2017 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC), 2017
Intense, ultra-broadband terahertz (THz) pulses can drive major advances in ultrafast dynamics, n... more Intense, ultra-broadband terahertz (THz) pulses can drive major advances in ultrafast dynamics, nonlinear THz optics, and bio-material imaging [1,2]. Single and two-color filamentation of ultrashort laser pulses in gases have been extensively used for the generation of such pulses [3,4]. However, filament formation in gases is hindered by the need of high laser pulse energies, motivating the exploration of alternate generation mechanisms [5]. On the other hand, filamentation can be achieved more easily in alternative target materials such as transparent solids and liquids [6,7]. Though, THz emission through either single or two-color filamentation in such materials, has not been investigated yet. Here we demonstrate, for the first time, strong THz emission through single and two-color filamentation in liquids and in fused silica (SiO2) respectively and a significant THz field enhancement when using high repetition rate laser sources.
2017 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC), 2017
Intense, ultra-broadband terahertz (THz) pulses can drive major advances in ultrafast dynamics, n... more Intense, ultra-broadband terahertz (THz) pulses can drive major advances in ultrafast dynamics, nonlinear THz optics, and bio-material imaging [1,2]. Single and two-color filamentation of ultrashort laser pulses in gases have been extensively used for the generation of such pulses [3,4]. However, filament formation in gases is hindered by the need of high laser pulse energies, motivating the exploration of alternate generation mechanisms [5]. On the other hand, filamentation can be achieved more easily in alternative target materials such as transparent solids and liquids [6,7]. Though, THz emission through either single or two-color filamentation in such materials, has not been investigated yet. Here we demonstrate, for the first time, strong THz emission through single and two-color filamentation in liquids and in fused silica (SiO2) respectively and a significant THz field enhancement when using high repetition rate laser sources.
2020 IEEE International Conference on Plasma Science (ICOPS), 2020
Intense femtosecond lasers, focused on a solid surface, can accelerate ultrashort pulses of elect... more Intense femtosecond lasers, focused on a solid surface, can accelerate ultrashort pulses of electrons to near-light speeds, launching megaampere currents into the solid material behind. Understanding the transport of these relativistic electrons through solids is central to many areas in laser-driven plasmas and their translational research, ranging from laser-driven fusion to the production of micro-accelerators for industrial and medical applications. In particular, the “transit time” of these relativistic electrons through the material - i.e. the duration of their lifetime inside the solid - is an important parameter that determines the efficiency of energy transfer to the lattice. For example this is critical for determining the efficacy of laser-driven particle sources for therapeutic applications. However, due to the inaccessibility of the side-products from this interaction, very little is known about the time the electrons spend inside a solid and no reliable methods exist to delineate this information. We have recently shown that “real-time” measurements of the transition of relativistic electrons through a solid dielectric can be obtained by monitoring their Cherenkov emission through an ultrafast-laser-driven Kerr-gate. The Kerr-gate provides an ultrafast shutter-speed camera to freeze-frame the electron motion inside the material, yielding invaluable information about their dynamics and lifetime inside solids1.
2020 IEEE International Conference on Plasma Science (ICOPS), 2020
Intense femtosecond lasers, focused on a solid surface, can accelerate ultrashort pulses of elect... more Intense femtosecond lasers, focused on a solid surface, can accelerate ultrashort pulses of electrons to near-light speeds, launching megaampere currents into the solid material behind. Understanding the transport of these relativistic electrons through solids is central to many areas in laser-driven plasmas and their translational research, ranging from laser-driven fusion to the production of micro-accelerators for industrial and medical applications. In particular, the “transit time” of these relativistic electrons through the material - i.e. the duration of their lifetime inside the solid - is an important parameter that determines the efficiency of energy transfer to the lattice. For example this is critical for determining the efficacy of laser-driven particle sources for therapeutic applications. However, due to the inaccessibility of the side-products from this interaction, very little is known about the time the electrons spend inside a solid and no reliable methods exist to delineate this information. We have recently shown that “real-time” measurements of the transition of relativistic electrons through a solid dielectric can be obtained by monitoring their Cherenkov emission through an ultrafast-laser-driven Kerr-gate. The Kerr-gate provides an ultrafast shutter-speed camera to freeze-frame the electron motion inside the material, yielding invaluable information about their dynamics and lifetime inside solids1.
