Nonlinear ptychographic coherent diffractive imaging.

M Odstrcil,C Gawith,J G Frey,W S Brocklesby,R Vrcelj,P Baksh

doi:10.1364/oe.24.020245

Abstract

Ptychographic Coherent diffractive imaging (PCDI) is a significant advance in imaging allowing the measurement of the full electric field at a sample without use of any imaging optics. So far it has been confined solely to imaging of linear optical responses. In this paper we show that because of the coherence-preserving nature of nonlinear optical interactions, PCDI can be generalised to nonlinear optical imaging. We demonstrate second harmonic generation PCDI, directly revealing phase information about the nonlinear coefficients, and showing the general applicability of PCDI to nonlinear interactions.

Highlights

Nonlinear optical processes have been the source of many novel and useful imaging modalities over the last 30 years
We demonstrate nonlinear Ptychographic Coherent Diffractive Imaging (PCDI) based on second harmonic generation, which is used to image the reversal of the sign of the nonlinear coefficients in a periodically-poled lithium niobate (PPLN) crystal and crystals of 4-nitro-4’ methylbenzylidene aniline (NMBA)
PPLN is a nonlinear optical crystal manufactured with a periodic reversal in the sign of the nonlinear coefficient; the well-controlled nature of the poling process in PPLN allows for a detailed knowledge of the crystal orientation, making this an ideal demonstration of the nonlinear CDI technique

Summary

Introduction

Nonlinear optical processes have been the source of many novel and useful imaging modalities over the last 30 years. Information gained using nonlinear techniques extends that obtained through conventional linear optical microscopy, for example Coherent Anti-Stokes Raman (CARS) microscopy allows bond-specific imaging via the Raman effect to enable identification of chemical compounds without fluorescent tagging. The area of linear imaging is undergoing a transformation because of the development of a range of new coherent imaging techniques, collectively known as ptychographic coherent diffractive imaging (PCDI); in these techniques, the use of an objective lens is made unnecessary by the use of algorithmic recovery of the phase information lost when the intensity of scattered light incident on a detector is measured. The lost phase information is recovered using extra information as constraints This technique originated from X-ray diffraction, but is used in many wavelength regimes. Nonlinear PCDI is applicable to all nonlinear microscopy techniques, and the ability to recover phase and amplitude of the generated light can significantly extend the capability of nonlinear imaging

Methods

Results

Conclusion