically aligned carbon nanotubes (VACNTs) for Fourier transform infrared spectroscopy (FTIR). This thermal source is an improvement over common emitters such as tungsten and silicon carbide (Globar) because VACNTs have an extremely high melting point >3000 K and near unity emissivity from visible through far-infrared. We compare our VACNT source to a Globar in the mid- to far-infrared, and present on the next phase of improvement for this infrared light source.

We report on initial fabrication efforts in the integration of superconducting nanowire single-photon detectors (SNSPDs) with vertically aligned carbon nanotubes (VACNTs) with the goal of creating a wideband single-photon detector. SNSPDs provide high detection efficiencies and low dark count rates, while the VACNTs are excellent broadband optical absorbers. Combining these technologies could potentially enable the development of highly sensitive and versatile optical sensors for a variety of applications, such as spectroscopy, optical communication, and imaging in light starved environments. We developed two fabrication processes for the integration of VACNTs on SNSPDs. The first involves capping the SNSPDs with a protective layer and growing the VACNTs directly above nanowires. Thermal and electrical characterizations of the devices demonstrated a degradation of the superconducting qualities of the SNSPDs. The second process involved suspending the SNSPDs on a thin membrane via a backside etch, where VACNTs were then grown on the backside of the membranes below the nanowires. The membrane style devices showed no degradation in the superconducting properties of the nanowires. Measurements of the membrane style devices before and after the VACNT growth display similar superconducting properties and photon count rates.

We have developed a low-cost micro-diffuse reflectance infrared Fourier transform spectroscopic (micro-DRIFTS) setup for measuring the reflectance of small area diffuse samples. The system performance is characterized and then demonstrated on small area vertically aligned carbon nanotube (VACNT) samples. We find that our system can measure samples with a spatial resolution of approximately 140 µm with sensitivities of 10s of ppm in the 2 µm – 18 µm spectral window. Our uncertainty budget is presented along with how our measured reflectance can be equated to directional-hemispherical reflectance.

BABAR-ERI is being developed for a CubeSat capable of imaging the Earth’s outgoing longwave radiation with a 1 km ground sample distance (GSD) using a push-broom imager. The detector is a silicon micromachined 32-pixel linear array of electrical substitution radiometers capable of broadband sensing from 0.3 $\mu$m to 100 $\mu$m using vertically aligned carbon nanotube absorbers located on each pixel. Our aim is to demonstrate data performance, with a CubeSat, against existing CERES instruments but at a smaller GSD. Electrical substitution radiometers are well suited to this task as they have heritage as ground calibration transfer standards and in space for total solar irradiance measurements.

Uncooled microbolometer arrays incorporating vertically aligned carbon nanotube absorbers are increasingly being adopted in satellite instrumentation for monitoring the Earth’s radiation budget. A key requirement for such microbolometers is a thermistor having high-temperature coefficient of resistance (TCR), low 1/f noise while surviving high-temperature carbon nanotube growth at 800 °C. In the present work, Pt thin-film thermistors are fabricated on SiNx/SiO2/Si substrates using DC magnetron sputtering. To achieve enhanced adhesion of the Pt thin film, an interlayer of AlOx is deposited on the substrate via reactive high-power impulse magnetron sputtering. To maximize the positive TCR, the Pt/AlOx is subjected to different annealing conditions by varying temperature, time, and gaseous environment. With an increase in the annealing temperature and duration, Pt/AlOx thin film exhibits an improvement in TCR. Microstructural and morphological investigations suggest that improvement in TCR is related to the recrystallization of Pt and the resulting increase in grain size. A relatively high TCR of 0.308%/°C (TCR of bulk Pt = 0.359%/°C) was obtained at an operational range of 20–50 °C when Pt was annealed at 800 °C for 1 h and 3 h in air and Ar, respectively. Deposition of Pt without an AlOx interlayer resulted in thin film blistering and delamination when annealed at 800 °C for 1 h in air. A Pt/AlOx thermistor with a TCR of 0.308%/°C, annealed at 800 °C for 3 h in Ar has the potential for use in microbolometers that must undergo high-temperature growth of vertically aligned carbon nanotube absorbers.

