Abstract
An extremely compact soft x-ray microscope operating in the "water window" region at the wavelength λ = 2.88 nm is presented, making use of a long-term stable and nearly debris-free laser-induced plasma from a pulsed nitrogen gas jet target. The well characterized soft x-ray radiation is focused by an ellipsoidal grazing incidence condenser mirror. Imaging of a sample onto a CCD camera is achieved with a Fresnel zone plate using magnifications up to 500x. The spatial resolution of the recorded microscopic images is about 100 nm as demonstrated for a Siemens star test pattern.
Highlights
Benefitting from the high absorption contrast between carbon and oxygen, transmission x-ray microscopy in the spectral range of the “water window” (λ = 2.3 – 4.4 nm) has been proven to be an extremely useful tool for the investigation of biological and mineralogical samples, accomplishing, e.g., tomographic studies of cryogenic cells [1,2,3,4,5] and spectromicroscopic analysis of soils, making use of the inherent element-specific contrast [6]
In the work presented here we demonstrate that soft x-ray microscopy in the “water window” range can be accomplished by an extremely compact and long-term stable setup, using a standard Q-switch ns laser and a pulsed gas jet as inherently debris-free target for plasma generation
Before installation of the Fresnel zone plate, the adjustment of the grazing incidence condenser mirror was optimized by the measurement of intensity profiles at various positions along the optical axis (z-axis), utilizing both the phosphor coated CCD chip and the back-illuminated CCD camera
Summary
The operation of liquid jet targets requires considerable experimental and technical effort including large pumping powers and liquid nitrogen cooling, impeding the development of compact devices Such inconveniences can be overcome by the use of short-pulsed gaseous targets, which enable the construction of rather clean, compact and long-term stable soft x-ray sources [15, 16]. Such devices have already been successfully applied in various fields, ranging from material ablation and structuring to absorption spectroscopy [17,18,19], their photon yields and peak brilliances are definitely smaller, as the plasma size increases to several hundreds of μm due to the lower particle density [15]. Along with a description of the new microscope operating with monochromatic radiation from He-like nitrogen at a wavelength of 2.88 nm first micrographs from various samples are presented
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