Notes on Bonding Holograms
with Norland Optical Adhesives

Bonding cover glasses to holographic plates is easy with NOA 60 or NOA 61 and it is an excellent way to protect them against moisture and scratches. The index matching qualities of these adhesives greatly reduces surface noise.

 

Which adhesive to use?

Major criteria for deciding on either NOA 60 or NOA 61 is the temperatures you expect the plate to see. NOA 60 can withstand temperatures from -40°C to 60°C and is suitable for most applications. NOA 61 has extra adhesion to glass which allows it to withstand the stress of harsher environments. It can withstand temperatures from -150°C to 125°C and is recommended for military applications.

 

Preparation

Gelatin plates should be completely free of moisture before they are bonded. Suggested methods are to heat plates in an oven at 60°C for 10 minutes or to use a hair dryer and blow hot air on them for 1 to 2 minutes before bonding. Any moisture that is in the gelatin can eventually rise to the surface and cause separations.

 

Applying Adhesive

One of the major advantages of NOA is its long pot life. This is important when bonding large holographic plates because it allows you to take as much time as you desire to spread the adhesive and work out any bubbles.

For small plates a drop of adhesive is applied to the center of the bottom plate. The top plate is lowered at an angle and then pressure is applied to work the adhesive to the edges.

For large plates (4" x 5" and up) it may be easier to apply a bead of adhesive from corner to corner forming an X pattern. Also apply extra into the center of the X. Now one edge of the top plate is lowered onto the bottom plate and gradually lowered so the whole plate is in contact. The adhesive in the corners will spread in the corner areas while the adhesive in the center will spread out in a circular fashion to the sides.

 

Bubbles

If care is taken when applying the adhesive and lowering the plate no bubble should form. Our one ounce bottles are notorious for forming bubbles on applications from its dropper tip. If these bottles are used for large plates we recommend removing the dropper tip and pouring the adhesive out to prevent bubbles.

As preventive maintenance, when the top plate is lowered, do not press the adhesive out but allow the weight of the plate to initially spread the adhesive. Inspect for bubbles at this time. With a thick layer of adhesive you can slide the edge of the plate over to the air bubble to release it. This is usually easier than pressing the air bubbles out with the adhesive. Once the bubbles are removed slight pressure can be applied to work adhesive to the edges.

 

Light Sources

Fluorescent black lights are the best light sources for curing large plates because a group of them can be arranged to give an even distribution of light. This is important for even cure, to prevent strains from forming.

 

Miscellaneous

It has been noted that NOA may cause a slight darkening of the silver halide emulsions (field effect) after bonding. Although the exact mechanism for this is not known, it has been shown that washing the plates copiously with water after the bleach process makes a tremendous difference in reducing it.

NOA makes an excellent molding surface in thin layers. It may have potential in replicating or embossing holograms.

 

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