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Search Publications by: Lei Chen (Fed)

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Displaying 26 - 50 of 76

Nanoparticle size determination using optical microscopes

October 27, 2014
Author(s)
Ravikiran Attota, Richard J. Kasica, Premsagar P. Kavuri, Hyeong G. Kang, Lei Chen
We present a simple method for size determination of nanoparticles using conventional optical microscopes. The method, called through-focus scanning optical microscopy (TSOM), makes use of the four-dimensional optical information collected at different

Scanning Ion Microscopy with Low Energy Lithium Ions

July 1, 2014
Author(s)
Kevin A. Twedt, Lei Chen, Jabez J. McClelland
Using an ion source based on photoionization of laser-cooled lithium atoms, we have developed a scanning ion microscope with probe sizes of a few tens of nanometers and beam energies from 500 eV to 5 keV. These beam energies are much lower than the typical

Fabrication of 200 nm Period Hard X-Ray Phase Gratings

June 11, 2014
Author(s)
Houxun Miao, Andrew A. Gomella, Nicholas Chedid, Lei Chen, Han Wen
Far field x-ray grating interferometry achieves extraordinary phase sensitivity in imaging weakly absorbing samples, provided that the grating period is within the transverse coherence length of the x-ray source. Here we describe a cost-efficient process

Motionless phase stepping in X-ray phase contrast imaging with a compact source

November 26, 2013
Author(s)
Houxun Miao, Lei Chen, Eric Bennett, Nick Adamo, Andrew A. Gomella, Alexa D. Luca, Ajay Patel, Nicole Y. Morgan, Han Wen
X-ray phase-contrast imaging offers a new way to look into the internal structures of objects. At hard x-ray energies the phase shift in some materials is many times the attenuation of intensity, promising greater image details with less radiation. Grating

Probing coherence in microcavity frequency combs via optical pulse shaping

August 29, 2012
Author(s)
Fahmida Ferdous, Houxun H. Miao, Pei-Hsun Wang, Daniel E. Leaird, Kartik Srinivasan, Lei Chen, Vladimir Aksyuk, Andrew M. Weiner
Recent investigations of microcavity frequency combs based on cascaded four-wave mixing have revealed a link between the evolution of the optical spectrum and the observed temporal coherence. Here we study a silicon nitride microresonator for which the

Spectral Line-by-Line Pulse Shaping of On-Chip Microresonator Frequency Combs

December 1, 2011
Author(s)
Fahmida Ferdous, Houxun H. Miao, Daniel E. Leaird, Kartik Srinivasan, Jian Wang, Lei Chen, Leo T. Varghese, Andrew M. Weiner
We report, for the first time to the best of our knowledge, spectral phase characterization and line-by-line pulse shaping of an optical frequency comb generated by nonlinear wave mixing in a micro-ring resonator. The comb is compressed to a train of near

Effect of Alternating Ar and SF6/C4F8 Gas Flow in Si Nano-Structure Plasma Etching

August 1, 2011
Author(s)
Lei Chen, Vincent K. Luciani, Houxun H. Miao
Si is very reactive to normal plasma etchants such as fluorine based chemicals and the reactions are inherently isotropic. To fabricate small and/or high aspect ratio nanoscale structures in Si, anisotropic profile is necessary. SF6 combined with C4F8 has