Synchronous nanoscale topographic and chemical mapping by differential-confocal controlled Raman microscopy

Han Cui,Weiqian Zhao,Lirong Qiu,Shucheng Li,Jonathan M Cooper,Yun Wang

doi:10.1364/prj.394537

Abstract

Confocal Raman microscopy is currently used for label-free optical sensing and imaging within the biological, engineering, and physical sciences as well as in industry. However, currently these methods have limitations, including their low spatial resolution and poor focus stability, that restrict the breadth of new applications. This paper now introduces differential-confocal controlled Raman microscopy as a technique that fuses differential confocal microscopy and Raman spectroscopy, enabling the point-to-point collection of three-dimensional nanoscale topographic information with the simultaneous reconstruction of corresponding chemical information. The microscope collects the scattered Raman light together with the Rayleigh light, both as Rayleigh scattered and reflected light (these are normally filtered out in conventional confocal Raman systems). Inherent in the design of the instrument is a significant improvement in the axial focusing resolution of topographical features in the image (to ∼ 1 nm ), which, when coupled with super-resolution image restoration, gives a lateral resolution of 220 nm. By using differential confocal imaging for controlling the Raman imaging, the system presents a significant enhancement of the focusing and measurement accuracy, precision, and stability (with an antidrift capability), mitigating against both thermal and vibrational artefacts. We also demonstrate an improved scan speed, arising as a consequence of the nonaxial scanning mode.

Highlights

Over the last four decades, conventional confocal Raman microscopy (CRM) has attracted considerable interest by providing a method of generating both two- and three-dimensional chemical mapping, creating images that have come to be called “molecular fingerprints.” The current methods combine the characteristics of Raman spectroscopy with the topographic imaging of confocal microscopy, enabling analytical applications in materials [1,2,3], biomedical sciences [4,5,6], and physical chemistry [7,8,9]
We provide a schematic illustration of the light path for differential-confocal controlled Raman microscopy (DCCRM) in Fig. 2, showing the use of separate optical paths optimized for both the Raman scattered light and the Rayleigh light
The objective lens was adjusted to the focus and the objective was moved in 1 nm steps in the axial direction, driven by the piezo-actuated objective scanner

Summary

Introduction

Over the last four decades, conventional confocal Raman microscopy (CRM) has attracted considerable interest by providing a method of generating both two- and three-dimensional chemical mapping, creating images that have come to be called “molecular fingerprints.” The current methods combine the characteristics of Raman spectroscopy with the topographic imaging of confocal microscopy, enabling analytical applications in materials [1,2,3], biomedical sciences [4,5,6], and physical chemistry [7,8,9]. Over the last four decades, conventional confocal Raman microscopy (CRM) has attracted considerable interest by providing a method of generating both two- and three-dimensional chemical mapping, creating images that have come to be called “molecular fingerprints.”. There are, a number of limitations associated with the technique These microscopes have been designed by using a single optical path for both topographic and Raman mapping or imaging. Since the intensity of Raman scattered light is ca. 10−6 times weaker than that of Rayleigh scattered light, in order to obtain good signalto-noise ratio, the size of the pinhole used in creating the confocal image has typically been significantly larger (∼ hundreds of micrometers) in diameter than the focused beam at the pinhole, thereby limiting the microscopes’ resolution. Where smaller pinholes have been used to improve this aspect of the performance, this has resulted in a decrease in the Raman signal intensity

Methods

Results

Discussion

Conclusion