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Search Publications by: John H. Lehman (Fed)

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Displaying 51 - 75 of 311

Time-Resolved Absorptance and Melt Pool Dynamics during Intense Laser Irradiation of a Metal

October 25, 2018
Author(s)
Brian J. Simonds, Jeffrey W. Sowards, Joshua A. Hadler, Erik A. Pfeif, Boris Wilthan, Jack R. Tanner, Paul A. Williams, John H. Lehman
Laser welding is a complex, dynamic process by which focused, high-intensity laser light is used to join two metallic surfaces and is being increasing deployed in a variety of industrial applications. Determining the time-dependent absorptance of the laser

Using Radiation Pressure to Develop a Radio-Frequency Power Measurement Technique Traceable to the Redefined SI

October 15, 2018
Author(s)
Christopher L. Holloway, Matthew T. Simons, David R. Novotny, John H. Lehman, Paul A. Williams, Gordon A. Shaw
We discuss a power measurement technique traceable to the International System of Units based on radiation pressure (or radiation force) carried by an electromagnetic wave. A measurement of radiation pressure offers the possibility for a power measurement

MEMS non-absorbing electromagnetic power sensor employing the effect of radiation pressure

September 8, 2018
Author(s)
Ivan Ryger, Aly Artusio-Glimpse, Paul A. Williams, Gordon A. Shaw, Matt Simons, Christopher L. Holloway, John H. Lehman
We demonstrate a compact electromagnetic power sensor based on force effects of electromagnetic radiation onto a highly reflective mirror surface. Unlike the conventional power measurement approach, the photons are not absorbed and can be further used in

Mechanical characterization of planar springs for compact radiation pressure power meters

September 7, 2018
Author(s)
Alexandra B. Artusio-Glimpse, Ivan Ryger, Paul A. Williams, Kyle A. Rogers, Daniel W. Rahn, Andrew J. Walowitz, John H. Lehman
Counter to conventional methods of measuring laser optical power, radiation pressure-based power meters operate by reflection rather than absorption. This provides an opportunity for in situ, non-destructive total beam power measurement. Compact radiation

Cryogenic Primary Standard for Optical Fibre Power Measurement

August 17, 2018
Author(s)
Malcolm G. White, Zeus Ruiz, Christopher S. Yung, Igor Vayshenker, Nathan A. Tomlin, Michelle S. Stephens, John H. Lehman
NIST has completed commissioning a new, state-of-the-art cryogenic primary standard for optical fibre power measurement and calibration. It establishes for the first time, a direct traceability route between the device under test and primary standard. Two

Micromachined force balance for optical power measurement by radiation pressure sensing

August 6, 2018
Author(s)
Ivan Ryger, Alexandra B. Artusio-Glimpse, Paul A. Williams, Nathan A. Tomlin, Michelle S. Stephens, Matthew T. Spidell, Kyle A. Rogers, John H. Lehman
We introduce a micromachined force scale for laser power measurement by means of radiation pressure sensing. With this technique, the measured laser light is not absorbed and can be utilized while being measured. We employ silicon micromachining technology

Point-of-Use, Nonexclusive, High-Power Laser Power Meter

June 19, 2018
Author(s)
Aly Artusio-Glimpse, Ivan Ryger, Paul A. Williams, John H. Lehman
We have developed a small-package, high-power laser power meter that directly measures radiation pressure on a high-reflectivity mirror for nonexclusive, in situ laser measurements without pick- off schemes. Furthermore, our non-inertial design inhibits

Characterisation of New Planar Radiometric Detectors using Carbon Nanotube Absorbers under Development at NIST

June 13, 2018
Author(s)
Malcolm G. White, Nathan A. Tomlin, Christopher S. Yung, Michelle S. Stephens, Ivan Ryger, Solomon I. Woods, John H. Lehman, Igor Vayshenker
Carbon nanotube technology, in conjunction with silicon micro-fabrication techniques, has enabled us to develop planar radiometric detectors, which has led to the establishment of a new generation of primary standards. The goal is to develop compact, fast

Reduction of Short Wavelength Reflectance of Multi-wall Vertically Aligned Carbon Nanotubes Through UV Laser Irradiation

May 29, 2018
Author(s)
Michelle S. Stephens, Brian J. Simonds, Christopher S. Yung, Davis R. Conklin, David J. Livigni, Alberto R. Oliva, John H. Lehman
Multi-wall carbon nanotube coatings are used as broadband, low-reflectance absorbers for bolometric applications, blackbody radiators, and for stray light control. Irradiation of single wall carbon nanotubes with UV laser light has been shown to remove

Optical Measurements of Dynamic Absorptance during High-power Laser Spot Welding

May 7, 2018
Author(s)
Brian Simonds, Jeffrey W. Sowards, Joshua A. Hadler, Boris Wilthan, Erik A. Pfeif, Jack R. Tanner, Chandler Harris, Paul A. Williams, John Lehman
We present precision measurements of the time-dependent absorptance during a 10 ms fiber-laser spot weld on 316L stainless steel. From these, the precise time and energy at which a keyhole is formed can be determined.

Carbon Nanotube-Based Black Coatings

February 15, 2018
Author(s)
John H. Lehman, Christopher S. Yung, Nathan A. Tomlin, Davis R. Conklin, Michelle S. Stephens
It has been shown that coatings comprised of carbon nanotubes are very black; that is, characterized by low reflectance over a broad wavelength range from the visible to far infrared. Arguably there is no other material that is comparable. This is