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Eye-safe laser detects Greenhouse gases

13 Mar 2006

Applications ranging from remote atmospheric gas sensing to medicine might benefit from the development of this new laser.

Researchers at INFM Pisa and the Milan Polytechnic, in Italy, have developed an eye-safe laser emitting at 1.93 microns. With a tuning range of 85 nm, the team says the laser is ideal for use in both LIDAR and DIAL systems and monitoring gases such as water, ozone, CO2 and NO2 in the atmosphere.

Based on a Tm-doped BaY2F8 crystal, the Q-switched laser has a pulse duration of 170 ns at a repetition rate of 5Hz and a peak power of 19 kW (Optics Express 12, 1518).

"The development of efficient and tuneable sources, in novel active materials from 1 to 2 microns, is a major challenge," Gianluca Galzerano, one of the team members, told Optics.org. "The major advantages of having Tm3+ doped active media are the direct diode pumping at 785 nm and quantum efficiency which is close to two; this means for one absorbed photon at 785 nm two ions are raised to the upper laser energy level."

The team pumps the BaYF crystal, which was doped with 12% Tm3+, with a continuous wave AlGaAs laser diode emitting at 780 nm.

The folded resonator consists of a plane high-reflectivity input mirror, adjacent to the active crystal, and a spherical folding mirror. The unabsorbed pump beam, transmitted beyond the spherical folding mirror, was reflected back onto the crystal using a second plane mirror and a focusing lens.

The researchers measured the pump absorption in the crystal to be 85% using this configuration. A 2 mm-thick quartz plate was inserted into the longest arm of the resonator to tune the laser's output wavelength. Active Q-switching, which increased the beams peak power to 19 kW, was then achieved using an intercavity Pockels cell.

"The next challenge for us in this specific wavelength range is to demonstrate sub-picosecond laser pulses using a passive mode-locking technique," said Galzerano.

"Developing high-efficiency solid-state laser sources in the spectral region around 2 microns is boosted by the increasing number of applications in areas like remote sensing and gas detection, high-resolution spectroscopy, and biomedicine," added Galzerano. "Liquid water shows strong absorption in the specific interval between 1.92 and 1.94 microns, which can be used for medical applications."

Darius Nikbin is Science/Technology Reporter on Optics.org and Opto & Laser Europe magazine.

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