X-ray generation and lens-less imaging

HHG facility A laser facility was constructed as part of an NWO-Groot project to develop a coherent X-ray source based on high-harmonic  generation (HHG) from high-power laser pulses. The idea is to enable imaging potentially with a resolution as high as 10 nm of biological or solid-state systems using light with a wavelength between 10-100 nm. The laser system for creating the HHG radiation is a 0.25 TW, 20 fs parametric amplifier laser system running at 300 Hz.  Parametric amplification allows to generate high-power laser pulses over a wide range of wavelengths, which in turn determines the wavelengths generated by the HHG process. Interestingly, the longer the 'driving' wavelength, the shorter the wavelength of the generated harmonics that can be generated. We published a paper about the 300 Hz Nd:YAG based pump laser (see below), and we have constructed the parametric amplifier that is pumped by this system. It is now used to produce high-harmonics with 20 fs pulses (with a potential for 10 fs with better compression in the future), and depending on the type of experiment we have a pulse energy of 0.5 to ~5 mJ available. Paper on the pump laser for this system: D.W.E. Noom, S. Witte, J. Morgenweg, R. Altmann, K.S.E. Eikema, High energy, high repetition rate picosecond pulses from a quasi-CW diode pumped Nd:YAG system Optics Letters 38, 3021-3023 (2013)

Lens-less imaging from NIR to XUV wavelengths Imaging with XUV or X-rays is a complicated task. Almost no normal optics exist for such short wavelengths (in our case the target is 10-100 nm). Fresnel zone plates could be used, but are difficult to make and certainly not ideal for broad bandwidth sources such as the X-ray source based on high-harmonic generation that is now under construction in our lab. Other forms of imaging such as holography also require a relatively narrow bandwidth source. A reduction in bandwidth through a monochromator is very lossy at X-ray wavelengths and leads to very low efficiency. For this reason we have developped new methods of lens-less imaging based on diffraction, that also work for broad-bandwidth light sources. Based on diffraction of two broadband laser pulses, we have  shown that  fast image reconstruction  is possible  over a wide field of view using  all the wavelengths within the pulse spectrum. Combined with high-harmonic generation we could also show that it even works at extreme ultraviolet wavelengths near 50 nm. We are now working on extending this method to shorter wavelengths. By using a combination of 4 birefringent prisms we were able to make ultra-stable (0.8 attosecond rms stability) pulse pairs, and performed spatially resolved Fourier-Transform spectroscopy in the XUV, which was published recently in Optica: G.S.M. Jansen, D. Rudolf, L. Freissem, K.S.E. Eikema, and S. Witte, Spatially resolved Fourier-transform Spectroscopy in the extreme ultraviolet Optica 3, 1122 (2016) https://www.osapublishing.org/optica/abstract.cfm?uri=optica-3-10-1122&origin=search A paper about the two-pulse diffractive lensless imaging method was published here: S. Witte, V.T. Tenner, D.W.E. Noom and K.S.E. Eikema Lenssless diffractive imaging with ultra-broadband table-top sources: from infrared to extreme ultraviolet wavelengths Light: Science and Applications 3, 1-7 (2014)  (open access) Moreover, we also demonstrated a lensless microcope using 3 different laser diodes: D.W.E. Noom, K.S.E. Eikema and S.Witte Lensless phase contrast microscopy based on multi-wavelength Fresnel diffraction Optics Letters 39, 193–196 (2014)

We gratefully acknowledge financial support from:

Questions? Contact: k.s.e.eikema@vu.nl