We report on a multiphoton-timing distributed temperature sensor (DTS) based on the concept of distributed anti-Stokes Raman thermometry. The sensor combines the advantage of very high spatial resolution (40 cm) with moderate measurement times. In 5 min it is possible to determine the temperature of as many as 4000 points along an optical fiber with an accuracy Δ T < 2 °C. The new feature of the DTS system is the combination of a fast single-photon avalanche diode with specially designed real-time signal-processing electronics. We discuss various parameters that affect the operation of analog and photon-timing DTS systems. Particular emphasis is put on the consequences of the nonideal behavior of sensor components and the corresponding correction procedures.
Thin YBaCuO films have been deposited on ZrO2(Y) and SrTiO3 substrates by a novel ablation method, using a pulsed intense electron beam generated by a pseudospark source. Films with zero resistance around 85 K were grown at substrate temperatures of 820 °C with high reproducibility. X-ray analysis indicates highly textured growth on both substrates. Jc values were 6×106 A/cm2 at 4.2 K and 1.1×105 A/cm2 at 77 K. Because of the high simplicity of the deposition system and the variety of changeable parameters it represents an interesting alternative to existing laser ablation methods.
The influence of detector nonidealities on multiphoton timing experiments is investigated. Deviations from ideal detector behavior include dead-time, afterpulsing, and a smeared detector response. A statistical model of dead-time effects combined with cumulative afterpulsing is developed which allows the correction of distorted experimental data. The theory is verified with both Monte Carlo simulations and experimentally, whereby particular emphasis is put on fiberoptic optical time-domain reflectometry measurements. Though the theory is applicable to any kind of detector we discuss the various effects for two examples of commercially available single photon avalanche diode modules. One of the two detectors is the passive quenched EG&G SPCM-100 while the other module contains an active quenching circuit and is manufactured at the Czech Technical University at Prague.
Thin films of ReBaCuO (Re=Y, Gd) and of BiCaSrCuO have been deposited onto A1 2 O 3, MgO , SrTiO 3, Si and ZrO 2 substrates by planar and inverted cylindrical magnetron sputtering. The main advantage of this preparation technique is the high reproducibility allowing detailed and systematic studies of the film properties as a function of deposition parameters. Optimum deposition parameters were a high oxygen partial pressure of 2×10−1 Torr in an oxygen-argon mixture and substrate temperatures near 800°C. Except for the substrate Si the films grow highly textured on all substrates. For the 1–2–3 material zero resistance is obtained near 90 K for the case of textured growth. For Si the best film showed zero resistance near 84 K. High critical currents between 4×105 and 5.5×106 A/cm 2 were determined for films of the 1–2–3 material on the substrates MgO , ZrO 2 and SrTiO 3. On films SrTio 3 tunnel junctions with Pb and In counterelectrodes could be prepared which showed a gap-like feature in their current-voltage characteristic. These junctions could be prepared with great reproducibility and experimental arguments could be provided which show that this gap-like feature is due to a superconducting density of states effect. Finally, first results are presented on YBaCuO thin films which were deposited by a novel ablation device which uses a pulsed electron beam instead of the laser beam.
We report on the prototype of a new digital multi-time-interval analyzer (MTIA-1) based on a counter/memory architecture. The occurrence of multiple events with respect to a common start can be determined with a timing resolution of 4 ns. Incoming standard TTL or ECL pulses are processed and stored immediately after their detection in a 4096×16 Bit RAM. By virtue of this real-time histogramming concept, data acquisition does not have to be interrupted during signal processing. The maximum repetition rate of events to be processed in real time can be in excess of 20 MHz. The MTIA-1 is designed for repetitive timing applications where multiple time intervals have to be processed with very high speed. The analyzer accepts standard TTL or ECL pulses and has a maximum measurement range of 4096 channels. After the end of an individual multi time interval measurement no additional time consuming postprocessing is needed for data transfer or data analysis. The article gives an overview of the structure of the analyzer and its principle of operation. We further present an example for an application where the MTIA-1 is used in fiberoptic distributed temperature sensing.
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