1. An optical strain sensor for detecting strain in an object, said sensor comprising: a first module comprising a first laser and a first image sensor, wherein said first module is configured to illuminate a first area on a surface of said object, and capture at least a portion of light reflected off said first area as a speckle image of said first area; a second module comprising a second laser and a second image sensor, wherein said second module is configured to illuminate a second area on said surface of said object, spaced apart from said first area, and capture at least a portion of light reflected off said second area as a speckle image of said second area; one or more members interconnecting said first and second modules configured to fix the length between said first and second modules and define a gauge length corresponding to the distance between said first and second areas; and a linear traverse, said first and second modules being shiftably mounted upon said linear traverse to permit translatory movement of said modules while said gauge length remains fixed.