DFG-RSF: Generation of Ultrashort Pulses in Millimeter and Submillimeter Bands for Spectroscopy and Diagnostic of Various Media Based on Passive Mode-locking in Electronic Devices with Nonlinear Cyclotron Absorber in the Feedback Loop.

该项目计划在DFG-RSF联合研究协作的框架内进行，即IHM、KIT、卡尔斯鲁厄和下诺夫哥罗德IAP-RAS之间的研究协作。该建议书描述了整个项目，包括RAS和DFG两个部分。使用具有可控光谱的亚毫米级辐射源，可以显著改进DNP-核磁共振的功能(灵敏度、分辨率、数据采集速度等)以及监测各种介质的其他方法(例如，密集聚变等离子体诊断)。所需的频谱控制不仅提供了中心频率在大范围内的平滑扫描，而且还产生了具有相关相位和可调整重复率的周期短脉冲序列。该项目旨在开发基于真空电子放大器(包括陀螺谐振放大器)的毫米和亚毫米频率范围的强宽带相干信号的产生和放大方法。首次提出在真空电子器件的基础上研究类似于被动锁模(激光物理中广泛使用的方法)的脉冲产生机制。为此，在发电机的反馈回路中放置了一个非线性幅度滤波器--吸收小幅度微波信号并以高功率传输信号的元件。该项目的理论计划包括在分析和计算机模型的框架内详细分析产生超短脉冲的新机制，以及将结果与工作在被动锁模模式下的激光系统的已知特性进行比较。在理论分析的基础上，将进行超短脉冲发生器的实验样机的研制。实验部分包括基于回旋吸收效应的非线性幅度滤波器的实现和研究，展示了现有的长毫米回旋行波管(工作频率为30 GHz)作为放大元件时产生超短脉冲的方式。同时，将开发出频率为260 GHz的螺旋波纹回旋行波管的关键元件，以及适合该频率范围的非线性回旋吸振器。

The project is planned to run in frame of a joint DFG-RSF research collaboration, namely between IHM, KIT, Karlsruhe and IAP-RAS, Nizhny Novgorod. This proposal describes the full project including both, RAS and DFG parts. Significant improvement of functionality of DNP-NMR (sensitivity, resolution, data acquisition speed, etc.), as well as other methods of monitoring the various media (e.g., dense fusion plasma diagnostic) can be achieved using submillimeter range radiation sources with controllable spectrum. The required spectrum controlling not only provides a smooth sweep of the center frequency over a wide range, but also the generation of a periodic sequence of short pulses with a correlated phase and adjustable repetition rate. This project aims for the development of methods for the generation and amplification of powerful wideband coherent signals of millimeter and submillimeter frequency range on the basis of vacuum electron amplifiers (including gyro-resonance amplifiers). For the first time it is proposed to investigate a mechanism of pulse generation similar to the method of passive mode locking (widely used in laser physics) on the basis of vacuum electronics devices. For this purpose, a nonlinear amplitude filter - the element that absorbs microwave signals with small amplitude and transmits signals with a high power - is placed into the feedback loop of the generator. The filter is expected to be implemented on the basis of the non-linear cyclotron absorption mechanism.The theoretical program of the project includes a detailed analysis of a new mechanism to generate ultrashort pulses within the framework of analytical and computer models, as well as a comparison of the results with the known characteristics of laser systems operating in the passive mode locking regime. Based on the theoretical analysis, the development of an experimental prototype of the ultrashort pulse generator will be performed.The experimental part of the project includes the implementation and study of the properties of non-linear amplitude filter based on the effect of the cyclotron absorption, demonstrating the regime of generation of ultrashort pulses when an existing long-mm wavelength gyro-TWT (operating frequency of 30 GHz) is used as the amplifying element. In parallel, the key elements for a helically corrugated gyro-TWT with a frequency of 260 GHz, as well as a non-linear cyclotron absorber appropriate for this frequency range will be developed.