2007 European Conference on Lasers and Electro-Optics and the International Quantum Electronics Conference, 2007
Summary form only given. The aim of this work is to study the amorphization dynamics upon pulsed ... more Summary form only given. The aim of this work is to study the amorphization dynamics upon pulsed laser irradiation (ns and fs) with highest temporal resolution (ns and fs). The pump laser used was a femtosecond-seeded regeneratively amplified laser system operating at 800 nm central wavelength with a pulse duration that could be switched from 120 fs to 8 ns
2003 Conference on Lasers and Electro-Optics Europe (CLEO/Europe 2003) (IEEE Cat. No.03TH8666), 2003
GeSbTe and AglnSbTe compounds are currently receiving strong interest as suitable materials for o... more GeSbTe and AglnSbTe compounds are currently receiving strong interest as suitable materials for optical data storage devices. We have set out to determine the cycability of samples with maximum optical contrast between phases using shorter pulse durations. It is possible to amorphize and recrystallize both GeSbTe-compositions with laser pulses of a few nanoseconds and that the transformation is accomplished in
We report the appearance of transient Newton rings in dielectrics (sapphire and lead-oxide glass)... more We report the appearance of transient Newton rings in dielectrics (sapphire and lead-oxide glass) during ablation with single fs laser pulses. Employing femtosecond microscopy with 800 nm excitation and 400 nm illumination, we observe a characteristic ring pattern that dynamically changes for increasing delay times between pump and probe pulse. Such transient Newton rings have been previously observed in metals and semiconductors at fluences above the ablation threshold and were related to optical interference of the probe beam reflected at the front surface of the ablating layer and at the interface of the non-ablating substrate. Yet, it had been generally assumed that this phenomenon cannot be (and has not been) observed in dielectrics due to the different ablation mechanism and optical properties of dielectrics. The fact that we are able to observe them has important consequences for the comprehension of the ablation mechanisms in dielectrics and provides a new method for investi...
In this work we report the application of 2 and 3-beam Single Pulse Laser Interference Lithograph... more In this work we report the application of 2 and 3-beam Single Pulse Laser Interference Lithography to thin polymer films of Poly (trimethylene terephthalate) (PTT). By irradiating the sample surface with temporary and spacially overlapped single pulses from two or three coherent beams and changing the angles of incidence, we have accomplished the fabrication of large-area polymer micro and sub-microgratings as well as sub-micrometric cavities arranged in a hexagonal lattice. The characterization of the structures in real space by atomic force microscopy (AFM) and scanning electron microscopy (SEM) has allowed us to determine the formation mechanism of the microgratings to be based on different ablation regimes depending on the local fluence. Moreover, complementary characterization of the sub-micrometric cavities in reciprocal space by grazing incidence small angle x-ray scattering (GISAXS) confirms the existence of large areas where two-dimensional order is present. The experiments...
Langmuir : the ACS journal of surfaces and colloids, Jan 29, 2014
In this work we report the application of two and three-beam single pulse laser interference lith... more In this work we report the application of two and three-beam single pulse laser interference lithography to thin polymer films of poly(trimethylene terephthalate) (PTT). By irradiating the sample surface with temporary and spatially overlapped single pulses from two or three coherent beams and changing the angles of incidence, we have accomplished the fabrication of large-area polymer micro and submicrogratings as well as submicrometric cavities arranged in a hexagonal lattice. The characterization of the structures in real space by atomic force microscopy (AFM) and scanning electron microscopy (SEM) has allowed us to determine the formation mechanism of the microgratings to be based on different ablation regimes depending on the local fluence. Moreover, complementary characterization of the submicrometric cavities in reciprocal space by grazing incidence small-angle X-ray scattering (GISAXS) confirms the existence of large areas where two-dimensional order is present. The experimen...
The properties of structures written inside dielectrics with high repetition rate femtosecond las... more The properties of structures written inside dielectrics with high repetition rate femtosecond lasers are known to depend strongly on the complex interplay of a large number of writing parameters. Recently, ion migration within the laser-excited volume has been identified as a powerful mechanism for changing the local element distribution and producing efficient optical waveguides. In this work it is shown that the transient plasma distribution induced during laser irradiation is a reliable monitor for predicting the final refractive index distribution of the waveguide caused by ion migration. By performing in-situ plasma emission microscopy during the writing process inside a La-phosphate glass it is found that the long axis of the plasma distribution determines the axis of ion migration, being responsible for the local refractive index increase. This observation is also valid when strong positive or negative spherical aberration is induced, greatly deforming the focal volume and inverting the index profile. Even subtle changes in the writing conditions, such as an inversion of the writing direction (quill writing effect), show up in the form of a modified plasma distribution, which manifests as a modified index distribution. Finally, it is shown that the superior control over the waveguide properties employing the slit shaping technique is caused by the more confined plasma distribution produced. The underlying reasons for this unexpected result are discussed in terms of non-linear propagation and heat accumulation.
