Holography: Optical forces for data storage

Appl. Phys. Lett. 109, 061106 (2016)

Photorefractive media cannot store holographic information permanently as the photoinduced change in refractive index fades away with time. Now, Ali Yetisen and colleagues from the USA and the UK have developed robust and rewritable 3D holography that relies on optical forces instead. The recording medium was composed of poly(2-hydroxyethyl methacrylate-co-methacrylic acid) (p(HEMA-co-MAA)) and silver metal nanoparticles (Ag⁰ NPs). A glass slide coated with a 10-μm-thick p(HEMA-co-MAA) film containing 1 vol% Ag⁰ NPs was placed on a plane mirror at an angle from the mirror surface. A Nd:YAG laser provided a reference beam that propagated through the glass slide and was further reflected by the plane mirror. The interference between the reference beam and its reflection off the mirror created high- and low-intensity regions in the recording medium. Optical forces originating from this intensity gradient directed the Ag⁰ NPs toward regions of minimum intensity, organizing them into reconfigurable 3D assemblies. The process of hologram recording was fully reversible, and holograms could be erased by making the glass slide parallel to the mirror.