J.E. Millaud

Detectors for single-molecule fluorescence imaging and spectroscopy.

Single-molecule observation, characterization and manipulation techniques have recently come to the forefront of several research domains spanning chemistry, biology and physics. Due to the exquisite sensitivity, specificity, and unmasking of ensemble averaging, single-molecule fluorescence imaging and spectroscopy have become, in a short period of time, important tools in cell biology, biochemistry and biophysics. These methods led to new ways of thinking about biological processes such as viral infection, receptor diffusion and oligomerization, cellular signaling, protein–protein or protein–nucleic acid interactions, and molecular machines. Such achievements require a combination of several factors to be met, among which detector sensitivity and bandwidth are crucial. Here, the necessary performance of photodetectors used in these types of experiments, the current state of the art for different categories of detectors, and actual and future developments of single-photon counting detectors for single-molecule imaging and spectroscopy, are investigated.

Fluorescence lifetime microscopy with a time- and space-resolved single-photon counting detector

We have recently developed a wide-field photon-counting detector (the H33D detector) having high-temporal and highspatial resolutions and capable of recording up to 500,000 photons per sec. Its temporal performance has been previously characterized using solutions of fluorescent materials with different lifetimes, and its spatial resolution using sub-diffraction objects (beads and quantum dots). Here we show its application to fluorescence lifetime imaging of live cells and compare its performance to a scanning confocal TCSPC approach. With the expected improvements in photocathode sensitivity and increase in detector throughput, this technology appears as a promising alternative to the current lifetime imaging solutions.

An ionization chamber shower detector for the LHC luminosity monitor

The front IR quadrupole absorbers (TAS) and the IR neutral particle absorbers (TAN) in the high luminosity insertions of the Large Hadron Collider (LHC) each absorb approximately 1.8 TeV of forward collision products on average per pp interaction (/spl sim/235 W at design luminosity 10/sup 34/ cm/sup -2/ s/sup -1/). This secondary particle flux can be exploited to provide a useful storage ring operations tool for optimization of luminosity. A novel segmented, multi-gap, pressurized gas ionization chamber is being developed for sampling the energy deposited near the maxima of the hadronic/electromagnetic showers in these absorbers. The system design choices have been strongly influenced by optimization of signal to noise ratio and by the very high radiation environment. The ionization chambers are instrumented with low noise, fast, pulse shaping electronics to be capable of resolving individual bunch crossings at 40 MHz. Data on each bunch are to be separately accumulated over multiple bunch crossings until the desired statistical accuracy is obtained. At design luminosity approximately 2/spl times/10/sup 3/ bunch crossings will suffice for a 1% luminosity measurement. In this paper we report the first experimental results of the ionization chamber and analog electronics. Single 450 GeV protons from the SPS at CERN are used to simulate the hadronic/electromagnetic showers produced by the forward collision products from the interaction regions of the LHC.

A Pixel Unit Cell Targeting 16ns Resolution and Radiation Hardness in a Column Read-Out Particle Vertex Detector

Abstract A pixel unit cell (PUC) circuit architecture , optimized for a column read out architecture, is reported. Each PUC contains an integrator, active filter, comparator, and optional analog store. The time-over-threshold (TOT) discriminator allows an all-digital interface to the array periphery readout while passing an analog measure of collected charge. Use of (existing) radiation hard processes, to build a detector bump-bonded to a pixel readout array, is targeted. Here emphasis is on a qualitative explanation of how the unique circuit implementation benefits operation for Super Collider (SSC) detector application.

Electrical design considerations for a 40 MHz gas ionization chamber

The front IR quadrupole absorbers (TAS) and the IR neutral particle absorbers (TAN) in the high luminosity insertions of the Large Hadron Collider (LHC) each absorb approximately 1.8 TeV of forward collision products on average per pp interaction (/spl sim/235 W at design luminosity 10/sup 34/ cm/sup -2/ s/sup -1/). This secondary particle flux can be exploited to provide a useful storage ring operations tool for optimization of luminosity. A novel segmented, multi-gap, pressurized gas ionization chambers is being developed for sampling the energy deposited near the maxima of the hadronic/electromagnetic showers in these absorbers. The ionization chamber must be capable of resolving individual bunch crossings at 40 MHz. The ionization chamber is segmented into quadrants; each quadrant consists of sixty (40/spl times/40) mm/sup 2/ Cu plates 1.0 mm thick, with 0.5 mm gaps. The 0.5 mm gap width has been chosen so that the time for the ionization electrons to drift across the gap, is short enough to produce at the output of the shaping amplifier, a signal that returns to the base line is less than the 25 ns bunch spacing of the LHC. From noise considerations in the presence of a cable the stack of plates are connected electrically 10 in parallel, 6 in series to achieve an equivalent detector capacitance C/sub d//spl sim/50 pF. This type connection forms an electrode inductive L/sub e/ and electrode capacitive C/sub e/ network that must be optimized to transfer charge from the chamber to the sensing amplifier. This paper describes the design of the collection electrodes optimized for 40 MHz operation.