**1. Introduction**

22 Holograms – Recording Materials and Applications

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[77] D. Sakai, K. Harada, S. I. Kamemaru, M. A. El-Morsy, M. Itoh, and T. Yatagai, (2005)

*SPIE* 5290, 74-80.

films," *Opt. Rev*., 12, 383-386.

Iwata, (2004) "A new type of optical diffuser with the directional property," *Proc.* 

"Direct fabrication of surface relief holographic diffusers in azobenzene polymer

Research on photosensitive materials is an active field where the main goal is to find materials with desirable characteristics for optical data storage. Some of these special characteristics are high sensibility, high resolution and wide spectral range, low cost, among others (Smith, 1975). For this purpose many kinds of materials that for this purpose, such as silver halide, photoresist, dichromated gelatin, photopolymers, thermal recording materials, photothermoplastics, photocromics, and photorefractive crystals (Bjelkhangen & Thompson, 1996; Hariharan, 1980; Kang et al., 2004; Koustuk, 1999) have been used. The most widely used at present are photopolymers.

Photopolymers have excellent holographic characteristics, such as high refraction index modulation, real time recording, low cost, etc. The response on these materials depends of parameters such as incident beam intensity, monomers concentration, polymerization velocity, humidity, temperature, thickness of the sample, etc. (Adhami et al., 1991; Gallego et al., 2005; Gleeson, et al., 2005). Recent papers show that photopolymer's thickness is of great importance (Neipp et al., 2003; Ortuño, et al., 2003). The spectral sensibility of these materials can be easily modified if the photopolymers are mixed with dyes such as crystal violet (Luna et al., 1997,1998; Ortiz et al. 2007).

Some photopolymers employed in optical storage are given in (K. & M. Budinski, 1999; Fernandez et al., 2006; Ibarra & Olivares, 2006; Leclere et al., 1995; Naydenova et al., 2006). One of these polymers is an adhesive called Norland Optical Adhesive 65® (NOA 65®). (Pinto & Olivares, 2002) and co-workers report that they have used NOA 65® in its natural form to record computer generated Fourier holograms using microlithography techniques. Recently (Aleksejeva & Teteris, 2010), the photopolymers NOA 60, NOA 61, NOA 63, NOA 65 and NOA 68 were studied as materials for fabrication of volume gratings, they recorded transmission and reflection diffraction gratings and used a He–Cd laser of 325nm line, obtaining diffraction efficiency >80%.

In this work a study became of the holographic material composed by Norland Optical adhesive 65 (NOA 65) mixed with crystal violet dye (CV) was made. In this material we recorded transmission real time phase holographic gratings and Fourier holograms. obtaining diffraction efficiency of 1.85% using a light beam at wavelength 598 nm from a He-Ne laser was obtained. The gratings were recorded changing parameters such as

Norland Optical Adhesive 65® as Holographic Material 25

Table 1 shows some properties of NOA 65 whereas Table 2 shows the typical cure times

Refractive Index of Cured Polymer 1.524 Elongation at Failure 80% Modulus of Elasticity (psi) 20,000 Tensile Strength (psi) 1,500 Hardness - Shore D 50 Temperature Range -15 to 60º

Lamp at 6 inches 1-10 mil 15 seconds 5 minutes

Lights at 3 inches 1-10 mil 60 seconds 20 minutes

Fig. 3 shows the absorbance spectra obtained with a FTIR spectrophotometer showing absorption peaks, indicating the presence of some compounds Table 3 displays brief analysis

of the NOA 65 IR spectrum. briefly analysis of the NOA 65® IR spectrum.

Solids 100% Viscosity at 25ºC 1,200

THICKNESS PRECURE FULL CURE

according to Norland Products instructions.

Table 1. Typical properties of NOA 65.

100 Watt Mercury\* Spot

2-15 Watt Fluorescent\* Black

Table 2. Typical cure times of NOA 65.

Fig. 3. Absorbance spectra in IR region

LIGHT SOURCE FILM

concentrations between NOA 65 and CV, sample thickness, beams intensity ratio and spatial frequency. The material shows refraction index modulation, which is calculated using the Kogelnik`s theory. The results obtained are show by the behavior of diffraction efficiency versus energy.
