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Nd:doped crystal shows its potential

23 May 2003

Researchers reveal that neodymium-doped barium-yttrium-fluoride can support sub-picosecond pulses.

Scientists in Italy have developed a diode-pumped laser based on a new type of neodymium-doped crystal. Offering output powers up to 2.4W at around 1 micron, the team says its neodymium-doped barium-yttrium-fluoride (Nd:BaYF)laser is an attractive alternative to the traditional sources emitting at this wavelength. (Optics Express 11 1149)

“We have shown that Nd:BaYF matches the performance of Nd:YLF (its most natural competitor) at the main laser transition at 1 µm when using multiwatt pumping,” report Antonio Agnesi and colleagues in their paper. They say this is due to similar parameters, such as the cross section and fluorescence lifetime of the crystal.

According to the authors, a collaboration from the universitites of Pavia and Pisa as well as Italian laser firm Bright Solutions, the BaYF crystal also offers some advantages compared with other neodymium-fluoride laser materials.

Firstly, they claim it’s long fluorescence lifetime and high saturation fluence can lead to efficient production of high-energy Q-switched pulses. Secondly, a broad fluorescence bandwidth means the BaYF crystal can allegedly support the generation of sub-picosecond pulses. And finally the team says it can be doped to levels up to 3.75% without reducing the laser efficiency.

Agnesi and colleagues pumped the crystal with a 12W fiber-coupled diode array tuned to match the crystal’s 804 nm absorption peak. “As much as 2.4 W at 6.2 W absorbed was obtained,” they report. “The highest slope efficiency measured was 51% with a 90%-reflectivity output coupler. The beam quality at the maximum output was M2~1.1.”

Having grown the BaYF crystal using the Czochralski method, the researchers then compared its thermo-optical properties with another common crystal composition, Nd:YVO4. The authors observed that thermal lensing was a factor of three lower in the BaYF compared with the YVO4.

“Nd:BaYF seems a promising material and should allow for the design of high-beam-quality diode end-pumped lasers with 10-W output,” conclude the authors. “To date, the major drawback seems to be a significantly smaller thermal fracture parameter with respect to that of Nd:YLF.”

Jacqueline Hewett is news reporter on Optics.org and Opto & Laser Europe magazine.

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