... spectrometer (0.05 rim, resolution), with 2 x magnification. The optical image of the plume i... more ... spectrometer (0.05 rim, resolution), with 2 x magnification. The optical image of the plume is scanned along the target normal to analyze different slices of it, with a spatial resolution of 60 ltm. The light emitted is collected by a ...
Resonance ionization spectroscopy combined with time of flight mass spectrometry is used to analy... more Resonance ionization spectroscopy combined with time of flight mass spectrometry is used to analyze the ejection of ions and neutrals from the surface of a Ge target irradiated with ultraviolet XeCl excimer laser pulses. The ejection of ions and neutrals has been observed to occur at temperatures well below the melting point of the target and, therefore, through a nonthermal mechanism that may be dominant for fluences below the threshold for visible plasma formation. Within this regime, the velocities of the ejected neutrals in the ground state are in the order of 3×104 cm/s.
The correlation between the optical properties and composition of lithium niobate films is invest... more The correlation between the optical properties and composition of lithium niobate films is investigated in films deposited by laser ablation of single-crystal LiNbO3 and Li enriched LiNbO3 sintered targets under different oxygen pressures and laser fluences. The results show that the variation of the film refractive index is in many cases related to the deposition process itself, rather than to a variation of the film composition. The experimental conditions to produce stoichiometric films with optical properties similar to those of the bulk material are discussed.
We report on the mechanisms responsible for the formation of optical waveguides upon femtosecond ... more We report on the mechanisms responsible for the formation of optical waveguides upon femtosecond laser irradiation of an alkaline lead-oxide silicate glass. MicroRaman spectroscopy and nonlinear fluorescence were employed to probe the local glass network structure and the formation of optically active defects respectively. At low laser pulse energies, the laser modified region is formed by a single light guiding region, whereas for pulses above 14 µJ the modified region is formed by a central dark zone, which does not guide light, accompanied by light guiding zones located in the surrounding of the dark one. This behavior is different from that observed in common silica glass systems but agrees with recent results obtained in phosphate and heavy metal oxide glasses. However, our results show that, unlike the latter glass, local densification of the glass occurs in the whole laser modified region, i.e., in the dark and the guiding zones. The suppression of light guiding in the dark region is explained by a high density of absorbing color centers.
Ultraviolet pulsed laser induced oxidation kinetics of crystalline germanium (c-Ge) is determined... more Ultraviolet pulsed laser induced oxidation kinetics of crystalline germanium (c-Ge) is determined from real-time optical measurements in conjunction with absolute measurements of the oxygen incorporation performed by nuclear reaction analysis. Although the oxidation process can be triggered at laser fluences initially below the melting threshold of c-Ge, it is strongly activated when surface melting occurs and therefore the fast oxidation process observed is mainly a thermally activated process. Because an optical coupling between the oxide layer and the c-Ge underneath, the growth kinetics is complex and leads to nonconstant rates. The oxygen incorporation reaches a saturation value which depends both on the laser fluence and the oxygen pressure. The results show that the oxygen incorporation is limited by an overlapped laser-induced material removal process rather than by the diffusion length of oxygen species.
To determine the energy distribution between the distance and near images formed in a model eye b... more To determine the energy distribution between the distance and near images formed in a model eye by spherical and aspheric apodized diffractive multifocal intraocular lenses (IOLs). METHODS. The IOL was inserted in a model eye with an artificial cornea with positive spherical aberration (SA) similar to that of the human cornea. The energy of the distance and near images, as a function of the pupil size, was experimentally obtained by image analysis. The level of SA on the IOL, which is pupil-sizedependent, was determined from simulations. The influence of the SA was deduced from results obtained in monofocal IOLs and by comparison of the experimentally obtained energy efficiency to theoretical results based solely on the diffractive profile of the IOL. RESULTS. In contrast with theoretical predictions, the energy efficiency of the distance image strongly decreased for large pupils, because of the high level of SA in the IOL. The decrease was smaller in the apodized diffractive multifocal lens with aspheric design. As for the near image, since the diffractive zone responsible for the formation of this image was the same in the spherical and aspheric lenses and the apertures involved were small (and so the level of SA), the results turned out to be similar for both designs. CONCLUSIONS. For large pupils, the energy efficiency of the distance image is strongly affected by the level of SA, although aspheric IOLs perform slightly better than their counterparts with a spherical design. For small pupils, there are no differences between the spherical and aspheric IOLs.
