skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: The formation of metallic nanoparticles in single crystal CaF{sub 2} under 157 nm excimer laser irradiation

Abstract

Single crystal calcium fluoride (CaF{sub 2}) is an important material for vacuum-ultraviolet optical components. Unfortunately, all metal halides tend to form defects when exposed to energetic particles and laser radiation, and these defects can degrade optical performance. Here we examine the consequences of exposing CaF{sub 2} to 157 nm excimer laser radiation and show that several tens of thousands of pulses at fluences near 1 J/cm{sup 2} can color the material. Absorption spectra of the exposed material confirm the formation of metallic calcium nanoparticles similar to those produced by other forms of energetic radiation. The rate of nanoparticle formation depends on the bulk temperature and displays a local maximum near 50 deg. C. Absorption measurements at 157 nm display a transient absorption component that grows during prolonged irradiation and disappears on time scales of several minutes after irradiation ceases. The implications of these effects in optical components are discussed.

Authors:
; ;  [1]
  1. Physics Department, Washington State University, Pullman, Washington 99164-2814 (United States)
Publication Date:
OSTI Identifier:
20787930
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 99; Journal Issue: 5; Other Information: DOI: 10.1063/1.2177931; (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; ABSORPTION; ABSORPTION SPECTRA; CALCIUM; CALCIUM FLUORIDES; EXCIMER LASERS; IRRADIATION; LASER RADIATION; MONOCRYSTALS; NANOSTRUCTURES; PARTICLES; POINT DEFECTS; ULTRAVIOLET RADIATION; ULTRAVIOLET SPECTRA

