title: Shifted knife-edge aperture digital in-line holography for fluid velocimetry.
abstract: We describe a digital holography technique that, with the simplicity of an in-line configuration, produces holograms where the real and virtual images are completely separated, as in an off-axis configuration. An in-line setup, in which the object is imaged near the sensor, is modified by placing a shifted knife-edge aperture that blocks half the frequency spectrum at the focal plane of the imaging lens. This simple modification of the in-line holographic configuration allows discriminating the virtual and real images. As a fluid velocimetry technique, the use of this aperture removes the minimum defocusing distance requisite and reduces the out-of-plane velocity measurement errors of classical in-line holography. Results with different test objects are shown.
authors.forename: Virginia
authors.initials: V
authors.lastname: Palero
authors.forename: Julia
authors.initials: J
authors.lastname: Lobera
authors.forename: Nieves
authors.initials: N
authors.lastname: Andrés
authors.forename: M Pilar
authors.initials: MP
authors.lastname: Arroyo
mesh_terms: D004867:Equipment Design; D005583:Fourier Analysis; D006696:Holography / Q000295:instrumentation / Q000379:methods*; D007089:Image Enhancement / Q000379:methods; D007909:Lenses; D055096:Optical Devices; D055620:Optical Phenomena; D012212:Rheology / Q000295:instrumentation / Q000379:methods*; D012815:Signal Processing, Computer-Assisted