Fig. 1.

(a) Schematic of the setup. A sample is embedded in agarose and moved parallel to the ring-plane by a scanning stage. Photoacoustic waves within the sample are excited by pulses from a frequency doubled Nd:YAG laser. The photoacoustic signals are picked up by graded-index polymer optical fiber rings which are part of fiber-optic Mach–Zehnder interferometers (FOMZI). (b) A photograph of the acrylic glass fiber-holder. The overlaid dotted red lines indicate the path of the fibers where they are not visible in the photograph. The fibers are held in place by ring-shaped notches. These ring-notches cannot be closed to form a complete circle as the optic fibers have to be fed into the notches with a minimal bend radius of 5 mm. The rounded openings (at 12 o’clock in the picture) ensure proper feeding of the fibers. Bubble wrap insulates the fibers from ultrasound where they deviate from the ring-shape. Duct tape fixes the bubble wrap and the fibers in the feeding lines. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)