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Search Publications by: Paul A. Williams (Fed)

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Displaying 1 - 25 of 111

The causal relationship between melt pool geometry and energy absorption measured in real time during laser-based manufacturing

December 16, 2021
Brian Simonds, Jack R. Tanner, Aly Artusio-Glimpse, Paul A. Williams, Niranjan Parab, Cang Zhao, Tao Sun
During laser powder bed fusion additive manufacturing, a protean pool of molten metal governs a complex energy absorption process as it presents as either a highly reflective surface, a deeply absorbing cavity (a keyhole), or some amalgamation thereof. To

Absolute radiation pressure detector using a diamagnetically levitating test mass

October 28, 2021
Anna Vaskuri, Daniel Rahn, Paul A. Williams, John H. Lehman
We have developed an absolute radiometer to measure laser power by means of radiation pressure in a closed control-loop configuration using diamagnetically levitated pyrolytic graphite as the soft spring and gravity as a contactless restoring force. Our

Comparison of electrostatic and photon pressure force references at the nanonewton level

May 3, 2021
Gordon Shaw, John A. Kramar, Paul Williams, Matthew Spidell, Richard Mirin, Julian Stirling
This work describes a comparison between nanonewton force references derived from an electrostatic force balance and photon pressure force from calibrated laser optical power in the 1 watt range. The NIST Electrostatic Force Balance (EFB) is used to

Simplified kilogram traceability for photon momentum radiometers

October 1, 2020
Kyle A. Rogers, Paul A. Williams, Gordon A. Shaw, John H. Lehman
High power laser applications in areas such as laser processing of materials can require an accurately measured laser power. Radiation pressure-based laser power measurement has been proven as a practical method for quantifying these high-power levels in

In Situ Monitoring of Cu/Al Laser Welding using Laser Induced Fluorescence

September 10, 2020
Brian Simonds, Tran N. Tran, Paul A. Williams
We investigate laser spot welding of 200 µm thick Cu and Al foils using laser-induced fluorescence (LIF). The key to strong Cu/Al welds is limited intermetallic compound formation through controlled molten metal interaction time. For laser lap welds, Cu in

Radiation Pressure Laser Power Meter for Industrial Laser Machining

September 10, 2020
Aly Artusio-Glimpse, Ivan Ryger, Natalia A. Azarova, Paul A. Williams, John H. Lehman
Demonstration and validation of a linear radiation pressure-based high-power laser power meter is presented. To date, this device is the most promising real-time, absolute power meter for laser material processing where power monitoring is crucial.

Simultaneous High-speed X-ray Transmission Imaging and Absolute Dynamic Absorptance Measurements during High-power Laser-metal Processing

September 10, 2020
Brian Simonds, Jack R. Tanner, Alexandra B. Artusio-Glimpse, Paul A. Williams, Niranjan Parab, Cang Zhao, Tao Sun
During high-power laser metal processing, the absorbed light is intimately related to the molten metal cavity shape. For the first time, we directly and simultaneously observe this relationship by implementing state-of-the-art techniques of high-speed x

HALO - High Amplification Laser-pressure Optic

June 21, 2020
Alexandra B. Artusio-Glimpse, Kyle A. Rogers, Paul A. Williams, John H. Lehman
Efforts are underway at the National Institute of Standards and Technology to drastically reduce the uncertainty of laser power measurements using radiation pressure. The High Amplification Laser-pressure Optic (HALO) system is a cornerstone of this effort

Inline Laser Power Measurement by Photon Momentum

February 6, 2019
John H. Lehman, Paul A. Williams, Daniel W. Rahn, Kyle A. Rogers
We present a measurement scheme and instrumentation for quantifying laser power by means of photon momentum. The optical design is optimized such that the incoming laser beam is minimally perturbed and is available for other purposes along the incoming

Radiation-Pressure Enabled Traceable Laser Sources at High CW Powers

January 4, 2019
Paul A. Williams, Alexandra B. Artusio-Glimpse, Joshua A. Hadler, Daniel King, Ivan Ryger, Tam Vo, John H. Lehman, Kyle A. Rogers
Radiation pressure has recently been shown to have practical application for multi-kilowatt CW laser power measurement. One key advantage lies in its ability to measure without absorbing the laser beam. This enables a new measurement paradigm where laser

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

October 25, 2018
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
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
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
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

Dynamic and absolute measurements of laser coupling efficiency during laser spot welds

September 3, 2018
Brian J. Simonds, Jeffrey W. Sowards, Joshua A. Hadler, Erik A. Pfeif, Boris Wilthan, Jack R. Tanner, Chandler Harris, Paul A. Williams
Laser absorptance (coupling efficiency) changes rapidly during laser metal processing due to temperature and multiple phase changes. We find that there is limited literature data available, but this property is vital for accurate process simulations, as

Micromachined force balance for optical power measurement by radiation pressure sensing

August 6, 2018
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
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

Correlation of Neutron-Based Strain Imaging and Mechanical Behavior of Armor Steel Welds Produced with the Hybrid Laser Arc Welding Process

June 11, 2018
Jeffrey W. Sowards, Daniel S. Hussey, David L. Jacobson, Stan Ream, Paul A. Williams
Bragg edge neutron transmission imaging was used to characterize the spatial distribution of thermally induced residual strains in a steel armor plate welded with a hybrid laser arc process. This residual strain distribution was compared to the spatial

Geometric contributions to chopper wheel optical attenuation uncertainty

December 9, 2017
Matthew T. Spidell, Joshua A. Hadler, Michelle S. Stephens, John H. Lehman, Paul A. Williams
Calibrated reflective optical choppers are used in NIST’s high power laser calibration services due to their advantages in performance and safety over wedges and semi-transparent materials for beam power reduction. While the design, operation, and

On-site multi-kilowatt laser power meter calibration using radiation pressure

December 1, 2017
Paul A. Williams, Joshua A. Hadler, Brian J. Simonds, John H. Lehman
We have demonstrated the calibration of a thermal power meter against a radiation-pressure power meter in the range of 20 kW in a manufacturing test environment. The results were compared to a traditional calorimeter-based laboratory calibration undertaken