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Spectral encoding of the broadband laser. A diffraction grating disperses the laser light, where different wavelengths probe distinct positions on the acoustic sensing surface.
Sagnac interferometer. (a) The QWP and FR provide the phase bias required for proper operation. The ultrasonic signals from all the receive elements are carried by the same optical fiber. (b) Possible light paths in the interferometer.
Acoustic signals measured with spectral encoding. (a) Wavefield plot and (b) beam plot of the transducer focus at the center of the array. (c) Wavefield plot and (d) beam plot of the transducer focus shifted by 250 μm. For comparison, the beam plot from (b) is shown by the dashed curve in (d).
Acoustic signals measured without spectral encoding. A single point detector is scanned across the pellicle. (a) Wavefield plot and (b) beam plot of the transducer focus. For comparison, the beam plot from the spectrally encoded data is shown by the dashed curve in (b).
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