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Title: Patterning of silica microsphere monolayers with focused femtosecond laser pulses

Abstract

We demonstrate the patterning of monolayer silica microsphere lattices with tightly focused femtosecond laser pulses. We selectively removed microspheres from a lattice and characterized the effect on the lattice and the substrate. The proposed physical mechanism for the patterning process is laser-induced breakdown followed by ablation of material. We show that a microsphere focuses radiation in its interior and in the near field. This effect plays an important role in the patterning process by enhancing resolution and accuracy and by reducing the pulse energy threshold for damage. Microsphere patterning could create controlled defects within self-assembled opal photonic crystals.

Authors:
;  [1];  [2]
  1. Department of Physics, University of Colorado, Boulder, Colorado 80309-0390 (United States)
  2. (United States)
Publication Date:
OSTI Identifier:
20778812
Resource Type:
Journal Article
Resource Relation:
Journal Name: Applied Physics Letters; Journal Volume: 88; Journal Issue: 11; Other Information: DOI: 10.1063/1.2183733; (c) 2006 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; ABLATION; BREAKDOWN; CRYSTALS; DAMAGE; FOCUSING; LASERS; MICROSPHERES; OPALS; PULSES; RESOLUTION; SILICON COMPOUNDS; SUBSTRATES

Citation Formats

Cai Wenjian, Piestun, Rafael, and Department of Electrical and Computer Engineering, University of Colorado, Boulder, Colorado 80309-0425. Patterning of silica microsphere monolayers with focused femtosecond laser pulses. United States: N. p., 2006. Web. doi:10.1063/1.2183733.
Cai Wenjian, Piestun, Rafael, & Department of Electrical and Computer Engineering, University of Colorado, Boulder, Colorado 80309-0425. Patterning of silica microsphere monolayers with focused femtosecond laser pulses. United States. doi:10.1063/1.2183733.
Cai Wenjian, Piestun, Rafael, and Department of Electrical and Computer Engineering, University of Colorado, Boulder, Colorado 80309-0425. Mon . "Patterning of silica microsphere monolayers with focused femtosecond laser pulses". United States. doi:10.1063/1.2183733.
@article{osti_20778812,
title = {Patterning of silica microsphere monolayers with focused femtosecond laser pulses},
author = {Cai Wenjian and Piestun, Rafael and Department of Electrical and Computer Engineering, University of Colorado, Boulder, Colorado 80309-0425},
abstractNote = {We demonstrate the patterning of monolayer silica microsphere lattices with tightly focused femtosecond laser pulses. We selectively removed microspheres from a lattice and characterized the effect on the lattice and the substrate. The proposed physical mechanism for the patterning process is laser-induced breakdown followed by ablation of material. We show that a microsphere focuses radiation in its interior and in the near field. This effect plays an important role in the patterning process by enhancing resolution and accuracy and by reducing the pulse energy threshold for damage. Microsphere patterning could create controlled defects within self-assembled opal photonic crystals.},
doi = {10.1063/1.2183733},
journal = {Applied Physics Letters},
number = 11,
volume = 88,
place = {United States},
year = {Mon Mar 13 00:00:00 EST 2006},
month = {Mon Mar 13 00:00:00 EST 2006}
}
  • We investigate experimentally and numerically the damage tracks induced by tightly focused (NA=0.5) infrared femtosecond laser pulses in the bulk of a fused silica sample. Two types of irreversible damage are observed. The first damage corresponds to a permanent change of refractive index without structural modifications (type I). It appears for input pulse energies beyond 0.1 {mu}J. It takes the form of a narrow track extending over more than 100 {mu}m at higher input powers. It is attributed to a change of the polarizability of the medium, following a filamentary propagation which generates an electron-hole plasma through optical field ionization.more » A second type of damage occurs for input pulse energies beyond 0.3 {mu}J (type II). It takes the form of a pear-shaped structural damage associated with an electron-ion plasma triggered by avalanche. The temporal evolution of plasma absorption is studied by pump-probe experiments. For type I damage, a fast electron-hole recombination is observed. Type II damage is linked with a longer absorption.« less
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  • We report on experimental study on chemical etch selectivity of fused silica irradiated by femtosecond laser with either linear or circular polarization in a wide range of pulse energies. The relationships between the etch rates and pulse energies are obtained for different polarization states, which can be divided into three different regions. A drop of the etch rate for high pulse energy region is observed and the underlying mechanism is discussed. The advantage of using circularly polarized laser is justified owing to its unique capability of providing a 3D isotropic etch rate.
  • An ultrahigh-resolution (20 nm) technique of selective chemical etching and atomic force microscopy has been used to study the photoinduced modification in fused silica produced at various depths by tightly focused femtosecond laser radiation affected by spherical aberration. We demonstrate that shapes of the irradiated zones near the threshold for modification can be predicted by taking proper account of spherical aberration caused by the refractive index mismatched air-silica interface. We establish a depth dependence of the pulse energy required to initiate modification and characterize the relationship between numerical aperture of the writing lens and practically achievable writing depth. We alsomore » show that spatial characteristics of the laser-modified zones can be controlled by a specially designed focusing system which allows correction for a variable amount of spherical aberration.« less
  • The focusing position inside fused silica irradiated by a loosely focused high power femtosecond laser pulse is studied both experimentally and numerically. The experimental measurement of plasma radiation shows that the laser pulse is focused behind the focal plane, which is also found in the numerical calculation and is attributed to a complex interplay between self-focusing due to the Kerr effect and defocusing because of the free electron plasma. Also, when more than one pulse is incident at the same spot in the sample, plasma radiation is observed at more than one spot along the laser propagation direction.