Publications (9)15.79 Total impact
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Article: Microscopic investigation of single-crystal diamond following ultrafast laser irradiation
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ABSTRACT: We present a structural investigation of single-crystal diamond following ultrafast laser irradiation of the surface and the bulk material. Optical microscopy, atomic force microscopy, scanning electron microscopy, and focused-ion beam and transmission electron microscopy techniques were utilized to selectively examine the final state of the samples. Laser induced periodic surface structures (LIPSS) with high- and low-spatial frequencies were obtained with multiple-pulse surface irradiation under both stationary and translated target conditions. High magnification transmission electron microscopy analysis of cross sections of the LIPSS revealed modified layers of a few tens of nanometers in thickness capping the crystalline diamond matrix. Sub-surface irradiation of diamond at high laser fluences led to damaged regions and cracks in the bulk material. When translational bulk irradiation of the diamond was performed, substantially sub-wavelength periodic structures were observed at the unpolished side facet of the diamond plate where the laser focus was translated out of the bulk. Spatial periods were 140nm and the structures largely consisted of single-crystal diamond with a 10nm modified layer. Finally, preliminary studies of single-shot laser ablation craters at high laser fluences exhibited suppression of material removal for peak values above 45J/cm2.Applied Physics A 05/2012; 103(1):185-192. · 1.63 Impact Factor -
Article: Cross-sectional study of femtosecond laser bulk modification of crystalline α-quartz
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ABSTRACT: Bulk irradiation of crystalline α-quartz was performed with ∼170-fs laser pulses with a wavelength of 800nm focused below the sample surface. Investigations were carried out using transmission electron microscopy on a cross-sectional specimen prepared using focused ion beam techniques. We observed alternating amorphous–crystalline structures with sharp transitions and associated density changes, surrounded by a highly strained crystalline structure. The alternating sub-surface structures are parallel to the laser’s electric field polarization and exhibit a spacing which is close to the laser wavelength in air. Cracking was also observed in the near proximity of these structures.Applied Physics A 04/2012; 98(4):849-853. · 1.63 Impact Factor -
Article: Ablation and structural changes induced in InP surfaces by single 10 fs laser pulses in air
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ABSTRACT: Ablation of single-crystalline (100) indium phosphide wafer surfaces with single 10 fs Ti:sapphire laser pulses in air has been studied by means of complementary cross-sectional transmission electron microscopy, scanning force microscopy, and optical microscopy. A local protrusion of ∼70 nm height is generated within the ablation craters for fluences exceeding 0.78 J / cm <sup>2</sup> . This morphological feature has been studied in detail, revealing the material structure of the laser-affected zone and its spatial extent. The resolidified layer (60–200 nm thick) consists of polycrystalline grains (5–15 nm diameter) and is covered by an ∼10 nm thick amorphous top layer. Interestingly, the sharp boundary of the solidified layer to the unaffected crystal underneath exhibits a Gaussian-like shape and does not follow the shape of the surface topography. Evidence is presented that the central crater protrusion is formed by near-surface optical breakdown, and that the absorption in the material transiently changes during the femtosecond-laser pulse.Journal of Applied Physics 11/2009; · 2.17 Impact Factor -
Article: Cross-sectional study of periodic surface structures on gallium phosphide induced by ultrashort laser pulse irradiation
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ABSTRACT: We present cross-sectional transmission electron microscopy studies of laser induced periodic surface structures (LIPSS) formed on gallium phosphide after irradiation with ultrashort laser pulses with a pulse duration of 150 fs and centered at a wavelength of 800 nm. LIPSS with spatial periods ( ∼ 165 nm) substantially smaller than the incident wavelength are found to have vertical profiles as high as ∼ 960 nm measured from the crest to the trough. The present observations provide important insights into the formation mechanisms of subwavelength LIPSS.Applied Physics Letters 06/2008; 92(22):221112-221112-3. · 3.84 Impact Factor -
Article: Femtosecond laser irradiation of metal and thermal oxide layers on silicon: studies utilising cross-sectional transmission electron microscopy
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ABSTRACT: We present the results of 800 and 400nm wavelength, femtosecond laser pulse irradiation of a sample consisting of a metal We present the results of 800 and 400nm wavelength, femtosecond laser pulse irradiation of a sample consisting of a metal film on thermally-grown oxide on silicon. On selected sites, cross-sectional transmission electron microscopy was performed film on thermally-grown oxide on silicon. On selected sites, cross-sectional transmission electron microscopy was performed to provide information on sub-surface changes not observable with surface scanning electron microscopy. A range of pulse energies to provide information on sub-surface changes not observable with surface scanning electron microscopy. A range of pulse energies in single-pulse irradiation exists for which the metal film was removed but the oxide was not appreciably thinned. For a sufficiently in single-pulse