Dual mode photoacoustic/acoustic microscopy with optical generation and detection

We present a dual mode scanning microscope which provides simultaneously ultrasonic and photoacoustic images. Short laser pulses are used to excite photoacoustic waves in a sample and to generate focused acoustic waves on a conical target. Ultrasound generation for pulse-echo mode is done by illuminating an acoustic axicon, resulting in quasi diffraction free acoustic pulses. An optical ring-shaped detector measures photoacoustic signals and backscattered acoustic waves. Due to the annular shape of the detector mainly acoustic waves coming from the symmetry axis, i.e. A-scans, are acquired; thus no reconstruction algorithm is needed. By reason of the transducers geometry, the setup is operated in backward mode. The annular detector is realized by a polymer optical fiber bent into a ring shape, being part of a fiber optic Mach-Zehnder interferometer. The annular detector mainly detects signals on the symmetry axis; however, also off-axis signals are detected. Reduction of the imaging artifacts is demonstrated on simulated data with a kspace algorithm taking the geometry of the problem into account. Furthermore, we present measurements on phantom samples.