1/f noise in external-cavity InGaN diode laser at 420  nm wavelength for atomic spectroscopy
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Boiko, Dmitri L.
We have extensively studied the frequency noise and relative intensity noise spectra in a tunable external-cavity InGaN diode laser at blue (420 nm) wavelengths. We report flicker (1/f) frequency-noise behavior at low Fourier frequencies measured using offset frequency-absorption spectroscopy on Rb85 vapor cells, which yields an estimated lasing linewidth of 870 kHz. From considerations of high-dislocation density in III nitride epitaxy, 1/f noise and linewidth were expected to be larger than in conventional III-V lasers. Surprisingly, the measured noise characteristics are comparable to or better than those of near-infrared distributed feedback lasers and external-cavity diode lasers. The noise-reduction mechanism is attributed to the wavelength dependence of 1/f noise. We discuss challenges in atomic spectroscopy applications caused by defects and mode-clustering effect in GaN lasers. Using the Hakki–Paoli analysis in an aged laser diode, we provide possible explanation about the origin of observed mode clustering.
Optics Letters, vol. 39 (6), pp. 1685-1688