irradiation exists for which the metal film was removed but the oxide was not appreciably thinned. For a sufficiently high pulse energy within this range, substantial defects were observed in the underlying silicon. Five infrared pulses of high pulse energy within this range, substantial defects were observed in the underlying silicon. Five infrared pulses of a relatively high fluence created significant defects, as well as producing polycrystalline material on top of the original a relatively high fluence created significant defects, as well as producing polycrystalline material on top of the original oxide and metal. We discuss various factors which may play a role in the formation of the observed features. oxide and metal. We discuss various factors which may play a role in the formation of the observed features.Applied Physics A 05/2008; 91(3):473-478. · 1.63 Impact Factor -
Article: Subsurface modifications in indium phosphide induced by single and multiple femtosecond laser pulses: A study on the formation of periodic ripples
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ABSTRACT: We use cross-sectional transmission electron microscopy to study the damage induced below the surface of indium phosphide (InP) samples by single and multiple femtosecond laser pulses with a photon energy lower than the InP band gap. Single-pulse irradiation creates a ∼ 100 nm deep crater with a resolidified surface layer consisting of quasiamorphous indium phosphide. The resolidified layer has a thickness of ∼ 60 nm at the center and extends laterally beyond the edge of the crater rim. Exposure to multiple femtosecond pulses of 2050 nm center wavelength results in the formation of laser-induced periodic surface structures (LIPSS) with two different periods, one ( ∼ 1730 nm) less than but close to the laser wavelength and one ( ∼ 470 nm) four times smaller. Segregation beneath both types of ripples leads to the formation of In-rich particles embedded in the resolidified surface layer. Extended defects are detected only below the center of the multiple-pulse crater and their distribution appears to be correlated with the LIPSS modulation. Finally, LIPSS formation is discussed in terms of the observed subsurface microstructures.Journal of Applied Physics. 02/2007; 101(3):033519-033519-8. -
Article: Femtosecond laser micromachining of grooves in silicon with 800 nm pulses
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ABSTRACT: Femtosecond laser micromachining of grooves in silicon is investigated using 150fs pulses with a center wavelength of 800nm. Ablation rates are investigated as a function of pulse energy, translation speed, and the number of consecutive passes. The effect of the laser polarization relative to the translation direction is observed, and the morphologies of the groove walls are examined. In addition, the uniformity of the groove depth is investigated as a function of the number of passes of the sample under the beam.Applied Physics A 04/2005; 80(8):1717-1724. · 1.63 Impact Factor -
Article: Femtosecond laser micromachining of grooves in indium phosphide
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ABSTRACT: Femtosecond laser micromachining of indium phosphide is investigated using 150fs light pulses at a center wavelength of 800nm. The ablation rate for micromachining of grooves is investigated as a function of pulse energy, feed rate, number of passes over the same groove, and the light polarization relative to the cutting direction. A logarithmic dependence of the groove depth on the laser fluence is observed with two regimes characterized by different ablation rates and different thresholds. The groove depth is found to be inversely proportional to the feed rate or equivalently linearly proportional to number of pulses delivered per unit area. With multiple passes over the same groove the depth increases linearly up to about 20 consecutive passes. Above 20 passes the ablation rate decreases until a depth limit is approached. The best results in terms of groove geometry and depth limit are obtained with the polarization of the beam perpendicular to the cutting direction.Applied Physics A 07/2004; 79(3):521-529. · 1.63 Impact Factor -
Article: Sub-surface damage in indium phosphide caused by micromachining of grooves with femtosecond and nanosecond laser pulses
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ABSTRACT: Grooves laser-micromachined in InP using 130fs and 8ns pulses with fluences 2 and 0.7J/cm2 are investigated by cross-sectional transmission electron microscopy. At the fluence of 2J/cm2, irradiation with both femtosecond and nanosecond laser pulses yield substantial resolidified layers with a maximum thickness of 0.5m. In contrast, at the fluence of 0.7J/cm2, irradiation with nanosecond pulses leads to a layer of similar thickness, while femtosecond irradiation produces laser induced periodic surface structures with minimal resolidified material. For both fluences, femtosecond pulses generate substantial densities of defects extending over a few microns in depth, while nanosecond laser irradiation leads to no observable damage beneath the resolidified layer. The high peak power density and the stress confinement obtained from femtosecond pulses, along with incubation effects, are identified as the major factors leading the observed plastic deformations.Applied Physics A 01/2004; 79(8):1887-1890. · 1.63 Impact Factor
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Institutions
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2005–2012
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McMaster University
- • Department of Physics and Astronomy
- • Department of Materials Science and Engineering
Hamilton, Ontario, Canada
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