We have investigated the use of tightly focused, temporally shaped femtosecond (fs)-laser pulses ... more We have investigated the use of tightly focused, temporally shaped femtosecond (fs)-laser pulses for producing nanostructures in two dielectric materials (sapphire and phosphate glass) with different characteristics in their response to pulsed laser radiation. For this purpose, laser pulses shaped by third-order dispersion (TOD) were used to generate temporally asymmetric excitation pulses, leading to the single-step production of subwavelength ablative and subablative surface structures. When compared to previous works on the interaction of tightly focused TOD-shaped pulses with fused silica, we show here that this approach leads to very different nanostructure morphologies, namely, clean nanopits without debris surrounding the crater in sapphire and well-outlined nanobumps and nanovolcanoes in phosphate glass. Although in sapphire the debris-free processing is associated with the much lower viscosity of the melt compared to fused silica, nanobump formation in phosphate glass is caused by material network expansion (swelling) upon resolidification below the ablation threshold. The formation of nanovolcanoes is a consequence of the combined effect of material network expansion and ablation occurring in the periphery and central part of the irradiated region, respectively. It is shown that the induced morphologies can be efficiently controlled by modulating the TOD coefficient of the temporally shaped pulses.
In this Letter, we report on the successful fabrication of low loss, high refractive index contra... more In this Letter, we report on the successful fabrication of low loss, high refractive index contrast waveguides via ion migration upon femtosecond laser writing in phosphate glass. Waveguides were produced in two different phosphate glass compositions with high and low La 2 O 3 content. In the La-rich glass, a large refractive index increase in the guiding region was observed due to the incoming migration of La accompanied by the out-diffusion of K. The much smaller refractive index change in the La-less glass is caused by rearrangements of the glass structure. These results confirm the feasibility of adapting the glass composition for enabling the laser writing of high refractive index contrast structures via spatially selective modification of the glass composition.
ABSTRACT Phase transition pathways of matter upon ablation with ultrashort laser pulses have been... more ABSTRACT Phase transition pathways of matter upon ablation with ultrashort laser pulses have been considered to be understood long-since for metals and semiconductors. We provide evidence that also certain dielectrics follow the same pathway, even at high pulse energies triggering optical breakdown. Employing femtosecond microscopy, we observe a characteristic ring pattern within the ablating region that dynamically changes for increasing time delays between pump and probe pulse. These transient Newton rings are related to optical interference of the probe beam reflected at the front surface of the ablating layer with the reflection at the interface of the non-ablating substrate. Analysis of the ring structure shows that the ablation mechanism is initiated by a rarefaction wave leading within a few tens of picoseconds to the formation of a transparent thin shell of reduced den- sity and refractive index, featuring optically sharp interfaces. The shell expands and eventually detaches from the solid material at delays of the order of 100 ps.
Ultrafast laser processing applications need fast approaches to assess the nonlinear propagation ... more Ultrafast laser processing applications need fast approaches to assess the nonlinear propagation of the laser beam in order to predict the optimal range of processing parameters in a wide variety of cases. We develop here a method based on the simple monitoring of the nonlinear beam shaping against numerical prediction. The numerical code solves the nonlinear Schrödinger equation with nonlinear absorption under simplified conditions by employing a state-of-the art computationally efficient approach. By comparing with experimental results we can rapidly estimate the nonlinear refractive index and nonlinear absorption coefficients of the material. The validity of this approach has been tested in a variety of experiments where nonlinearities play a key role, like spatial soliton shaping or fs-laser waveguide writing. The approach provides excellent results for propagated power densities for which free carrier generation effects can be neglected. Above such a threshold, the peculiarities of the nonlinear propagation of elliptical beams enable acquiring an instantaneous picture of the deposition of energy inside the material realistic enough to estimate the effective nonlinear refractive index and nonlinear absorption coefficients that can be used for predicting the spatial distribution of energy deposition inside the material and controlling the beam in the writing process.
