Fig. 1. Schematic diagram of a change in polarization status of light through a solid sample in which an ultrasonic wave propagates. Under the influence of the ultrasonic wave (wavelength λu) propagation, the solid is compressed and rarified depending on location and time, which produces nonuniform stress and strain fields. This leads to an anisotropic distribution of the refractive index and produces a phase difference δ of light through the 3D infinitesimal volume element. The phase difference can be detected by our PIMI system.

Fig. 2. Experimental setup of ultrasonic field sensing. It consists of an ultrasonic excitation system and a PIMI system. The excitation system was employed to generate ultrasonic waves in the sample, and the PIMI system was used to image and characterize the ultrasonic field by extracting variations of optical properties of the sample with and without ultrasonic excitation.

Fig. 3. PIMI images under different ultrasonic conditions (a)–(c) without and (d)–(f) with ultrasonic excitation. (a) and (d) Average of polarization intensities Idp, (b) and (e) polarization phase difference sinδ, (c) and (f) polarization angle of slow axis Φ.

Fig. 4. PIMI images of the Stokes parameters under different ultrasonic conditions (a)–(d) without and (e)–(h) with ultrasonic excitation. (a), (e) S0; (b), (f) S1; (c), (g) S2; (d), (h) S3.

Fig. 5. Difference between PIMI images without ultrasonic excitation and those with ultrasonic excitation. (a) sinδ, (b) Φ, and (c) S1.

Fig. 6. Image of Φ under different ultrasonic phases. (a) Phase 0, (b) phase π/4, (c) extracted intensity curves along the line in (a) and (b), (d) difference between (a) and Fig. 3(c), (e) difference between (b) and Fig. 3(c), (f) extracted intensity curves along the line in (d) and (e).

Fig. 7. PIMI images under different ultrasonic conditions (a)–(c) without and (d)–(f) with ultrasonic excitation: (a) and (d) sinδ, (b) and (e) Φ, (c) and (f) S1. Difference between the PIMI images without ultrasonic excitation and those with ultrasonic excitation: (g) sinδ, (h) Φ, and (i) S1.