Abstract
In ultrasound-modulated optical tomography, the incident light is frequency-shifted and phase-modulated simultaneously by ultrasound. Both the optical frequency shift and phase modulation can cause ultrasonic modulation of coherent light. However, the two types of ultrasonic modulation have not been obtained separately so far. In this paper, the two types of ultrasonic modulation are obtained separately by Raman–Nath diffraction, and analyzed theoretically and experimentally. The dependences of ultrasonic modulation on the optical frequency shift and phase modulation are therefore revealed. The intensity of ultrasound-modulated light based on the optical frequency shift varies periodically with the ultrasonic frequency. Additionally, the intensity of ultrasound-modulated light based on the optical phase modulation varies periodically at twice the ultrasonic frequency. At last, the maximum modulation depths based on the optical frequency shift and phase modulation are 0.5 and 1.67, respectively.
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