An ultraviolet nanosecond light pulse generator using a light emitting diode for test of photodetectors
ABSTRACT An optical function pulse generator that emits (1) short pulse of 1 ns duration, (2) double pulse with variable time interval, and (3) square waveform pulse of variable width in nanosecond range is devised using an InGaN/AlGaN double heterostructure light emitting diode (LED). Although the LED emits a 450 nm (blue) light under conventional dc operation below 30 mA, 380 nm light due to the InGaN/AlGaN component appears when a current larger than 50 mA is applied. This phenomenon is used to realize a pulsed ultraviolet light source. Under large nanosecond current pulsing (peak current >1 A), an intense pulsed emission of 380 nm is obtained. Pulse waveform of the LED emission can be adjusted electrically by applying a shaped current to the LED. To evaluate the potential of the pulse generator as a test source of photodetectors, the response waveforms of photomultiplier tubes were measured. © 1997 American Institute of Physics.
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ABSTRACT: We have recently shown that only a small part of a Si bipolar junction transistor (BJT) conducts the current in a short-pulsing mode (≤2 ns), and a complicated temporal variation takes place in the size of operating emitter-base perimeter. Namely, the switched-on region in the corner of an emitter finger first shrinks down to just a few micrometers and only then spreads to ~100 μm by the end of the transient. Additionally important is the demonstrated ability of a tiny filament (≤10 μm) to quench the switching in the entire perimeter (1.6 mm). This creates the impression that an initial triggering inhomogeneity of the smallest size will always win the switching competition. It has been shown experimentally, however, that the sharpest corners (<10 μm in size) "lose out" to the ~100 μm corners, a fact that has not been explained so far. It is shown here using quasi-3-D modeling that an optimal curvature for the corner of an emitter finger exists that provides minimal switching delay, resulting in the shortest current pulses of the highest amplitude. This finding is especially important when designing unique subnanosecond avalanche BJTs, the 3-D transient properties of which are of major importance.IEEE Transactions on Electron Devices 03/2014; PP(99):1-1. DOI:10.1109/TED.2014.2300505 · 2.36 Impact Factor
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ABSTRACT: We demonstrate measurement of the intrinsic fluorescence decay of a protein excited with a new and inexpensive optical source based on a light emitting diode (LED) giving 600 ps pulses at ~280 nm. We believe this source will offer significant new capabilities for fluorescence research and development.Measurement Science and Technology 11/2004; 15(11). DOI:10.1088/0957-0233/15/11/L02 · 1.35 Impact Factor
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ABSTRACT: Here, we present the design, construction and test of two nanosecond pulsed light sources. The first source emits light centered at 470nm (Blue) while second one is centered at 362nm (Ultraviolet). The Blue source works with a free-running relaxation oscillator composed of a complementary pair of ultra-speed bipolar transistors. The Ultraviolet source uses a high current pulse generator, based on avalanche transistors which is externally triggered. Both sources can operate at three different modes: Continuous mode, Monochromatized mode and Pulsed mode. In the pulsed mode, short pulses are observed with a characteristic duration time of 13ns at a repetition rate of 10kHz. In the monochromatized mode, the linewidth of the source is reduced by means of an optical monochromator, thus providing a tunable source over a range of 12 nm. Furthermore, in order to illustrate the usefulness of this source to applied studies we present spectroscopy studies from fluorescence emission of an organic specimen solution (C460 molecule). The light sources presented here have the advantage of being constructed with conventional and low cost components, and have a wide scope for applications both applied and fundamental.