US Patent 9999354 Biological tissue inspection method and system

A method and system for inspecting biological tissue that has no applied coatings or treatments to improve reflectivity comprises an optical detection system with an exposed surface for inspection by an optical detection system; and a laser for exciting an ultrasonic wave within the tissue, which wave propagates within the tissue at least near the surface. The optical detection system includes: a laser to emit a pulsed detection laser beam onto the surface at a detection spot, the pulsed laser beam having a wavelength at which there is large scattering and little absorption by the tissue, and a pulse duration is chosen to correspond with ultrasonic propagation times associated with a range of depths of the scan, whereby the fluence of the detection laser is not applied unless ultrasonic information regarding a given depth is being obtained; and large étendue collection optics for collecting reflected and backscattered light from the detection spot; and a demodulator to extract information from the ultrasonic wave from the collected light.