Comb-based spectroscopy with synchronous sampling for real-time averaging

摘要

A method of comb-based spectroscopy for measuring a CW source at time-bandwidth limited resolution by using frequency combs with a high degree of mutual coherence (<1 radian phase noise).

主权项

1. A method of comb-based spectroscopy comprising:
generating a first comb that transmits a first pulse train that is optically combined with a continuous-wave source (CW source); detecting a first overlap of each pulse of the first comb with the CW source in a first photodetector; digitizing a photodetector response from the first photodetector for each pulse of the first pulse train to generate digitized samples of the CW source measured from the first comb; generating a second comb that is optically coherent with the first comb and separately combined with the CW source, said second comb transmits a second pulse train that has a pulse period that differs by a change in time from the first pulse train and a pulse repetition frequency that differs by a change in a repetition rate from the first pulse train, wherein ΔT represents the change in time, fr represents the repetition rate, and Δfr represents the change in repetition rate; detecting a second overlap of each pulse of the second comb with the CW source in a second photodetector; digitizing a photodetector response from the second photodetector for each pulse of the second pulse train to generate digitized samples of the CW source measured from the second comb; multiplying the digitized samples from the first overlap by the digitized samples of the second overlap to produce a product data point record, wherein a length of the product data point record is fr/Δfr points over a duration in time of 1/Δfr; modifying a point separation for the product data point record to be the ΔT; Fourier transforming the product data point record to yield a wideband spectrum of the CW source at a resolution given by the repetition rate fr to provide an absolute frequency of the CW source with respect to a CW reference laser to which the first comb and the second comb are locked; and at least one of:
directing at least a portion of the CW source through a apectroscopy sample to generate a resulting transmission signal to obtain spectroscopic information about the spectroscopy sample, ordirecting at least a portion of the CW source into a laser ranging and detection (LADAR) system to generate a LADAR signal representing a range to a target.