A nanometer axial resolution x-ray coherence tomography with a broadband SXR radiation emitted from a compact laser plasma double-stream gas-puff target source

Abstract

The optical coherence tomography (OCT), typically used in the visible wavelength range, due to relatively long wavelength is limited by the axial resolution to approximately a few hundreds of nanometers to a micron. Visible light is also incapable of resolving multilayered structures of tens of nanometers periods. Thus, the extension of the OCT to shorter wavelengths, such as the extreme ultraviolet (EUV) and soft X-ray (SXR), in the so-called X-ray coherence tomography (XCT), allows mitigating those problems. We present a nanometer resolution XCT using broadband SXR radiation with 2 nm axial resolution using a compact laser plasma soft X-ray source. The laser-produced Kr/He plasma was formed by the interaction of nanosecond laser pulses with a gaseous target in a double stream gas puff target approach, emitting 2 to 5 nm wavelength broadband radiation. The coherence parameters of the SXR radiation allowed for the OCT measurements of a bulk multilayer structure composed of Mo/Si multilayers with 10 nm period, with an axial resolution of about 2 nm, the interface position accuracy of sub-nm and detection of multilayer interfaces up to a depth of about 100 nm. The experimental data were compared to the OCT simulations.