Semiconductor Devices for Control of Laser Dynamics

十多年来，半导体可饱和吸收器已经在实验室中非常成功地用于模拟各种固态和光纤激光器。本课题将研究两种用于激光动力学控制的新型半导体器件。第一个装置是传统半导体可饱和吸收镜的扩展，用于激光的模型锁定，通过将其与附加的光学可控调制器集成，例如通过自由载流子吸收。即使激光器没有q开关，吸收器也必须强烈饱和，即取决于激光器的设计，甚至超过饱和能量的十倍，以抑制这种不希望的q开关。然而，这样的操作给吸收器带来了沉重的热负荷，从而降低了它的使用寿命。因此，本提案的第一个目标是证明吸收器不仅控制模式锁定，而且还控制激光的q开关。这种器件能够抑制在饱和吸收器模型锁定激光器中经常发生的不希望的q开关，并大大降低了吸收器的寿命。有了这些吸收剂，激光系统可以在连续或调q锁模状态下工作，而不受其他激光参数的影响，如泵浦功率、重复频率、输出功率、模式体积、上态寿命等。在本项目中，该装置将应用于高重复频率激光器的模型锁定。该研究项目的第二个目标是寻找全新的控制元件，即半导体器件，能够直接从激光输出中检测脉冲的绝对光学相位。这样的装置允许相位控制的少周期激光脉冲和相关数量的绝对光学相位是超敏感的，如腔内脉冲能量。具体来说，我们想要研究最近发现的砷化镓中的载波拉比跳变（也应该发生在其他材料系统中）是否可以用于构建光学鉴相器。所设想的设备在固态激光动力学控制方面的改进将使新一代更紧凑、稳定和可靠的激光源具有更大的参数范围，如更高的重复率和更高的功率处理能力。此外，这些器件将导致全新一代的少周期激光源，其中直接从振荡器发射的激光脉冲的绝对光相位可以被控制。这在频率测量和强场超快激光物理中有着广泛的应用。该项目之所以成为可能，是因为两组之间的密切合作，一组提供设备制造所需的材料科学知识，另一组能够在先进的激光系统中表征和测试设备。

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.