PURPOSE To evaluate the changes in pupil diameter in women and men after cataract surgery. The co... more PURPOSE To evaluate the changes in pupil diameter in women and men after cataract surgery. The correlation of pupillary changes with the variables age and anterior chamber depth will be analyzed. METHODS The values of 109 randomized eyes who underwent cataract surgery were obtained and divided into two groups, 71 women and 38 men. Pupil diameter was measured preoperatively and 3-months postoperatively using the pupillometer software of the Topolyzer Vario (Wavelight Laser Technologie AG). Anterior chamber depth was obtained with Pentacam® (Oculus). Differences in pupillary diameters were investigated and correlations with age and anterior chamber depth were analyzed. RESULTS For mesopic pupils, the male group had greater reduction in their postoperative pupillary diameter, -0.56 mm (-12.4%), than the female group, -0.38 mm (-8.2%), P = 0.025. Photopic postoperative pupils reduced to a lesser extent, yet more in men than in women (-0.11mm [-4.5%] vs. -0.04 [-1.6%], P = 0.048). Weak significant negative correlation was found between photopic pupillary changes in women with age (r = -0.24, P = 0.041), and positive correlation for mesopic pupillary changes in men with age (r = +0.34, P = 0.039). CONCLUSIONS Patients experience pupil reduction after cataract surgery in general, but more in men than in women and for both photopic and mesopic lighting conditions. The differences are statistically significant and have moderate clinical relevance. Concerning pupillary changes, weak but opposite sign correlations were found between male/female gender and age. Trial registration number at ClinicalTrials.gov Identifier: NCT04286646.
Proceedings of European Meeting on Lasers and Electro-Optics CLEOE-96, 1996
... 18, 93053 Regensbury, Germany Tel/Fax: (t49) 941-781222, [email protected]. de... more ... 18, 93053 Regensbury, Germany Tel/Fax: (t49) 941-781222, [email protected]. de University of New South Wales, Sydney 2052 ... email: [email protected] and N. Lupon, F. Laguarta, J. Armengol, F. Vega Ilepanament d'ilptica i Optometiia Universitat Politbcnica ...
This work describes the phase transitions occurring at the film-substrate interface of amorphous ... more This work describes the phase transitions occurring at the film-substrate interface of amorphous germanium films upon nanosecond laser-pulse-induced melting of the surface. Films with thickness ranging from 50 to 130 nm deposited on glass substrates were studied. Real-time reflectivity measurements with subnanosecond time resolution performed both at the air-film and film-substrate interfaces were used to obtain both surface and in-depth information of the process. In the thicker films ͑ജ80 nm͒, the enthalpy released upon solidification of a shallow molten surface layer induces a thin buried liquid layer that self-propagates in-depth towards the film-substrate interface. This buried liquid layer propagates with a threshold velocity of 16± 1 m / s and causes, eventually, melting at the film-substrate interface. In the thinnest film ͑50 nm͒ there is no evidence of the formation of the buried layer. The presence of the self-propagating buried layer for films thicker than 80 nm at low and intermediate laser fluences is discussed in terms of the thermal gradient in the primary melt front and the heat released upon solidification.
... Applied Surface Science 69 (1993) 149-155 North-Holland Lithium niobate films grown by excime... more ... Applied Surface Science 69 (1993) 149-155 North-Holland Lithium niobate films grown by excimer laser deposition CN Afonso , F. Vega , J. Gonzalo a and C. Zaldo b Instituto de ... Films are grown onto glass, quartz and carbon-coated mica substrates held at room temperature. ...
This work reports a systematic study of the growth of copper oxide thin films by laser evaporatio... more This work reports a systematic study of the growth of copper oxide thin films by laser evaporation from a Cu foil or a Cu sintered powder target in an oxygen atmosphere. The experimental conditions to deposit CuzO and CuO thin films are determined. Particle-free single-phase films are obtained from the foil target. The laser-deposited films have good optical properties. For comparison, DC-sputtered films deposited from the same Cu foil were studied. To obtain the same phase the former method requires higher oxygen pressure during deposition. The microstructure formed in the laser-deposited samples is always polycrystalline with a homogeneous grain size whereas sputtering can form columnar growth.
