Optical detection of ultrasound is a promising technique for high resolution imaging arrays. The detection resolution approaches the optical resolution, which is on the order of the optical wavelength. We describe here an optical technique for ultrasound detection based on a thin Fabry-Perot etalon. The method is optimized for high resolution detection using a very thin etalon (10μm). The detection SNR outperforms that of a piezoelectric transducer over a 100MHz bandwidth. Array functionality was demonstrated by scanning a probe beam along a line. A photoacoustic technique was applied to generate acoustic waves in a test phantom containing a single "point-like" source. An image of the source was reconstructed using signals acquired from the etalon detector array.