Vertically aligned carbon nanotube microbolometers are being developed for broadband, far-infrared sensing of Earth’s outgoing radiation. The current challenge for microfabrication is integrating thin film thermistors with the devices. The thin film thermistor should survive all fabrication steps, including the high-temperature carbon nanotube growth. This paper explores microfabrication routes to produce Pt thin film thermistors on silicon nitride using an aluminum oxide underlayer. To improve crystallinity and surface uniformity, we determine sputtering parameters for optimal growth of giant Pt grains, such as the critical film thickness, O_2/Ar ratio, and wafer mounting schemes. In addition, we compare the differences between lift-off defined Pt thermistors to that of ion-milled defined Pt thermistors. Finally, the Pt thermistors were submitted to carbon nanotube growth to assess changes in the temperature coefficient of resistance (TCR) resulting from exposure to hydrogen and C_2H_4 plasma at 800 °C. Graphical abstract

We have developed a low-cost setup for absolute infrared micro-reflectance to measure microstructures (< 1 mm). This setup is designed to characterize carbon nanotube microbolometers for use in space-based global energy imbalance measurements.

We present the results of a recent, extensive measurement campaign validating the traceability of the solar irradiance record and Earth radiation budget data. The campaign also established future traceability, thus ensuring confidence in the continuing climate-data record. The total solar irradiance radiometer facility (TRF) at the Laboratory for Atmospheric and Space Physics (LASP) Boulder, uses a liquid helium cooled cryogenic radiometer as the reference standard for the validation of spaceflight total solar irradiance (TSI) instrumentation. In 2008 the radiometer was directly compared to the National Institute of Standards and Technology (NIST) Primary Optical Watt Radiometer (POWR) at a wavelength of 532.12 nm. At TSI power levels, a correction factor of 1.000 306 with an associated standard uncertainty (u) of 0.000 098, was reported for the TRF radiometer scale when using external voltage measurement electronics, and not correcting for cavity heating non-equivalence or cavity absorptance. The TRF radiometer has recently been revalidated at LASP using a POWR calibrated silicon photodiode trap transfer standard named TT4. We report a correction factor of 0.999 787, u = 0.000 285 to align the TRF radiometer scale with the current NIST POWR scale. A new room temperature reference standard radiometer was established. It measured 133 parts per million (ppm) higher than POWR using the same silicon transfer standard as above, and in a separate direct measurement, 168 ppm lower than the TRF radiometer shuttered at 400 s full shutter cycle. The difference agrees within stated uncertainties. A correction of 0.999 867, u = 0.000 247 will align the new radiometer scale with the NIST radiant power scale of POWR.

BABAR microbolometers are instruments for far-infrared sensing of Earth radiation from space. To improve the signal-to-noise-ratio of the instrument, a high temperature coefficient of resistance (TCR) was achieved in Pt-thermistors by overcoming challenges of microfabrication.

The Earth radiation budget, a 40-year data record of the balance between solar radiation reaching the Earth and the amount reflected, and emitted from the Earth, is a key climate record for determining whether the Earth is warming or cooling. The need for accurate and cost-effective space-based measurements is driving the technology development of broadband bolometers and linear microbolometer arrays. We describe the performance of microfabricated bolometers and 1 x 32 linear microbolometer arrays developed for this purpose. To accurately measure the total outgoing radiation from 0.3 μm to over 100 μm, consisting of reflected shortwave solar radiation and emitted longwave thermal radiation, a vertically aligned carbon nanotube thermal absorber is incorporated with an electrical substitution heater that provides on-board calibration capabilities. A silicon nitride heat link is used to optimize response time while minimizing noise and the inequivalence between thermal and optical heating. The devices operate at room temperature with noise floors at nW/√Hz or lower at the measurement frequency of 7 Hz. Response times below 10 ms have been demonstrated in closed-loop operation using the electrical heater. Thin film Pt thermistors measure the change in microbolometer temperature. The deposition of the thin film thermistors has been optimized to maximize the temperature coefficient of resistance, which is key to meeting the demanding signal-to-noise requirement of this application.

