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

太赫兹辐射(0.1-10太赫兹)由于其独特的性质引起了人们的极大兴趣，使其在安全、生物、医学和通信等领域有了许多新的应用。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，产生容易识别的吸收峰。这些显著的特性使得太赫兹光谱和多光谱成像在分析物质、材料、设备和产品方面非常有前途和强大的技术。即使第一个商业系统出现，THz源的开发仍然需要大量的努力才能在日常应用中充分利用THz波的特性。到目前为止，没有一种太赫兹产生技术提供了一种同时紧凑、高效(高功率)、宽可调、在室温下工作的光源。在二极管泵浦的光纤激光器系统泵浦的非线性晶体中，基于差频产生(DFG)的太赫兹光源非常有吸引力，因为它们结合了功率可伸缩性和光纤集成装置的固有优势。然而，这一强大的方法尚未与THz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IPHTS和XLIMs在高功率光纤激光器和放大器创新设计方面的专业知识来解决这一瓶颈。使用具有定制调谐特性的可配置光纤Bragg光栅阵列，IPHT最近展示了电子可调谐纳秒光纤激光器的创纪录调谐带宽(Yb频段为74 nm)。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，从而实现了独特的双频操作制度。单光纤集成谐振器首次实现了发射波长可调的2个脉冲的同步发射。与XLIM开发的新型超大模面积有源光纤一起，在抑制系统非线性失真的同时，显示出对高功率单横模放大器的独特限制特性，这些技术使得利用非线性晶体中的DFG实现脉冲宽可调高功率THz源成为可能。TERATUNE旨在利用这一概念，基于掺Tm光纤激光器和放大器方案，开发两类高功率THz源：(I)在0.3-1 THz的频率范围内连续可调，适用于大多数THz应用；(Ii)离散可调，几乎覆盖整个THz区域。这一雄心勃勃的项目的成功需要在光子技术、特殊激光架构和用于超高功率光放大系统的新型光纤方面拥有高水平的科学专业知识。这些技能在IPHT和XLIM的合作中结合在一起，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.