No abstract

In this article, we present the drifts phenomena that affect the temporal resolution of a standard synchroscan streak camera and some techniques to correct them in order to enhance the long-term resolution of these cameras. First, we give a comprehensive list of the components of the synchroscan streak camera which are sensitive to temporal and thermal drift: from the trigger circuit to the deflection plate of the tube. The way in which these components make the camera drift is explained and then quantified. A measure of drift realized on two streak cameras at the same time and in the same conditions (the same synchroscan signal) shows that each camera has its own intrinsic and stochastic drift. Second, two techniques to stabilize the camera are then described. The first method stabilizes the phase difference between the synchroscan signal and the deflection plate voltage. The second uses a laser reference trace on the phosphor screen and a digital data processing technique to reach the ultimate stability. The results show that a stabilized camera can be used immediately after it is turned on (due to suppression of the warm-up time) and still has very good temporal resolution even with a long-time exposure (2.4 ps full width at half maximum with a time exposure of 2 h has been achieved). This allows more exploration in the detection of very weak signals.

We describe an experimental setup for time-resolved diffuse optical tomography that uses a seven-channel light guide to transmit scattered light to a streak camera. This setup permits the simultaneous measurement of the time profiles of photons reemitted at different boundary sites of the objects studied. The instrument, its main specifications, and detector-specific data analysis before image reconstruction are described. The instrumentation was tested with phantoms simulating biological tissue, and the absorption and reduced scattering images that were obtained are discussed.

In this papa, a validation of a new UV-A laser-induced fluorescence imaging system implemented in an all-road car for near-field remote sensing of vegetati will be presented. It has been developed as a part of a European Community Program 1NTERREG II and is consisting ofthree main parts: excitation, detection and control units. The excitation source is a frequency tripied Nd:YAG laser and the laser spot size is adjusted via a variable beam expander. Fluorescence images are recorded at four characteristic fluorescence bands: 440, 520, 690 and 740 urn with a gated intensified digital CCD camera. The laser head and camera are situated on a directed in site and azimuth platform which can be high up to 6 meters. The platform positioning, localisation and distance detection, spot size determination and adjustment, focus, sharpness, selection ofthe filter, laser and camera synchronization, gain ofthe intensifier, real time visualisation of images, acquisition time are controlled by a newly developed software which allows also image storage, analysis and treatment. Examples of remote sensing fluorescence images from several plant species recorded at a distance of 10 -30 m will be given and discussed further in this paper.