Unified system for holographic measurement in fluid and solid mechanics: use of the system for 3D velocity measurement in fluids through a thick curved window

摘要

Abstract: A new holographic technique has been developed to measure displacement in solid and fluid mechanics. The method uses double exposure holograms of large numerical aperture to record the light scattered from a solid surface or seeding particles that are assumed to follow the fluid motion. Analysis of the resulting hologram is performed in a piece- wise fashion through spatial correlation of the field that passes through a sampling aperture placed in the real image. In this way it is possible to map 3D displacement of an irregular surface or map the movement of seeding throughout an extended volume of fluid. This paper discusses the cancellation of gross aberrations using a phase conjugate holographic optical element to generate a converging reference wave. Seeded flow or solid surfaces recorded with this reference wave geometry can be reconstructed efficiently using a fiber-optic probe. In addition to aberration cancelling the technique allows a method of image shifting to be introduced thus resolving the direction of the flow or surface displacement. !10