In-line digital holography with double knife edge

C. RAMIREZ; C. IEMMI; J. CAMPOS

Munich

Conferencia; Modeling aspects in Optical Metrology; 2015

SPIE

We study and test a new technique for in-line digital holography which avoids the formation of the conjugate images. Inlinedigital holography is based in a common path configuration. In this case, the hologram is produced by theinterference between the reference wave front and the diffracted wave front by an almost transparent object. Twinimages are obtained with obscured rings that difficult the determination of the best focusing plane. To avoid theconjugated image, the information of the magnitude and phase of the wave front are needed.In a recent work a new in-line digital holography technique was proposed. In this method the object is illuminated with acollimated wave front. A plane, close to the particles distribution is imaged onto a CCD by means of a convergent lensand at the same time, a knife edge is placed in the focal plane of the lens in order to block half of spatial frequencyspectrum. In this way, by means of a numerical processing performed on the Fourier plane, it is possible to eliminate oneof the components (real or conjugate) of the reconstructed images nevertheless it is observed a tiny deformation of theresulting hologram image.To compensate this effect, we propose a new configuration in which we implement the knife edge technique on bothparts of the spectrum at the same time. Finally in the computer, we process the holograms to build one complete withoutdeformation. This hologram is used to recover the wave front at different planes without the influence of the conjugateimage.