Measurement of the temporal coherence properties of pulsed single-mode laser diodes.

The coherence of a single-mode laser diode, under high-speed pulsed modulation, is limited by instabilities in the lasing wavelength arising from transient phenomena in the junction region of the laser. This paper reports the results of an experiment to characterize the effects of these modal instabilities on the temporal coherence of pulsed laser diodes. The primary intent of the experiment was measurement of the cumulative effect of the modal instabilities on the fringe visibility in interferometric time integrating optical processors. A conclusion of this study is that commercially available laser diodes can be used as pulsed light sources in interferometric applications in which the pulse width of the laser is long compared to its characteristic coherence time constant and short compared to its characteristic thermal time constant. Furthermore, the interpulse modal instability can be minimized by prudent choice of operating conditions.