Mode spectrum of a laser diode - free running versus ECDL configuration

This shows how the spectrum of a red laser diode (Ushio HL63643DG) changes when the operating current is changed. The output is from a CCD spectrum analyzer with a resolution of 85Ghz (or 0.12nm) per div (in the first part, and half of that in the second). Note that the spectrum of the free running diode is mostly multimode and continuously shifts with the current. The sound reflects noise in the power spectrum (sampled via a photodiode) and is strongest when modes are chaotic. The spectrum of the ECDL configuration is mostly single mode and confined to a small region. Mode transitions are discrete jumps associated with a popping noise.

For more info, see: http://hololaser.kwaoo.me/laser/ECDL....