This invention is a method and apparatus to pick up a photoacoustic signal purely via optical means and via an endoscope. The photoacoustic endoscope invention relies only on optical excitation and detection methods. A light focus spot generates a photoacoustic signal at the distal end of a multimode fiber endoscope. A membrane is positioned at the distal end whose vibration is excited by the acoustic signal. A light beam brought at the distal end of the multimode endoscope via the single mode core of a dual clad multimode fiber is reflected by the said vibrating membrane. The light reflected is capture by the multimode core of the dual clad fiber and propagates to the proximal end. The speckle pattern thus generated at the proximal end depends on the membrane acoustic vibration. By correlating the speckle pattern with a known reference pattern stored prior to the generation of the photoacoustic signal, the signal can be sent to a single detector for the purpose of collecting more power and for detecting the fast acoustic signal which is in the range of Mhz to several tens of MHz.
