Interferometry-based optoacoustic tomography

The use of optical methods to measure stress waves has been pursued as an alternative to piezoelectric transducers for over 40 years [1-3]. While a variety of optical approaches using knife-edge, beam deflection, and diffraction have been developed [2,4], interferometric methods now seem to predominate. Optical methods have several attractive characteristics that differentiate their usage from conventional piezoelectric transducers. Specifically, optical methods do not require acoustic contact between target and sensor [5], and provide for simple strategies to measure stress waves at locations coincident with the delivery of laser radiation. Moreover, optical techniques generally have better bandwidth characteristics and require no calibration [6]. In fact, the use of laser interferometry for the calibration of hydrophones has already become standard practice [7]. Optical approaches, when used in conjunction with imaging optics, also allow measurement over a broad area with high spatial resolution [8,9]. These benefits notwithstanding, the robust use of interferometric methods for optoacoustic imaging requires careful design and implementation to minimize difficulties associated with alignment and long-term stability for biomedical application