Abstract
Over the last decades, remarkable efforts have been made to improve the resolution in photon-based microscopes. The employment of compact sources based on table-top laser-produced soft X-ray (SXR) in the “water window” spectral range (λ = 2.3–4.4 nm) and extreme ultraviolet (EUV) plasma allowed to overcome the limitations imposed by large facilities, such as synchrotrons and X-ray free electron lasers (XFEL), because of their high complexity, costs, and limited user access. A laser-plasma double stream gas-puff target source represents a powerful tool for microscopy operating in transmission mode, significantly improving the spatial resolution into the nanometric scale, comparing to the traditional visible light (optical) microscopes. Such an approach allows generating the plasma efficiently, without debris, providing a high flux of EUV and SXR photons. In this review, we present the development and optimization of desktop imaging systems: a EUV and an SXR full field microscope, allowing to achieve a sub-50 nm spatial resolution with short exposure time and an SXR contact microscope, capable to resolve internal structures in a thin layer of sensitive photoresist. Details about the source, as well as imaging results for biological applications, will be presented and discussed.
Highlights
According to the Rayleigh criterion [1], the spatial resolution in photon-based imaging systems can be improved by decreasing the illumination wavelength
The recently developed extreme ultraviolet (EUV) microscope [71], having a total volume of (W × D × H) 100 cm × 70 cm × 161 cm, represents one of the most compact having a total volume of (W × D × H) 100 cm × 70 cm × 161 cm, represents one of the most compact microscopes reported in the literature and was developed as a technological demonstrator, based on microscopes reported in the literature and was developed as a technological demonstrator, based on similar experimental systems [72]
It is possible to observe that starting from 42◦ the field of view (FOV) results darker, because the edge of the membrane supporting the sample becomes visible and, in other words, thicker, formed from the phosphate-buffered saline (PBS) medium, as shown in Figure 22a, which was acquired with an optical microscope (40× objective)
Summary
According to the Rayleigh criterion [1], the spatial resolution in photon-based imaging systems can be improved by decreasing the illumination wavelength. Technological advancements lead to the development of laboratory-compact sources for high-resolution imaging, operating in short wavelengths In this regard, laser-plasma sources based on a double stream gas-puff target presents several advantages. The double stream gas-puff target source represents a versatile alternative to perform experiments in small academic laboratories without the necessity to access to large-scale facilities, and can be regarded as complementary diagnostic tools for high spatial resolution imaging, obtaining additional information about the objects not directly available using other microscopy techniques. The double stream gas-puff target represents an excellent source to acquire contrast images in this wavelength range and can be successfully employed for contact microscopy of biological samples, achieving a half-pitch spatial resolution of about 80 nm [67]. The development of such microscopes provides the opportunity for imaging of various samples and for identifying additional information about them, which cannot be directly observed using other imaging methods
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