A new integration method suited for spatially coherent high-power laser beams is demonstrated. Th... more A new integration method suited for spatially coherent high-power laser beams is demonstrated. The integrator system is based on a mirror with two facets, one of which can vibrate under the action of a piezoelectric translator. After reflection in the faceted mirror, the beam intensity distribution is modified to obtain greater uniformity. However, because of the coherence of the reflected beamlets, this distribution is affected by an interference pattern. The active integration consists of a periodic displacement of the moving facet that causes the interference pattern to vibrate, and its contribution to the intensity profile therefore averages out (fringe visibility within a 5% range). The combination of a faceted mirror and a simple imaging system results in an intensity profile with good uniformity over large spot sizes. Both simulated and experimental results are presented, the latter showing that a final uniformity within a 10% range can be achieved and it is limited mainly by diffraction at the edges of the facets.
Ultraviolet (UV) laser pulses are used to irradiate c-Ge and c-Sb both in vacuum and in an oxygen... more Ultraviolet (UV) laser pulses are used to irradiate c-Ge and c-Sb both in vacuum and in an oxygen pressure while a HeNe laser beam is used to record the real time reflectivity (RTR) transients. It will be shown that the removal of the native oxide and therefore surface cleaning is produced when irradiating in vacuum while an oxidation process occurs when irradiating in an oxygen environment. The optical coupling between the growing oxide layer with the bulk material underneath is responsible of the high sensitivity of the RTR measurements to the presence or transformation of small thickness oxide layers at the surface. The RTR transients can be used to optically control pulse-to-pulse the laser energy density in order to induce surface oxidation at a constant rate and to minimize material losses during the oxidation process.
Determination of optical damage cross-sections and volumes surrounding ion bombardment tracks in ... more Determination of optical damage cross-sections and volumes surrounding ion bombardment tracks in GaAs using coherent acoustic phonon spectroscopy J. Appl. Phys. 112, 013514 Microwave-induced nonequilibrium temperature in a suspended carbon nanotube Appl. Phys. Lett. 100, 223112 (2012) Empirical modeling of the cross section of damage formation in ion implanted III-V semiconductors Appl. Phys. Lett. 100, 192108 (2012) Nitrogen-promoted formation of graphite-like aggregations in SiC during neutron irradiation Rapid solidification phenomena have been studied in amorphous germanium films on silicon substrates by means of real time reflectivity measurements performed during irradiation with nanosecond laser pulses. The influence of the thermal response of the film/substrate system has been investigated by comparing the behavior of films with thicknesses in the range of 30-180 nm. Two different solidification scenarios are observed depending on the ratio between film thickness (d) and the thermal diffusion length (l) of amorphous germanium ͑lϷ80 nm for 12 ns laser pulses͒. In the thinner films (dϽl), reamorphization occurs upon solidification. Recalescence is observed in the thicker ones (dуl) when the melt depth induced is above of Ϸ80 nm. Above this threshold, crystalline phases are nucleated upon solidification. The origin of this melt depth threshold is discussed in terms of the heat flow into the substrate, the supercooling prior to solidification, and the need of a minimum amount of initially solidified material.
Pressure-induced series of phase transitions in sodium azide J. Appl. Phys. 113, 033511 (2013) St... more Pressure-induced series of phase transitions in sodium azide J. Appl. Phys. 113, 033511 (2013) Structure and phase transitions in 0.5(Ba0.7Ca0.3TiO3)-0.5(BaZr0.2Ti0.8O3) from −100°C to 150°C Relaxation and crystallization of amorphous germanium films on silicon are induced by nanosecond laser pulses. Real time reflectivity measurements and Raman spectroscopy show that amorphous regrowth occurs upon melting and rapid solidification of the film because the thermal conductivity of the silicon substrate is .high enough to extract the laser energy absorbed by the film in a very efficient way. The amorphous regrown film is in a relaxed state when compared to the as-grown amorphous material. Further pulses induce fast crystallization of the film. An increase of the melting threshold is found upon relaxation and crystallization of the film.
UV-laser-induced oxidation of crystalline Ge (c-Ge) is analyzed by means of real-time optical mea... more UV-laser-induced oxidation of crystalline Ge (c-Ge) is analyzed by means of real-time optical measurements, lrradiations are performed in a controlled oxygen atmosphere with laser fluences above the melting threshold. The meh duration determined from the reflectivity transients depends strongly on the oxygen pressure and on the number of laser pulses. The reflectivity of the material tends to decrease as the number of pulses is increased. The results indicate that the irradiation induces the growth of a surface oxide layer at a non-constant rate. The optical coupling between the oxide layer and the bulk material underneath at the irradiation wavelength explains the results and is found responsible for an enhancement of the oxide growth rate.
