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30 Jun 2004
Researchers develop a long-lasting solid-state dye laser based on a rotating disc and clever pumping scheme.
Researchers from Moscow and Berlin have made a tunable solid-state dye laser (605 - 635 nm) that delivers a stable 1.5 W (<3% power fluctuations) for up to 4 hours. The result is a boost to the development of solid dye lasers, which are a long sought alternative to today's hard to handle liquid dye sources. (Appl. Phys. Lett. 84 4902)
To date, the development of solid-state dye lasers has been hindered by strong photodegradation of the polymer gain medium and short operating lifetimes (less than 1 hour).
The Russian-German team was able to create a long-lasting pulsed laser by employing a transverse pumping scheme and optimizing the duty cycle.
"We found out that if you wait for a short moment, the excited state of the dye can relax and degradation is tremendously reduced," Klaus Lips from the Hahn-Meitner-Institut in Berlin told Optics.org. "The idea came up of using a laser disc, a plastic disc that rotates so that you don't hit the same spot all the time."
The team then took the idea a stage further by inserting a shutter mechanism to extend the time between pulses. Introducing a 10 second pause after every minute of operation dramatically enhanced the operating time of the polymer gain medium.
"We could get this laser to work with an output power of 1 W for more than 20 hours basically without degradation," said Lips. "Now we're up to 50 hours."
A 10 W copper vapour laser (lambda = 510.6 and 578.2 nm, repetition rate 16 kHz, pulse duration 20 ns) pumps light into the edge of the polymer disc rotating at 42 Hz.
The lasing action takes place at right angles to the pumping direction. This transverse configuration enhances the dye's stability by reducing the pumping power density.
The polymer disc measures 94 mm in diameter and 20 mm thick and crucially its outer edge contains no dye. This transparent external layer efficiently focuses the pump light onto the dye. The gain medium consists of a copolymer mix of 80% methyl methacrylate and 10% methyl acrylic acid, impregnated with rhodamine B dye (10%).
The team is now waiting for patent approval and plans to negotiate with companies to develop the system commercially. Co-authors Vladimir Kytin and Irina Kytina (Moscow Lomonosov State University) told Optics.org that potential applications of the laser include cancer treatment and the investigation of fingerprints and other human traces.
Author
James Tyrrell is reporter on Optics.org and Opto & Laser Europe magazine.
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