Optics & Laser Technology 40 (2008) 120–128 Information reduction using lensless Fourier transform digital composite holography Md. Mosarraf Hossain, Dalip Singh Mehta, Chandra Shakher à Laser Applications and Holography Laboratory, Instrument Design Development Center, Indian Institute of Technology, New Delhi 110016, India Received 17 July 2006; received in revised form 12 January 2007; accepted 18 March 2007 Available online 18 May 2007 Abstract An optical hologram contains substantially more information than necessary for some specific applications. Practical methodology of handling huge information contents in these holograms for such applications is cumbersome. In this paper, a method of information reduction, which aims at efficient storage and transmission of holograms, is investigated using digital composite holography in lensless Fourier transform configuration. The maximum information reduction factor obtained in our experiment is 105. The advantages/ disadvantages of this method over an earlier method used in optical holography [Lin LH. A method of hologram information reduction by spatial frequency sampling. Appl Opt 1968;7:545] are also discussed. r 2007 Elsevier Ltd. All rights reserved. Keywords: Information reduction; Digital composite holography 1. Introduction Holographic techniques so far have been extensively used in diverse applications such as microscopy, contour generation, vibration analysis, strain measurement, three- dimensional displacement measurement, nondestructive testing, holographic optical element based optical scan- ning, holographic display, photo-voltaic applications, security systems and data storage [1–15]. Traditionally high-resolution ð5000 lines=mmÞ films were used to record holograms. Wet processing of these films is tedious and time consuming. With the availability of high capacity computers and digital sensors with more pixels and reduced pixel size, it has now become possible to record a hologram digitally and to process the resultant data numerically to reconstruct the image. The flexibility coupled with the potential to evaluate the numerical values of amplitude and phase of the reconstructed wave in three- dimensional (3-D) space makes digital holography a powerful tool for scientific and industrial applications. To make recording, reconstruction and processing of the acquired data fast, reliable and real-time, various ideas executed in conventional holography are gradually being used in digital holography. Consequently, there have been many publications [16–30] in digital holographic metrology and microscopy recently. It is well known that an ordinary hologram contains far more information than necessary for some specific applica- tions, such as, visual display of 3-D image of a normal object. Because of this huge information content, a practical method of storage and transmission of optical holograms is cumbersome. In conventional holography, different techniques have been proposed to reduce the information content in a hologram [31–35]. There are also many authors who have recently presented the results of research that involve the compression of information content in digital holograms [36–39]. These works are intended for keeping the storage space and transmission time requirements within reasonable limits. One such method of information reduction was proposed by Lin [31] using Fourier transform composite holography. In Lin’s method, by means of Fourier transform hologram of some particular size and form, a number of discrete bands of spatial frequencies from a subject is sampled and ARTICLE IN PRESS www.elsevier.com/locate/optlastec 0030-3992/$ - see front matter r 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.optlastec.2007.03.004 à Corresponding author. Tel.: +91 11 2659 1432; fax: +91 11 26862037. E-mail addresses: cshakher@hotmail.com, cshakher2001@yahoo.co.in, cshakher@iddc.iitd.ernet.in (C. Shakher).