2007 European Conference on Lasers and Electro-Optics and the International Quantum Electronics Conference, 2007
Summary form only given. The aim of this work is to study the amorphization dynamics upon pulsed ... more Summary form only given. The aim of this work is to study the amorphization dynamics upon pulsed laser irradiation (ns and fs) with highest temporal resolution (ns and fs). The pump laser used was a femtosecond-seeded regeneratively amplified laser system operating at 800 nm central wavelength with a pulse duration that could be switched from 120 fs to 8 ns
2003 Conference on Lasers and Electro-Optics Europe (CLEO/Europe 2003) (IEEE Cat. No.03TH8666), 2003
GeSbTe and AglnSbTe compounds are currently receiving strong interest as suitable materials for o... more GeSbTe and AglnSbTe compounds are currently receiving strong interest as suitable materials for optical data storage devices. We have set out to determine the cycability of samples with maximum optical contrast between phases using shorter pulse durations. It is possible to amorphize and recrystallize both GeSbTe-compositions with laser pulses of a few nanoseconds and that the transformation is accomplished in
We report the appearance of transient Newton rings in dielectrics (sapphire and lead-oxide glass)... more We report the appearance of transient Newton rings in dielectrics (sapphire and lead-oxide glass) during ablation with single fs laser pulses. Employing femtosecond microscopy with 800 nm excitation and 400 nm illumination, we observe a characteristic ring pattern that dynamically changes for increasing delay times between pump and probe pulse. Such transient Newton rings have been previously observed in metals and semiconductors at fluences above the ablation threshold and were related to optical interference of the probe beam reflected at the front surface of the ablating layer and at the interface of the non-ablating substrate. Yet, it had been generally assumed that this phenomenon cannot be (and has not been) observed in dielectrics due to the different ablation mechanism and optical properties of dielectrics. The fact that we are able to observe them has important consequences for the comprehension of the ablation mechanisms in dielectrics and provides a new method for investi...
In this work we report the application of 2 and 3-beam Single Pulse Laser Interference Lithograph... more In this work we report the application of 2 and 3-beam Single Pulse Laser Interference Lithography to thin polymer films of Poly (trimethylene terephthalate) (PTT). By irradiating the sample surface with temporary and spacially overlapped single pulses from two or three coherent beams and changing the angles of incidence, we have accomplished the fabrication of large-area polymer micro and sub-microgratings as well as sub-micrometric cavities arranged in a hexagonal lattice. The characterization of the structures in real space by atomic force microscopy (AFM) and scanning electron microscopy (SEM) has allowed us to determine the formation mechanism of the microgratings to be based on different ablation regimes depending on the local fluence. Moreover, complementary characterization of the sub-micrometric cavities in reciprocal space by grazing incidence small angle x-ray scattering (GISAXS) confirms the existence of large areas where two-dimensional order is present. The experiments...
Langmuir : the ACS journal of surfaces and colloids, Jan 29, 2014
In this work we report the application of two and three-beam single pulse laser interference lith... more In this work we report the application of two and three-beam single pulse laser interference lithography to thin polymer films of poly(trimethylene terephthalate) (PTT). By irradiating the sample surface with temporary and spatially overlapped single pulses from two or three coherent beams and changing the angles of incidence, we have accomplished the fabrication of large-area polymer micro and submicrogratings as well as submicrometric cavities arranged in a hexagonal lattice. The characterization of the structures in real space by atomic force microscopy (AFM) and scanning electron microscopy (SEM) has allowed us to determine the formation mechanism of the microgratings to be based on different ablation regimes depending on the local fluence. Moreover, complementary characterization of the submicrometric cavities in reciprocal space by grazing incidence small-angle X-ray scattering (GISAXS) confirms the existence of large areas where two-dimensional order is present. The experimen...
The properties of structures written inside dielectrics with high repetition rate femtosecond las... more The properties of structures written inside dielectrics with high repetition rate femtosecond lasers are known to depend strongly on the complex interplay of a large number of writing parameters. Recently, ion migration within the laser-excited volume has been identified as a powerful mechanism for changing the local element distribution and producing efficient optical waveguides. In this work it is shown that the transient plasma distribution induced during laser irradiation is a reliable monitor for predicting the final refractive index distribution of the waveguide caused by ion migration. By performing in-situ plasma emission microscopy during the writing process inside a La-phosphate glass it is found that the long axis of the plasma distribution determines the axis of ion migration, being responsible for the local refractive index increase. This observation is also valid when strong positive or negative spherical aberration is induced, greatly deforming the focal volume and inverting the index profile. Even subtle changes in the writing conditions, such as an inversion of the writing direction (quill writing effect), show up in the form of a modified plasma distribution, which manifests as a modified index distribution. Finally, it is shown that the superior control over the waveguide properties employing the slit shaping technique is caused by the more confined plasma distribution produced. The underlying reasons for this unexpected result are discussed in terms of non-linear propagation and heat accumulation.