CERTIFICATION OF COMPREHENSIVE EXAMS SHEET Today, Monday July 27 th 2020, we have administered a ... more CERTIFICATION OF COMPREHENSIVE EXAMS SHEET Today, Monday July 27 th 2020, we have administered a comprehensive test examination to: 1. Name Lamin Jassey 2. Student Number 11160820000122 3. Department Accounting 4. Thesis Title Factors determining employee fraud: the role of ethical corporate culture as mediating variable. After careful observation and attention to appearance and capabilities relevant for comprehensive examination process, it was decided that the above named student passed the comprehensive examination as one of the requirements to obtain a Bachelor of Economics in the faculty of Economics and Business Syarif
CERTIFICATION OF COMPREHENSIVE EXAMS SHEET Today, Monday July 27 th 2020, we have administered a ... more CERTIFICATION OF COMPREHENSIVE EXAMS SHEET Today, Monday July 27 th 2020, we have administered a comprehensive test examination to: 1. Name Lamin Jassey 2. Student Number 11160820000122 3. Department Accounting 4. Thesis Title Factors determining employee fraud: the role of ethical corporate culture as mediating variable. After careful observation and attention to appearance and capabilities relevant for comprehensive examination process, it was decided that the above named student passed the comprehensive examination as one of the requirements to obtain a Bachelor of Economics in the faculty of Economics and Business Syarif
Study of the formation and evolution of large scale, ordered structures is an enduring theme in s... more Study of the formation and evolution of large scale, ordered structures is an enduring theme in science. Generation, evolution and control of large sized magnetic domains are challenging tasks, given the complex nature of competing interactions in a magnetic system. Here, we demonstrate large scale non-coplanar ordering of spins, driven by picosecond, megagauss magnetic pulses derived from a high intensity, femtosecond laser. Our studies on a specially designed yttrium iron garnet (YIG) dielectric/metal film sandwich target, show the creation of complex, large, concentric, elliptical shaped magnetic domains which resemble the layered shell structure of an onion. The largest shell has a major axis over hundreds of micrometers, in stark contrast to sub micrometer scale polygonal, striped or bubble shaped magnetic domains in magnetic materials, or large dumbbell shaped domains produced in magnetic films irradiated with accelerator based relativistic electron beams. Micromagnetic simula...
Study of the formation and evolution of large scale, ordered structures is an enduring theme in s... more Study of the formation and evolution of large scale, ordered structures is an enduring theme in science. Generation, evolution and control of large sized magnetic domains are challenging tasks, given the complex nature of competing interactions in a magnetic system. Here, we demonstrate large scale non-coplanar ordering of spins, driven by picosecond, megagauss magnetic pulses derived from a high intensity, femtosecond laser. Our studies on a specially designed yttrium iron garnet (YIG) dielectric/metal film sandwich target, show the creation of complex, large, concentric, elliptical shaped magnetic domains which resemble the layered shell structure of an onion. The largest shell has a major axis over hundreds of micrometers, in stark contrast to sub micrometer scale polygonal, striped or bubble shaped magnetic domains in magnetic materials, or large dumbbell shaped domains produced in magnetic films irradiated with accelerator based relativistic electron beams. Micromagnetic simula...
pulses generate relativistic electron pulses,important for many applications[?]. In this paper, w... more pulses generate relativistic electron pulses,important for many applications[?]. In this paper, we present a femtosecond time-resolved and micrometer space resolved giant magnetic fields generated by 10 19 W cm −2 , 800 nm, 30 fs, high intensity contrast laser pulses in using pump-probe Cotton Mouton polarimetry[?]. The space and time resolved maps of the magnetic fields at the front and rear of targets reveal turbulence in the magnetic fields [?]. We also present data from shadowgraphy and Cherenkov emission along with model calculations to build up a picture of the transport process.
pulses generate relativistic electron pulses,important for many applications[?]. In this paper, w... more pulses generate relativistic electron pulses,important for many applications[?]. In this paper, we present a femtosecond time-resolved and micrometer space resolved giant magnetic fields generated by 10 19 W cm −2 , 800 nm, 30 fs, high intensity contrast laser pulses in using pump-probe Cotton Mouton polarimetry[?]. The space and time resolved maps of the magnetic fields at the front and rear of targets reveal turbulence in the magnetic fields [?]. We also present data from shadowgraphy and Cherenkov emission along with model calculations to build up a picture of the transport process.
