2,623 research outputs found
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
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