Terahertz ptychography

Abstract

We realized a phase retrieval technique using terahertz (THz) radiation as an alternative to THz digital holography, named THz ptychography. Ptychography has been used in x-ray imaging as a groundbreaking improvement of conventional coherent diffraction imaging. Here we show that ptychography can be performed at THz frequencies too. We reconstructed an amplitude and a phase object with both simulated and real data. Lateral resolution accounts to <2λ, while depth variations as low as λ/30 can be assessed.

Resolution limits of terahertz ptychography

“…However, for more strongly diffracting phase objects, flat regions could be successfully reconstructed with a standard deviation as low as 3 µm (≈ λ/30). 12…”

“…As an alternative to THz digital holography, we have recently migrated an emerging X-ray coherent imaging technique, namely ptychography, 11 to the THz spectrum, showing performances comparable to the holographic approach. 12 Ptychography is a non-holographic lensless solution to the phase problem, whose first concept was developed by W. Hoppe for imaging periodic (crystalline) objects with electrons. 13 Interestingly enough, holography was also conceived in order to improve electron microscopy by disposing of electron objectives.…”

Coherent reconstruction of a textile and a hidden object with terahertz radiation

“…Although originally demonstrated in the visible range, the SBMIR algorithm can be migrated to the THz regime without fundamental changes. However, as already pointed out for THz ptychography [18,19], the increase of the wavelength by almost three orders of magnitude implies Fresnel numbers on the order of ∼10, making the far-field approximation not applicable. This also plays a role in the choice of the recording distances, which is further detailed in Supplement 1 along with a study on the lateral resolution of the reconstructions.…”

Correction of axial position uncertainty and systematic detector errors in ptychographic diffraction imaging

“…[1][2][3] Its ability to recover illumination and object information with phase contrast sensitivity without the need for sophisticated specimen preparation makes it suitable for both beam diagnostics 4,5 and quantitative imaging [6][7][8][9] in a variety of spectral ranges and experimental geometries. [10][11][12][13] However, PCDI relies on accurate experimental calibration, and incorrect modeling of the data can lead to reconstruction artifacts. Here, we report on correction schemes to mitigate detector-sided systematic errors, namely axial position uncertainty, point spread, and inhomegeneous response.…”