Photodiode, fast response

Samples were irradiated by a 10 ps single or 2 ns electron pulse from a 35 MeV linear accelerator for pulse radiolysis studies (17). The fast response optical detection systems of the pulse radiolysis system for absorption spectroscopy (18) is composed of a very fast response photodiode (R1328U, HTV.), a transient digitizer (R7912, Tektronix), a computer (PDP-11/34) and a display unit. The time resolution is about 70 ps which is determined by the rise time of the transient digitizer. 

The resistor, R, protects the diode against overload and accidental reversal of the supply voltage. The capacitor, C, provides a low-impedance RF-retum path to ground. The capacitor must be a low-impedance surface-mount type. The resistor is not critical. The connection length in the path GND-C-Photodiode-Connector must be kept to a minimum, or a 50 Ohm strip line on a printed circuit board must be used. Please note that the circuit gives a fast response only if the output is terminated with 50 Ohm. 

Eighteen equally spaced instrument ports are located along the entire length of the test vessel. Detonation pressure is measured using flush-mounted, piezoelectric pressure transducers, with a quoted risetime of 1 microsecond. Flame time-of-arrival is measured with fast response TCs and li t sensors (e.g., photodiodes). 

Diagnostics Smoked foil, piezoelectric, pressure transducers, photodiodes, ion detectors, fast response thermocouples, gas sampling, and gas chromo to graphy Smoked foil, piezoelectric pressure transducers, photodiodes, ion detectors, fast response thermocouples, gas sampling, and gas chromotography ... 

The detectors used in UV-vis spectroscopy are typically photomultiplier tubes, photodiodes, or charge-coupled devices (CCDs). Photomultipliers are very sensitive to UV and visible radiation and have fast response times, but with amplification factors of 10 electrons per incident photon, they are limited to measuring low light intensities. Photodiode or CCD arrays allow parallel detection of many wavelengths of radiation simultaneously if the array is positioned at the output focal plane of the monochromator. With many hundreds or thousands of chaimels, UV-vis spectra can be can be acquired very rapidly. 

In the typical setup, excitation light is provided by a pulsed (e.g., nanosecond) laser (emitting in the visible range, e.g., at 532 nm, if Mb is investigated), while the probe is delivered by a continuous-wave (cw) laser. The two beams are spatially overlapped in the sample, and the temporal changes in the optical properties (such as optical absorption or frequency shift) that follow the passage of the pump pulse are registered by a detector with short response time (relative to time scale of the processes monitored), such as a fast photodiode. 

Photodiodes are used as detectors in many automated systems either as individual components or in multiples as an array. Photomultiplier tubes are required in many immunoassay systems to provide adequate sensitivity and fast detector response times for fluorescent and chemiluminescent measurements. Several approaches have been used for the electrooptical integration and packaging in different analyzers. A logarithmic amplifier or microprocessor and/or computer software converts transmittance to absorbance. Low-cost analog-to-digital converters with conversion times... 

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