Lab-XCT_Nanometer resolution Optical Coherence Tomography (OCT) using extreme ultraviolet and soft X-rays produced with laboratory laser-driven sources

• Applicant: Professor Dr. Gerhard G. Paulus
• Subject Area: Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas ; Synthesis and Properties of Functional Materials
• Term: from 2017 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 381425468

Optical Coherence Tomography (OCT) is a well-established interferometric imaging technique providing high resolution cross-sectional views of objects (tomograms). The axial resolution of OCT is limited to about 1 µm when using infrared and optical wavelengths. An evident way to improve the resolution is the reduction of the wavelength of the probing light. Optical Coherence Tomography using broad bandwidth radiation in the nanometer spectral range (extreme ultraviolet and soft X-rays) has been proposed and demonstrated recently. This variant of OCT, referred to as XCT, allows for a reduction of the axial resolution from micrometers to a few nanometers. We were able to achieve tomographic imaging with an axial resolution better than 8 nm using extreme ultraviolet and soft X-rays from a synchrotron. The aim of this project is the demonstration of XCT using compact laboratory sources based on laser plasmas and high-order harmonic generation (HHG). Laser plasma sources will be developed by the Polish partner that utilize a double-stream gas puff target irradiated with high-intensity nanosecond laser pulses. The targets are produced by pulsed injection of the working gas into an additional annular stream of gas using a high-pressure electromagnetic valve system with a double nozzle setup. The gas puff target approach allows for an efficient generation of broad-bandwidth extreme ultraviolet radiation and X-rays without target debris production. Laser-driven HHG sources developed by the German partner are based on high harmonic generation (HHG) from gases and solid surfaces. Generation of broad bandwidth radiation in the extreme ultraviolet range (the wavelengths from about 10 nm to about 40 nm) and in the water window soft X-ray range (the wavelengths from 2.3 nm to 4.4 nm) will be investigated with the goal to apply the radiation for XCT. The milestone of this proposal is the demonstration of XCT using optimized laser-driven light sources for the first time. We propose to investigate several samples with laboratory XCT, e.g., semiconductors based on silicon, functional materials and biological samples. For that purpose, the XCT technique will be further improved by reducing artefacts of XCT measurements.

• DFG Programme: Research Grants
• International Connection: Poland
• Partner Organisation: Narodowe Centrum Nauki (NCN)
• Co-Investigators: Professor Dr. Christian Rödel; Dr. Slawomir Skruszewicz
• Cooperation Partners: Dr. Andrzej Bartnik; Professor Dr. Henryk Fiedorowicz; Dr. Karol Adam Janulewicz; Dr. Przemyslaw Wojciech Wachulak, Ph.D.