High-frequency optoacoustic arrays using parallel etalon detection

Here we present an ultrasound detection system with an optical end capable of parallel probe. An erbium-doped fiber amplifier, driven by a tunable laser, outputs light at 27 dBm. A lens collimates the light to probe a 6-μm thick SU-8 etalon and controls the parallel detection area (total array size). A two-lens system guides the reflected light into a photodetector and controls the active area (array element size) on the etalon surface. A translation stage carries the photodetector to detect signals from different array elements. The output of the photodetector is recorded using an oscilloscope. The system's noise equivalent pressure was estimated to be 6.5 kPa over 10~50 MHz using a calibrated piezoelectric transducer when the -3 dB parallel detection area was 1.8 mm in diameter. The detection bandwidth was estimate to exceed 70 MHz using a focused 50 MHz piezoelectric transducer. Using a single probe wavelength, a 1D array with 41 elements and a 1.06 mm aperture length was formed to image a 49 μm black bead photoacoustically. The final image shows an object size of about 95 μm in diameter. According to the results, realizing high-frequency 2D optoacoustic arrays using an etalon is possible.