光学外文文献及翻译

学号********** 昆明理工大学

专业英语

专业光学

姓名辜苏

导师李重光教授

分数

导师签字

日期2015年5月6日

研究生部

专业英语考核

In digital holography, the recording CCD is placed on the ξ-ηplane in order to register the hologram

x ',y 'when the object lies in

the x-y plane. For

the reconstruction of

the information of

the object wave,phase-shifting digital holography includes two steps:(1) getting object

wave on hologram plane, and (2) reconstructing original object wave.

2.1 Getting information of object wave on hologram plate

Doing phase shifting N-1 times and capturing N holograms. Supposing the interferogram after k- 1 times phase-shifting is

]),(cos[),(),(),,(k k b a I δηξφηξηξδηξ-⋅+= （1） Phase detection can apply two kinds of algorithms:synchronous phase detection algorithms [9]and the least squares iterative algorithm [10]. The four-step algorithm in synchronous phase detection algorithm is in common use. The calculation equation is

)2/3,,(),,()]2/,,()0,,([2/1),(πηξπηξπηξηξηξiI I iI I E --+=

2.2 Reconstructing original object wave by reverse-transform algorithm

Object wave from the original object spreads front.The processing has exact and clear description and expression in physics and mathematics. By phase-shifting technique, we have obtained information of the object wave spreading to a certain distance from the original object. Therefore, in order to get the information of the object wave at its initial spreading position, what we need to do is a reverse work.

Fig.1 Geometric coordinate of digital holography

exact registering distance.

The focusing functions normally applied can be divided into four types: gray and gradient function, frequency-domain function, informatics function and statistics function. Gray evaluation function is easy to calculate and also robust. It can satisfy the demand of common focusing precision. We apply the intensity sum of reconstruction image as the evaluation function:

min ),(11==∑∑==M k N

l l k S

The calculation is described in Fig.2. The position occurring the turning point correspondes to the best registration distanced, also equals to the reconstructing distance d '.

It should be indicated that if we only need to reconstruct the phase map of the object wave, the registration distance substituted into the calculation equation is permitted having a departure from its true value.

4 Spatial resolution of digital holography

4.1 Affecting factors of the spatial resolution of digital holography

It should be considered in three respects: (1) sizes of the object and the registering material, and the direction of the reference beam, (2) resolution of the registering material, and (3) diffraction limitation.

For pointx2on the object shown in Fig.3, the limits of spatial frequency are λ

ξθλθθ⎥⎦⎤⎢⎣⎡⎪⎪⎭⎫ ⎝⎛-'-=-=-0211max

max tan sin sin sin sin z x f R R Fig.2 Determining reconstructing distance