Benjamin R. Galloway

Lorentz drift compensation in high harmonic generation in the soft and hard X-ray regions of the spectrum

We present a semi-classical study of the effects of the Lorentz force on electrons during high harmonic generation in the soft and hard X-ray regions driven by near- and mid-infrared lasers with wavelengths from 0.8 to 20 μm, and at intensities below 1015 W/cm2. The transverse extent of the longitudinal Lorentz drift is compared for both Gaussian focus and waveguide geometries. Both geometries exhibit a longitudinal electric field component that cancels the magnetic Lorentz drift in some regions of the focus, once each full optical cycle. We show that the Lorentz force contributes a super-Gaussian scaling which acts in addition to the dominant high harmonic flux scaling of λ-(5-6) due to quantum diffusion. We predict that the high harmonic yield will be reduced for driving wavelengths > 6 μm, and that the presence of dynamic spatial mode asymmetries results in the generation of both even and odd harmonic orders. Remarkably, we show that under realistic conditions, the recollision process can be controlled and does not shut off completely even for wavelengths >10 μm and recollision energies greater than 15 keV.

High harmonic interferometry of the Lorentz force in strong mid-infrared laser fields

The interaction of intense mid-infrared laser fields with atoms and molecules leads to a range of new opportunities, from the production of bright, coherent radiation in the soft x-ray range to imaging molecular structures and dynamics with attosecond temporal and sub-angstrom spatial resolution. However, all these effects, which rely on laser-driven recollision of an electron removed by the strong laser field and the parent ion, suffer from the rapidly increasing role of the magnetic field component of the driving pulse: the associated Lorentz force pushes the electrons off course in their excursion and suppresses all recollision-based processes, including high harmonic generation, elastic and inelastic scattering. Here we show how the use of two non-collinear beams with opposite circular polarizations produces a forwards ellipticity which can be used to monitor, control, and cancel the effect of the Lorentz force. This arrangement can thus be used to re-enable recollision-based phenomena in regimes beyond the long-wavelength breakdown of the dipole approximation, and it can be used to observe this breakdown in high-harmonic generation using currently-available light sources.

Sub-wavelength transmission and reflection mode tabletop imaging with 13nm illumination via ptychography CDI

EUV lithography is promising for addressing upcoming, <10nm nodes for the semiconductor industry, but with this promise comes the need for reliable metrology techniques. In particular, there is a need for actinic mask inspection in which the imaging wavelength matches that of the intended lithography process, so that the most relevant defects are detected. Here, we demonstrate tabletop, ptychographic, coherent diffraction imaging (CDI) in reflection- and transmission-modes of extended samples, using a 13 nm high harmonic generation (HHG) source. We achieve the first sub-wavelength resolution EUV image (0.9λ) in transmission, the highest spatial resolution using any 13.5 nm source to date. We also present the first reflection-mode image obtained on a tabletop using 12.7 nm light. This work represents the first 12.7 nm reflection-mode image using any source of a general sample.

First Demonstration of Sub-Wavelength Imaging at Short Wavelengths

By combining tabletop 13.5nm high-harmonic EUV beams with novel ptychography reconstruction algorithms, we demonstrate diffraction-limit high-NA and sub-wavelength resolution imaging at EUV wavelengths for the first time, representing a record resolution for full-field light-based microscopy.

Coherent Ptychographic Imaging Microscope With 17.5nm Spatial Resolution Employing 13.5nm High Harmonic Light

High-resolution imaging is an essential tool for understanding nanoscale systems. In particular, tabletop extreme ultraviolet (EUV) coherent diffractive imaging (CDI) techniques based on high harmonic generation (HHG) are ideal for investigating complex nanostructured systems, including their static and dynamic electronic, phononic and magnetic properties. Tabletop EUV CDI combines elemental and chemical selectivity with nanometer spatial resolution, with pulse durations in the femtosecond (fs)-toattosecond (as) range [1-5]. In this work, we use ptychographic CDI [6-7] with high-spatial-coherence 13.5nm tabletop HHG to obtain 17.5nm spatial resolution images of a zone plate. This is the highest demonstrated resolution for a full-field tabletop microscope using any light source.

Bright Isolated Attosecond Soft X-Ray Pulses

By driving the high harmonic generation process with multi-cycle mid-infrared laser pulses, we demonstrate bright isolated, attosecond soft X-ray pulses for the first time.