FemtoLab

Downer group sets world record in laser plasma acceleration: 2 GeV. The Downer group published the paper Wang et al., “Quasimonoenergetic laser-plasma acceleration of electrons to 2 GeV,” Nature Communications 4, 1988 (2013) on their landmark experiments using the Texas Petawatt Laser. The result surpassed a previous world record of 1 GeV set in 2006 [Leemans et al., Nat. Physics (2006)]. The 100 Joule, 150 femtosecond Texas Petawatt laser pulse captured approximately 1 billion electrons from a tenuous plasma and accelerated them to the record-setting energy with only 5% energy spread and a half-milliradian angular divergence in a distance of approximately one inch. The high quality of the energetic electron bunch is important for developing tabletop x-ray free electron lasers, an important research tool in biological, materials and medical sciences. Publication of the results prompted reports in the popular press internationally:

The petawatt laser-plasma acceleration team next to their apparatus in the Texas Petawatt Laser target bay. L to R: Neil Fazel, Dr. Watson Henderson, Dr. Rafal Zgadzaj, Dr. Xiaoming Wang and Zhengyan Li. The hand symbol signifies “2 GeV”.

Prof. Downer delivers tutorial lecture at CLEO 2013. Prof. Downer delivered an invited tutorial lecture entitled “Laser Plasma Acceleration of Electrons and Plasma Diagnostics at High Laser Fields” at the 2013 Conference on Lasers and Electro-Optics in San Jose, CA.

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Prof. and Mrs. Downer join UT-PKU exchange kickoff. Prof. Downer participated in a UT–PKU Physics Exchange Workshop held at the International Center for Quantum Materials at Peking University in Beijing, China during May 21–24, 2013. Through lectures, lab tours, and personal communications, the two sides explored common interests for potential collaborations through a Dual-Degree Agreement signed earlier.

Dr. Xiaohui Gao takes postdoctoral position at Cornell University. After successfully defending his Ph.D. dissertation “Characterization of Cluster/Monomer Ratio in Pulsed Supersonic Gas Jets" in November 2012, Dr. Xiaohui Gao has started a postdoctoral appointment at Cornell University in the group supervised by Prof. Alex Gaeta. Xiaohui is the 32nd Ph.D. from the Downer group since its inception in 1985. Xiaohui’s publications from his Ph.D. work include:

Drs. Junwei Wei and Ming Lei earn Ph.D.s, take positions in semiconductor industry. Immediately after defending their respective Ph.D. dissertations “Optical spectroscopy of silicon nanocrystals” and “Optical characterization of semiconductor device structures”, Junwei Wei and Ming Lei began work as research scientists at KLA-Tencor in Milpitas, CA and GlobalFoundries, Inc. in Malta, NY, respectively. Junwei and Ming are the 30th and 31st Ph.D.s from the Downer group since its inception in 1985. There work was supported primarily by the Robert Welch Foundation and the National Science Foundation. Junwei’s publications from his Ph.D. work include:

J. Wei et al., “Second-harmonic and linear optical spectroscopic study of silicon nanocrystals embedded in SiO2,” Phys. Rev. B 84, 165316 (2011).

J. Wei et al., “Size-dependent optical properties of Si nanocrystals embedded in amorphous SiO2 measured by spectroscopic ellipsometry, J. Vac. Sci. Technol. B 29, 04D112 (2011).

C. Hessel, J. Wei et al., “Raman spectroscopy of oxide-embedded and ligand-stabilized silicon nanocrystals,” J. Phys. Chem. Lett. 3, 1089-1093 (2012).

Ming’s work received the 2011 Hyer Research Award of the Texas Section of the American Physical Society, as described in a September 2011 news item. In addition to the publications listed therein, Ming more recently published the following new work:

M. Lei et al., “Characterization of anti-phase boundaries in hetero-epitaxial polar-on-nonpolar semiconductor films by optical second-harmonic generation,” Appl. Phys. Lett. 102, 152103 (2013).

Downer group hosts the 2012 Advanced Accelerator Concepts Workshop. Prof. Downer chaired the 15th Advanced Accelerator Concepts Workshop (AAC 2012) held on the UT Campus during June 10-15, 2012. The meeting drew more than 250 scientists, including 70 students, from around the world to discuss recent advances in particle accelerator science and technology. Dr. Rafal Zgadzaj edited the Proceedings published on-line through the American Institute of Physics. Photos of the week’s events are available at:

Ming Lei and Prof. Downer receive 2011 Hyer Research Award. Prof. Downer and his graduate student Ming Lei received the 2011 Robert S. Hyer Award of the Texas Section of the American Physical Society for excellence in graduate level research presented at a Texas APS meeting. Ming developed a new technique to characterize nanometer-thick silicon-on-insulator (SOI) films, a platform for a multitude of high-performance electronic and photonic devices. Using internal photoemission and optical second-harmonic generation, Ming determined the energy level structure of performance-limiting interface defects. Ming applied these same techniques to characterize band offsets and point defects in high-K dielectric films. Among Ming’s publications from the work recognized by the Hyer Award were:

M. Lei, J. Price and M. C. Downer, “Hot carrier injection from nanometer-thick silicon-on-insulator films measured by optical second-harmonic generation,” Appl. Phys. Lett. 96, 241105 (2010).

J. Price, M. Lei and M. C. Downer, “Charge-trapping defects in Si/SiO2/Hf1-xSixO2 film stacks characterized by spectroscopic second-harmonic generation,” J. Vac. Sci. Technol. B 29, 04D101 (2011).

J. H. Yum, M. Lei et al., “Epitaxial ALD BeO: efficient oxygen diffusion barrier for EOT scaling and reliability improvement,” IEEE Trans. Electron. Devices 58, 4384-4392 (2011).

M. Lei, J. H. Yum, J. Price, T. W. Hudnall, C. W. Bielawski, S. K. Banerjee, P. S. Lysaght, G. Bersuker and M. C. Downer, “Spectroscopic evaluation of band alignment of atomic layer deposited BeO on Si(100), Appl. Phys. Lett. 100, 122906 (2012).

M. Lei, J. H. Yum, S. K. Banerjee, G. Bersuker and M. C. Downer, “Band offsets of atomic layer deposited Al2O3 and HfO2 on Si measured by linear and nonlinear internal photoemission,” Phys. Status Solidi B 249, 1160-1165 (2012).

The article"Snapshots of laser wakefields" appeared in the Physics Update section of Physics Today 59, 28 (December 2006). The article featured work on visualization of laser wakefield structures by our group published in Matlis et al., "Snapshots of laser wakefields," Nature Physics 2, 749 (2006) and Maksimchuk et al.,Physics of Plasmas 15, 056703 (2008), including a picture from that work.

One of the "snapshots" of laser wakefields from our work Matlis et al., "Snapshots of laser wakefields," Nature Physics 2, 749 (2006) was published with permission in the new book "The Plasma Universe" (Cambridge University Press 2008).