Ptychographic amplitude and phase reconstruction of bichromatic vortex beams

Abstract

We experimentally demonstrate that ptychographic coherent diffractive imaging can be used to simultaneously characterize the amplitude and phase of bichromatic orbital angular momenta-shaped vortex beams, which consist of a fundamental field, together with its copropagating second-harmonic field. In contrast to most other orbital angular momentum characterization methods, this approach solves for the complex field of a hyperspectral beam. This technique can also be used to characterize other phase-structured illumination beams, and, in the future, will be able to be extended to other complex fields in the extreme ultraviolet or X-ray spectral regions, as well as to matter waves.

Second-harmonic generation and the conservation of spatiotemporal orbital angular momentum of light

“…A fundamental pulse at central wavelength λ = 800 nm from a Ti:Sapphire amplifier is sent to a custom ST-OAM pulse shaper to generate light with ST-OAM of ℓ = 1 (see Methods). Unlike conventional OAM beams which can be characterized by space-based methods such as fork hologram 19 , coherent diffractive imaging 20 Briefly, a long, 800-nm fundamental, ST-OAM pulse of ~500 fs of ℓ = 1 was interfered with a short, 800-nm fundamental, Gaussian reference pulse of ~45 fs to form interference fringes.…”

“…1b. A fundamental pulse at central wavelength λ = 800 nm from a Ti:Sapphire amplifier is sent to a custom ST-OAM pulse shaper to generate light with ST-OAM of ℓ = 1 (see Methods). Unlike conventional OAM beams which can be characterized by space-based methods such as fork holograms 18 , coherent diffractive imaging 19 , structured apertures 20 , ST-OAM pulses require a space-time or equivalently space-frequency based characterization method. Figures 1c and 1d show experimentally measured and reconstructed 3D intensity isosurface profiles of the fundamental and second-harmonic ST-OAM pulse, respectively.…”

The influence of strain on image reconstruction in Bragg coherent X-ray diffraction imaging and ptychography

“…The finite pixel size of detectors increases the reconstruction error and distorts the retrieved image which presents a particular problem for Bragg CXDI from crystalline samples with large strain (Ihli et al, 2016;Cha et al, 2010). Also, there are several reports about successful reconstructions of strong phase objects using the ptychography method, but sharp edge structures are often blurred and unphysical phase and modulus fluctuations are observed (Esashi et al, 2018;Mochi et al, 2020).…”

Generation and characterization of focused helical x-ray beams

“…Likewise, wavefront sensing at short wavelengths has been transformed by the emergence of ptychographic coherent diffraction imaging (PCDI) (4), which is rapidly becoming a standard technique for high-resolution microscopy with coherent x-rays (5,6). Primarily used for imaging across large samples at sub-20-nm spatial resolution (7,8), ptychography can also be harnessed for wavefront sensing and beam characterization (5,(9)(10)(11)(12). While alternative wavefront sensing approaches based on the transport of intensity equation (13,14) suffer from singular behavior and nonuniqueness in the presence of vortices in a wave field (15,16), PCDI has been demonstrated to solve this problem by scanning an object laterally through a beam (10).…”