... spectrometer (0.05 rim, resolution), with 2 x magnification. The optical image of the plume i... more ... spectrometer (0.05 rim, resolution), with 2 x magnification. The optical image of the plume is scanned along the target normal to analyze different slices of it, with a spatial resolution of 60 ltm. The light emitted is collected by a ...
Resonance ionization spectroscopy combined with time of flight mass spectrometry is used to analy... more Resonance ionization spectroscopy combined with time of flight mass spectrometry is used to analyze the ejection of ions and neutrals from the surface of a Ge target irradiated with ultraviolet XeCl excimer laser pulses. The ejection of ions and neutrals has been observed to occur at temperatures well below the melting point of the target and, therefore, through a nonthermal mechanism that may be dominant for fluences below the threshold for visible plasma formation. Within this regime, the velocities of the ejected neutrals in the ground state are in the order of 3×104 cm/s.
The correlation between the optical properties and composition of lithium niobate films is invest... more The correlation between the optical properties and composition of lithium niobate films is investigated in films deposited by laser ablation of single-crystal LiNbO3 and Li enriched LiNbO3 sintered targets under different oxygen pressures and laser fluences. The results show that the variation of the film refractive index is in many cases related to the deposition process itself, rather than to a variation of the film composition. The experimental conditions to produce stoichiometric films with optical properties similar to those of the bulk material are discussed.
We report on the mechanisms responsible for the formation of optical waveguides upon femtosecond ... more We report on the mechanisms responsible for the formation of optical waveguides upon femtosecond laser irradiation of an alkaline lead-oxide silicate glass. MicroRaman spectroscopy and nonlinear fluorescence were employed to probe the local glass network structure and the formation of optically active defects respectively. At low laser pulse energies, the laser modified region is formed by a single light guiding region, whereas for pulses above 14 µJ the modified region is formed by a central dark zone, which does not guide light, accompanied by light guiding zones located in the surrounding of the dark one. This behavior is different from that observed in common silica glass systems but agrees with recent results obtained in phosphate and heavy metal oxide glasses. However, our results show that, unlike the latter glass, local densification of the glass occurs in the whole laser modified region, i.e., in the dark and the guiding zones. The suppression of light guiding in the dark region is explained by a high density of absorbing color centers.
Ultraviolet pulsed laser induced oxidation kinetics of crystalline germanium (c-Ge) is determined... more Ultraviolet pulsed laser induced oxidation kinetics of crystalline germanium (c-Ge) is determined from real-time optical measurements in conjunction with absolute measurements of the oxygen incorporation performed by nuclear reaction analysis. Although the oxidation process can be triggered at laser fluences initially below the melting threshold of c-Ge, it is strongly activated when surface melting occurs and therefore the fast oxidation process observed is mainly a thermally activated process. Because an optical coupling between the oxide layer and the c-Ge underneath, the growth kinetics is complex and leads to nonconstant rates. The oxygen incorporation reaches a saturation value which depends both on the laser fluence and the oxygen pressure. The results show that the oxygen incorporation is limited by an overlapped laser-induced material removal process rather than by the diffusion length of oxygen species.
To determine the energy distribution between the distance and near images formed in a model eye b... more To determine the energy distribution between the distance and near images formed in a model eye by spherical and aspheric apodized diffractive multifocal intraocular lenses (IOLs). METHODS. The IOL was inserted in a model eye with an artificial cornea with positive spherical aberration (SA) similar to that of the human cornea. The energy of the distance and near images, as a function of the pupil size, was experimentally obtained by image analysis. The level of SA on the IOL, which is pupil-sizedependent, was determined from simulations. The influence of the SA was deduced from results obtained in monofocal IOLs and by comparison of the experimentally obtained energy efficiency to theoretical results based solely on the diffractive profile of the IOL. RESULTS. In contrast with theoretical predictions, the energy efficiency of the distance image strongly decreased for large pupils, because of the high level of SA in the IOL. The decrease was smaller in the apodized diffractive multifocal lens with aspheric design. As for the near image, since the diffractive zone responsible for the formation of this image was the same in the spherical and aspheric lenses and the apertures involved were small (and so the level of SA), the results turned out to be similar for both designs. CONCLUSIONS. For large pupils, the energy efficiency of the distance image is strongly affected by the level of SA, although aspheric IOLs perform slightly better than their counterparts with a spherical design. For small pupils, there are no differences between the spherical and aspheric IOLs.
