Abstract: Distributed acoustic sensing (DAS) system for quasi-coherent detection of at least one multi-frequency signal over an optical fiber, including a multi-frequency pulse generator, a circulator, a coherent detector and a processor, the pulse generator for generating at least one multi-frequency pulse train including at least two pulses each having a different frequency, the pulse train including a plurality of carriers, the coherent detector for receiving at least one backscattered signal from the optical fiber and the processor for quasi-coherent aggregation of the carriers in the backscattered signal, wherein the processor channelizes the backscattered signal into at least one complex signal for each frequency in the carriers and wherein for each complex signal, the processor respectively extracts at least one of an amplitude change and a phase change for each one of the carriers and selectively aggregates at least one of the changes for the carriers for determining if an event has occurred over the optical fi

Abstract: Distributed acoustic sensing (DAS) system for quasi-coherent detection of at least one multi-frequency signal over an optical fiber, including a multi-frequency pulse generator, a circulator, a coherent detector and a processor, the pulse generator for generating at least one multi-frequency pulse train including at least two pulses each having a different frequency, the pulse train including a plurality of carriers, the coherent detector for receiving at least one backscattered signal from the optical fiber and the processor for quasi-coherent aggregation of the carriers in the backscattered signal, wherein the processor channelizes the backscattered signal into at least one complex signal for each frequency in the carriers and wherein for each complex signal, the processor respectively extracts at least one of an amplitude change and a phase change for each one of the carriers and selectively aggregates at least one of the changes for the carriers for determining if an event has occurred over the optical fi

Abstract: A method for circuit fabrication includes inspecting an array of solder bumps on a circuit substrate so as to identify a solder bump having a height above the substrate that is greater than a predefined maximum. A first laser beam is directed toward the identified solder bump so as to ablate a selected amount of a solder material from the identified solder bump. Alternatively or additionally, a further solder bump having a height above the substrate that is less than a predefined minimum is identified, and one or more molten droplets of the solder material are deposited on the further solder bump. After ablating or depositing the solder material, a second laser beam is directed toward the identified solder bump with sufficient energy to cause the solder material in the identified solder bump to melt and reflow.