Imaging with Diffractive Axicons Rapidly Milled on Sapphire by Femtosecond Laser Ablation

TL;DR

This paper demonstrates rapid fabrication of diffractive axicons on sapphire using femtosecond laser ablation, achieving smooth, high-quality micro-optical components with fewer steps and reduced processing time.

Contribution

It introduces a novel femtosecond laser milling process for directly fabricating binary axicons on sapphire, including innovative configurations like photon sieve axicons and sparse PSA.

Findings

Single pulse burst fabrication yields smoother profiles.

Processed elements show reduced surface roughness and damage.

Optical testing confirms effective diffractive performance.

Abstract

Fabrication of large area (sub 1 cm cross-section) micro-optical components in a short period of time (approximately 10 min) and with lesser number of processing steps is highly desirable and cost-effective. In the recent years, femtosecond laser fabrication technology has revolutionized the field of manufacturing by offering the above capabilities. In this study, a fundamental diffractive optical element, binary axicon i.e axicon with two phase or amplitude levels, has been designed in three configurations namely conventional axicon, photon sieve axicon (PSA) and sparse PSA and directly milled onto the Sapphire substrate. The fabrication results revealed that a single pulse burst fabrication can produce a flat and smooth profile than pulse overlapped fabrication which gives rise to surface damage and increased roughness. The fabricated elements were processed in IsoPropyl Alcohol and Potassium Hydroxide to remove debris and redeposited amorphous Sapphire. An incoherent illumination was used for optical testing of the components and a non-linear optical filter was used for cleaning the noisy images generated by the diffractive optical elements.