Imaging with diffractive axicons rapidly milled on sapphire by femtosecond laser ablation

Daniel Smith,Karl Glazebrook,Soon Hock Ng,Vijayakumar Anand,Saulius Juodkazis,Molong Han,Tomas Katkus

doi:10.1007/s00340-021-07701-x

Abstract

Fabrication of large area (sub-1 cm cross-section) micro-optical components in a short period of time (~ 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–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 a sapphire substrate. The fabrication results revealed that a single pulse burst fabrication can produce a flatter and smoother 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.

Highlights

Generation and precise control of optical fields is crucial in many optical instruments and imaging systems [1]
Even though it may be argued that photolithography can transfer large area patterns, the time is still spent on fabrication of the mask
In both I-coded aperture correlation holography (COACH) and the imaging with photon sieve axicon (PSA), the object information can be reconstructed by a cross-correlation between the multi-points intensity distribution and the point spread functions (PSFs)

Summary

Introduction

Generation and precise control of optical fields is crucial in many optical instruments and imaging systems [1]. The diffractive optical elements (DOEs) can be manufactured using different techniques such as photolithography [13], electron beam lithography [14], ion beam lithography [15], depending upon the feature sizes and area of the design. One current limitation of fs-laser fabrication is in its low capability to deliver practical solution for large area (mm-to-cm) scale micro-optical elements. The focus of this study is on the rapid fabrication approach for manufacturing large area diffractive optical elements for astronomical imaging applications. The summary and conclusion are presented in the final section

Methodology

Fabrication

Optical testing

Conclusion