Temporal-contrast imperfections as drivers for ultrafast laser modifications in bulk silicon

Andong Wang,Amlan Das,David Grojo

doi:10.1103/physrevresearch.2.033023

Andong Wang, Amlan Das + Show 1 more

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https://doi.org/10.1103/physrevresearch.2.033023

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Abstract

This paper uncovers the role of the temporal contrast in achieving internal modifications in semiconductors with ultrafast lasers and explores how it may influence three dimensional fabrication of monolithic silicon microsystems.

Highlights

Focused to small focal spots in transparent materials, intense femtosecond light pulses lead to local nonlinear energy deposition that makes possible to induce various microscale modifications anywhere in a three-dimensional (3D) space
As we will show in this paper, the controversy persists because all comparisons are made on the basis of the usual triplet of control parameters, namely the pulse duration, the pulse energy and the numerical aperture (NA) of the focusing lens. While this is usually appropriate with no apparent anomaly in the dependencies of the material responses to this triplet for surface or bulk dielectric interaction studies, we show in this paper that the temporal contrast, a laser-technology-dependent parameter, is a somewhat more important aspect to relate the observables inside narrow gap materials
We have reviewed the recent but rapidly growing literature on ultrafast laser writing inside bulk silicon

Summary

Introduction

Focused to small focal spots in transparent materials, intense femtosecond light pulses lead to local nonlinear energy deposition that makes possible to induce various microscale modifications anywhere in a three-dimensional (3D) space. With the advent of new sources directly emitting in the shortwave infrared (SWIR) region of the spectrum (1.1–2.5 μm), one should see similar technologies applied to narrow gap materials as important as silicon but those are much slower in coming This is because first attempts have faced abnormally strong requirements on the irradiation conditions in comparison to dielectrics. The explanation given today is strong detrimental nonlinearities intrinsic to narrow gaps and the use of long wavelengths These include propagation phase distortions and losses caused by ionization and plasma effects developing prior to the focus and preventing in most cases enough space-time localization of laser energy to achieve permanent modifications [3,4,5,6]

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