For several decades, the National Institute of Standards and Technology (NIST) has actively supported metrology programs for extreme ultraviolet (EUV) lithography. We will describe our existing programs in optics lifetime, reflectometry, and radiometry. Recent developments include developing quantitative models for both carbonization and oxidation of optics under UV illumination and use of a cryogenic radiometer to calibrate transfer-standard detectors from 4 nm to 400 nm. We describe two programs currently in planning. The first of these is development of a method to calibrate high-power pulsed radiation detectors using a calorimeter. Our current primary standard detectors for 13 nm are based on synchrotron radiation with incident powers of a few microwatts or less. EUV production tools need to measure pulse trains with many hundreds of watts of average power. We will begin this work on our existing low-power detector-calibration facility and use higher-power beamlines with overlapping power ranges and the linearity of synchrotron radiance with stored beam current to extend the calibrations to higher powers. Second, we present a Mueller matrix ellipsometry and scatterometry system covering the far-to-extreme ultraviolet spectral range. This system is expected to achieve the requisite variable polarization and diattenuation control with an entirely reflective optical system. By extending scatterometry to short wavelengths, we intend to demonstrate improved sensitivity and accuracy of parameter retrieval from microfabricated devices. These programs complement NIST's existing far- and extreme-ultraviolet radiometry and metrology programs and expand our support for critical semiconductor manufacturing.

As the COVID-19 pandemic was overtaking the world in the spring of 2020, the National Institute of Standards and Technology (NIST) began collaborating with the National Biodefense Analysis and Countermeasures Center to study the inactivation of SARS-CoV-2 after exposure to different ultraviolet (UV) and blue light wavelengths. This paper describes a 1 kHz pulsed laser and projection system used to study the doses required to inactive SARS-CoV-2 over the wavelength range of 222 to 488 nm. This paper builds on NIST’s previous work for water pathogen inactivation using UV laser irradiation. The design of the laser and projection system and its performance in a Biosafety Level 3 (BSL-3) laboratory are given. The SARS-CoV-2 inactivation results (published elsewhere by Schuit, M.A., et al ., expected 2022) demonstrate that a tunable laser projection system is an invaluable tool for this research.

The objective of the airborne lunar spectral irradiance (air-LUSI) project is to make low uncertainty, SI-traceable measurements of the LUSI in the visible to near-infrared region from an aircraft above most of the optically absorbing components of the atmosphere. The measurements are made from a NASA ER-2 aircraft, which can fly at altitudes of approximately 20 km above sea level. Air-LUSI measurements, corrected for residual atmospheric attenuation, are designed to provide a matrix of low uncertainty top-of-the-atmosphere lunar irradiances at known lunar phase and libration angles to be compared and combined with other lunar irradiance data sets to constrain the uncertainties in models of lunar irradiance and reflectance. The measurements are also expected to provide insight into the differences between models and satellite sensor measurements of lunar irradiance. This paper describes the development and characterization of the air-LUSI subsystem for acquiring lunar measurements, called the irradiance instrument subsystem, prior to flight.

Numerous studies have demonstrated that SARS-CoV-2 can be inactivated by ultraviolet (UV) radiation. However, there are few data available on the relative efficacy of different wavelengths of UV radiation and visible light, which complicates assessments of UV decontamination interventions. The present study evaluated the effects of monochromatic radiation at 16 wavelengths from 222 nm through 488 nm on SARS-CoV-2 in liquid aliquots and dried droplets of water and simulated saliva. The data were used to generate a set of action spectra which quantify the susceptibility of SARS-CoV-2 to genome damage and inactivation across the tested wavelengths. UVC wavelengths (<= 280 nm) were most effective for inactivating SARS-CoV-2, although inactivation rates were dependent on sample type. Results from this study suggest that UV radiation can effectively inactivate SARS-CoV-2 in liquids and dried droplets, and provide a foundation for understanding the factors which affect the efficacy of different wavelengths in real-world settings.

