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After we replaced the argon mini-arc with a laser-driven light source in the Ultraviolet Spectral Comparator Facility at the National Institute of Standards and Technology (NIST), we realized that the optical power should be sufficient to use the comparator system for absolute-cryogenic radiometry. Calibrating working standard detectors directly against an absolute-cryogenic radiometer in the system used for calibrations would eliminate all uncertainties resulting from the use of transfer standards, which were calibrated in a separate system using a different light source and optics. The transfer standards are the middlemen we refer to in the title. Any uncertainty caused by differences in bandpass, out-off-band radiation, spectral purity, collimation, or data interpolation would be removed. In the end, we successfully set up a twin system resembling the Ultraviolet Spectral Comparator Facility and used this system to perform a primary calibration of several photodiodes, based on an absolute-cryogenic radiometer. Using this system, we were able to reduce relative standard uncertainties at wavelengths below 220 nm from above 1 % ( k = 1 ) to below 0.5%. We refer to this system as the Ultraviolet Scale Realization Facility or UV-SRF.

We have developed a new method for the exact calculation of synchrotron radiation for the National Institute of Standards and Technology Synchrotron Ultraviolet Radiation Facility, SURF III. Instead of using the Schwinger formula, which is only an approximation, we develop formulae based on Graf’s addition theorem for Bessel functions and accurate asymptotic expansions for Hankel functions and Bessel functions. By measuring the radiation intensity profile at two distances from the storage ring, we also confirm an apparent vertical emittance that is consistent with the vertical betatron oscillations that are intentionally introduced to extend beam lifetime by spreading the electron beam spatially. Finally, we determine how much diffraction by beamline apertures enhances the spectral irradiance at an integrating sphere entrance port at the end station. This should eliminate small but treatable components of the uncertainty budget that one should consider when using SURF III or similar synchrotrons as standard, calculable sources of ultraviolet and other radiation. https://doi.org/10.1063/1.5018412

IR-enhanced Si photodiodes have improved radiometric and electronic characteristics as compared to other widely used Si photodiodes and can be used as responsivity standards in the wavelength range from 300 nm to 1000 nm. Their low predicted uncertainty for radiant power responsivity measurements can result in improvements in the existing monochromator-based Si responsivity scales. They have several advantages over traditionally used Si-trap detectors, such as wider acceptance angle, higher shunt resistance, and higher responsivity in the NIR region. Radiometric and electronic measurement results are discussed to illustrate these characteristics. The spectral power responsivity scales can be improved using a set of the IR-enhanced Si photodiodes not only to transfer the calibration from the cryogenic radiometer, but for use in the monochromator facility as working standards. This improvement will reduce the length of the calibration chain and create a one-step scale transfer between the cryogenic radiometer- and the monochromator-based facility.

Interest in the use of synchrotron radiation (SR) as a source of continuum in the extreme ultraviolet (EUV) spectral region was stimulated by the 1956 Physical Review article by Diran Tomboulian and Paul Hartman [1] of Cornell University. In their all-too-brief access to the Cornell 320 MeV electron synchrotron, they showed that SR should be an extremely useful intensity standard in the EUV. They also showed the continuum nature of SR by observing structure at the K-edge of Be at 112 eV.

At present, broadband radiometric measurements of LEDs with uniform and low-uncertainty results are not available. Currently, either complicated and expensive spectral radiometric measurements or broadband photometric LED measurements are used. The broadband photometric measurements are based on the CIE standardized V(λ) function, which cannot be used in the UV range and leads to large errors when blue or red LEDs are measured in its wings, where the realization is always poor. Reference irradiance meters with spectrally constant response and high-intensity LED irradiance sources were developed here to implement the previously suggested broadband radiometric LED measurement procedure [1, 2]. Using a detector with spectrally constant response, the broadband radiometric quantities of any LEDs or LED groups can be simply measured with low uncertainty without using any source standard. The spectral flatness of filtered-Si detectors and low-noise pyroelectric radiometers are compared. Examples are given for integrated irradiance measurement of UV and blue LED sources using the here introduced reference (standard) pyroelectric irradiance meters. For validation, the broadband measured integrated irradiance of several LED-365 sources were compared with the spectrally determined integrated irradiance derived from an FEL spectral irradiance lamp-standard. Integrated responsivity transfer from the reference irradiance meter to transfer standard and field UV irradiance meters is discussed.

