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Japanese researchers recently found that "femtosecond-laser filamentation can generate useful refractive-index changes, while thermal treatment helps improve the diffraction efficiency," according to a technical paper posted Nov. 19, 2009, on the SPIE Web site.

Diffractive optical elements (DOEs) were fabricated using filaments embedded in polymers, reported researchers Wataru Watanabe and Hiroyuki Mochizuki of the Photonics Research Institute, part of the National Institute of Advanced Industrial Science and Technology in Ikeda, Japan. Using a femtosecond laser with a pulse wavelength of 800nm focused through a microscope objetive lens, the researchers generated structures with a period of 10µm in the polymers by scanning a filament along a direction perpendicular to the optical axis.

Polymer materials are widely used to fabricate micro-optical elements because of numerous advantageous characteristics, including low cost, ease of manufacture, and high transmission in the visible spectral region. Diffractive optical elements (DOEs) are attractive examples of such materials because of their compactness and high optical potential. They are commonly applied in areas such as beam shaping, material processing, sensing, optical metrology, and lighting, and their design and fabrication can be tailored to the specific application need. Integration of DOEs in monolithic bulk materials provides good mechanical stability and high integration density.


The diagram shows the process used to fabricate DOEs.

"We are currently working to improve the fabrication of volume gratings of various types within polymers," the researchers wrote. "Direct micromachining using femtosecond-laser filamentation opens the door to 3-D integration of high-efficiency DOEs in polymers."