Abstract: Apparatus and method for identifying a remote target (7; 7a) is described. The remote target (6; 6a) is illuminated with radiation (5; 5a) generated by a laser (1; 1a) and the radiation scattered by the target (6; 6a) is modulated in phase by the surface (6; 6a) vibrations of the target (7; 7a). A portion of the scattered radiation is collected by multiple optical receivers (8, 9, 10; 8a, 9a, 10a) and demodulated by a phase demodulator to generate a signal proportional to the vibrational displacement of the remote target (7; 7a). The radiation scattered by the remote target (7; 7a) will also include laser ‘speckle’, generated when radiation is scattered by a rough solid surface. This speckle can generate errors in the signal demodulated, which can in turn cause identification errors. Apparatus is disclosed where the signals generated are substantially unaffected by laser speckle, improving the accuracy of remote target identification.