In 2004, the National Institute of Standards and Technology established the ultraviolet spectral irradiance scale from 200 nm to 400 nm using the calculable irradiance of the Synchrotron Ultraviolet Radiation Facility (SURF). Since the establishment of the scale, spectral irradiance calibrations of many customer lamps have been performed in direct comparison with synchrotron radiation. However, to ensure long-term stability of the scale, three check-standard deuterium lamps were calibrated using SURF III at the same time as customer lamps were being calibrated. Here, we present the results of the long-term monitoring of the scale using these check-standard lamps to ensure customer lamps are calibrated within the expanded calibration uncertainty (k = 2) of 1.2%.

Synchrotron radiation was recognized as an important tool for radiometry shortly after the advent of dedicated storage rings as radiation sources more than four decades ago. [1] Initially, synchrotron radiation was conceived as a calculable primary standard for absolute calibration of radiation sources. With the explosion of synchrotron radiation facilities around the globe during the last several decades, synchrotron-radiation-based radiometry has been actively pursued among many national standard laboratories in countries including the U.S., Germany, the U.K., Japan, and Russia because of increasing demands from semiconductor photolithography, UV curing industry, medical diagnostics and treatments, and solar radiation monitoring. To date, the use of synchrotron radiation for radiometry is no longer limited to a primary radiation standard. Dispersed synchrotron radiation, although usually not calculable, provides radiation from IR to X-rays for radiometric characterization of detector response and materi...

We report experimental results on the stability of photodiodes obtained at three different wavelengths in the vacuum ultraviolet spectral region. Two of these experiments were based on radiation damage inflicted with excimer lasers at 193 and 157 nm and one of them used 135 nm synchrotron radiation. It was found that the detector degradation rate increased considerably with the photon energy and depended on the structure of the photodiodes. Detectors based on the Si/SiO 2 interface were damaged much faster than Schottky-type diodes or Si diodes with metal passivating layers. Possible damage mechanisms to the Si/SiO 2 interface and its electronic structure are reviewed. In the end, a model to quantify the dependence of the damage on the photon energy is introduced.

A new source-based radiometry beamline was recently constructed at the Synchrotron Ultraviolet Radiation Facility (SURF III). The goal of this beamline is to establish a national source standard with a wide spectral range from the far ultraviolet to the infrared by using the calculability of SURF III. The new beamline is a straight-through white-light beamline with few, if any, optical components involved in delivering the radiation to the user end-station for applications such as source and irradiance intercomparisons. Due to the low tunable operating electron energy of SURF III (from 380 MeV to less than 100 MeV), the beamline is uniquely suited to work in the ultraviolet to infrared spectral range. In this paper we discuss the design of the beamline and present first results on the vertical angular distribution of the radiation determined with filtered radiometers in the ultraviolet, visible and near-infrared spectral ranges.

The Synchrotron Ultraviolet Radiation Facility (SURF III) at the National Institute of Standards and Technology provides a unique opportunity for high-accuracy ultraviolet (UV) to infrared radiometry due to the 70-fold improvement in the uniformity of the magnetic field from the previous generation of SURF. This improvement enables the properties of the output radiation, such as spectral power, angular spread, and polarization, to be more accurately predicted based on the use of the Schwinger’s equation. The radiation from SURF III is completely characterized by only three parameters, the magnetic field, the radius of the electron beam trajectory, and the electron beam current. For radiometry, the calculability of SURF III provides an important standard light source for source intercomparison. In contrast to the widely used blackbody source where the thermal radiation is completely characterized by the temperature and the emissivity of the blackbody walls, synchrotron radiation extends the wavelength range to UV and x ray which is impractical for blackbody sources. At SURF III, a new beamline, beamline 3, is constructed as a white light beamline for source-based radiometry. We describe the design of the new beamline 3 and its front-end high accuracy electron beam current monitor. This monitor not only measures one of the three fundamental parameters, the electron beam current, it also serves as an electron beam diagnostic tool. We also discuss ways to verify the calculability of SURF III using filter radiometers.

