Dynamic axial control over optically levitating particles in air with an electrically-tunable variable-focus lens.

Wenguo Zhu,Avinash Upadhya,Andrei V Rode,Woei Ming Lee,Niko Eckerskorn,Li Li

doi:10.1364/boe.7.002902

Wenguo Zhu, Avinash Upadhya + Show 4 more

Open Access

https://doi.org/10.1364/boe.7.002902

Copy DOI

Abstract

Efficient delivery of viruses, proteins and biological macromelecules into a micrometer-sized focal spot of an XFEL beam for coherent diffraction imaging inspired new development in touch-free particle injection methods in gaseous and vacuum environments. This paper lays out our ongoing effort in constructing an all-optical particle delivery approach that uses piconewton photophoretic and femtonewton light-pressure forces to control particle delivery into the XFEL beam. We combine a spatial light modulator (SLM) and an electrically tunable lens (ETL) to construct a variable-divergence vortex beam providing dynamic and stable positioning of levitated micrometer-size particles, under normal atmospheric pressure. A sensorless wavefront correction approach is used to reduce optical aberrations to generate a high quality vortex beam for particle manipulation. As a proof of concept, stable manipulation of optically-controlled axial motion of trapped particles is demonstrated with a response time of 100ms. In addition, modulation of trapping intensity provides a measure of the mass of a single, isolated particle. The driving signal of this oscillatory motion can potentially be phase-locked to an external timing signal enabling synchronization of particle delivery into the x-ray focus with XFEL pulse train.

Highlights

X-ray free-electron lasers (XFELs), operating at wavelengths of a few nanometers and pulse lengths of ~50 fs, focused down to a few micrometer (0.1 μm – 5 μm) offer near-atomic resolutions in structural imaging of nanometer- to micrometer-sized objects such as membrane proteins and viruses that are very complex, and difficult or impossible to crystallise for conventional X-ray crystallography [1]
This paper lays out our ongoing effort in constructing an all-optical particle delivery approach that uses piconewton photophoretic and femtonewton lightpressure forces to control particle delivery into the XFEL beam
As a proof of concept, stable manipulation of opticallycontrolled axial motion of trapped particles is demonstrated with a response time of 100ms

Summary

Introduction

X-ray free-electron lasers (XFELs), operating at wavelengths of a few nanometers and pulse lengths of ~50 fs, focused down to a few micrometer (0.1 μm – 5 μm) offer near-atomic resolutions in structural imaging of nanometer- to micrometer-sized objects such as membrane proteins and viruses that are very complex, and difficult or impossible to crystallise for conventional X-ray crystallography [1]. Particle delivery instruments in an XFEL imaging system need to be capable of introducing contamination-free, uncharged, mono-dispersed, with high density and micrometer-scale positional precision. A precise touch-free particle manipulation technique is desired for high-throughput particle delivery solution. Liquid jet injectors are ideal in that they introduce biomolecules in physiological conditions, but they produce background scatter that can severely limit resolution in the case of single-particle imaging. Non-crystalline particles would be introduced in the gas phase, with only a few monolayers of solvent surrounding each particle to ensure structures of physiological relevance but with minimal solvent scatter

Methods

Results

Conclusion