We have investigated the use of tightly focused, temporally shaped femtosecond (fs)-laser pulses ... more We have investigated the use of tightly focused, temporally shaped femtosecond (fs)-laser pulses for producing nanostructures in two dielectric materials (sapphire and phosphate glass) with different characteristics in their response to pulsed laser radiation. For this purpose, laser pulses shaped by third-order dispersion (TOD) were used to generate temporally asymmetric excitation pulses, leading to the single-step production of subwavelength ablative and subablative surface structures. When compared to previous works on the interaction of tightly focused TOD-shaped pulses with fused silica, we show here that this approach leads to very different nanostructure morphologies, namely, clean nanopits without debris surrounding the crater in sapphire and well-outlined nanobumps and nanovolcanoes in phosphate glass. Although in sapphire the debris-free processing is associated with the much lower viscosity of the melt compared to fused silica, nanobump formation in phosphate glass is caused by material network expansion (swelling) upon resolidification below the ablation threshold. The formation of nanovolcanoes is a consequence of the combined effect of material network expansion and ablation occurring in the periphery and central part of the irradiated region, respectively. It is shown that the induced morphologies can be efficiently controlled by modulating the TOD coefficient of the temporally shaped pulses.
In this Letter, we report on the successful fabrication of low loss, high refractive index contra... more In this Letter, we report on the successful fabrication of low loss, high refractive index contrast waveguides via ion migration upon femtosecond laser writing in phosphate glass. Waveguides were produced in two different phosphate glass compositions with high and low La 2 O 3 content. In the La-rich glass, a large refractive index increase in the guiding region was observed due to the incoming migration of La accompanied by the out-diffusion of K. The much smaller refractive index change in the La-less glass is caused by rearrangements of the glass structure. These results confirm the feasibility of adapting the glass composition for enabling the laser writing of high refractive index contrast structures via spatially selective modification of the glass composition.
ABSTRACT Phase transition pathways of matter upon ablation with ultrashort laser pulses have been... more ABSTRACT Phase transition pathways of matter upon ablation with ultrashort laser pulses have been considered to be understood long-since for metals and semiconductors. We provide evidence that also certain dielectrics follow the same pathway, even at high pulse energies triggering optical breakdown. Employing femtosecond microscopy, we observe a characteristic ring pattern within the ablating region that dynamically changes for increasing time delays between pump and probe pulse. These transient Newton rings are related to optical interference of the probe beam reflected at the front surface of the ablating layer with the reflection at the interface of the non-ablating substrate. Analysis of the ring structure shows that the ablation mechanism is initiated by a rarefaction wave leading within a few tens of picoseconds to the formation of a transparent thin shell of reduced den- sity and refractive index, featuring optically sharp interfaces. The shell expands and eventually detaches from the solid material at delays of the order of 100 ps.
Ultrafast laser processing applications need fast approaches to assess the nonlinear propagation ... more Ultrafast laser processing applications need fast approaches to assess the nonlinear propagation of the laser beam in order to predict the optimal range of processing parameters in a wide variety of cases. We develop here a method based on the simple monitoring of the nonlinear beam shaping against numerical prediction. The numerical code solves the nonlinear Schrödinger equation with nonlinear absorption under simplified conditions by employing a state-of-the art computationally efficient approach. By comparing with experimental results we can rapidly estimate the nonlinear refractive index and nonlinear absorption coefficients of the material. The validity of this approach has been tested in a variety of experiments where nonlinearities play a key role, like spatial soliton shaping or fs-laser waveguide writing. The approach provides excellent results for propagated power densities for which free carrier generation effects can be neglected. Above such a threshold, the peculiarities of the nonlinear propagation of elliptical beams enable acquiring an instantaneous picture of the deposition of energy inside the material realistic enough to estimate the effective nonlinear refractive index and nonlinear absorption coefficients that can be used for predicting the spatial distribution of energy deposition inside the material and controlling the beam in the writing process.
Uploads
Papers by Jan Siegel