Spectral and time resolved scanning near-field microscopy of broad area 405 nm InGaN laser diode dynamics

Abstract

Ridge widths of GaN laser diodes (LDs) are typically in the order of few mm. In contrast to GaAs material systems, beam quality of GaN broad area lasers is still a critical point. By time resolved scanning near-field optical microscopy (SNOM) on pulsed electrically pumped LDs with different ridge widths we observe dynamic features caused by thermal and carrier induced changes of the refractive index like filamentation and lateral mode competition, which strongly influence the far-field of the LDs. Using a high spectral resolution spectrometer we can additionally resolve the individual longitudinal modes of the laser spectrum both time resolved and correlated to the lateral position in the waveguide. Especially on samples with broad ridges we observe complex spectral and spatial dynamics of the laser mode like different filaments lasing on different longitudinal mode combs. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)