Imaging an electron beam with visible light is a common method of diagnostics applied to electron accelerators. It is a straightforward way to deduce the transverse electron distribution as well as its changes over time. The electrons stored in the Synchrotron Ultraviolet Radiation Facility (SURF) III at the National Institute of Standards and Technology (NIST) were studied over an extended period of time to characterize the upgraded accelerator. There is good agreement between experimental and theoretical horizontal beam sizes at three different electron energies.

The National Institute of Standards and Technology (NIST) operates the newly upgraded Synchrotron Ultraviolet Radiation Facility (SURF III) mainly as a light source for radiometry. SURF III provides continuum radiation from the far-infrared to the soft X-ray spectral range and has its peak output in the extreme ultraviolet. SURF III is a circular-orbit, weak-focusing (single dipole magnet) storage ring, a feature which is advantageous if the synchrotron radiation output is calculated. We report the improvements achieved during a recent upgrade from SURF II to SURF III and our strategy to accurately determine the magnetic flux density, radio frequency (RF), beam current, and beam size, which are the parameters necessary to characterize the source completely.

The completion of the upgrade of the synchrotron facilities at the National Institute of Standards and Technology (NIST) has yielded a better characterized broadband source of ultraviolet (UV) radiation at the Synchrotron Ultraviolet Radiation Facility (SURF III). A cryogenic-radiometer-based facility that uses the monochromatized radiation from SURF III has been established on beamline 4 (BL-4) to characterize detectors and optical materials in the wavelength range 125 nm to 325 nm. This upgraded cryogenic radiometry facility will be used to measure the spectral responsivity of detectors in the UV with a relative standard uncertainty of less than 10 ±2 . To demonstrate the capability of BL-4, we have performed a transmittance measurement of calciumuoride (CaF2 ). Accurate transmittance measurements of optical materials in the UV are urgently needed to evaluate which materials are the best choices for use in making lenses for UV lithography. A study of CaF2 in spectral transmittance, surface scattering, and surface absorption is presented.

We have constructed a new ultraviolet (UV) radiometry facility at the Synchrotron Ultraviolet Radiation Facility (SURF II) at the National Institute of Standards and Technology (NIST). The facility combines a high-throughput normal-incidence monochromator with an absolute cryogenic radiometer (ACR) optimized for UV measurements to provide absolute detector-based radiometric calibrations in the spectral range 125 nm to approximately 320 nm. The system can be configured for spectroradiometric calibration of photodetectors with completely automated mapping of detector spatial and angular responsivity. The facility can easily be adapted for other spectroradiometric measurements including transmittance and reflectance and the spectral range can be extended to about 50 nm.

A technique has been developed for coating commercial off the shelf (COTS) detector arrays with a thin, uniform layer of quantum dots. The quantum deposition is accomplished using an Optomec Aerosol Jet rapid prototyping system. When illuminated by UV andvacuumUV (VUV) the quantum dots will fluoresce and those emitted photons will be detected by the underlying detector array. The size of the quantum dots used determines the fluorescence wavelength and that would be matched to the peak sensitivity of the underlying detector array. The devices have been tested at the NIST synchrotron facility in Gaithersburg and have shown sensitivity down to 150nm. Performance at wavelengths below 150nm is limited by absorption by solvent residues from deposition process.

The National Institute of Standards and Technology (NIST) has operated the Synchrotron Ultraviolet Radiation Facility (SURF) continuously since the early 1960s. The original accelerator was converted into a storage ring, called SURF II, in 1974. Then in 1998, motivated mainly by limitations in the accuracy of radiometric calibrations and the wish to extend the spectrum of the emitted synchrotron radiation to shorter wavelengths, a second major upgrade was performed. This time the whole magnet system was replaced to improve the calculability and allow for higher magnetic fields. Since the recommissioning of SURF III we have been working to improve the stability of the stored electron beam through modifications of the radio-frequency system, leading to operations with unprecedented stability and new record injection currents topping 700 mA.

Suppression of beam instabilities has become an important goal at synchrotron radiation light sources, where highly sensitive applications like metrology, Fourier transform spectroscopy, and microscopy are now in use. We describe measurements connecting beam size and position changes to the onset of the saw-tooth instability and an instability generated by attempts to enlarge the vertical beam size for lifetime improvements.

