**4. Holographic image storage in fulgide film**

#### **4.1 Reference beam reconstruction hologram and phase conjugated beam reconstruction hologram (including transmission type hologram and reflection type hologram)**

#### **4.1.1 Experiment methods**

The experimental setups for non-collinear holographic storage are shown in Fig.23and Fig.24. Fig.23 is the experimental setup of reference beam reconstruction holography. Fig.24 is the experimental setup of conjugated beam reconstruction holography. In every one of these two optical setups, the transmission type holographic recording and reflection type holographic recording both can be realized.

Fig. 23. Experimental setup of reference beam reconstruction holography

Fig. 24. Experimental setup of conjugated beam reconstruction holography

In Fig.23, the reference beam reconstruction is used. The nonpolarized He-Ne laser(632.8nm, 3mW) is split into three beams by beam splitters BS1 and BS2. The three beams are object beam *I*O and two phase conjugated beams *I*R and *I*C. In transmission type holographic recording, reference beam is *I*R,which is *I*C in reflection type holographic recording. The signal of object beam is loaded by the Mask, which is imaged on the CCD's photosensitive surface by the positive lens L1 and L2. The focused *I*O beam cross with reference beams after the focus of L1, where a recording medium, the fulgide/PMMA film, has been placed for recording the hologram. In reconstruction process, using the reference beam as reconstruction beam, diffractive image is captured by the CCD. The shutter S is used to control the exposure time (the best exposure time is 10s in this experiment). The continuously adjustable attenuators A1, A2 and A3 are used to adjust the intensities of *I*O, *I*<sup>R</sup> and *I*C. Polarizer P1, P2 and P3 are used to adjust the polarization states of *I*O, *I*R and *I*C. Polarizer P4 in front of CCD is used to filter scattered light. For the ordinary holographic storage the Polarizers are not used. The intensities of object wave and reference wave are both 6mW/cm2 in experiment. The angles between the two recording waves are 7° and 173°. The intensity of reconstruction beam is 60μW/cm2. And the diameter of hologram is about 2mm.

In Fig.24, the phase conjugated beam is used as reconstruction beam. *I*R and *I*C are conjugate with each other. For transmission type holographic recording, reference and reconstruction beams are *I*R and *I*C respectively, which are exchanged with each other, for reflection type holographic recording experiment. Diffracted beam *I*D is conjugated with object beam *I*O. After being reflected by BS3, the diffracted image can be detected by CCD real-timely. Other conditions are same with that of set up shown in Fig.23.
