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

• Applicant: Professor Dr. Stefan Nolte
• Subject Area: Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 448663633

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.

• DFG Programme: Research Grants
• International Connection: Russia
• Partner Organisation: Russian Foundation for Basic Research, until 3/2022
• Cooperation Partner: Dr. Ivan Mukhin, until 3/2022