To monitor global environments from space, satellites must be calibrated accurately and consistently across time, missions and instruments. This requires the use of a stable, common reference that is continuously accessible to Earth observing satellites, whether they make up series of missions spanning long periods of time or comprise constellations acquiring many simultaneous observations across the planet. The Moon can serve well as such a common reference. Its surface reflectance is stable to within one part in 108. It is theorized that its radiant output with time changes repeatedly and very predictably with viewing and illumination geometry. In addition, it has a radiant flux more comparable to the Earth’s surface than the Sun and can be viewed directly by the instrument. Currently, to predict the lunar irradiance given an illumination and viewing geometry, the United States Geological Survey (USGS) has developed the Robotic Lunar Observatory (ROLO) Model of exo-atmospheric lunar spectral irradiance. The USGS ROLO model represents the current most precise knowledge of lunar spectral irradiance and is used frequently as a relative calibration standard by space-borne Earth-observing sensors. Current knowledge of the Moon's spectral irradiance is thought to be limited to 5-10% uncertainty. However, monitoring changing Earth environments calls for an absolute lunar reference with higher accuracy. The development of the ROLO model and subsequent attempts to better characterize the lunar spectral irradiance cycle were based on observations made from the Earth surface. This requires applying corrections to remove effects of the atmosphere, which limits the accuracy. The Airborne LUnar Spectral Irradiance (Air-LUSI) system was developed to make highly accurate, SI-traceable measurements of lunar spectral irradiance from NASA’s ER-2 aircraft flying at 21 km, above 95% of the atmosphere. To that end, the air-LUSI system employs an autonomous, robotic telescope system that tracks the Moon in flight and a stable spectrometer housed in an enclosure providing a robustly controlled environment. During November 2019, the Air-LUSI system was demonstrated with flights on five consecutive nights acquiring observations of the Moon at lunar phases of 10°, 21°, 34°, 46°, and 59°. Air-LUSI is now ready for operational use. This paper provides an overview of this new capability and how it, along with other efforts underway, can help transform how we monitor the Earth from space.

This paper describes advances in measuring the characteristic spatial distribution of surface temperature and emissivity during laser-metal interaction under conditions relevant for laser powder bed fusion (LPBF) additive manufacturing processes. Detailed descriptions of the measurement process, results, and approaches to determining uncertainties are provided. Measurement uncertainties have complex dependencies on multiple process parameters, so the methodology is demonstrated on one set of process parameters and one material. Well-established literature values for high-purity nickel solidification temperature and emissivity at the solidification temperature were used to evaluate the predicted uncertainty of the measurements. The standard temperature measurement uncertainty is found to be approximately 0.9 % of the absolute temperature (16 °C), and the standard relative emissivity measurement uncertainty is found to be approximately 8 % at the solidification point of high-purity nickel, both of which are satisfactory. This paper also outlines several potential sources of test uncertainties, which may require additional experimental evaluation. The largest of these are the metal vapor and ejecta that are produced as process by-products, which can potentially affect the imaging quality, reflectometry results, and thermal signature of the process, while also affecting the process of laser power delivery. Furthermore, the current paper focuses strictly on the uncertainties of the emissivity and temperature measurement approach and therefore does not detail a variety of uncertainties associated with experimental controls that must be evaluated for future generation of reference data.

To monitor global environments from space, satellites must be calibrated accurately and consistently across time, missions and instruments. This requires the use of a stable, common reference that is continuously accessible to Earth observing satellites, whether they make up series of missions spanning long periods of time or comprise constellations acquiring many simultaneous observations across the planet. The Moon can serve well as such a common reference. Its surface reflectance is stable to within one part in 108. It is theorized that its radiant output with time changes repeatedly and very predictably with viewing and illumination geometry. In addition, it has a radiant flux more comparable to the Earth’s surface than the Sun and can be viewed directly by the instrument. Currently, to predict the lunar irradiance given an illumination and viewing geometry, the United States Geological Survey (USGS) has developed the Robotic Lunar Observatory (ROLO) Model of exo-atmospheric lunar spectral irradiance. The USGS ROLO model represents the current most precise knowledge of lunar spectral irradiance and is used frequently as a relative calibration standard by space-borne Earth-observing sensors. Current knowledge of the Moon's spectral irradiance is thought to be limited to 5-10% uncertainty. However, monitoring changing Earth environments calls for an absolute lunar reference with higher accuracy. The development of the ROLO model and subsequent attempts to better characterize the lunar spectral irradiance cycle were based on observations made from the Earth surface. This requires applying corrections to remove effects of the atmosphere, which limits the accuracy. The Airborne LUnar Spectral Irradiance (Air-LUSI) system was developed to make highly accurate, SI-traceable measurements of lunar spectral irradiance from NASA’s ER-2 aircraft flying at 21 km, above 95% of the atmosphere. To that end, the air-LUSI system employs an autonomous, robotic telescope system that tracks the Moon in flight and a stable spectrometer housed in an enclosure providing a robustly controlled environment. During November 2019, the Air-LUSI system was demonstrated with flights on five consecutive nights acquiring observations of the Moon at lunar phases of 10°, 21°, 34°, 46°, and 59°. Air-LUSI is now ready for operational use. This paper provides an overview of this new capability and how it, along with other efforts underway, can help transform how we monitor the Earth from space.

