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56 results on '"Jennifer L Herek"'

53. Extraction of optical Bloch modes in a photonic-crystal waveguide

Author

Peter Lodahl, Søren Stobbe, Georgios Ctistis, Jennifer L. Herek, Pepijn W. H. Pinkse, Willem L. Vos, Simon R. Huisman, Faculty of Science and Technology, Optical Sciences, and Complex Photonic Systems

Subjects
Physics, Field (physics), business.industry, FOS: Physical sciences, General Physics and Astronomy, Physics::Optics, Reconstruction algorithm, Edge (geometry), law.invention, symbols.namesake, Superposition principle, Transverse plane, Fourier transform, Optics, Optical microscope, law, 2023 OA procedure, symbols, business, Physics - Optics, Optics (physics.optics), Photonic crystal
Abstract

We perform phase-sensitive near-field scanning optical microscopy on photonic-crystal waveguides. The observed intricate field patterns are analyzed by spatial Fourier transformations, revealing several guided transverse electric (TE) and transverse magnetic (TM) like modes. Using the reconstruction algorithm proposed by Ha et al. [Opt. Lett. 34, 3776 (2009)], we decompose the measured two-dimensional field pattern in a superposition of propagating Bloch modes. This opens new possibilities to study specific modes in near-field measurements. We apply the method to study the transverse behavior of a guided TE-like mode, where the mode extends deeper in the surrounding photonic crystal when the band edge is approached

54. Historical perspective on: Femtosecond transition-state spectroscopy of iodine—From strongly bound to repulsive surface dynamics [Volume 161, Issues 4–5, 22 September 1989, Pages 297–302]

Author

Jennifer L. Herek, R.M. Bowman, Ahmed H. Zewail, and Marcos Dantus

Subjects
Physics, Liberal arts education, State (polity), media_common.quotation_subject, Transition (fiction), General Physics and Astronomy, Art history, Nanotechnology, Surface dynamics, Physics and Astronomy(all), Physical and Theoretical Chemistry, Literature study, media_common
Abstract

Summary by J.L. Herek. Nobel prize-winner: Professor Ahmed Zewail. In the spring of 1990, I was a young liberal arts student soon to graduate from Lawrence University in Wisconsin, dreaming of a career in chemical physics. Thanks to an elective course on applications of lasers in chemistry and physics, which also required a literature study and report, I had found that a revolution in chemical physics was underway, with many groups clamouring to conquer new territory in the study of chemical reactions: the elusive and fleeting transition state. My interest in this emerging field dictated my choices of potential graduate schools, with Caltech and the group of Ahmed Zewail at the top of my list.

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55. Influence of the length and grafting density of PNIPAM chains on the colloidal and optical properties of quantum dot/PNIPAM assemblies.

Author

Oya Tagit, Nikodem Tomczak, Aliakbar Jafarpour, Dominik Janczewski, Ming Yong, G Julius, Vancso and, and Jennifer L Herek

Subjects
QUANTUM dots, COLLOIDAL crystals, FLUORESCENCE, POLYMERS, TEMPERATURE effect, BIOMOLECULES, ACRYLAMIDE
Abstract

Structural and optical characterization of water soluble, thermo-responsive quantum dot/poly(N-isopropyl acrylamide) (QD/PNIPAM) hybrid particles using fluorescence correlation spectroscopy (FCS) and time-correlated single photon counting (TCSPC) measurements performed at temperatures below and above the lower critical solution temperature (LCST) of PNIPAM is reported. By increasing the temperature above the LCST, the signature of the PNIPAM chain collapse covering the QDs is revealed by FCS measurements. Despite the significant structural change, the TCSPC measurements show that the fluorescence lifetimes remain of the same order of magnitude at T > LCST. Such QD/PNIPAM hybrid particles with water solubility and robust thermo-responsive behavior at physiologically relevant temperatures are potentially useful for (bio)molecular sensing and separation applications. [ABSTRACT FROM AUTHOR]

Published
2011
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56. Temperature-modulated quenching of quantum dots covalently coupled to chain ends of poly(N-isopropyl acrylamide) brushes on gold.

Author

Oya Tagit, Nikodem Tomczak, Edmondo M Benetti, Yanina Cesa, Christian Blum, Vinod Subramaniam, Jennifer L Herek, and G Julius

Subjects
QUANTUM dots, METAL quenching, GOLD compounds, POLYACRYLAMIDE, SURFACE chemistry, POLYMERIZATION, TEMPERATURE effect
Abstract

A thermo-responsive polymer/quantum dot platform based on poly(N-isopropyl acrylamide) (PNIPAM) brushes 'grafted from' a gold substrate and quantum dots (QDs) covalently attached to the PNIPAM layer is presented. The PNIPAM brushes are grafted from the gold surface using an iniferter-initiated controlled radical polymerization. The PNIPAM chain ends are functionalized with amine groups for coupling to water-dispersible COOH-functionalized QDs. Upon increasing the temperature above the lower critical solution temperature (LCST) of PNIPAM the QD luminescence is quenched. The luminescence was observed to recover upon decreasing the temperature below the LCTS. The data obtained are consistent with temperature-modulated thickness changes of the PNIPAM layer and quenching of the QDs by the gold surface via nonradiative energy transfer. [ABSTRACT FROM AUTHOR]

Published
2009
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