Phase-Modulated Degenerate Parametric Amplification Microscopy

TL;DR

This paper introduces phase-modulated degenerate parametric amplification microscopy, a versatile optical technique that retrieves amplitude and phase of second-order nonlinear responses, enabling high-resolution imaging of nanostructures and materials.

Contribution

The paper presents a novel phase-modulated DPA method that improves nonlinear optical imaging by providing phase information and flexible wavelength detection capabilities.

Findings

Successfully imaged MoS2 grain boundaries with high contrast

Identified crystal orientations of MoS2 domains

Achieved sub-diffraction-limited spatial resolution

Abstract

Second-order nonlinear optical interactions, including second harmonic generation (SHG) and sum-frequency generation (SFG), can reveal a wealth of information about chemical, electronic, and vibrational dynamics at the nanoscale. Here, we demonstrate a powerful and flexible new approach, called phase-modulated degenerate parametric amplification (DPA). The technique, which allows for facile retrieval of both the amplitude and phase of the second-order nonlinear optical response, has many advantages over conventional or heterodyne-detected SHG, including the flexibility to detect the signal at either the second harmonic or fundamental field wavelength. We demonstrate the capabilities of this approach by imaging multi-grain flakes of single-layer MoS2. We identify the absolute crystal orientation of each MoS2 domain and resolve grain boundaries with high signal contrast and sub-diffraction-limited spatial resolution. This robust all-optical method can be used to characterize structure and dynamics in organic and inorganic systems, including biological tissue, soft materials, and metal and semiconductor nanostructures, and is particularly well-suited for imaging in media that are absorptive or highly scattering to visible and ultraviolet light.