High-speed thermography is useful tool for researching the laser powder bed fusion process by providing thermal information in heat affected zone. However, it is not directly possible to ascertain the position of the laser spot with respect to the melt pool, which could provide key information regarding how laser energy is distributed and absorbed. In this paper, we demonstrate a procedure for registering the laser spot position with the melt pool using a bright illumination source co-axially aligned with the laser to project a sharp spot on the build plane. This spot is fixed to the laser position and used as a reference frame for registering the laser spot with the melt pool radiance temperature distribution. Measurement results demonstrate the effect of varying process parameters (laser power and scan speed) on the melt pool thermal field and respective position of the laser spot.

Absolute flux calibration of standard stars, traceable to the International System of Units (SI) standards, is essential for 21st century astrophysics. Dark energy investigations that rely on observations of Type Ia supernovae and precise photometric redshifts of weakly lensed galaxies require a minimum uncertainty of 0.5% (k=1) in the absolute color calibration. Other areas of astronomy and astrophysics, e.g. fundamental stellar astrophysics, will also benefit. In the era of large telescopes and all sky surveys, well-calibrated standard stars that do not saturate, are available over the whole sky, and extend to fainter magnitudes are needed. Our collaboration, NIST Stars, has developed a novel, fully SI-traceable laboratory calibration strategy that will enable achieving the demanding 0.5% requirement which we shall describe here. We discuss our results from a pilot study to determine the top-of-the-atmosphere absolute spectral irradiance of bright stars and the next steps.

We have designed a non-imaging telescope for measurement of the spectral irradiance of the moon. The telescope was designed to be integrated into a wing pod of a National Aeronautics and Space Administration ER-2 research aircraft to measure lunar spectral irradiance during flight. The telescope and support system were successfully flown in August 2018 at altitudes near 21 km and at speeds of ∼760 km/h. The wing pod in which the telescope is mounted has an opening through which the moon can be observed. The mount exposes the telescope to high winds, low pressures, temperatures near -60 °C, and vibrations both due to flight and due to the motion of the aircraft on the ground. This required a telescope design with high thermal stability and high resistance to shock. The optical design of the telescope is optimized to have high throughput and spatially uniform transmission from 380 nm to 1000 nm over a field of view about three times the angular size of the moon as viewed from the Earth. The final design resulted in a telescope with singlet design incorporating a 139.7 mm lens with an effective focal length of 377 mm and a field of view of 1.6°. The light from the telescope is introduced into an integrating sphere, which destroys the image and the polarization for measurement by a fiber-coupled spectroradiometer. Herein, we present an overview of the instrument and support system with emphasis on the telescope design.

Melt pool monitoring (MPM) is a technique used in laser powder bed fusion (LPBF) to extract features from insitu sensor signals that correlate to defect formation or general part fabrication quality. Various melt pool phenomena have been shown to relate to measured transient absorption of the laser energy, which in turn, can be relatable to the melt pool emission measured in MPM systems. This paper describes use of a reflectometer-based instrument to measure the dynamic laser energy absorption during single-line laser scans. Scans are conducted on bare metal and single powder layer of nickel alloy 625 (IN625) at a range of laser powers. In addition, a photodetector aligned co-axially with the laser, often found in commercial LPBF monitoring systems, synchronously measured of the incandescent emission from the melt pool with the dynamic laser absorption. Relationships between the dynamic laser absorption, co-axial MPM, and surface features on the tracks are observed, providing illustration of the melt pool dynamics that formed these features. Time-integrated measurements of laser absorption are shown to correlate well with MPM signal, as well as indicate the transition between conduction and keyhole mode. This transition is corroborated by metallographic cross-section measurement, as well as topographic measurements of the solidified tracks. Ultimately, this paper exemplifies the utility of dynamic laser absorption measurements to inform both the physical nature of the melt pool dynamics, as well as interpretation of process monitoring signals.

Additive manufacturing (AM) technologies are increasingly being studied and introduced into the modern industry, but for wide applications there exists some "lack of confidence" about the quality of the parts produced by AM.This distrust has an objective basis: it was shown that the final 3D object is a superposition of a huge number of tracks and layers, and deviations from the optimal process parameters can lead to non-regular shape, unmelted places (lack of fusion) and porosity.Experiments with different bare substrates were performed to classify instabilities and artifacts in single tracks derived from laser beam characteristics, the optical system, scanning strategy, etc. demonstrating an adjustment scheme for testing and verifying LPBF equipment.An important point is that this research can be useful for the custom experimental setup.The paper describes the importance of checking the system before each build to identify problems caused by optical system operation.Also, possible deviations from the stable process, methods of their diagnostics and solutions are described.The proposed method is a cost-free way to diagnose the stability of the selective laser melting, which does not imply the necessity of having additional systems for detecting problems.The diagnostic scheme was used to evaluate in situ diagnostics of the LPBF processes on the Additive Manufacturing Metrology Testbed (AMMT) at the National Institute of Standards and Technology (NIST).

