Plastic records infrared light

Photorefractive polymers are plastic materials that can be altered by light to record data, holograms and medical images.

Researchers from the University of Arizona have extended the sensitivity of photorefractive polymers so that they can be used at the common infrared communications frequency of 1550 nanometers.

The previous longest wavelength a photorefractive polymer could absorb was 975 nanometers, according to the researchers. The 1550-nanometer wavelength is commonly used for infrared applications because it does not damage eyes and transmits well through the atmosphere.

The key to making the infrared-absorbing plastic was choosing a molecular structure that absorbs photons only if they come two at a time from a short laser pulse.

The material could eventually be used to sense infrared signals coming through fiber communications lines and through the air; it could also be used in optical coherence tomography medical imaging and to image through turbulent and scattering media like gases, according to the researchers.

The method uses a pulsed laser beam to write a hologram and a continuous laser beam of the same wavelength to read the information stored in the hologram. The reading beam does not generate two photons at a time and so does not erase the recorded hologram, which makes it possible to use the very powerful reading beams required when signal-to-noise ratios are low.

The material is relatively inexpensive, making it practical to manufacture large-area films that are sensitive to infrared radiation.

The researchers are working on increasing the speed and sensitivity of the material to make it better suited for through-the-air communications.

The infrared sensitive polymers could be used practically in five to ten years, according to the researchers. The work appeared in the November 15, 2004 issue of Applied Physics Letters.