Using in situ Raman scattering in a confocal microscopy setup, we have observed changes in the network structure of fused silica after modifying regions inside the glass with tightly focused 800-nm 130-fs laser pulses at fluences of 5-200 J cm(-2). The Raman spectra show a large increase in the peaks at 490 and 605cm(-1), owing to 4- and 3-membered ring structures in the silica network, indicating that densification occurs after exposure to the femtosecond laser pulses. The results are consistent with the formation of a localized plasma by the laser pulse and a subsequent microexplosion inside the glass.
"However, UV optical properties of fused silica are often degraded by preexisting and laserinduced point defects, since they induce optical absorption and fluctuation of the refractive index . Moreover, the concentration of laser-induced defects can be increased by laser irradiation, and light absorption caused by laserinduced defects may further produce laser-induced damage   . Hence, elucidating the nature of light absorption and fluorescence of point defects in the laser modified fused silica is important for controlling the evolution of laser damage and designing an effective damage mitigation procedure in excimer laser applications and power solid laser facility . "
[Show abstract][Hide abstract] ABSTRACT: High-purity fused silica irradiated by third harmonic of the Nd:YAG laser in vacuum with different laser pulse parameters was studied experimentally. Laser-induced defects are investigated by UV spectroscopy, and fluorescence spectra and correlated to the structural modifications in the glass matrix through Raman spectroscopy. Results show that, for laser fluence below laser-induced damage threshold (LIDT), the absorbance and intensity of fluorescence bands increase with laser energies and/or number of laser pulses, which indicates that laser-induced defects are enhanced by laser energies and/or number of laser pulses in vacuum. The optical properties of these point defects were discussed in detail.
"When femtosecond laser pulses are focused into transparent materials, modifications mediated by multiphoton absorption occur in the focal volume alone, leaving the surrounding region unaffected. The devices fabricated with femtosecond laser micromachining can be broadly divided into three categories: (1) buried devices, based on waveguides, gratings and couplers, are fabricated by exploiting the change in refractive index             ; (2) devices fabricated on the surface of substrates by localized laser ablation of materials like surface channels, nano-pits, microlenses, etc.    ; 3) devices fabricated by a postprocessing step after laser irradiation, such as microchannels, microlasers, and optofluidic devices [22–41]. The femtosecond laser irradiation and chemical etching (FLICE) process  belongs to the third category of processing and is widely used for fabrication of microfluidic channels in fused silica substrates. "
[Show abstract][Hide abstract] ABSTRACT: We report on the fabrication of 3D buried micro-structures in fused silica glass using the selective chemical etching along femtosecond laser irradiated zones. Specifically, we have exploited a novel approach combining two different etching agents in successive steps. The widely used hydrofluoric acid solution, which provides fast volume removal, and potassium hydroxide solution, which exhibits high selectivity, are used to fabricate microfluidic structures. We demonstrate that this hybrid approach takes advantage of both of the individual etchants' special characteristics and facilitates prototyping and fabrication of complex geometries for microfluidic devices.
Journal of Micromechanics and Microengineering 06/2013; 23(8):085002. DOI:10.1088/0960-1317/23/8/085002 · 1.73 Impact Factor
"The increase in intensity corresponds to an increase in relative number of these ring structures in the glass network. Similar changes are observed for silica subjected to femtosecond laser treatment . "
[Show abstract][Hide abstract] ABSTRACT: We report the unique growth of nanofibers in silica and borosilicate glass using femtosecond laser radiation at 8 MHz repetition rate and a pulse width of 214 fs in air at atmospheric pressure. The nanofibers are grown perpendicular to the substrate surface from the molten material in laser-drilled microvias where they intertwine and bundle up above the surface. The fibers are few tens of nanometers in thickness and up to several millimeters in length. Further, it is found that at some places nanoparticles are attached to the fiber surface along its length. Nanofiber growth is explained by the process of nanojets formed in the molten liquid due to pressure gradient induced from the laser pulses and subsequently drawn into fibers by the intense plasma pressure. The attachment of nanoparticles is due to the condensation of vapor in the plasma.
Nanoscale Research Letters 11/2009; 4(11):1263-1266. DOI:10.1007/s11671-009-9390-y · 2.78 Impact Factor
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