| 摘要 |
Disclosed are light extinction-type optical particle detection systems and methods for their use. One such system comprises a laser source that produces a laser beam. The laser beam propagates from the laser source in response to a drive current having an amplitude that reaches a lasing threshold. The laser beam is characterized by mode-hopping noise energy that is produced by spurious switching of laser operating modes. The system also comprises a view volume through which the laser beam propagates and a stream of target particles immersed in a carrier fluid flows. The system also comprises a light-extinction type detector positioned on a side of the view volume opposite of the laser source. The laser beam strikes the target particles and thereby affects an amount of the laser beam that is incident on the detector, which produces, in response to the incident laser beam, a detection signal corresponding to a number of target particles in the view volume. The system also comprises a signal generator that produces the drive current such that the drive current amplitude transitions across the lasing threshold by a selected amount and at a selected frequency to purposefully cause the laser beam to operate simultaneously in multiple lasing modes. The selected amount and frequency cooperate to spread the mode-hopping noise energy over a spectral range established by the number of simultaneously operating lasing modes, such that the detector does not appreciably respond to the mode-hopping noise energy when producing the detection signal. Other systems and methods rapidly turn alternately on and off the laser such that the laser is on for no continuous period of time long enough to undergo undesired mode hopping, or vary the drive current amplitude in such a way to substantially inhibit undesired mode hopping.
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