Semiconductor Devices for Control of Laser Dynamics

Massachusetts Institute Of Technology, Cambridge MA

Investigators

Abstract

For over a decade semiconductor saturable absorbers have been used very successfully in laboratories to modelock a variety of solid-state and fiber lasers. In this project, two new semiconductor devices for control of laser dynamics shall be investigated. The first device is an extension of the conventional semiconductor saturable absorber mirror used for modelocking of lasers by integrating it with an additional optically controllable modulator, for example by free carrier absorption. Even if the laser does not Q-switch, the absorber has to be saturated strongly, i.e. depending on the laser design by even more than ten times the saturation energy, to suppress this undesired Q-switching. However, such operation puts a heavy thermal load on the absorber, which reduces its lifetime. Therefore, the first goal of this proposal is to demonstrate absorbers that do not only control the mode locking but in addition the Q-switching of the laser. Such a device is able to suppress the undesired Q-switching, which often occurs in saturable absorber modelocked lasers and greatly reduces the life time of the absorber. With these absorbers a laser system can be operated in the continuous or Q-switched mode-locked regime independent of its other laser parameters such as pump power, repetition rate, output power, mode volume, upper-state lifetime, etc. In this project, the device will be applied to modelocking of high-repetition rate lasers. The second goal of this research project is to search for entirely novel control elements, i.e. semiconductor devices, that are able to detect the absolute optical phase of the pulses directly from the laser output. Such devices allow for phase control of few-cycle laser pulses and related quantities to which the absolute optical phase is ultra-sensitive, such as the intracavity pulse energy. Specifically, we want to investigate whether the recently discovered carrier-wave rabi-flopping in GaAs, which should also occur in other material systems, can be used to construct an optical phase detector. The improvement in control of solid-state laser dynamics by the envisioned devices will enable a new generation of more compact, stable and reliable laser sources with extended parameter ranges such as higher repetition rates and higher power handling capabilities. In addition, these devices will lead to a completely new generation of few-cycle laser sources, in which the absolute optical phase of the laser pulse directly emitted from the oscillator can be controlled. This has a broad range of applications in frequency metrology and strong-field ultrafast laser physics. The project is only possible because of the close cooperation between groups, which provide the know-how in material science necessary for device fabrication and groups that are able to characterize and test the devices in advanced laser systems.