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Search Publications by: Brian Simonds (Fed)

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Displaying 26 - 45 of 45

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

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

September 3, 2018
Author(s)
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

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 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.

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

December 1, 2017
Author(s)
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

Low-Cycle Fatigue Behavior of Fiber-Laser Welded, Corrosion-Resistant, High-Strength Low Alloy Sheet Steel

February 21, 2017
Author(s)
Jeffrey W. Sowards, Erik A. Pfeif, Matthew J. Connolly, Joseph D. McColskey, Stephanie L. Miller, Brian J. Simonds, James R. Fekete
Incorporation of high-strength steels into ground vehicles provides a weight-savings advantage by using thinner sections of material, which increases vehicle efficiency. Advanced welding techniques such as fiber laser welding are a potential method for

Dual-beam laser thermal processing of silicon photovoltaic materials

March 14, 2016
Author(s)
Brian J. Simonds, Anthony Teal, Tian Zhang, Joshua A. Hadler, Zibo Zhou, Sergey Varlamov, Ivan Perez-Wurfl
Laser processing for photovoltaics (PV) has traditionally been used for very small dimension features where focused beams are rastered to create lines for edge isolation, scribing, and selective emitter formation and for drilling holes for drilling in wrap

Pulsed KrF excimer laser dopant activation in nanocrystal silicon in a silicon dioxide matrix

February 22, 2016
Author(s)
Tian Zhang, Brian Simonds, Keita Nomoto, Binesh Puthen Veettil, Ziyun Lin, Ivan Perez Wurfl, Gavin Conibeer
We demonstrate that a pulsed KrF excimer laser (λ=248 nm, τ=22 ns) can be used as a post-furnace annealing method to greatly increase the electrically active doping concentration in nanocrystal silicon (ncSi) embedded in SiO2. The application of a single

Portable high-accuracy non-absorbing laser power measurement at kilowatt levels by means of radiation pressure

February 16, 2016
Author(s)
Paul A. Williams, Joshua A. Hadler, Frank C. Maring, Robert Lee, Kyle A. Rogers, Brian J. Simonds, Matthew T. Spidell, Ari D. Feldman, John H. Lehman
We describe a unique optical power meter which measures the radiation pressure to accurately determine a laser’s optical power output. This approach traces its calibration of the optical Watt to the kilogram. Our power meter is designed for high-accuracy

Why the long-term charge offset drift in Si single-electron tunneling transistors is much smaller (better) than in metal-based ones: Two-level fluctuator stability

August 7, 2008
Author(s)
Neil M. Zimmerman, W H. Huber, Brian J. Simonds, Emmanouel S. Hourdakis, Fujiwara Fujiwara, Yukinori Ono, Yasuo Takahashi, Hiroshi Inokawa, Miha Furlan, Mark W. Keller
A common observation in metal-based (specifically, those with AlOx tunnel junctions) single- electron tunneling (SET) devices is a time-dependent instability known as the long-term charge offset drift. This drift is not seen in Si-based devices. Our aim is

Charge Offset Stability in Tunable-Barrier Si SET Devices

January 17, 2007
Author(s)
Neil M. Zimmerman, Brian Simonds, Mikio Fujiwara, Yukinori Ono, Yasuo Takahashi, Hiroshi Inokawa
The problem of charge offset drift in single-electron tunneling devices, based on the Coulomb blockade, can preclude their useful application in metrology and integrated devices. We demonstrate that in tunable-barrier Si-based SET transistors there is

An Upper Bound to the Frequency Dependence of the Cryogenic Vacuum-Gap Capacitor

September 6, 2006
Author(s)
Neil M. Zimmerman, Brian Simonds, Yicheng Wang
In attempting to develop a capacitance standard based on the charge of the electron, one question which has been open for many years is the frequency dependence of the vacuum-gap cryogenic capacitor. In this paper, we succeed in putting an upper bound on

Sub-micron gap capacitor for measurement of breakdown voltage in air

March 24, 2006
Author(s)
Emmanouel S. Hourdakis, Brian Simonds, Neil M. Zimmerman
We have developed a new method for measuring the value of breakdown voltage in air for electrode separations from 400 nm to 45 'm. The electrodes used were thin film Au lines evaporated on sapphire. The resulting capacitors had an area of 80 'm by 80 'm
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