Ghostbuster: A phase retrieval diffraction tomography algorithm for cryo-EM.

Ewald sphere curvature correction, which extends beyond the projection approximation, stretches the shallow depth of field in cryo-EM reconstructions of thick particles. Here we show that even for previously assumed thin particles, reconstruction artifacts which we refer to as ghosts can appear. By retrieving the lost phases of the electron exitwaves and accounting for the first Born approximation scattering within the particle, we show that these ghosts can be effectively eliminated. Our simulations demonstrate how such ghostbusting can improve reconstructions as compared to existing state-of-the-art software. Like ptychographic cryo-EM, our Ghostbuster algorithm uses phase retrieval to improve reconstructions, but unlike the former, we do not need to modify the existing data acquisition pipelines.

Heuristic model for sum frequency generation in chirped quasi-phase-matching gratings with application to selective, cascaded harmonic generation.

The use of chirped quasi-phase-matching (CQPM) for cascaded harmonic generation (CHG) in a single crystal has gained attraction in recent years. CHG involves multiple stages of second harmonic and sum frequency generation processes, of which their complex dynamics in CQPM structures are not well understood when far from the adiabatic limit. This subsequently poses a challenge to design CQPM structures for the optimization of higher order harmonic generation via cascaded processes. In this paper, we derive a heuristic model with analytical expressions for the approximation of the efficiency, location and length of second harmonic and sum frequency generation processes in CQPM structures in the non-adiabatic, fully nonlinear regime (i.e. with pump depletion). With the developed model, we present a design framework to create cascaded CQPM structures for the generation of any arbitrary harmonic with efficiency close to 100%.

Gaussian beam solutions in a longitudinally varying medium with a transverse quadratic-index profile.

Research in laser-plasma interaction, high harmonic generation, and filamentation involves Gaussian beams propagating through inhomogeneous media, where the refractive index varies spatially in both the transverse and longitudinal directions. However, most analytical Gaussian beam solutions to the paraxial wave equation for inhomogeneous media are limited to media with the refractive index only varying quadratically in the transverse direction. In this paper, we present a new class of Gaussian beam solutions for a longitudinally varying medium with a transverse quadratic-index profile. We also highlight a few examples from this class of solutions, which include features such as a one-parameter generalization of the free-space Gaussian beam, beam "collimation," beam self-focusing, and the existence of multiple beam waists.