180 research outputs found
Summary Report: Working Group 7 On ''Laser Sources For Particle Acceleration''
No full textPhysic
Novel toroidal and superconducting metamaterials
No full textThis thesis reports on new solutions for sensing and controlling the electromagnetic radiation, and explores some novel effects of electrodynamics, using metamaterials.I have demonstrated the first superconducting metamaterial-based electro-optical modulator controlled by passing current through the network of meta-molecules. The meta- material, fabricated out of thin niobium film, modulated the sub-terahertz radiation through magnetic-field-induced suppression of superconductivity as well as through thermal effect. Transmission modulation up to 45% has been observed and main mechanisms of modulation have been studied.I have demonstrated a resonant radiation-harvesting bolometer for the sub-terahertz frequency range using a superconducting metamaterial fabricated out of thin niobium film. The strong electromagnetic interactions between the meta-molecules allowed harnessing of the radiation incident on the metamaterial and channeling it into a small radiation sensor, thus boosting the device sensitivity and selectivity. Bolometer sensitivity band-width of 1% has been achieved.I have suggested and experimentally demonstrated a new type of quantum metamaterial that engages the quantization of magnetic flux trapped in the meta-molecules. The metamaterial, fabricated out of high-temperature superconductor YBCO, has been designed to display nonlinear response associated with switching between the magnetic flux states. Although switching experiments have not been performed, a detailed characterization of the metamaterial, including the study of superconducting metamaterial structures that model different switching states, has been conducted.I have, for the first time, investigated highly nonlinear superconducting sub-terahertz metamaterial that exploits critical current and thermal nonlinearity. The metamaterial was fabricated out of thin niobium film with every meta-molecule containing wire segments of nanoscale thickness. The transmission change of up to 13% has been observed in response to ramping up the intensity of incident radiation to 8 W/m2.I have developed a novel analytical formalism that, for the first time, linked the reflection and the transmission of the metamaterial with the microscopic multipole excitations taking into account the electric, magnetic and toroidal multipoles of the constituent meta-molecules. A planar superconducting metamaterial with strong toroidal dipole response has been fabricated to test the formalism experimentally, and a very good agreement between the experiment and the analytical predictions has been observed.I have, for the first time, numerically and analytically studied the non-radiating configuration observed in the microwave experiment with the toroidal void metamaterial. It has been found that the non-radiating configuration is non-trivial and results from the destructive interference between the co-located electric and toroidal dipoles. Such non-radiating configurations shall allow designing high-Q metamaterial resonances and the generation of oscillating vector-potential for the study of the time-dependent Aharonov-Bohm effect
High average power, high energy, femto-second fiber chirped pulse amplification system
No full textWe have demonstrated an Yb-fiber laser system incorporating a CFBG stretcher, bandwidth optimised amplifiers and dielectric grating compressor. The system produced 135 W average power with pulse energy of 13.5 µJ. The recompressed pulse duration was 360 fs
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Femtosecond growth dynamics of an underdense ionization front measured by spectral blueshifting
No full textA comprehensive report of time-resolved spectral blue shifts of 100-femtosecond laser pulses caused by ionization of atmospheric density N[sub 2] and noble gases subjected to high (10[sup 14] W/cm[sup 2] - 10[sup 16] W/cm[sup 2]) light intensities is presented. Included are data for two experiments: (1) self-shifting of the ionizing laser pulses for varying peak intensities, pressures (1-5 atm.), and gas species; and (2) time-resolved blueshifts of a weak copropagating probe pulse for the same range of ionization conditions. The self-shift data reveal a universal, reproducible pattern in the shape of the blueshifted spectra: as laser intensity, gas pressure, or atomic number increase, the self-blueshifted spectra develop from a near replica of the incident pulse spectrum into a complex structure consisting of two spectral peaks. The time-resolved data reveal different temporal dependence for each of these two features. A quantitative model for a simplified cylindrical focal geometry is presented which explains the presence of the two spectral features in terms of two distinct ionization mechanisms: collisionless tunneling ionization, which dominates early in the ionizing pulse profile, and electron impact ionization, which dominates during the intense maximum of the ionizing pulse. Transient resonant enhancements may also contribute to ionization near the peak of the pulse
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Femtosecond growth dynamics of an underdense ionization front measured by spectral blueshifting
