Diode Laser Velocimeter for Flow Measurements

Using non-traditional techniques, optical velocity measurements can be made at a cost far below that of traditional LDVs and coherent laser radar systems. Despite extreme simplicity, including the use of low power COTS diode lasers, we have demonstrated that the proposed devices have nearly quantum limited sensitivity. This has been demonstrated to be sufficient to easily and accurately measure the speed of single micron size aerosol particles. The sensor performance, coupled with extreme compactness and low cost, makes it ideally suited for US Navy water flow measurements near submerged structures, such as propeller blades. The operating principle of the basic sensor is different from traditional LDV systems, in that radial, rather than transverse, velocities are measured. This difference only implies that the sensor look angles need to be changed. Furthermore, it appears feasible to configure the proposed sensors such that transverse measurements are made. If this proves successful, there is no difference at all in the two sensor types. We propose to demonstrate in Phase I the applicability of these sensors to vector velocity recovery in water flows. We will also build a waterproof prototype unit for testing by the U S Navy.