PURPOSE To evaluate the changes in pupil diameter in women and men after cataract surgery. The co... more PURPOSE To evaluate the changes in pupil diameter in women and men after cataract surgery. The correlation of pupillary changes with the variables age and anterior chamber depth will be analyzed. METHODS The values of 109 randomized eyes who underwent cataract surgery were obtained and divided into two groups, 71 women and 38 men. Pupil diameter was measured preoperatively and 3-months postoperatively using the pupillometer software of the Topolyzer Vario (Wavelight Laser Technologie AG). Anterior chamber depth was obtained with Pentacam® (Oculus). Differences in pupillary diameters were investigated and correlations with age and anterior chamber depth were analyzed. RESULTS For mesopic pupils, the male group had greater reduction in their postoperative pupillary diameter, -0.56 mm (-12.4%), than the female group, -0.38 mm (-8.2%), P = 0.025. Photopic postoperative pupils reduced to a lesser extent, yet more in men than in women (-0.11mm [-4.5%] vs. -0.04 [-1.6%], P = 0.048). Weak significant negative correlation was found between photopic pupillary changes in women with age (r = -0.24, P = 0.041), and positive correlation for mesopic pupillary changes in men with age (r = +0.34, P = 0.039). CONCLUSIONS Patients experience pupil reduction after cataract surgery in general, but more in men than in women and for both photopic and mesopic lighting conditions. The differences are statistically significant and have moderate clinical relevance. Concerning pupillary changes, weak but opposite sign correlations were found between male/female gender and age. Trial registration number at ClinicalTrials.gov Identifier: NCT04286646.
Proceedings of European Meeting on Lasers and Electro-Optics CLEOE-96, 1996
... 18, 93053 Regensbury, Germany Tel/Fax: (t49) 941-781222, [email protected]. de... more ... 18, 93053 Regensbury, Germany Tel/Fax: (t49) 941-781222, [email protected]. de University of New South Wales, Sydney 2052 ... email: [email protected] and N. Lupon, F. Laguarta, J. Armengol, F. Vega Ilepanament d'ilptica i Optometiia Universitat Politbcnica ...
This work describes the phase transitions occurring at the film-substrate interface of amorphous ... more This work describes the phase transitions occurring at the film-substrate interface of amorphous germanium films upon nanosecond laser-pulse-induced melting of the surface. Films with thickness ranging from 50 to 130 nm deposited on glass substrates were studied. Real-time reflectivity measurements with subnanosecond time resolution performed both at the air-film and film-substrate interfaces were used to obtain both surface and in-depth information of the process. In the thicker films ͑ജ80 nm͒, the enthalpy released upon solidification of a shallow molten surface layer induces a thin buried liquid layer that self-propagates in-depth towards the film-substrate interface. This buried liquid layer propagates with a threshold velocity of 16± 1 m / s and causes, eventually, melting at the film-substrate interface. In the thinnest film ͑50 nm͒ there is no evidence of the formation of the buried layer. The presence of the self-propagating buried layer for films thicker than 80 nm at low and intermediate laser fluences is discussed in terms of the thermal gradient in the primary melt front and the heat released upon solidification.
... Applied Surface Science 69 (1993) 149-155 North-Holland Lithium niobate films grown by excime... more ... Applied Surface Science 69 (1993) 149-155 North-Holland Lithium niobate films grown by excimer laser deposition CN Afonso , F. Vega , J. Gonzalo a and C. Zaldo b Instituto de ... Films are grown onto glass, quartz and carbon-coated mica substrates held at room temperature. ...
This work reports a systematic study of the growth of copper oxide thin films by laser evaporatio... more This work reports a systematic study of the growth of copper oxide thin films by laser evaporation from a Cu foil or a Cu sintered powder target in an oxygen atmosphere. The experimental conditions to deposit CuzO and CuO thin films are determined. Particle-free single-phase films are obtained from the foil target. The laser-deposited films have good optical properties. For comparison, DC-sputtered films deposited from the same Cu foil were studied. To obtain the same phase the former method requires higher oxygen pressure during deposition. The microstructure formed in the laser-deposited samples is always polycrystalline with a homogeneous grain size whereas sputtering can form columnar growth.
