There is a need for temporally short laser pulses in various applications including vehicle safety devices, 3D imaging, laser tomography, time imaging, and spectroscopy. For a number of applications, particularly in biotechnology and biological measurements, the required pulse energy is in the order of at least a few nanojoules, whereas the optimal pulse duration is of the order of a few tens to hundreds of picoseconds.
It is also desirable from the practical point of view that the optical pulse is generated efficiently, with an injection current pulse of a modest amplitude and more than a nanosecond long, and thus relatively straightforwardly available from commercial silicon electronics.
From the perspective of optical collimation, it is desirable to minimize the emitting surface, or maximize the brightness or intensity of the laser light which have been resolved by gain-switching of an edge-emitting semiconductor laser with an extremely large ratio of the active layer width da to the optical confinement factor Γa. A limitation inherent in edge emitters, however, is a low beam quality. Besides, in a number of applications, a narrow spectral linewidth is significant, in which case the massively longitudinally multimode nature of edge emitting laser light is a disadvantage. Hence, there is a need for a better laser.