High frequency ultrasound imaging using Fabry-Perot optical etalon

An etalon is an optical resonator where light is confined to a thin transparent layer having reflecting coatings on the sides. Optical reflection from this structure is highly sensitive to local mechanical perturbation. This is the basic principle allowing these devices to act as 2D ultrasound detector arrays. Optical probing of the etalon surface defines the array geometry and detection size of each element in the array. Element size on the order of several microns is easily realized. The detection bandwidth is limited primarily by the acoustic propagation time thru the layer thickness. We have developed etalon structures optimized for high frequency ultrasound detection using thin polymer layers (less than 10 μm). The detection bandwidth of these devices is typically 100MHz. The sensitivity of the etalon detector was demonstrated to be comparable to that of a piezoceramic detector. The etalon was integrated into a photoacoustic imaging system. High resolution images of phantom targets and biological tissue (nerve cord) were obtained. The additional information of optical absorption obtained by photoacoustic imaging, along with the high resolution detection of the etalon, offer unique advantages for intravascular and neurological imaging applications.