Semiconductor Devices for Control of Laser Dynamics

十多年来，半导体可饱和吸收体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。在本项目中，将研究两种用于控制激光动力学的新型半导体器件。第一种装置是传统半导体可饱和吸收镜的延伸，用于通过将其与附加的光学可控调制器集成在一起来锁定激光器，例如通过自由载流子吸收。即使激光器没有调Q，吸收体也必须强烈饱和，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调Q。然而，这样的操作会给吸收塔带来很大的热负荷，从而降低其使用寿命。因此，这项提议的第一个目标是展示不仅控制锁模而且还控制激光器的Q开关的吸收体。这种器件能够抑制可饱和吸收体模型锁定激光器中经常出现的不希望出现的调Q现象，并大大缩短了吸收体的使用寿命。有了这些吸收体，激光系统可以工作在连续或调Q锁模模式下，而不受抽运功率、重复频率、输出功率、模式体积、上态寿命等其他激光参数的影响。该研究项目的第二个目标是寻找能够直接从激光输出中检测脉冲的绝对光学相位的全新的控制元件，即半导体器件。这样的装置允许对几个周期的激光脉冲和绝对光学相位超敏感的相关量(例如腔内脉冲能量)进行相位控制。具体地说，我们想要研究最近在GaAs中发现的载波Rabi-flopping，它也应该在其他材料系统中出现，是否可以用来构造光学鉴相器。设想的设备在控制固态激光动力学方面的改进将使新一代更紧凑、更稳定和更可靠的激光光源具有更大的参数范围，例如更高的重复频率和更高的功率处理能力。此外，这些器件将导致全新的一代少周期激光光源，其中可以控制从振荡器直接发射的激光脉冲的绝对光学相位。它在频率测量和强场超快激光物理中有着广泛的应用。该项目之所以可能，是因为小组之间的密切合作，这些小组提供制造设备所需的材料科学知识，以及能够对先进激光系统中的设备进行表征和测试的小组。

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.