Figure 1 shows the experimental setup. A CW laser (Coherent, Santa Clara, CA, Verdi V-5) outputs a beam at (its optical frequency is denoted as ). The beam was transmitted through an electro-optic modulator (EOM) and split into two beams by a polarizing beam splitter. The transmitted beam was further split into a signal beam and a collimated reference beam . The beam was collimated as the conjugated reference beam that counter propagated as once reflected by mirror M3. The signal beam was transmitted through two acousto-optic modulators (AOMs), where its optical frequency was tuned to and incident on the tissue-mimicking phantom. Two identical immersion type focused ultrasonic transducers T1 and T2 (Olympus NDT, Waltham, MA, A381S-SU-F1.50IN-PTF) operating in long-burst mode with different frequencies were employed: one at and the other at . The acoustic axis of T1 was aligned along the axis, whereas the acoustic axis of T2 was aligned in the plane. The two ultrasound beams intersected at their foci at an angle of 45 deg, with both acoustic axes perpendicular to the optical axis of the signal beam . The TRUE signal was detected by a photodiode. During the hologram recording stage, when both transducers were used to modulate the signal beam inside the turbid sample, the two AOMs were tuned to match the beat frequency of the transducers so that . The photons initially had an electric field of . Ultrasonic modulation by the two ultrasound beams resulted in photons encoded (or tagged) with different frequency shifts. The spectral components that have frequencies of , , and are the first-order signals and will not interfere with the reference beam to form a stationary interferogram in the (BSO) crystal (Elan, Russia). Inside the intersection volume of the two ultrasound fields, the photons encoded by both ultrasound beams are the second-order signals, which have an electric field of . Some scattered second-order light was collected by two lenses and directed onto the PR crystal, where it interfered with the reference beam , forming a stationary volume hologram.