Ultrafast Detection of THz Radiation with Large Area Field Effect Transistors

拟议的项目旨在开发一种新的超快太赫兹探测器。该探测器将是非常宽的，单个设备的工作范围几乎覆盖整个太赫兹频段(0.1太赫兹-7太赫兹)。它还将能够以优于30ps的分辨率同步探测光脉冲和太赫兹脉冲。这种探测器是对准和校准光学泵浦太赫兹探头和太赫兹泵浦光学探头装置的关键元件。探测器概念还提供了高损伤阈值，允许在高功率台式脉冲系统和自由电子激光中实施。该探测器由一组整流场效应晶体管(大面积场效应管，LA-FET)并联组成。整流效应是由平行于源漏方向极化的入射太赫兹波同时调制栅区中的载流子浓度和沟道中的载流子速度而产生的。这种效应在比相应晶体管的电流和功率放大频率高3分贝频率数量级的太赫兹频率下仍然非常有效。对光学/近红外脉冲的敏感性是由外部DC源漏偏导致的光电流造成的，分离了光学产生的载流子。首次利用(Al)GaAs高电子迁移率晶体管进行了原理验证实验，证明了这种探测器具有很高的应用前景。然而，原理验证实验打开了一系列我们想要在拟议的项目中回答的问题：尚不清楚设备的哪个部分负责快速的光学响应。此外，光需要投射到太赫兹脉冲和场效应管之间的电磁相互作用的细节中。这一建议的目的是建立一个一致的模型，用于光学和太赫兹探测，并考虑到二维电子气通道中等离子体激子的激发和相互作用。它将基于传输线模型。随后，我们将在自由电子激光FELBE上优化和测试一组设备，以改进功能，Helmholtz-Zentum Dresden-Rossendorf。这包括针对超高速、高线性度范围、高损伤阈值、低噪声当量功率和大工作频率范围的优化。这项工作的结果将对未来的光泵浦太赫兹探测器和太赫兹泵浦太赫兹探测器实验产生重大影响，因为探测器极大地简化了此类装置的对准和校准。另一组LA-FET将作为快速功率计应用于桌面系统。响应度的提高将以牺牲设备速度为代价。我们的目标是开发出比最先进的热探测器快至少5个数量级的探测器，具有类似甚至更低的噪声等效功率。这允许极快的数据采集。

The proposed project aims for the development of a new ultrafast THz detector. The detector will be extremely broadband with an operation range covering almost the complete THz band (0.1 THz- 7 THz) with a single device. It will also be able to detect optical and THz pulses synchronously at a resolution better than 30 ps. Such detectors are key elements for aligning and calibrating optical pump-THz probe and THz pump-optical probe setups. The detector concept further provides a high damage threshold allowing for implementation in high power table-top pulsed systems and free electron lasers. The detector consists of an array of rectifying field effect transistors (large area FETs, LA-FETs) in parallel connection. The rectification effect results from simultaneous modulation of the carrier concentration in the gated region and the carrier velocity in the channel by an incident THz wave that is polarized parallel to the source-drain direction. This effect remains highly efficient at THz frequencies orders of magnitude above the current and power amplification 3 dB frequency of the respective transistor. The sensitivity to optical/NIR pulses results from the photocurrent due to an external DC source drain bias, separating optically generated carriers. First proof-of-principle experiments using (Al)GaAs high electron mobility transistors have demonstrated the high prospect of these detectors. The proof-of-principle experiments, however, have opened a series of questions that we want to answer within the proposed project: It is unclear which part of the device is responsible for the fast optical response. Furthermore, light needs to be shed into the details of the electromagnetic interaction between the THz pulses and the FETs. This proposal aims for developing a consistent model for both optical and THz detection, taking excitation of and interaction with plasmons in the two dimensional electron gas channel into account. It will be based on a transmission line model. Subsequently, we will optimize and test a set of devices for improved functionality at the free electron laser FELBE, Helmholtz-Zentrum Dresden-Rossendorf. This includes optimization with respect to ultra-high speed, high linearity range, high damage threshold, low noise equivalent power, and large operation frequency range. The results of this work will have high impact on future optical pump-THz probe and THz pump-THz probe experiments since the detectors strongly simplify the alignment and calibration of such setups.Another set of LA-FETs will be optimized for application in table top systems as fast power meters. The responsivity will be improved at the expense of device speed. We target for developing detectors that are at least 5 orders of magnitude faster than state-of-the-art thermal detectors with a comparable or even lower noise equivalent power. This allows for extremely fast data acquisition.