Terahertz lasing without inversion based on quantum coherence between intersubband transitions: Pumping and lasing

洪堡大学柏林（HUB）和保罗-德鲁德研究所（PDI）的共同目标是演示基于量子相干增益的激光发射以及对潜在物理过程的全面理解。该系统由高功率中红外量子级联激光器（MIR QCL）泵浦和光泵浦、电驱动的太赫兹量子激光器（TQL）组成。HUB组实现共同目标的目标是优化MIR泵浦QCL的功率、光束质量和外腔内的可调谐性，使用两种新方法优化MIR QCL和TQL结构之间的耦合，以及与PDI一起演示和研究功能性TQL。为了实现这些目标和共同的目标，MIR QCL的有源区必须优化注入效率，需要更深入地了解将电子散射到更高能态的机制。这种理解将允许将发射功率增加到所需的30 W。同时，QCL有源区也需要进行优化，以实现足够的外腔调谐，保持较大的转换效率。此外，将追求两种方法来优化MIR发射到TQL结构中的耦合：外腔QCL的对接耦合和在MIR QCL和TQL结构上使用高阶光栅的横向耦合。最后，在第三个目标中将研究TQL结构对内耦合MIR辐射的响应，以证明TQL的功能。特别是，太赫兹发射作为MIR功率，偏置，耦合和温度的函数将被测量。该提案特别关注于开发用于该系统的光泵浦部分的MIR QCL，并将10-pm激发光束耦合到TQL结构中。这种GaAs/（Al，Ga）As基级联结构定义了太赫兹发射跃迁，将在PDI组提交的并行项目中开发和研究。该项目的目标是演示基于量子相干的完整太赫兹激光器，将与PDI小组合作开发。

The common goal of the groups at the Humboldt-Universität zu Berlin (HUB) and the Paul-Drude- Institut (PDI) is the demonstration of lasing based on gain due to quantum coherence as well as the comprehensive understanding of underlying physical processes. The proposed system consists of a high-power mid-infrared quantum-cascade laser (MIR QCL) for pumping and an optically pumped, electrically driven terahertz quantum laser (TQL). The objectives of the HUB group to realize the common goal are the optimization of the MIR pump QCLs in terms of power, beam quality, and tunability within an external-cavity, the optimization of the coupling between the MIR QCL and the TQL structure using two new approaches, and, together with the PDI, the demonstration and investigation of a functional TQL. To achieve these objectives and the common goal, the active region of the MIR QCL must be optimized for injection efficiency, requiring a deeper understanding of the mechanisms that scatter electrons into higher-lying energy states. This understanding will allow for an increase of the emission power to the required 30 W. At the same time, the QCL active region also needs to be optimized for sufficient external-cavity tuning, maintaining a large transition efficiency. In addition, two approaches will be pursued to optimize the coupling of the MIR emission into the TQL structure: butt coupling of an external cavity QCL and lateral coupling using higher-order gratings on both the MIR QCL and the TQL structures. Finally, the response of the TQL structure to the incoupled MIR radiation will be investigated in the third objective in order to demonstrate the functionality of the TQL. In particular, THz emission as a function of MIR power, bias, coupling, and temperature will be measured. This proposal is specifically focused on developing the MIR QCLs for the optical pumping part of this system and coupling the 10-pm excitation beam into the TQL structure. This GaAs/(AI,Ga)Asbased cascade structure that defines the THz emission transitions will be developed and investigated within the parallel project submitted by the PDI group. The project goal, the demonstration of a complete THz laser based on quantum coherence, will be developed in collaboration with the PDI group.