A new facility for measuring irradiance in the UV was commissioned recently at the National Institute of Standards and Technology (NIST). The facility uses the calculable radiation from the Synchrotron Ultraviolet Radiation Facility as the primary standard. To measure the irradiance from a source under test, an integrating sphere spectrometer-detector system measures both the source under test and the synchrotron radiation sequentially, and the irradiance from the source under test can be determined. In particular, we discuss the calibration of deuterium lamps using this facility from 200 to 400 nm. This facility improves the current NIST UV irradiance scale to a relative measurement uncertainty of 1.2% (k=2).

Recent improvements to the synchrotron ultraviolet radiation facility led to unprecedented performance. High injection currents and beam stability, as well as tunable electron energies over a wide range make this storage ring a prime source for synchrotron radiation from the extreme‐ultraviolet to far‐infrared spectral regions. We will discuss plans to capitalize on this unprecedented performance through implementation of new experimental stations and extension of existing ones. It also will be shown that for applications using extreme‐ultraviolet to infrared synchrotron radiation a low electron energy storage ring has distinct advantages.

Strong evidence for self-excited emission of coherent synchrotron radiation in the microwave spectral region was observed at the Synchrotron Ultraviolet Radiation Facility (SURF III) electron storage ring at the NIST. The microwave emission between 25 and 35 mm was dominated by intense bursts of radiation. The intensity enhancement during these bursts was on the order of 10 000 to 50 000 over the incoherent value. The shape, width, and period of the bursts depend strongly on the operational parameters of the storage ring. Coherent microwave emission was observed only when the beam was unstable, namely, during bunch-length relaxation oscillations. We report on the measurements of the microwave bursts, and correlate the data with signals from a beam monitor electrode and photodiode detector. The coherent enhancement of the radiation intensity is ascribed to spontaneous self-induced microbunching of the electrons within the bunch.

The conversion of the electron storage ring at NIST (the National Institute of Standards and Technology) to SURF III (the Synchrotron Ultraviolet Radiation Facility) has resulted in a significant improvement to the azimuthal uniformity of the magnetic field as well as the capability for operating at higher beam energies. Measurements of magnetic field strength revealed azimuthal uniformity of better than ±0.05% at field strengths equivalent to operating energies of 52 MeV to 417 MeV. Initial operation is restricted to energies up to 331 MeV due to temporary limitations in the rf transmission system. Even at 331 MeV there is already a significant extension of the usable short wavelength range of the synchrotron radiation as compared to the range available at the 284 MeV operating energy of SURF II. These and other improvements have a major impact on SURF programs including: the Nanodetector, a conversion microscope which is a prototype real-time imaging system for EUV (extreme ultraviolet) lithography; the Spectrometer Calibration Beamline, used for high-accuracy absolute calibration of spectrometers; and the National EUV Reflectometry Facility, used to measure optical constants of thin-film multilayer optics.

The Synchrotron Ultraviolet Radiation Facility (SURF III) at the National Institute of Standards and Technology (NIST) provides a unique opportunity for high-accuracy vacuum ultraviolet (VUV) to visible radiometry with the completion of a recent upgrade to improve the uniformity of the magnetic field along the electron trajectory. In response to the rapid development from the semiconductor industry to astrophysics instrumentation, the major goal for UV radiometry at SURF III includes improving the UV radiometric standard of the nation for detector calibration and a national standard UV light source for source intercomparison. To further enhance the existing radiometric program at SURF III, two more beamlines (beamlines 3 and 4) are now dedicated for radiometry from the VUV to the visible range. The major component of beamline 4 is an Absolute Cryogenic Radiometer, which measures the incident radiation by an electrical substitution method. The beamline provides a facility for UV detector calibration and re...

The National Institute of Standards and Technology operates two spectral comparator facilities, both of which are used to provide detector calibrations from the ultraviolet to the near-infrared spectral range. One, the Ultraviolet Spectral Comparator Facility (UV SCF), has been in operation for more than two decades, providing one of the core calibration services. Recently, the illumination source used in the UV SCF has been changed from an argon mini-arc source to a laser-driven plasma light source. This new source has higher brightness, a smaller source size, better temporal stability, and much better conversion efficiency than the previous source. The improvements in the capabilities are summarized.