The basic understanding of high-intensity femtosecond laser absorption in a solid is crucial for ... more The basic understanding of high-intensity femtosecond laser absorption in a solid is crucial for high-energy-density science. This multidimensional problem has many variables like laser parameters, solid target material, and geometry of the excitation. This is important for a basic understanding of intense laser-matter interaction as well for applications such as `plasma mirror'. Here, we have experimentally observed high-intensity, high-contrast femtosecond laser absorption by an optically polished fused silica target at near-relativistic laser intensities ($\sim$10$^{18}$ W/cm$^2$). The laser absorption as a function of angle of incidence and incident energy is investigated for both $p$- and $s$-polarized pulses in detail, providing a strong indication of the presence of collisionless processes. At an optimum angle of incidence, almost as large as 80% of the laser ($p$-polarized) energy gets absorbed in the target. Such a high percentage of absorption at near-relativistic inte...
The basic understanding of high-intensity femtosecond laser absorption in a solid is crucial for ... more The basic understanding of high-intensity femtosecond laser absorption in a solid is crucial for high-energy-density science. This multidimensional problem has many variables like laser parameters, solid target material, and geometry of the excitation. This is important for a basic understanding of intense laser-matter interaction as well for applications such as `plasma mirror'. Here, we have experimentally observed high-intensity, high-contrast femtosecond laser absorption by an optically polished fused silica target at near-relativistic laser intensities ($\sim$10$^{18}$ W/cm$^2$). The laser absorption as a function of angle of incidence and incident energy is investigated for both $p$- and $s$-polarized pulses in detail, providing a strong indication of the presence of collisionless processes. At an optimum angle of incidence, almost as large as 80% of the laser ($p$-polarized) energy gets absorbed in the target. Such a high percentage of absorption at near-relativistic inte...
We demonstrate an interesting modulation of fast electron temperature and yield as a function of ... more We demonstrate an interesting modulation of fast electron temperature and yield as a function of the thickness of nanocrystalline coating on a dielectric target, in femtosecond, intense laser interaction with a solid target. We measure the fast electron energy spectrum for fused silica targets coated with ultrathin, nanocrystalline Cu films with thickness ranging from 30 to 100 nm and compare them with those from a planar, uncoated polished silica surface. The fast electron temperature exhibits an unexpected dependence on the film thickness, peaking at 30 and 45 nm and falling off for films with higher thicknesses. During these experiments, the size of the Cu nanograins was kept constant and only the film thickness was varied. We find that—in the low thickness limit—the target thickness acts as an additional length scale, independent of the surface topography, and needs to be separately optimized for maximizing the generation of fast electrons from high-intensity, ultrashort laser–matter interaction.
We demonstrate an interesting modulation of fast electron temperature and yield as a function of ... more We demonstrate an interesting modulation of fast electron temperature and yield as a function of the thickness of nanocrystalline coating on a dielectric target, in femtosecond, intense laser interaction with a solid target. We measure the fast electron energy spectrum for fused silica targets coated with ultrathin, nanocrystalline Cu films with thickness ranging from 30 to 100 nm and compare them with those from a planar, uncoated polished silica surface. The fast electron temperature exhibits an unexpected dependence on the film thickness, peaking at 30 and 45 nm and falling off for films with higher thicknesses. During these experiments, the size of the Cu nanograins was kept constant and only the film thickness was varied. We find that—in the low thickness limit—the target thickness acts as an additional length scale, independent of the surface topography, and needs to be separately optimized for maximizing the generation of fast electrons from high-intensity, ultrashort laser–matter interaction.
