Optical velocimeter using the double-exposure specklegram

A new type velocimeter using a double-exposure specklegram is proposed. In the method, a double-exposure specklegram is used to produce Young's fringes over a probing area, instead of forming the fringes as the result of interference of two beams in the case of a differential-type laser Doppler velocimeter. Compared to conventional laser Doppler velocimetry, the present method has special advantages such as simplicity in the optical arrangement and adaptability in the measuring range together with high stability. Preliminary experiments were performed to examine the validity of the method, especially under the existence of speckle noise. The results support the validity of the proposed method.