A new integration method suited for spatially coherent high-power laser beams is demonstrated. Th... more A new integration method suited for spatially coherent high-power laser beams is demonstrated. The integrator system is based on a mirror with two facets, one of which can vibrate under the action of a piezoelectric translator. After reflection in the faceted mirror, the beam intensity distribution is modified to obtain greater uniformity. However, because of the coherence of the reflected beamlets, this distribution is affected by an interference pattern. The active integration consists of a periodic displacement of the moving facet that causes the interference pattern to vibrate, and its contribution to the intensity profile therefore averages out (fringe visibility within a 5% range). The combination of a faceted mirror and a simple imaging system results in an intensity profile with good uniformity over large spot sizes. Both simulated and experimental results are presented, the latter showing that a final uniformity within a 10% range can be achieved and it is limited mainly by diffraction at the edges of the facets.
Ultraviolet (UV) laser pulses are used to irradiate c-Ge and c-Sb both in vacuum and in an oxygen... more Ultraviolet (UV) laser pulses are used to irradiate c-Ge and c-Sb both in vacuum and in an oxygen pressure while a HeNe laser beam is used to record the real time reflectivity (RTR) transients. It will be shown that the removal of the native oxide and therefore surface cleaning is produced when irradiating in vacuum while an oxidation process occurs when irradiating in an oxygen environment. The optical coupling between the growing oxide layer with the bulk material underneath is responsible of the high sensitivity of the RTR measurements to the presence or transformation of small thickness oxide layers at the surface. The RTR transients can be used to optically control pulse-to-pulse the laser energy density in order to induce surface oxidation at a constant rate and to minimize material losses during the oxidation process.
Determination of optical damage cross-sections and volumes surrounding ion bombardment tracks in ... more Determination of optical damage cross-sections and volumes surrounding ion bombardment tracks in GaAs using coherent acoustic phonon spectroscopy J. Appl. Phys. 112, 013514 Microwave-induced nonequilibrium temperature in a suspended carbon nanotube Appl. Phys. Lett. 100, 223112 (2012) Empirical modeling of the cross section of damage formation in ion implanted III-V semiconductors Appl. Phys. Lett. 100, 192108 (2012) Nitrogen-promoted formation of graphite-like aggregations in SiC during neutron irradiation Rapid solidification phenomena have been studied in amorphous germanium films on silicon substrates by means of real time reflectivity measurements performed during irradiation with nanosecond laser pulses. The influence of the thermal response of the film/substrate system has been investigated by comparing the behavior of films with thicknesses in the range of 30-180 nm. Two different solidification scenarios are observed depending on the ratio between film thickness (d) and the thermal diffusion length (l) of amorphous germanium ͑lϷ80 nm for 12 ns laser pulses͒. In the thinner films (dϽl), reamorphization occurs upon solidification. Recalescence is observed in the thicker ones (dуl) when the melt depth induced is above of Ϸ80 nm. Above this threshold, crystalline phases are nucleated upon solidification. The origin of this melt depth threshold is discussed in terms of the heat flow into the substrate, the supercooling prior to solidification, and the need of a minimum amount of initially solidified material.
Pressure-induced series of phase transitions in sodium azide J. Appl. Phys. 113, 033511 (2013) St... more Pressure-induced series of phase transitions in sodium azide J. Appl. Phys. 113, 033511 (2013) Structure and phase transitions in 0.5(Ba0.7Ca0.3TiO3)-0.5(BaZr0.2Ti0.8O3) from −100°C to 150°C Relaxation and crystallization of amorphous germanium films on silicon are induced by nanosecond laser pulses. Real time reflectivity measurements and Raman spectroscopy show that amorphous regrowth occurs upon melting and rapid solidification of the film because the thermal conductivity of the silicon substrate is .high enough to extract the laser energy absorbed by the film in a very efficient way. The amorphous regrown film is in a relaxed state when compared to the as-grown amorphous material. Further pulses induce fast crystallization of the film. An increase of the melting threshold is found upon relaxation and crystallization of the film.
UV-laser-induced oxidation of crystalline Ge (c-Ge) is analyzed by means of real-time optical mea... more UV-laser-induced oxidation of crystalline Ge (c-Ge) is analyzed by means of real-time optical measurements, lrradiations are performed in a controlled oxygen atmosphere with laser fluences above the melting threshold. The meh duration determined from the reflectivity transients depends strongly on the oxygen pressure and on the number of laser pulses. The reflectivity of the material tends to decrease as the number of pulses is increased. The results indicate that the irradiation induces the growth of a surface oxide layer at a non-constant rate. The optical coupling between the oxide layer and the bulk material underneath at the irradiation wavelength explains the results and is found responsible for an enhancement of the oxide growth rate.
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