Dual wavelength optical metrology using ptychography

Abstract

We describe an experimental implementation of ptychography to optical metrology, in particular topography measurement, in combination with the dual wavelength method. This is the first published account of the application of the dual wavelength method to ptychography or any other phase retrieval method in order to obtain surface height information over a wide range of scales, from small fractions of a wavelength up to many tens of wavelengths, in reflection mode. Moreover, the work presented here is the first report on the application of lensless reflection mode ptychography. Advantages of the ptychographic dual wavelength method are compared with other optical topography measurement techniques, especially with respect to the experimental procedures and constraints and the analysis of the data. We show that dual wavelength ptychography can remove material-specific phase changes which adversely affect topography measurements using white light profilometry.

Fourier ptychography: current applications and future promises

“…It was further developed by Rodenburg and colleagues several decades later, who extended its capabilities to image continuous objects and also applied it to X-ray and optical imaging setups [4][5][6][7][8]. Its unique advantages for X-ray microscopy were first clearly demonstrated in 2007 [9] and modern computing hardware has provided a huge boost to performance, spreading the field of ptychography to also include illumination wavefront sensing [10], tomography [11], partially coherent [12,13] and reflection modalities [14,15], for example, along with the development of a large suite of robust algorithms [10,[16][17][18][19][20].…”

Ptychographic microscopy via wavelength scanning

“…The radiation source was the OPO (EKSPLA PT257, with a tunable wavelength from 690 to 990 nm) and each wavelength was monitored in line with the spectrometer to avoid the wavelength drift. 44 High coherence of illumination source is crucial for any coherent diffractive imaging system, and partial coherence will lead to blurry diffraction patterns and reduced reconstruction contrast. The typical pulse duration of the OPO source used in our experiment is 3-4 ps and typical time bandwidth product is less than 0.8 according to the manufacture's sheet; hence, the maximum bandwidth is less than 0.54 nm.…”

Coherent X-ray diffractive imaging on the single-cell-level of microbial samples

“…Moreover, the ptychographic method has also been used for elemental speciation [21,135,285] and for sequential imaging of chemical reactions [142]. More recent ptychographic studies investigate the maximum derivable information from ptychographic data under non-simple experimental conditions for the illuminating wave-eld or the object such as position uncertainties [20,110,182], partial coherence and multiple wavelenghts [15,44,78,299], multiple object planes [181,284] and undersampling of the recorded di racted intensities [71]. In the rst place, however, the probably most important result has been the understanding that the ptychographic method not only is able to solve for the encoded object information but also for the illuminating wave-eld [183,294,296] making ptychography a valuable tool for analysing the wave-elds of X-rays [134,144,159,160,265,268].…”