Hemmel Amrania

Fano Resonances in Nanoscale Plasmonic Systems: A Parameter-Free Modeling Approach

The interaction between plasmonic resonances, sharp modes, and light in nanoscale plasmonic systems often leads to Fano interference effects. This occurs because the plasmonic excitations are usually spectrally broad and the characteristic narrow asymmetric Fano line-shape results upon interaction with spectrally sharper modes. By considering the plasmonic resonance in the Fano model, as opposed to previous flat continuum approaches, here we show that a simple and exact expression for the line-shape can be found. This allows the role of the width and energy of the plasmonic resonance to be properly understood. As examples, we show how Fano resonances measured on an array of gold nanoantennas covered with PMMA, as well as the hybridization of dark with bright plasmons in nanocavities, are well reproduced with a simple exact formula and without any fitting parameters.

Comparison of a diode pumped Er:YSGG and Er:YAG laser in the bounce geometry at the 3 μm transition

A comparative study is made of the laser crystals 50 at. % Er:YAG and 50 at. % Er:YSGG. Both lasers are constructed in the bounce geometry with quasi continuous wave (QCW) diode pumping. In Er:YAG, pulse energies of up to ~31mJ, slope efficiency of 12.6% and a red-shift in laser wavelength are observed with a final and dominant wavelength of 2.936μm. In Er:YSGG, higher performance is achieved with pulse energies of ~55mJ, slope efficiency of 20.5% and a single transition wavelength of 2.797μm observed. The study indicates that diode pumped Er:YSGG is a superior laser source at 3μm than Er:YAG and it has greater energy storage potential for Q-switched operation.

Ultrafast infrared chemical imaging of live cells

Mid-infrared (mid-IR) spectroscopy provides a unique chemical fingerprint of biomaterials, including DNA and proteins, from single molecules to highly organised structures and, ultimately, to live cells and tissues. However, acquiring good signal–to–noise mid-IR spectroscopic images, at the cellular level, typically involves a synchrotron, with imaging times of order of minutes. Here we use a new laser-based table-top IR spectroscopic micro-imaging system, to obtain vibrational fingerprint signatures of living human ovarian cancer cells at a diffraction limited spatial resolution, and at a spectral resolution (< 20 cm−1) sufficient to map out the spatial distributions of chemical moieties inside the cell itself. The bright laser pulses give very high signal–to–noise images, and ∼100 psec image acquisition times that are roughly 1011 times faster than current mid-IR spectroscopic imaging techniques. The imaging method is quantitative, non-phototoxic, marker-free and easily fast enough to “freeze” moving, living specimens. It can be applied to a range of cell-level biochemical processes, and we believe it could impact on the fields of drug action, cell physiology, pathology and disease as a whole.

A benchtop, ultrafast infrared spectroscopic imaging system for biomedical applications.

We discuss the potential biomedical applications for a novel infrared spectroscopic microimaging system. A tunable, table top solid-state laser has been coupled to a commercial infrared microscope, fitted with a modified high resolution infrared camera, to create a unique tool for midinfrared imaging. The system is capable of performing broadband imaging at a diffraction-limited spatial resolution, as is demonstrated here by spatially resolved spectroscopy of polymer test samples with a spectral resolution of 20 cm(-1). The large pulse energies (tens of microjoules) offer previously unobtainable combinations of high signal-to-noise levels and rapid data collection times which are superior to current stand-alone laboratory instruments by many decades. Coupled with the short (100 ps) short pulse duration, these characteristics promise to make a wide range of time-resolved and reflection mode imaging experiments possible with live biological systems.

Progress Toward Realizing an Intermediate Band Solar Cell—Sequential Absorption of Photons in a Quantum Well Solar Cell

In order to realize an intermediate band solar cell, which promises high photovoltaic energy conversion efficiency, achieving higher photocurrent while maintaining the cell voltage is essential. We report on a transient photocurrent due to the sequential absorption of photons in a single quantum well by continuously pumping to stimulate interband transitions (from a valence band to an intermediate band) and showing an intersubband transition (from an intermediate band to a conduction band) with a pulsed infrared laser. We demonstrate the extent to which multiple-photon absorption can be achieved in quantum well devices and propose that a quantum well is a suitable candidate for an intermediate band solar cell. From the combination of this and other sequential absorption results, it is clear that enhancing the short lifetime of a carrier in the intermediate band is the next step toward achieving a working intermediate band solar cell. In light of this, we enhance our previous suggestion, the photon ratchet intermediate band solar cell, as a means of increasing the electron lifetime.

Spectral Pathology: General discussion

Parvez Haris opened the discussion of the introductory lecture by Max Diem: Varying degrees of accuracy have been obtained for discrimination between cancerous and non-cancerous tissues using vibrational spectroscopic methods. What are the explanations for these variation in accuracy between cancerous and non-cancerous tissues and how do they correlate with accuracy from other techniques including histopathology?

Optical chopper Q-switching for flashlamp-pumped Er,Cr:YSGG lasers

We present a novel way of Q-switching a flashlamp-pumped, λ = 2.8 μm Er,Cr:YSGG laser, wherein a rotating polygon is used as an optical chopper. Single pulse energies of ~3.8 mJ were achieved with pulsewidths of ~305 ns. The scheme benefits from the simplicity of design, and, compared with other Q-switching methods, a reduction in losses and laser damage problems from intracavity components. We also investigate the optimization of the laser output through purging of the laser with nitrogen, and find a 29% increase in peak output energy.

Widely Tunable Midinfrared Radiation from GaSe OPO

Discussed is a mid IR, gallium selenide, angle-tuned, singly resonant OPO with a tuning range of λ ~ 4-18 μm, pumped by a λ = 2.8 μm Er,Cr:YSGG Q-switched laser. The system will achieve anticipated pulse energies of up to 1 mJ.

High energy diode pumped Er:YSGG laser at 3µm transition

Lasing of the trivalent erbium ion in garnet hosts at wavelengths close to 3µm has attracted considerable interest. This is primarily due to the strong absorption by water around this wavelength, making erbium doped lasers suitable for use in a range of medical and biological applications [1–3]. A variety of erbium doped hosts have been investigated to date, of which Er:YAG has been the most intensively researched. However, Er:YSGG shows promise for the construction of a more efficient laser system owing to its longer upper laser level lifetime of 1.3ms compared with 0.12ms in Er:YAG [1]. In this work we report operation of a quasi continuous wave (QCW) diode pumped 30 at. % Er:YSGG laser in the bounce geometry, yielding pulse energies of up to 41mJ and a slope efficiency of 12.6%.