Dark GPC: extended nodal beam areas from binary-only phase

Mark Jayson Villangca,Darwin Palima,Andrew R Bañas,Jesper Glückstad

doi:10.1117/1.oe.55.12.125102

Mark Jayson Villangca, Darwin Palima + Show 2 more

Open Access

https://doi.org/10.1117/1.oe.55.12.125102

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Abstract

We show a simplified method of generating extended regions of destructive interference with near arbitrary shapes using the generalized phase contrast (GPC) method. For Gaussian input beams, GPC typically results in a 3× intensified user-defined input mask shape against a dark background. In this work, we investigate conditions wherein GPC’s synthetic reference wave destructively interferes with what is typically the foreground pattern. Using alternate conditions for the input phase mask, the locations of light and darkness are interchanged with respect to typical GPC output mappings. We show experimentally how “dark GPC” allows the dark regions to be easily reshaped using a binary-only phase mask encoded on a spatial light modulator. Similar to standard GPC, the method does not require complex calculations or the fabrication of complex gray-level phase elements. The simplified approach and flexibility in the output shapes make dark GPC attractive for applications such as optical trapping of low-index particles or superresolution microscopy like stimulated emission depletion.

Highlights

Structured light distributions have been used in applications such as optical trapping and manipulation,[1,2,3] optical sorting,[4,5] advanced microscopy, and selective uncaging or excitation[6] in neurophotonics or optogenetics.[7]
Bounded regions of darkness are used in defining potential distributions for atom trapping, optical trapping of low-index media,[8,9,10] and in stimulated emission depletion microscopy.[11]
Since the phase contrast filter (PCF) is usually fixed in our applications, we look for phase mask distributions, φðx; yÞ, that will cause Eq (1) to nullify at the phaseencoded shaped region

Summary

Introduction

Structured light distributions have been used in applications such as optical trapping and manipulation,[1,2,3] optical sorting,[4,5] advanced microscopy, and selective uncaging or excitation[6] in neurophotonics or optogenetics.[7]. Bounded regions of darkness are used in defining potential distributions for atom trapping, optical trapping of low-index media,[8,9,10] and in stimulated emission depletion microscopy.[11]. Another important imaging application is coronography in astronomy. Having control over the darkness shapes while maintaining sharp transitions from dark to bright brings more possibilities and flexibility Engineering such dark regions to shapes other than circular can lead to designed dipole traps.[18] Potential uses in lasermaterials processing can include shielding or cutting out user-defined shapes. Villangca et al.: Dark generalized phase contrast: extended nodal beam areas from binary-only phase

Theory

Experiments and Results

Conclusion