Distortionless interferogram recording by use of holographic field lenses for fluid velocimetry

Two optical systems based on holographic field lenses are presented. They have been specifically designed for the CCD camera acquisition of the interferograms obtained from a fluid plane, when one uses holographic interferometry to measure fluid velocities. The use of these systems allows for easy recording of interferograms, all having the same size and position on the CCD, independent of the fluid-plane observation direction. The holographic lenses act as directional field lenses; they change the divergent beam that reaches the lens into a convergent beam that focuses on the camera aperture. These distortionless interferogram recording systems have been demonstrated in a Rayleigh-Bénard convective flow.