Ultrafast Detection of THz Radiation with Large Area Field Effect Transistors

提出的项目旨在开发一种新的超快太赫兹探测器。该探测器的工作范围将非常宽，几乎覆盖整个太赫兹波段（0.1太赫兹- 7太赫兹）。它还将能够以高于30 ps的分辨率同步检测光脉冲和太赫兹脉冲。这种探测器是对准和校准光泵浦-太赫兹探头和太赫兹泵浦-光探头装置的关键元件。探测器概念进一步提供了高损伤阈值，允许在高功率台式脉冲系统和自由电子激光器中实现。该探测器由一组并联的整流场效应晶体管（large area fet, la - fet）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门控区域的载流子浓度和通道中的载流子速度而产生的。当太赫兹频率高于电流和功率放大频率3db时，这种效应仍然非常有效。对光学/近红外脉冲的灵敏度来自外部直流源漏极偏置引起的光电流，分离光学生成的载流子。使用（Al）GaAs高电子迁移率晶体管的首次原理验证实验证明了这些探测器的高前景。然而，原理验证实验也提出了一系列问题，我们想在这个项目中回答这些问题：目前还不清楚设备的哪个部分负责快速的光学响应。此外，需要深入研究太赫兹脉冲和场效应管之间电磁相互作用的细节。本提案旨在建立一个光学和太赫兹探测的一致模型，考虑二维电子气体通道中等离子体激元的激发和相互作用。它将基于传输线模型。随后，我们将在Helmholtz-Zentrum Dresden-Rossendorf FELBE自由电子激光器上对一组器件进行优化和测试，以提高其功能。这包括对超高速、高线性范围、高损伤阈值、低噪声等效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-太赫兹探针和太赫兹泵浦-太赫兹探针实验产生重大影响，因为探测器极大地简化了这些装置的校准和校准。另一组la - fet将优化应用于桌面系统作为快速功率计。响应性将以牺牲设备速度为代价得到提高。我们的目标是开发比最先进的热探测器至少快5个数量级的探测器，并且具有相当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.