Next generation chirped volume Bragg gratings by means of fs laser inscription and investigation of their potential for new application ranges

超短脉冲激光系统是各种应用的关键推动者，例如显微镜，光谱学，传感或材料加工。对于许多这些应用，紧凑和可靠的激光系统是必不可少的。近年来，啁啾体积布拉格光栅（CVBG）已经可用，取代了传统上在啁啾脉冲放大系统的压缩器中使用的大块光栅，并允许紧凑和坚固的系统设计。通常，CVBG是基于光热折射玻璃，这限制了特定的拉伸参数，功率水平和波长范围的应用。正是这些限制在本提案中得到解决，以扩大适用性，例如在功率或新的光谱区域方面。例如，在中红外波长范围内的所谓指纹区域，可以实现特定的光谱应用，是非常有前途的。然而，目前可用的CVBG并不适用于此，因为它们的主体材料在这些波长下不透明。更重要的是，由于制造原因，激光脉冲的最大可实现拉伸/压缩受到最大光栅/主体材料长度的限制，并且由于固有吸收，平均功率受到限制。超短脉冲激光刻字是在其他材料（玻璃和晶体）上实现VBG的一种很有前途的替代方法。虽然基于这种方法已经证明了高效反射的标准vbg，例如熔融二氧化硅，但CVBG仍需在这种高质量水平上开发。此外，目前基于超短的VBG的孔径不均匀性限制了其在高功率激光系统中的应用。这就是耶拿弗里德里希席勒大学应用物理研究所（FSU）和俄罗斯科学院应用物理研究所（RAS）的联合项目将做出独特贡献的地方。该项目的目的是开发一种可靠的铭文技术，用于孔径高达5mmx5mm的高质量CVBG。主要焦点将放在熔融二氧化硅作为主体材料，使其在机械和光学功率方面具有极高的鲁棒性和均匀的光栅结构。然后将这些器件进行迭代测试，并与高功率超短脉冲激光系统中的市售光栅进行比较，最后扩展光栅特性，涉及任何可用的CVBG无法实现的拉伸和带宽值。此外，新的主体材料将被研究和评估其与超短激光脉冲的可改性性，最终证明CVBG在新玻璃或晶体中非常适合特定应用，例如处理极高的平均功率或新的光谱范围。此外，该项目开发的技术将为超短激光脉冲系统的持续优化创造巨大的杠杆作用。

Ultrashort pulse laser systems are key enablers for a variety of applications, e.g. in microscopy, spectroscopy, sensing or materials processing. For many of these applications, compact and reliable laser systems are essential. In recent years, chirped volume Bragg gratings (CVBG) have become available, replacing the traditionally used bulk gratings in the compressor of chirped-pulse-amplification systems and allowing for compact and rugged system designs. Typically, CVBG are based on photo-thermo-refractive glass, which limits the application to specific stretching parameters, power levels and wavelengths regimes. Exactly these limitations are addressed within this proposal to widen the applicability e.g. with respect to power or new spectral regions. As an example, the so-called fingerprint region in the mid-infrared wavelength range, which enables specific spectroscopic applications, is highly promising. However, currently available CVBG are not applicable here as their host material is not transparent at these wavelengths. Even more, the maximum achievable stretching/compression of laser pulses is limited by the maximum grating/host material length due to manufacturing reasons and the average power is limited due to intrinsic absorption.Ultrashort pulse laser inscription is a promising alternative for realizing VBG in other materials (glasses and crystals). While efficient reflective standard VBGs have already been demonstrated based on this approach for example in fused silica, CVBG are still to be developed at this high quality level. In addition, current ultrashort based VBG suffer from an inhomogeneity across their aperture limiting their application in high power laser systems.This is where the joint project between the Institute of Applied Physics at the Friedrich Schiller University in Jena (FSU) and the Institute of Applied Physics of the Russian Academy of Sciences (RAS) will make a unique contribution. The aim of the project is the development of a reliable inscription technique for high quality CVBG with an aperture up to 5mmx5mm. The main focus will be on fused silica as host material enabling for extremely robust - with respect to mechanical and optical power - and homogeneous grating structures. These devices will then iteratively be tested and compared to commercially available gratings within high power ultrashort pulse laser systems before finally extending the grating properties concerning stretching and bandwidth values not achievable with any available CVBG. Additionally, new host materials will be investigated and evaluated concerning their modifiability with ultrashort laser pulses to finally demonstrate CVBG within new glasses or crystals perfectly suited for specific applications dealing for example with extremely high average powers or new spectral ranges. Moreover, the technology developed within this project will create a large leverage for the ongoing optimization of ultrashort laser pulse systems.