Digital holography
Holography provides a way to record, save and restore not only the intensity but
also the phase of a given wave front.The phase is encoded by a reference wave.
Assuming a linear transformation between the intensity of the interference field and
the amplitude transmission of the recording media there will be the following
intensity distribution h on the media. h results from the interference between the
reference wave r and the object wave o:
h ¼ ðr þ oÞðr þ oÞ ¼ rr þ ro þ ro þ oo: ð1Þ
The holographic reconstruction is usually done by using the reference wave as a
reconstruction wave.Thi s wave front is diffracted by h.Ther e are four terms in the
expression for the transmitted light (Eq.(1)). The two mixed terms carry the
information about the original object wave.Two of the diffraction terms can be
eliminated by subtracting the reference wave’s and the object wave’s intensity (jrj2
and joj2) from the hologram h so that there is no zero order in the reconstructed
image.
One important disadvantage of the classical recording methods is the use of
photographic plates which have to be developed by a wet chemical process.Due to
new progresses in high resolution camera technology and computer hardware, it is
now possible to record holograms directly on the CCD target of a camera.Phas e and
intensity of the object wave can be recalculated directly in the computer.In Fig. 2a
one can see a detail of a digitally recorded hologram.Fig. 2b shows the intensity of
the object wave of a diffusely reflecting surface, the so-called objective speckle
pattern without interference with the reference beam.
The basic optical setup which is used to get the hologram is drawn in Fig.3. A
beam splitter is used to couple the reference wave onto the CCD target of the
camera.Ther efore compact setups can be achieved.
The reconstruction of the object wave in the plane of the object is done with the
computer by numeric solution of the physical diffraction process.Ther e are several
mathematical approaches for this procedure (Fresnel-approach [1], Fourierapproach
[2], convolution-approach [7]).Here we will consider only the so-called
Lensless Fourier Holography which is the fastest and most suitable algorithm for
small objects.The corresponding setup is shown in Fig. 3.It allows to choose the
106 S. Seebacher et al. / Optics and Lasers in Engineering 36 (2001) 103–126
lateral resolution in a range from a few microns to hundreds of microns without any
additional optics.
參考答案:数字式全息术
全息术提供一个方式记录， 保存并且恢复不仅强度，而且
特定波前的阶段。阶段由参考波输入。
假设线性变革在干涉领域的强度和
那里录音媒介的高度传输之间将是以下
强度发行h在媒介。 h起因于干涉在
参考波r和物体波o之间：
h ¼ ðr þ oÞðr þ oÞ ¼ rr þ r o þ ro þ oo ： ð1Þ
全息照相的重建由使用参考波通常完成作为
重建波浪。Thi s波前由h.衍射。那里e是四个期限在
表示为透过光(Eq。(1)). 二个被混合的期限传播关于
原始的物体波的信息。二衍射期限可以
被减去参考波的和物体波的强度消灭(jrj2
和joj2)从全息图h，以便没有零的顺序在被重建的
图象。
古典录音方法的一重要缺点是必须
由一个湿化学过程发展对干版的用途。由于
新在高分辨率照相机技术和计算机硬件进步， 记录
全息图直接地在照相机的CCD目标现在是可能的。物体波的
Phas e和强度直接地在计算机可以被重估。在。 2a
你能看一张数字式地记录的全息图的细节。。 2b显示散开地反射的
表面的物体波的强度， 没有干涉的所谓的
客观斑纹模式与参考波。
用于得到全息图的基本的光学设定得出在。
光束分束器使用结合参考波照相机的CCD目标
。那里efore紧凑设定可以达到。
物体波的重建在对象的飞机用计算机
完成由物理衍射过程的数字解答。那里e是几种
数学方法为这个做法(菲涅耳接近[1]， Fourierapproach
[2]， 卷积接近[7])。我们这里将考虑是
最快速和最适当的算法为小对象仅的所谓的Lensless
傅立叶全息术。对应的设定显示在。 3.它准许选择
106 S。 Seebacher等。 / 光学和Lasers在工程学36 (2001) 103-126
侧面决议在一个范围从几微米到数百没有任何另外的
光学的微米。这就是正确答案。
