Efficient high harmonic generation sources for applications in X-Ray imaging

The observation of structures on small scales is useful for a range of applications, particularly in biological studies where higher resolution images allow examination of more intricate organic architectures. The development of coherent, high brightness sources at short wavelengths has driven a range of lensless imaging techniques that have been implemented successfully and pushed the resolution limit. However, such sources tend to be only available at large-scale, multi-user facilities. High harmonic generation (HHG) allows spatially coherent, short wavelength radiation to be available on a table-top set up, but with low beam stability due to the nonlinearity of the process. The work in this thesis focuses on characterization and optimization of a HHG source at 29 nm (42eV) specifically for use in coherent, lensless imaging. A model of the EUV beam is used to guide experimental efforts to empirically find the phase matching conditions for which the spatial coherence and flux properties are maximized whilst carefully controlling the source position and intensity stability. The resulting illumination is then put to the test in ptychographic imaging, where quantitative information about biological samples is obtained at an effective transverse resolution of 80 nm and axia lsensitivity of 1 nm, with no observed radiation damage. Finally, the images obtained with EUV ptychography are correlated with wide field and super resolution fluorescence images of the same sample region to provide direct comparison of our technique with more standard microscopy methods. A clear improvement in both resolution and contrast is observed. The fluorescence markers add information about sample composition that verifies our sample thickness measurements, and the object structure comparison motivates the use of EUV ptychography to complement fluorescence microscopy and assist in interpretation of features in the image