- Frequency-Doubled Diode Laser Emits More Than 100 mW of Green Light
Quasi-phase matching converts more than 50 percent to second harmonic in a single pass.
In yet another approach to dethroning the diode-pumped, frequency-doubled solid-state laser athe dominant design for rugged and efficient visible lasers (see previous article), scientists at Corning Inc. in Corning, N.Y., have explored directly frequency doubling a diode laser. From a package only 22 mm in length, they have produced 107 mW of 530-nm output.
Figure 1. The 1060-nm diode laser was externally frequency doubled in a quasi-phase-matched periodically poled MgO:LiNbO 3 (PPMgLN) waveguide.
They pumped a 12-mm-long, periodically poled MgO:LiNbO3 waveguide with the 1060-nm output of a distributed feedback diode laser (Figure 1). The single-wavelength diode laser had a single InGaAs quantum well with a 2 percent compressive strain. The LiNbO3 waveguide was mounted on a temperature-controlled plate, and its faces were polished with a 10° tilt and were antireflection-coated at both the fundamental and harmonic wavelengths.
Figure 2. A maximum second-harmonic power of 107 mW was obtained, with a conversion efficiency from the fundamental of 51 percent.
The Corning scientists’ measurements showed that 61 percent of the laser’s output was coupled into the waveguide and that up to 51 percent of the IR radiation was converted to the second harmonic. As expected, the conversion efficiency was directly proportional to the power in the waveguide, and the second-harmonic power was proportional to the square of the fundamental power (Figure 2). Quasi-phase matching was obtained at a waveguide temperature of 25 °C, with a 2.7 °C full width at half maximum.
Figure 3. No long-term degradation of the green power occurred over 12 hours. The inset shows the results of lifetime tests of 10 distributed feedback diode lasers similar to those used in the work.
The second-harmonic output was very stable in time. The researchers measured the power using a detector with a bandwidth of 82 kHz for a sampling time of 1 s and observed less than 1 percent variation in the average power over one hour. They also noted that no long-term degradation occurred over 12 hours. And in separate tests, nine of 10 distributed feedback lasers operating at 1060 nm were still going strong after 5000 hours (Figure 3).
IEEE Photonics Technology Letters, March 1, 2006, pp. 682-684.
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