The success of the infrared program at the National Synchrotron Light Source has motivated the establishment of an infrared beamline at the Synchrotron Ultraviolet RAdiation Facility (SURF II) of the National Institute of Standards and Technology. Here, we describe the design of the infrared beamline and its associated infrared microscope instrumentation and show preliminary Fourier-transform infrared spectra. In addition, we present measurements of the long wavelength (> 1 cm) synchrotron emission and the noise spectrum of the infrared synchrotron radiation. The microwave measurements were undertaken to help assess the utility of SURF II as a submillimeter and far-infrared source.

Author Institution: Optical Technology Division, National Institute of Standards and Technology; Electron and Optical Physics Division, National Institute of Standards and Technology; Department of Chemistry, Princeton University

To compare the calibration capabilities for the spectral responsivity in the vacuum-ultraviolet spectral region between 135 nm and 250 nm, PTB and NIST agreed on a bilateral comparison. Calibrations of semiconductor photodiodes as transfer detectors were performed using monochromatized synchrotron radiation and cryogenic electrical substitution radiometers as primary detector standards. Great importance was attached to the selection of suitable transfer detector standards due to their critical issues in that wavelength regime. The uncertainty budgets were evaluated in detail. The comparison showed a reasonable agreement between the participants. However, it became obvious that the uncertainty level for this comparison cannot easily be further reduced due to the lack of sufficiently radiation-hard and long-term stable transfer standard detectors. Main text. To reach the main text of this paper, click on Final Report. The final report has been peer-reviewed and approved for publication by the CCPR-WGKC.

Carbon nanosheets, a two-dimensional carbon nanostructure, are promising electron cathode materials for applications in vacuum microelectronic devices. This letter demonstrates a simple approach to improve the spatial emission uniformity of carbon nanosheets by coating them with a chromium oxide thin film. Photoelectron emission microscopy observations and in situ field emission tests revealed that chromium oxide coated carbon nanosheets not only have spatial uniformity but also have coating thickness dependent field emission properties. For example, a coating thickness of ∼1.5nm gave a substantially greater field emission than as-grown nanosheets or other thickness coatings.

We have studied the performance of polytetrafluoroethylene integrating spheres in the ultraviolet (UV) region with wavelengths as short as 200 nm. Two techniques were used for this study; first, the spectral throughput of an integrating sphere irradiated by a deuterium lamp was analyzed by a monochromator. Second, a UV laser beam was directed into an integrating sphere, and spectrally dispersed laser induced fluorescence was studied. Significant absorption and fluorescence features were observed in the UV region and attributed to the contamination in the integrating sphere. We demonstrate that integrating spheres are easily contaminated by environmental pollutants such as polycyclic aromatic hydrocarbons emitted from engine exhaust. Baking of the contaminated integrating sphere can reverse some but not all of the effects caused by contaminants. The implications for using integrating spheres for UV measurement are discussed.

The combination of a cryogenic radiometer and synchrotron radiation enables detector scale realization in spectral regions that are otherwise difficult to access. Cryogenic radiometry is the most accurate primary detector-based standard available to date, and synchrotron radiation gives a unique broadband and continuous spectrum that extends from x ray to far IR. We describe a new cryogenic radiometer-based UV radiometry facility at the Synchrotron Ultraviolet Radiation Facility II at the National Institute of Standards and Technology. The facility is designed to perform a variety of detector and optical materials characterizations. The facility combines a high-throughput, normal incidence monochromator with an absolute cryogenic radiometer optimized for UV measurements to provide absolute radiometric measurements in the spectral range from 125 nm to approximately 320 nm. We discuss results on photodetector characterizations, including absolute spectroradiometric calibration, spatial responsivity mapping, spectroreflectance, and internal quantum efficiency. In addition, such characterizations are used to study UV radiation damage in photodetectors that can shed light on the mechanism of the damage process. Examples are also given for UV optical materials characterization.

A method to include the influence of the vertical electron beam emittance onto the calculability of synchrotron radiation is introduced. It accounts for the finite vertical size and angular spread of the electron beam through a convolution procedure. The resulting angular spread of synchrotron radiation can differ significantly from the ideal Schwinger result, depending on the conditions. For the Synchrotron Ultraviolet Radiation Facility detailed results on the influence of the electron emittance for total power and polarization calculations are presented.