Photoacoustic Generation of .X-waves and theirApplication in a Dual Mode Scanning Acoustic Microscope

摘要

Photoacoustic imaging is based on the excitation of ultrasound waves by irradiating objects with short laser pulses. Absorbing laser energy causes thermal expansion, which leads to broadband ultrasonic waves, carrying information about size, location and optical properties of the observed target. Images reveal purely optical contrast, yet the technique is acoustic. Classical ultrasonic imaging generates images with purely acoustical contrast based on the impedance differences of structures in observed samples. For developing a dual mode scanning acoustic microscope, which uses simultaneously both contrast mechanism (acoustic pulse-echo and photoacoustic image contrast) ultrasonic pulses with a large depth of field are advantageous. By illuminating special conically shaped transducers, so called axicons, with short laser pulses, broadband ultrasonic pulses with a large depth of field at small lateral extension can be excited. These special pulses, so called X-waves and their use in a microscope are investigated.