No full textA comprehensive report of time-resolved spectral blue shifts of 100-femtosecond laser pulses caused by ionization of atmospheric density N{sub 2} and noble gases subjected to high (10{sup 14} W/cm{sup 2} - 10{sup 16} W/cm{sup 2}) light intensities is presented. Included are data for two experiments: (1) self-shifting of the ionizing laser pulses for varying peak intensities, pressures (1-5 atm.), and gas species; and (2) time-resolved blueshifts of a weak copropagating probe pulse for the same range of ionization conditions. The self-shift data reveal a universal, reproducible pattern in the shape of the blueshifted spectra: as laser intensity, gas pressure, or atomic number increase, the self-blueshifted spectra develop from a near replica of the incident pulse spectrum into a complex structure consisting of two spectral peaks. The time-resolved data reveal different temporal dependence for each of these two features. A quantitative model for a simplified cylindrical focal geometry is presented which explains the presence of the two spectral features in terms of two distinct ionization mechanisms: collisionless tunneling ionization, which dominates early in the ionizing pulse profile, and electron impact ionization, which dominates during the intense maximum of the ionizing pulse. Transient resonant enhancements may also contribute to ionization near the peak of the pulse
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Femtosecond Coherent Spectroscopy at 800nm: MI-FROG Measures High-Field Ionization Rates in Gases
No full textThe authors report the first quantitative phase-sensitive measurement of ultrafast ionization rates in gases using Multi-phase Interferometric Frequency-Resolved Optical Gating. Ultrafast probe depletion via frequency mixing in the ionization front is observed
Supersensitive PSA-Monitored neoadjuvant hormone treatment of clinically localized prostate cancer: Effects on positive margins, tumor detection and epithelial cells in bone marrow
No full textObjective: The present study was done to investigate the effects of supersensitive PSA-controlled inductive treatment on positive margins, detection of tumor and epithelial cells in bone marrow of 101 patients with untreated and clinically localized prostatic carcinoma (cT1-3N0M0). Methods: Hormonal treatment was given until PSA (DPD Immulite(R) third-generation assay) reached 0.3 ng/ml in only 1 case. Of the 101 patients, 82 had a measurable hypoic lesion on initial transrectal ultrasound. 84% of these became smaller, 7.5% remained unchanged and 8.5% increased. Of the 101 prostatectomy specimens, 20 (20%) were margin-positive. The incidence of affected margins was relatively high (35% from 55 patients) with cT3 tumors, but almost negligible (2% from 46 patients) in cT1-2 tumor. Our pathologists, despite their great experience in evaluating hormonally treated prostates (>500 cases) and using immunohistochemical staining, were unable to detect carcinoma in 15 (15%) specimens. Whereas only 2 (4%) of the 55 cT3 specimens were without detectable tumor, this incidence rised to 28% (13 of 46 prostates) in patients with cT1-2 tumors. Of the initial 29 patients with epithelial cells in bone marrow, only 4 (14%) remained positive after controlled induction and all of them had fewer cells than before. Conclusion: Endocrine induction controlled by a supersensitive PSA assay and continued until reaching PSA nadir is highly effective in clearing surgical margins and eliminating tumor cells from bone marrow. It seems to be clearly superior to the conventional 3 months of pretreatment at least in cT1-2 tumors in respect to surgical margins and detectability of tumor in the resected prostate. A definitive statement about the value of endocrine induction can only be given by prospective randomized studies, with optimal drugs, doses and treatment time. But the conventional 3 months of pretreatment are far from exploiting the possibilities of this therapeutic option
David Frum - Conservative Author, Former Presidential Speechwriter
No full textDavid Frum is best known as an advocate for the reform and modernization of the Republican party. He is a contributing editor for Newsweek and The Daily Beast and is also a CNN contributor. Frum serves on the board of directors of the Republican Jewish Coalition and as vice chairman and an associate fellow of the R Street Institute.
Frum is the author of eight books including most recently the e-book, Why Romney Lost, and his first novel, Patriots. From 2001 to 2002, Frum served as speechwriter and special assistant to President George W. Bush. From 2007 to 2008, he was a senior policy adviser to the Giuliani-for-president campaign. Frum is Canadian-American but was a citizen of Canada when he joined the Bush administration.
Not afraid to challenge his own party, Frum expressed intense dissatisfaction with supply-siders, evangelicals, and nearly all Republican politicians in his 1994 book Dead Right. In a 2009 Newsweek column entitled Why Rush Is Wrong, Frum defended his conservatism and challenged the country’s most vocal conservative broadcaster. His editorial columns have appeared in a variety of Canadian and American magazines and newspapers, including the National Post and The Week.
A volunteer for the Reagan campaign in 1980, Frum is proud that he’s attended every Republican convention since 1988, was president of the Federalist Society chapter of his law school, and worked as editorial page editor of The Wall Street Journal from 1989 to 1992. Frum graduated from Yale University in 1982 with simultaneous Bachelor and Master of Arts degrees in history.https://corescholar.libraries.wright.edu/archives_presidential_lecture_series/1014/thumbnail.jp
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Observation of Optical Pulse and Material Dynamics on the Femtosecond Time-Scale
No full textThe widespread availability of lasers that generate pulses on the femtosecond scale has opened new realms of investigation in the basic and applied sciences, rendering available excitations delivering intensities well in excess of 10{sup 21} W/cm{sup 2}, and furnishing probes capable of resolving molecular relaxation timescales. As a consequence and a necessity, sophisticated techniques to examine the pulse behavior on the femtosecond scale have been developed and are of crucial importance to gain insight on the behavior of physical systems. These techniques will be discussed with specific application to guided pulse propagation and ionization dynamics of noble gases
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