Citation Formats

Cramer, L.P., Langford, S.C., and Dickinson, J.T.. The formation of metallic nanoparticles in single crystal CaF{sub 2} under 157 nm excimer laser irradiation. United States: N. p., 2006. Web. doi:10.1063/1.2177931.
Cramer, L.P., Langford, S.C., & Dickinson, J.T.. The formation of metallic nanoparticles in single crystal CaF{sub 2} under 157 nm excimer laser irradiation. United States. doi:10.1063/1.2177931.
Cramer, L.P., Langford, S.C., and Dickinson, J.T.. Wed . "The formation of metallic nanoparticles in single crystal CaF{sub 2} under 157 nm excimer laser irradiation". United States. doi:10.1063/1.2177931.
@article{osti_20787930,
title = {The formation of metallic nanoparticles in single crystal CaF{sub 2} under 157 nm excimer laser irradiation},
author = {Cramer, L.P. and Langford, S.C. and Dickinson, J.T.},
abstractNote = {Single crystal calcium fluoride (CaF{sub 2}) is an important material for vacuum-ultraviolet optical components. Unfortunately, all metal halides tend to form defects when exposed to energetic particles and laser radiation, and these defects can degrade optical performance. Here we examine the consequences of exposing CaF{sub 2} to 157 nm excimer laser radiation and show that several tens of thousands of pulses at fluences near 1 J/cm{sup 2} can color the material. Absorption spectra of the exposed material confirm the formation of metallic calcium nanoparticles similar to those produced by other forms of energetic radiation. The rate of nanoparticle formation depends on the bulk temperature and displays a local maximum near 50 deg. C. Absorption measurements at 157 nm display a transient absorption component that grows during prolonged irradiation and disappears on time scales of several minutes after irradiation ceases. The implications of these effects in optical components are discussed.},
doi = {10.1063/1.2177931},
journal = {Journal of Applied Physics},
number = 5,
volume = 99,
place = {United States},
year = {Wed Mar 01 00:00:00 EST 2006},
month = {Wed Mar 01 00:00:00 EST 2006}
}
  • Wide band gap insulators containing defects exposed to nanosecond pulses of UV laser radiation at fluences close to the damage threshold often display highly localized flashes of light. In this work, we show that flashes observed during irradiation of cleaved, single crystal NaCl at relatively low fluences are due to localized plume fluorescence. By comparing time-resolved optical images of this fluorescence with subsequent scanning electron microscope images of surface topography, we show that these flashes are often associated with micron-dimension surface and near-surface damage, typically associated with cleavage steps. With continued laser irradiation, plume fluorescence at previously damaged regions usuallymore » grows stronger from pulse to pulse. In some cases, weak plume fluorescence disappears after one laser pulse, and may or may not reappear with continued irradiation. We interpret these results in terms of localized laser absorption by deformation-induced defects generated during cleavage. Deliberately deformed material, produced by indentation, is damaged at considerably lower laser fluences, consistent with this interpretation. We suggest that mobile excitations produced by laser absorption preferentially decay along dislocation cores, which strongly localizes laser-induced thermal stresses and damage.« less
  • Single crystal calcium fluoride (CaF{sub 2}) is an important material for vacuum-ultraviolet optics. Nevertheless, prolonged exposure to energetic radiation can color the material by producing calcium metal nanoparticles. We compare the effectiveness of laser conditioning treatments at wavelengths ranging from the near infrared to the deep ultraviolet in removing this coloration. Treatments at 157, 532, and 1064 nm can significantly reduce the visible coloration due to nanoparticles. In contrast, irradiation at 248 nm has little effect at fluences below the damage threshold for the material employed in this work. We present evidence that the effect of laser irradiation on colorationmore » is principally thermal and is largely confined to the first 50 ns after each laser pulse. We attribute the wavelength dependence of the bleaching process to the wavelength dependence associated with Mie absorption by metal nanoparticles. The consequences of these observations with regard to laser conditioning processes in bulk optical materials are discussed.« less
  • Ultraviolet laser-induced desorption of neutral atoms and molecules from nominally transparent, ionic materials can yield particle velocities consistent with surface temperatures of a few thousand Kelvin, even in the absence of visible surface damage. The origin of the laser required for this surface heating has been often overlooked. In this work, we report simultaneous neutral emission and laser transmission measurements on single crystal NaCl exposed to 248-nm excimer laser radiation. As much as 20% of the incident radiation at 248 nm must be absorbed in the near surface region to account for the observed particle velocities. We show that themore » laser absorption grows from low values over several pulses and saturates at values sufficient to account for the surface temperatures required to explain the observed particle velocity distributions. The growth of absorption in these early pulses is accompanied by a corresponding increase in the emission intensities. Diffuse reflectance spectra acquired after exposure suggest that near surface V-type centers are responsible for most of the absorption at 248 nm in single crystal NaCl.« less
  • Ultraviolet laser-induced desorption of neutral atoms and molecules from nominally transparent, ionic materials can yield particle velocities consistent with surface temperatures of a few thousand kelvin even in the absence of visible surface damage. The origin of the laser absorption required for this surface heating has been often overlooked. In this work, we report simultaneous neutral emission and laser transmission measurements on single-crystal NaCl exposed to 248-nm excimer laser radiation. As much as 20% of the incident radiation at 248 nm must be absorbed in the near-surface region to account for the observed particle velocities. We show that the lasermore » absorption grows from low values over several pulses and saturates at values sufficient to account for the surface temperatures required to explain the observed particle velocity distributions. The growth of absorption in these early pulses is accompanied by a corresponding increase in the emission intensities. The diffuse reflectance spectra acquired after exposure suggest that near-surface V-type centers are responsible for most of the absorption at 248 nm in single-crystal NaCl.« less
  • We observe intense Zn ion and atom emissions when single-crystal ZnO is exposed to 193-nm excimer laser radiation at fluences below the threshold for optical breakdown. Zn+ and ground state Zn are readily identified by mass-selected, time-of-flight techniques using a quadrupole mass spectrometer. Particles are also detected with Channeltron electron multipliers that cannot be mass selected. We provide evidence that these particles correspond to high lying Rydberg states of atomic Zn produced by a resonance excitation involving two laser photons.