We present ultrafast pump-probe reflectivity and Doppler spectrometry of a silicon target at rela... more We present ultrafast pump-probe reflectivity and Doppler spectrometry of a silicon target at relativistic laser intensity. We observe an unexpected rise in reflectivity to a peak approximately $9 ps after the main pulse interaction with the target. This occurs after the reflectivity has fallen off from the initially high "plasma-mirror" phase. Simultaneously measured time-dependent Doppler shift data show an increase in the blue shift at the same time. Numerical simulations show that the aforementioned trends in the experimental measurements correspond to a strong shock wave propagating back toward the laser. The relativistic laser-plasma interaction indirectly heats the cool-dense (n e ! 10 23 cm À3 and T e $ 10 eV) target material adjacent to the corona, by hot electron induced return current heating, raising its temperature to around 150 eV and causing it to explode violently. The increase in reflectivity is caused by the transient steepening of the plasma density gradient at the probe critical surface due to this explosive behavior.
We present ultrafast pump-probe reflectivity and Doppler spectrometry of a silicon target at rela... more We present ultrafast pump-probe reflectivity and Doppler spectrometry of a silicon target at relativistic laser intensity. We observe an unexpected rise in reflectivity to a peak approximately $9 ps after the main pulse interaction with the target. This occurs after the reflectivity has fallen off from the initially high "plasma-mirror" phase. Simultaneously measured time-dependent Doppler shift data show an increase in the blue shift at the same time. Numerical simulations show that the aforementioned trends in the experimental measurements correspond to a strong shock wave propagating back toward the laser. The relativistic laser-plasma interaction indirectly heats the cool-dense (n e ! 10 23 cm À3 and T e $ 10 eV) target material adjacent to the corona, by hot electron induced return current heating, raising its temperature to around 150 eV and causing it to explode violently. The increase in reflectivity is caused by the transient steepening of the plasma density gradient at the probe critical surface due to this explosive behavior.
Remote manipulation (triggering and guiding) of lightning in atmospheric conditions of thundersto... more Remote manipulation (triggering and guiding) of lightning in atmospheric conditions of thunderstorms has been the subject of intense scientific research for decades. High power, ultrashort-pulse lasers are considered attractive in generating plasma channels in air that could serve as conductors/diverters for lightning. However, two fundamental obstacles, namely the limited length and lifetime of such plasma channels prevented their realization to this date. In this paper, we report decisive experimental results of our multi-element broken wire concept that extends the generated plasma channels to the required tens of meters range. We obtain 13-meter-long plasma wire, limited only by our current experimental setup, with plasma conditions that could be sufficient for the leader initiation. This advance, coupled with our demonstrated method of laser heating for long time sustenance of the plasma channel, is a major, significant step towards controlling lightning.
Remote manipulation (triggering and guiding) of lightning in atmospheric conditions of thundersto... more Remote manipulation (triggering and guiding) of lightning in atmospheric conditions of thunderstorms has been the subject of intense scientific research for decades. High power, ultrashort-pulse lasers are considered attractive in generating plasma channels in air that could serve as conductors/diverters for lightning. However, two fundamental obstacles, namely the limited length and lifetime of such plasma channels prevented their realization to this date. In this paper, we report decisive experimental results of our multi-element broken wire concept that extends the generated plasma channels to the required tens of meters range. We obtain 13-meter-long plasma wire, limited only by our current experimental setup, with plasma conditions that could be sufficient for the leader initiation. This advance, coupled with our demonstrated method of laser heating for long time sustenance of the plasma channel, is a major, significant step towards controlling lightning.
2017 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC), 2017
Intense, ultra-broadband terahertz (THz) pulses can drive major advances in ultrafast dynamics, n... more Intense, ultra-broadband terahertz (THz) pulses can drive major advances in ultrafast dynamics, nonlinear THz optics, and bio-material imaging [1,2]. Single and two-color filamentation of ultrashort laser pulses in gases have been extensively used for the generation of such pulses [3,4]. However, filament formation in gases is hindered by the need of high laser pulse energies, motivating the exploration of alternate generation mechanisms [5]. On the other hand, filamentation can be achieved more easily in alternative target materials such as transparent solids and liquids [6,7]. Though, THz emission through either single or two-color filamentation in such materials, has not been investigated yet. Here we demonstrate, for the first time, strong THz emission through single and two-color filamentation in liquids and in fused silica (SiO2) respectively and a significant THz field enhancement when using high repetition rate laser sources.
