Multi-Wavelength Ptychography for Wavefront Sensing

Increasing the resolution of imaging systems has been a driving force for science, ranging from biomedicine to semiconductor applications. According to the diffraction limit, the achievable imaging resolution can be improved by using short wavelengths. Specifically, extreme ultraviolet (XUV) light enables nm-scale resolution. Coherent XUV light can be generated by means of high harmonic generation (HHG), where a driving laser with high pulse energy interacts with a non-linear medium. Since the use of lenses in this spectral range is highly challenging, lensless imaging methods such as ptychography [1] have proven to be effective [2]. In ptychography, complex-valued images of both the object and the wavefront of the light beam are numerically reconstructed from a series of diffraction patterns acquired by scanning an object laterally to the source. In this work we develop ptychography into a high-resolution, multi-wavelength XUV wavefront sensor, and use it to characterize our HHG source. The spectrally-resolved wavefront reconstructions provide insight into physical processes that happen during HHG, and can facilitate the use of the high harmonic beams for imaging purposes.