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- 2011 (3) (entfernen)
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- Active thermography (1)
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The spontaneous emission of a GaAs-based tapered laser diode emitting at λ = 1060 nm was measured through a window in the transparent substrate in order to study the carrier density distribution inside the device. It is shown that the tapered geometry is responsible for nonuniform amplification of the spontaneous/stimulated emission which in turn influences the spatial distribution of the carriers starting from below threshold. The carrier density does not clamp at the lasing threshold and above it the device shows lateral spatial hole-burning caused by high stimulated emission along the cavity center.
Mechanisms and fast kinetics of the catastrophic optical damage (COD) in GaAs-based diode lasers
(2011)
COD diagram determined for a batch of broad-area AlGaAs diode lasers. The time to COD within a single current pulse is plotted versus the actual average optical power in the moment when the COD takes place. Full circles stand for clearly identified COD events (right ordinate), whereas open circles (left ordinate) represent the pulse duration in experiments, where no COD has been detected. A borderline (gray) exists between two regions, i. e., parameter sets, of presence (orange) and absence of COD (blue). This borderline is somewhat blurred because of the randomness in filamentation of the laser nearfield and scatter in properties of the involved individual devices.
We present an all-purpose crack detection algorithm for flying spot thermography which is directly applicable to a thermogram sequence without the need of any additional information about the experimental setup. A single image containing distinct crack signatures is derived in two steps. Firstly, the spatial derivative is calculated for each frame of the sequence and, secondly, the resulting data set is sorted pixel wise along the time axis. The feasibility of the proposed procedure is proven by testing a piece of rail that comprises roll contact fatigue cracks and by comparing the results with magnetic particle testing.