Highly tunable, high power, efficient terahertz source based on dual-frequency synchronous Thulium-doped fiber laser source

太赫兹辐射（0.1 - 10thz）因其独特的特性而引起了人们的极大兴趣，在安全、生物、医学和通信领域实现了许多新的应用。虽然太赫兹辐射被非金属非极化材料弱吸收，但它对生物组织起非电离作用，并与许多分子相互作用，导致易于识别的吸收峰。这些显著的特性使得太赫兹光谱和多光谱成像技术在分析物质、材料、器件和产品方面非常有前途和强大的技术。即使出现了第一个商业系统，在日常应用中充分利用太赫兹波的特性，仍然需要在太赫兹源开发方面做出巨大努力。到目前为止，许多太赫兹产生技术都没有提供一种同时紧凑、高效（高功率）、广泛可调并在室温下工作的源。二极管泵浦光纤激光系统中基于非线性晶体差频产生的太赫兹源由于其结合了功率可扩展性和光纤集成装置的固有优势而具有很高的吸引力。然而，这种强大的方法还没有与太赫兹光谱和多光谱成像应用所必需的频率可调性相结合。这个雄心勃勃的项目旨在通过利用由IPHTs和XLIMs在高功率光纤激光器和放大器的创新设计方面的专业知识开发的新型光纤激光器架构来解决这一瓶颈。利用具有定制调谐特性的可配置光纤布拉格光栅阵列，IPHT最近在电子可调谐纳秒光纤激光器中展示了创纪录的调谐带宽（Yb波段为74nm）。在一种新颖的谐振器设计中，IPHT增强了这一原理，实现了频谱独立的脉冲往返时间，实现了独特的双频工作状态。第一次，单个光纤集成谐振器能够同步发射具有可调谐发射波长的2个脉冲。与XLIM开发的新型甚大模区有源光纤一起，在抑制系统非线性畸变的同时，展示了高功率单横模放大器的独特约束特性，这些技术在非线性晶体中使用DFG实现了脉冲宽可调谐的高功率太赫兹源。TERATUNE的目标是利用基于tm掺杂光纤激光器和放大器方案的这一概念来开发两类高功率太赫兹源：(i)在0.3 - 1太赫兹的频率范围内连续可调谐，适用于大多数太赫兹应用；（ii）几乎覆盖整个太赫兹范围的离散可调谐。这个雄心勃勃的项目的成功需要高水平的科学专业知识，光子技术，特种激光架构和超高功率光放大器系统的新型光纤。这些技能在ipt和XLIM的协作中结合在一起，具有互补的能力。

Terahertz radiation (0.1 - 10 THz) has attracted great interest due to its unique properties, enabling many new applications in the security sector, biology, medicine, and in communications. While THz radiation is weakly absorbed by non-metallic non-polarizing materials, it acts non-ionizing on biological tissue and interacts with many molecules, resulting in readily identifiable absorption peaks. These remarkable properties make THz spectroscopy and multi-spectral imaging very promising and powerful techniques for analyzing substances, materials, devices and products.Even if first commercial systems emerge, large efforts in THz source developments are still required for fully exploiting the properties of THz waves in daily applications. So far, none of numerous THz generation techniques provides a source, which is simultaneously compact, highly efficient (high power), broadly tunable, and works at room temperature. THz sources based on difference frequency generation (DFG) in a nonlinear crystal pumped by diode pumped fiber laser systems are highly attractive since they combine power scalability with the inherent advantages of fiber-integrated setups. However this powerful approach has not been merged yet with frequency tunability essential for THz spectroscopy and multi-spectral imaging applications.This ambitious project aims to tackle this bottleneck by exploiting a novel fiber laser architecture developed by IPHTs and XLIMs expertise in innovative designs for high-power fiber lasers and amplifiers. Using a configurable fiber Bragg grating array with tailored tuning characteristics, the IPHT has recently demonstrated a record tuning bandwidth (74nm in the Yb band) in an electronically tunable nanosecond fiber laser. In a novel resonator design, the IPHT has enhanced this principle towards spectrally independent pulse round trip times enabling a unique dual-frequency operation regime. For the first time, a single fiber-integrated resonator enables a synchronous emission of 2 pulses with tunable emission wavelengths. Together with novel Very Large Mode Area active fibers developed by XLIM, exhibiting unique confinement properties for high power single transverse mode amplifiers while suppressing nonlinear distortions in the system, these techniques enable a pulsed broadly tunable high-power THz source using DFG in a nonlinear crystal.TERATUNE aims to exploit this concept based on a Tm-doped fiber laser and amplifier scheme for developing two classes of high-power THz sources: (i) continuously tunable over the frequency range 0.3 - 1 THz adapted to most THz applications, (ii) discretely tunable covering almost the entire THz regime. The success of this ambitious project demands a high-level of scientific expertise in, photonic technology, specialty laser architecture and novel fibers for ultra-high power optical amplifier systems. These skills come together in the collaboration of IPHT and XLIM with complementary competences.