Laser Radiometry

Accurate characterization of optoelectronic equipment is important to applications such as optical telecommunications, medical devices, materials processing, photolithography, as well as laser safety. This project focuses on metrology of selected critical laser parameters, especially the calibration of optical-fiber power meters and power meters of commonly used lasers. Project staff participate in national and international standards committees for laser safety and optoelectronic devices. They extend and improve source and detector characterizations, including development of low-noise, spectrally flat, highly uniform pyroelectric detectors; high-accuracy transfer standards for optical-fiber and laser power measurements; and advanced laser systems for laser power and energy measurements.

Meeting the needs of the laser and optoelectronics industries and anticipating emerging technologies requires investigation and development of improved measurement methods and instrumentation for high-accuracy laser metrology over a wide range of powers, energies, and wavelengths. NIST has historically used electrically calibrated laser calorimeters to provide traceability to the SI units for laser power and energy. We also have developed measurement capabilities based on a Laser Optimized Cryogenic Radiometer, which provides an order of magnitude in accuracy improvement for laser power measurements, compared to electrically calibrated radiometers.

With few exceptions, all of the primary measurement standards for establishing traceability to fundamental units for radiometry are based on thermal detectors. We have recently demonstrated thermal detectors with absorber coatings consisting of either purified single-wall carbon nanotubes or multiwall carbon nanotubes. To support advanced carbon nanotube coatings, we have developed a set of characterization tools for practical measurements of bulk nanomaterials using non-contact probes pioneered at NIST. Existing measurement tools are neither practical nor useful for current and future large-scale production of nanomaterials. These tools often rely on physical contact between the test probe and the material under study. However, physical contact between probes and nanomaterials may alter the material property of interest; for example differentiating bulk resistance from contact resistance. Advanced, cost effective analytical techniques are needed so that manufacturers, product developers, and regulatory agencies can truly "see" what they have. Photons, being massless and chargeless, are an ideal, non-contact probe. These non-contact techniques, relying on photon-matter interactions, include resonant-coupled photoconductive decay, high-Q dielectric measurements, absorption spectroscopy, and fluorescence.

• International comparisons with Germany, Great Britain, Japan, Mexico, Russia, and Switzerland.
• Novel power meter for high-efficiency laser diode sources
• Carbon nanotube-coated optical detector with spectral response variations less than 1 % over wavelength range from 600 nm to 1800 nm. 
• Absolute reflectance and absorbance measurements of carbon nanotube films, suggesting reflectance dominates at wavelengths near excitonic transitions
• Demonstrated laser cleaning of bulk carbon nanotubes