Asynchronous optical sampling THz spectroscopy system based on monolithically modelocked laser diodes

基于单片锁模激光二极管的异步光学采样太赫兹光谱系统

• 批准号: 236759088
• 负责人: Professor Dr. Martin Hofmann
• 金额: --
• 依托单位: Ferdinand-Braun-Institut gGmbH, Leibniz-Institut für Höchstfrequenztechnik (FBH)
• 依托单位国家: 德国
• 项目类别: Research Grants
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/236759088?language=en
• 关键词: Asynchronous; optical; sampling; THz; spectroscopy

Our fundamental goal in this continuation project remains the development and realization of an operating extremely compact THz Time-domain sampling measurement system. Our concept is based on monolithically modelocked diode lasers and asynchronous optical sampling. In our first approach, one laser diode in combination with a photoconductive antenna acts as THz sender, and a second identical laser diode is synchronized to the first but operates on a slightly different repetition frequency in order to sample the THz signal received at the receiver photoconductive antenna asynchronously. For an even more compact system, we aim to integrate sender and receiver laser on one chip and to address the photoconductive antennas with fibers. In our second and new approach, we will realize an ASOPS-system with only one monolithically modelocked laser diode. The repetition frequency of the laser diode will be slowly varied and the receiver will be gated with a signal that is delayed with respect to the sender. This principle (Optical Sampling by Cavity Tuning, OSCAT) shall be demonstrated here with compact diode lasers for the first time. In the first part of the project we have demonstrated the first diode laser based THz-ASOPS-system. After this first demonstration with compact modelocked external cavity laser diodes, a first system with monolithically modelocked diodes and synchronization electronics has been set up. In addition to the proof-of-principle, our studies have shown the major challenges of the concept which we plan to address in this continuation project. These challenges include the specifications of the used laser systems, in particular the output power, the pulse width of the emitted pulses, and he stability of the repetition frequency. For the output power, we plan a further increase to > 50 mW average power, in order to achieve a better signal to noise ratio for the THz signal. To optimize the pulse width of the pulses hitting the antennas, two steps are required: first, the gain material of the semiconductor has to support the generation of pulses with a sufficient spectral bandwidth, and second, the strongly chirped pulses emitted by the laser diodes have to be compressed. For that, we use optimized semiconductor material using chirped quantum wells for a large gain bandwidth and compress the pulses with fibers with tailored dispersion and length. We aim to achieve pulse widths below 500fs and a THz bandwidth above 1.5 THz. The stability of the repetition frequency is a further major challenge. We plan to realize pulse trains with temporal jitter below 500 fs by different approaches. First we will reduce the jitter in the current ASOPS approach by optimized electronics, optical feedback and integration of the two lasers on one chip. Second, we will analyze, as a new approach, Optical Sampling by Cavity Tuning (OSCAT) with only one monolithically modelocked diode laser with slow repetition frequency variation.

我们在这个延续项目中的基本目标仍然是操作非常紧凑的THZ时域抽样测量系统的开发和实现。我们的概念是基于单层模型的二极管激光器和异步光学采样的。在我们的第一种方法中，一个激光二极管与光电导向性天线的结合起作用，用作THZ发件人，第二个相同的激光二极管同步到第一个，但以略有不同的重复频率进行操作，以便采样在接收机光导纳na异位上接收到的THZ信号。对于更紧凑的系统，我们旨在将发件人和接收器激光器集成在一个芯片上，并用纤维来解决光电机天线。在我们的第二种和新方法中，我们将仅使用单一模型的激光二极管实现一个ASOPSSTEM。激光二极管的重复频率将缓慢变化，并且接收器将用相对于发件人延迟的信号门控。此原理（通过腔体调谐，OSCAT进行光学采样）应首次使用紧凑的二极管激光器进行演示。在项目的第一部分中，我们演示了第一个基于二极管激光的thz-asops-System。在第一次使用紧凑型模型的外部腔激光二极管进行了第一次演示之后，已经建立了一个具有单一模型的二极管和同步电子设备的第一个系统。除了原理证明外，我们的研究还表明了我们计划在这个延续项目中解决的概念的主要挑战。这些挑战包括使用的激光系统的规格，尤其是输出功率，发射脉冲的脉冲宽度以及重复频率的稳定性。对于输出功率，我们计划进一步增加到> 50 mW的平均功率，以便获得THZ信号的更好信号与噪声比。为了优化撞击天线的脉冲的脉冲宽度，需要两个步骤：首先，半导体的增益材料必须支撑具有足够光谱带宽的脉冲的产生，其次，必须压缩激光二极管发出的强烈chi刺脉冲。为此，我们使用chir的量子井使用优化的半导体材料，以进行大增益带宽，并用具有定制的分散和长度的纤维压缩脉冲。我们的目标是使脉冲宽度低于500fs和1.5 THz以上的THZ带宽。重复频率的稳定性是另一个重大挑战。我们计划通过不同的方法来实现500 fs以下的时间抖动的脉冲火车。首先，我们将通过优化的电子设备，两个激光器在一个芯片上的光学反馈和整合来减少当前ASOP方法中的抖动。其次，我们将通过新方法分析腔体调整（OSCAT）的光学采样（OSCAT），只有一个单一模型的二极管激光器具有缓慢的重复频率变化。