## 5 Discussion and Conclusions  
Progress in science requires the investigation of nanostructures on the micro- and nano-scales. Employing short wavelength radiation, it was possible to develop compact Fresnel zone plates based microscopes performing imaging experiments in transmission mode and overpassing the limited accessibility and high costs of large facilities such as synchrotrons and XFEL installations. Microscopes based on laser-plasma EUV and SXR sources with double stream gas-puff targets, coupled with diffractive optics, such as FZPs, represent a good way to perform experiments in small scales, achieving sub-100 nm half-pitch spatial resolution, and represent an important alternative for high-resolution imaging, which can be employed for different applications, opening the possibility of their widespread and commercialization in the near future. The laser-plasma source based on a double stream gas-puff target was successfully optimized for efficient generation of radiation in the SXR range, developing a desktop \"water window\" microscope, based on emission at a wavelength of 2.88 nm from N\({}_{2}\) ions. Such a system, easily accessible and simple to use, allows acquiring magnified images of the objects with a 60 nm half-pitch spatial resolution, magnification (sample to CCD) of 220\(\times\) or higher, and exposure time as low as a few seconds. Exploiting a natural, optical contrast in the \"water window\" spectral range, the microscope represents a very useful tool for biological, materials science, and nanotechnology imaging applications, and may be considered as a complementary imaging system to other already well-established techniques. A compact stand-alone transmission microscope, employing an Ar-based double stream gas-puff target EUV source, under incoherent illumination, operating at a 13.84 nm wavelength, close to the lithography one (of 13.5 nm), with a sub-50 nm half-pitch spatial resolution. Such a system, developed as a demonstrator, can be employed for semiconductor applications as well as for nanotechnology, material science, and nano-lithographic mask inspections, to observe small features with high-resolution. Moreover, due to the high contrast, the EUV radiation enables the study of thin external cell features, such as the morphology of the cellular membranes, thanks to the absorption of the EUV light in carbon. A contact-type microscopy system using a laser-produced plasma soft X-ray source operating in the \"water window\" spectral range was also developed. The applicability of the source for contact microscopy experiments was demonstrated by acquiring images of biological samples. From the presented results, a half-pitch spatial resolution of \(\sim\)80 nm was successfully achieved. Although contact microscopy allows acquiring images with high spatial resolution without the need for expensive tools and optics, it is limited by the resolution of the photoresist, which can be destroyed during the SXR irradiation. Therefore it was demonstrated that the contact soft X-ray microscopy can efficiently provide complementary information concerning biological samples, integrating other existing microscopy techniques. The photon fluxes obtained with the gas-puff source allow performing high-resolution imaging experiments. The flux achieved with EUV radiation, of \(1.36\times 10^{11}\) photons/s for a single pulse, is comparable (or even higher) to that obtainable employing other compact systems. Laser-plasma EUV sources for lithography are currently capable to obtain a flux of \(10^{8}\) photons/s [98], while ptychography sources enable a gain of \(10^{11}\) photons/s at 18 nm [99]. Recent progress pushed forward this limit, obtaining up to \(\sim\)\(2\times 10^{12}\) photons/s with compact systems employing HHG [100]. Depending on the experiment performed in the SXR range, the gas-puff target source permits to achieve a photon flux in the range of \(10^{9}\)-\(10^{11}\) photons/pulse.