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Fiber laser creates hidden icons in glass

21 Jun 2006

IMRA's icon writing process turns ordinary glass panels into flashing signs.

Fiber laser maker IMRA has come up with a method of writing "hidden" symbols in glass that can be revealed by side-illuminating the panel with a low-power laser diode or LED. The idea came about following an optical waveguide writing experiment, where the team discovered some unwanted features that were scattering light and turned the result into a display application.

"Because the marks are written inside the glass, the display can be very rugged, less sensitive to the environment and inexpensive," Alan Arai of IMRA's Applications Research Lab told Optics.org. "There is a trade-off between the transparency of the mark when not illuminated and its visibility when illuminated from the side and this requires more study."

To create a sample icon, engineers used a prototype version of the firm's latest fiber laser, the µJewel D-1000, to write a pattern of 50 µm sized structures inside 6.35 mm thick window glass. Based on fiber chirped pulse amplification (FCPA) technology, the laser offers up to 10 microjoules of pulse energy in the near infrared (1045 nm) with sub 700 fs pulses.

According to Arai, the laser's ultrashort pulses and high repetition rate allow precise control of energy deposition below the surface of transparent materials. Here, the team used 200 ps pulses with a repetition rate of 50 kHz. He believes that the smaller features formed by the FCPA will be less prone to crack propagation compared with structures written using longer pulses.

The firm is now enhancing its process to give brighter more complex marks and plans to work with other materials such as transparent plastics. Arai is confident that the processing time can be optimized to suit a production environment.

James Tyrrell is News Editor on Optics.org and Opto & Laser Europe magazine.

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