In this paper we present an all-optical silicon based modulator suggested also for high power operation and for pulse picker application being used as part of fiber lasers system. The paper theoretically and experimentally investigates several new and important insights involving the dependence of the relative transmission on the pump pulse energy for different finesse values of the constructed cavity as well as the dependence of the response rate of the device to the pump wavelength due to coexistence of two physical recombination processes: fast surface effect and slow bulk recombination. To adapt the constructed silicon based cavity to be used in lasers applications, we aligned the pump and the signal beams to co-propagate through the device while the usage of a cavity allowed a low power pump to yield a significant extinction ratio at the output of the device.
An open-path spectrometer for fast spatial detection and identification of gaseous plumes in a realistic environmental conditions is presented. Gases are released in a 500 m 3 hall; detection and identification is performed by spectroscopic means-measuring the light spectral absorption (at 8 to 10 μm) by shining an externalcavity quantum cascade laser beam through the inspected volume. Real-time identification is demonstrated for gas plumes of CH 2 FCF 3 (R134a) and CHF 3 at a distance of 30 m round trip with a minimum identification level of 0.2 ppm (response times of 2 to 10 s). The relatively wide spectral coverage allows a high probability of detection (PD) and low probability for a false alarm to be obtained in these realistic conditions. It is also demonstrated that the use of several lines-of-sight improves PD as gas spreading in the hall in these conditions is slow and unpredictable.
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