The paper describes efforts to establish traceable measurements of radiance temperature on laser-induced heated metal surfaces on the NIST Additive Manufacturing Metrology Testbed (AMMT). Knowledge of radiance temperature with a well understood uncertainty budget is a necessary initial step towards an ultimate project goal of traceable emittance and true surface temperature across the heat affected zone, which is a key objective in additive manufacturing research, and the subject of another paper at this conference. Reliable measurements of radiance temperature with an imaging system require (1) calibration of its responsivity at select radiance levels, (2) establishing a calibration equation that interpolates between these levels, (3) dealing with finite spectral bandpass and spatial non-uniformity of the sensor responsivity, and (4) ability for compensate effects of imperfect optical imaging and readout electronics on spatial distribution of the target. The developed system includes an integrating sphere-based calibration source, a pyrometer for its calibration against external blackbody, and an imaging system co-axially aligned with the heating laser, each of which using identical narrow band filters. This paper describes the evaluation of an 850 nm band, with additional wavebands planned for the future. This paper presents experimental results, description of measurement equation and processing algorithm, as well as a framework for establishing an uncertainty budget, including current estimates and future performance goals.

NIST’s Physical Measurement and Engineering Laboratories are jointly developing the Additive Manufacturing Measurement Test bed (AMMT)/ Temperature and Emittance of Melts, Powders and Solids (TEMPS) facilities. These facilities will be co-located on an open architecture laser-based powder bed fusion system allowing users full access to the system’s operation parameters. This will provide users with access to machine-independent monitoring and control of the powder bed fusion process. In this paper there will be emphasis on the AMMT, which incorporates in-line visible light collection optics for monitoring and feedback control of the powder bed fusion process. We shall present an overview of the AMMT/TEMPs program and it goals. The optical and mechanical design of the open architecture powder-bed fusion system and the AMMT will be also be described. In addition, preliminary measurement results from the system along with the current system status of the system the will be described.

A critical component of high-performance EUV lithography source optics is the reflecting multilayer coating. The ideal multilayer will have both high reflectance and high stability to thermal load. Additionally the capping layers must provide resistance to degradations from exposure to an EUV source, and also be compatible with, or enhance, the systems used for cleaning an exposed multilayer coating. We will report on the results of development of C and B4C stabilized Mo/Si multilayers used to increase the as-deposited peak reflectivity (Rp) as well as decreasing the loss of peak reflectivity (Rp) as a function of annealing temperature. Previous results demonstrate that these layers prevent loss of Rp for temperatures up to 600 degrees C. Results on the use of reactively-sputtered oxide capping layers such as SiO2 and ZrO2 will be presented as well, along with results of exposure testing. The deposition is performed in a dual process-chamber inline magnetron system, using reactive sputtering for the production of capping layers. The reflectometer and exposure apparatus at the NIST Physics Laboratory is used for evaluation of the performance. Exposure results on the resistance to oxidation in the presence of water vapor will be presented and discussed.

Laser-produced plasma (LPP) sources for extreme ultraviolet lithography (EUVL) systems utilize CO2 lasers operating with wavelength 10.6μm. Since multilayer-coated optics have high reflectivity for this infrared radiation (IR), a significant and detrimental amount of IR is passed through the EUVL system. One method to remove the IR from the system is to utilize a binary diffraction grating. When this grating is applied directly to the surface of the primary collector optic of the source, the majority of the IR is diverted outside the radius of the exit aperture at the intermediate focus (IF). This paper will report details on the performance of a full size (410mm diameter) Demonstration Collector utilizing IR rejection (IRR) technology with the capability to produce over 125X suppression of IR, equaling the performance of a IR spectral filter. Additional details will be reported on the technology development and use of a glassy smoothing layer to enable high EUV performance, a weighted average multilayer reflectance of 50.9% for unpolarized EUV radiation.

The NIST Extreme Ultraviolet (EUV) Reflectometry Facility was designed in the 1990s to accommodate the largest multilayer optics envisioned at that time. However, with increasing power requirements for an EUV scanner, source collection optics have grown larger and more steeply curved than the original design would allow. To accommodate these changes, the mechanical and operational parameters of the facility have been upgraded. To access the entire surface of a larger optic, an auxiliary off-axis rotation stage has been installed allowing an increase in maximum optic size from 350 mm to 450 mm. Likewise, to deal with the deeper sags and steeper slopes of these optics, we have had to significantly expand our data analysis capabilities. In order to make these measurements, the incident radiation is reflected out of the vertical plane, allowing for measurements of effectively unpolarized radiation, an advantage for EUV lithography optics such as source collectors.