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Compact, Efficient Blue Laser Utilizes Periodically Poled KTP

Photonics Spectra
Jan 2004
Breck Hitz

Yet another nail in the coffin of blue gas lasers has been delivered by an international team's demonstration of what it believes is the highest wall-plug efficiency recorded in the blue spectral region from a second-harmonic laser source. By placing a periodically poled KTP crystal inside the resonator of a vertical-extended-cavity surface-emitting laser (VECSEL), the group generated more than 42 mW of 489-nm blue light from 3.25 W of electrical power, for an overall efficiency of approximately 1.3 percent.

Compact, Efficient Blue Laser Utilizes Periodically Poled KTP

With a wall-plug efficiency of approximately 1.3 percent, the intracavity-doubled vertical-extended-cavity surface-emitting laser produces more than 42 mW of blue output.

The researchers were from the University of St. Andrews in the UK, from Novalux Inc. in Sunnyvale, Calif., and from Cobolt AB and the Royal Institute of Technology, both in Stockholm, Sweden.

The laser was only 23 mm long, with an intracavity, periodically poled KTP crystal that measured 1 × 5 × 10 mm (see figure). When operating at its fundamental wavelength and with a near-optimum output coupler (10 percent), it produced 550 mW of 980-nm output for an injection current of 1.2 A. When the scientists inserted an antireflection-coated KTP crystal into the resonator and substituted a dielectric mirror (highly reflective at 980 nm and highly transmissive at 489 nm) for the output coupler, they observed more than 42 mW of 489-nm light and output in a low-order, multimode-profile beam.

The researchers believe that further refinements to the laser will boost the output to more than 100 mW. They plan to improve the output power by using a new generation of VECSEL laser with smaller apertures. They also plan to improve the quality of the antireflection coatings on the KTP crystal, to redesign the resonator and to reduce the size of the intracavity beam to increase the power density in the crystal. These enhancements will increase significantly the second-harmonic conversion efficiency.


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