High performance NbN nanowire superconducting single photon detectors fabricated on MgO substrates

We demonstrate high-performance nanowire superconducting single photon detectors (SSPDs) on ultrathin NbN films grown at a temperature compatible with monolithic integration. NbN films ranging from 150nm to 3nm in thickness were deposited by dc magnetron sputtering on MgO substrates at 400C. The superconducting properties of NbN films were optimized studying the effects of deposition parameters on film properties. SSPDs were fabricated on high quality NbN films of different thickness (7 to 3nm) deposited under optimal conditions. Electrical and optical characterizations were performed on the SSPDs. The highest QE value measured at 4.2K is 20% at 1300nm

Towards jitter-free pump-probe measurements at seeded free electron laser facilities

X-ray free electron lasers (FEL) coupled with optical lasers have opened unprecedented opportunities for studying ultrafast dynamics in matter. The major challenge in pump-probe experiments using FEL and optical lasers is synchronizing the arrival time of the two pulses. Here we report a technique that benefits from the seeded-FEL scheme and uses the optical seed laser for nearly jitter-free pump-probe experiments. Timing jitter as small as 6 fs has been achieved and confirmed by measurements of FEL-induced transient reflectivity changes of Si3N4 using both collinear and non-collinear geometries. Planned improvements of the experimental set-up are expected to further reduce the timing jitter between the two pulses down to fs level

Optics and Quantum Electronics

Contains table of contents for Section 2 and reports on eleven research projects.Joint Services Electronics Program Contract DAAL03-89-C-0001National Science Foundation Grant EET 87-00474U.S. Air Force - Office of Scientific Research Contract F49620-88-C-0089Charles S. Draper Laboratory Contract DL-H-404179National Center for Integrated PhotonicsNational Science Foundation Grant ECS 87-18417NEC Research InstituteNational Science Foundation Grant ECS 85-52701Medical Free Electron Laser Program Contract N00014-86-K-0117National Institutes of Health Grant 5-RO1-GM35459Lawrence Livermore National Laboratory Contract B048704U.S. Department of Energy Grant DE-FG02-89-ER14012Columbia University Contract P016310

New insights into the laser-assisted photoelectric effect from solid-state surfaces

Photoemission from a solid surface provides a wealth of information about the electronic structure of the surface and its dynamic evolution. Ultrafast pump-probe experiments are particularly useful to study the dynamic interactions of photons with surfaces as well as the ensuing electron dynamics induced by these interactions. Time-resolved laser-assisted photoemission (tr-LAPE) from surfaces is a novel technique to gain deeper understanding of the fundamentals underlying the photoemission process. Here, we present the results of a femtosecond time-resolved soft X-ray photoelectron spectroscopy experiment on two different metal surfaces conducted at the X-ray Free-Electron Laser FLASH in Hamburg. We study photoemission from the W 4f and Pt 4f core levels using ultrashort soft X-ray pulses in combination with synchronized infrared (IR) laser pulses. When both pulses overlap in time and space, laser-assisted photoemission results in the formation of a series of sidebands that reflect the dynamics of the laser-surface interaction. We demonstrate a qualitatively new level of sideband generation up to the sixth order and a surprising material dependence of the number of sidebands that has so far not been predicted by theory. We provide a semi-quantitative explanation of this phenomenon based on the different dynamic dielectric responses of the two materials. Our results advance the understanding of the LAPE process and reveal new details of the IR field present in the surface region, which is determined by the dynamic interplay between the IR laser field and the dielectric response of the metal surfaces.Comment: 18 pages, 3 figure

Laser Based Mid-Infrared Spectroscopic Imaging – Exploring a Novel Method for Application in Cancer Diagnosis

A number of biomedical studies have shown that mid-infrared spectroscopic images can provide both morphological and biochemical information that can be used for the diagnosis of cancer. Whilst this technique has shown great potential it has yet to be employed by the medical profession. By replacing the conventional broadband thermal source employed in modern FTIR spectrometers with high-brightness, broadly tuneable laser based sources (QCLs and OPGs) we aim to solve one of the main obstacles to the transfer of this technology to the medical arena; namely poor signal to noise ratios at high spatial resolutions and short image acquisition times. In this thesis we take the first steps towards developing the optimum experimental configuration, the data processing algorithms and the spectroscopic image contrast and enhancement methods needed to utilise these high intensity laser based sources. We show that a QCL system is better suited to providing numerical absorbance values (biochemical information) than an OPG system primarily due to the QCL pulse stability. We also discuss practical protocols for the application of spectroscopic imaging to cancer diagnosis and present our spectroscopic imaging results from our laser based spectroscopic imaging experiments of oesophageal cancer tissue