Design and fabrication of an integrated holographic laser-Doppler optics

The authors present two types of miniaturized laser Doppler optics composed of holographic optical elements. The first type consists of a holographic beamsplitter, two holographic lenses, which focus the laser light to the detection volume, and a holographic lens, which collects the scattered light. These components are integrated into a compact optical system. The operation wavelength is 514 nm. The laser light is guided from the laser source to the laser Doppler velocimeter (LDV) optics with the help of a polarization-preserving monomode fiber. The collecting lens focuses the signal scattered by the particles onto the face of a light cable, which transports the signal to the electronics. The second type is a miniaturized holographic laser Doppler optics which produces two detection volumes close to each other. The distance between these volumes is of variable length. With this optics, the gradients of the velocity field in a swirling flow were measured. Of particular interest are the small size and weight of the holographic devices compared to the weight and size of the bulky glass components usually utilized in the fabrication of LDV optics. Hence, the holographic optics can be positioned at a strategic location in the simulation facility