Emerging applications require a calibration at 1 W with greater accuracy than is currently available. Conventional free beam absolute electrical substitution radiometers (ESRs) operate at cryogenic conditions have historically provided the highest accuracy but operate at optical power levels < 2 mW. To improve the accuracy of calibrations at 1 W, we compare possible approaches to realize a primary standard for 1 W optical power measurements. We describe and evaluate two diverse concepts based on bolometer detectors: The first design is an adapted cryogenic approach while the second system is operating at room temperature (RT). With the proposed uncertainty budgets, we estimate an expanded uncertainty for the RT layout to be < 0.06 % (k = 2) while the cryogenic design approaches 0.02 % (k = 2).

The technique of phase contrast imaging, combined with tomographic reconstructions, can rapidly measure ultrasonic fields propagating in water, including ultrasonic fields with complex wavefront shapes, which are difficult to characterize with standard hydrophone measurements. Furthermore, the technique can measure the absolute pressure amplitudes of ultrasonic fields without requiring a pressure calibration. Absolute pressure measurements have been previously demonstrated using optical imaging methods for ultrasonic frequencies below 2.5 MHz. The present work demonstrates that phase contrast imaging can accurately measure ultrasonic fields with frequencies up to 20 MHz and pressure amplitudes near 10 kPa. Accurate measurements at high ultrasonic frequencies are performed by tailoring the measurement conditions to limit optical diffraction as guided by a simple dimensionless parameter. In some situations, differences between high frequency measurements made with the phase contrast method and a calibrated hydrophone become apparent, and the reasons for these differences are discussed. Extending optical imaging measurements to high ultrasonic frequencies could facilitate quantitative applications of ultrasound measurements in nondestructive testing and medical therapeutics and diagnostics such as photoacoustic imaging.

We introduce a planar absolute radiometer for room temperature (PARRoT) that will replace NIST’s 50-year-old detector standard for free-space CW laser power measurements and lower the measurement uncertainty (k = 2) from 0.86% to 0.12%.

The design and performance of a room temperature electrical substitution radiometer for use as an absolute standard for measuring continuous-wave laser power over a wide range of wavelengths, beam diameters, and powers are described. The standard achieves an accuracy of 0.46% (k = 2) for powers from 10 mW to 100 mW and 0.83% (k = 2) for powers from 1 mW to 10 mW and can accommodate laser beam diameters (1/e2) up to 11 mm and wavelengths from 300 nm to 2 μm. At low power levels, the uncertainty is dominated by sensitivity to fluctuations in the thermal environment. The core of the instrument is a planar, silicon microfabricated bolometer with vertically aligned carbon nanotube absorbers, commercial surface mount thermistors, and an integrated heater. Where possible, commercial electronics and components were used. The performance was validated by comparing it to a National Institute of Standards and Technology primary standard through a transfer standard silicon trap detector and by comparing it to the legacy "C-series" standards in operation at the U.S. Air Force Metrology and Calibration Division (AFMETCAL).

We apply pulsed optical phase contrast microscopy to measure the absolute pressure amplitudes of complex ultrasonic fields generated by planar and focused transducers at frequencies up to 20 MHz. 2021 National Institute of Standards and Technology.

We have developed a planar absolute radiometer for room temperature (PARRoT) that will replace the legacy C-series calorimeter as the free-space continuous-wave laser power detector standard at the National Institute of Standards and Technology (NIST). This instrument will lower the combined relative expanded measurement uncertainty (k = 2) from 0.84 % to 0.13 %. PARRoT's performance was validated by comparing its response against a transfer standard silicon trap detector traceable to NIST's primary standard laser optimized cryogenic radiometer (LOCR) and against the C-series calorimeter. On average, these comparisons agreed to better than 0.008 % and 0.05 %, respectively.

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.