2017 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC), 2017
Intense, ultra-broadband terahertz (THz) pulses can drive major advances in ultrafast dynamics, n... more Intense, ultra-broadband terahertz (THz) pulses can drive major advances in ultrafast dynamics, nonlinear THz optics, and bio-material imaging [1,2]. Single and two-color filamentation of ultrashort laser pulses in gases have been extensively used for the generation of such pulses [3,4]. However, filament formation in gases is hindered by the need of high laser pulse energies, motivating the exploration of alternate generation mechanisms [5]. On the other hand, filamentation can be achieved more easily in alternative target materials such as transparent solids and liquids [6,7]. Though, THz emission through either single or two-color filamentation in such materials, has not been investigated yet. Here we demonstrate, for the first time, strong THz emission through single and two-color filamentation in liquids and in fused silica (SiO2) respectively and a significant THz field enhancement when using high repetition rate laser sources.
2020 IEEE International Conference on Plasma Science (ICOPS), 2020
Intense femtosecond lasers, focused on a solid surface, can accelerate ultrashort pulses of elect... more Intense femtosecond lasers, focused on a solid surface, can accelerate ultrashort pulses of electrons to near-light speeds, launching megaampere currents into the solid material behind. Understanding the transport of these relativistic electrons through solids is central to many areas in laser-driven plasmas and their translational research, ranging from laser-driven fusion to the production of micro-accelerators for industrial and medical applications. In particular, the “transit time” of these relativistic electrons through the material - i.e. the duration of their lifetime inside the solid - is an important parameter that determines the efficiency of energy transfer to the lattice. For example this is critical for determining the efficacy of laser-driven particle sources for therapeutic applications. However, due to the inaccessibility of the side-products from this interaction, very little is known about the time the electrons spend inside a solid and no reliable methods exist to delineate this information. We have recently shown that “real-time” measurements of the transition of relativistic electrons through a solid dielectric can be obtained by monitoring their Cherenkov emission through an ultrafast-laser-driven Kerr-gate. The Kerr-gate provides an ultrafast shutter-speed camera to freeze-frame the electron motion inside the material, yielding invaluable information about their dynamics and lifetime inside solids1.
2020 IEEE International Conference on Plasma Science (ICOPS), 2020
Intense femtosecond lasers, focused on a solid surface, can accelerate ultrashort pulses of elect... more Intense femtosecond lasers, focused on a solid surface, can accelerate ultrashort pulses of electrons to near-light speeds, launching megaampere currents into the solid material behind. Understanding the transport of these relativistic electrons through solids is central to many areas in laser-driven plasmas and their translational research, ranging from laser-driven fusion to the production of micro-accelerators for industrial and medical applications. In particular, the “transit time” of these relativistic electrons through the material - i.e. the duration of their lifetime inside the solid - is an important parameter that determines the efficiency of energy transfer to the lattice. For example this is critical for determining the efficacy of laser-driven particle sources for therapeutic applications. However, due to the inaccessibility of the side-products from this interaction, very little is known about the time the electrons spend inside a solid and no reliable methods exist to delineate this information. We have recently shown that “real-time” measurements of the transition of relativistic electrons through a solid dielectric can be obtained by monitoring their Cherenkov emission through an ultrafast-laser-driven Kerr-gate. The Kerr-gate provides an ultrafast shutter-speed camera to freeze-frame the electron motion inside the material, yielding invaluable information about their dynamics and lifetime inside solids1.
CERTIFICATION OF COMPREHENSIVE EXAMS SHEET Today, Monday July 27 th 2020, we have administered a ... more CERTIFICATION OF COMPREHENSIVE EXAMS SHEET Today, Monday July 27 th 2020, we have administered a comprehensive test examination to: 1. Name Lamin Jassey 2. Student Number 11160820000122 3. Department Accounting 4. Thesis Title Factors determining employee fraud: the role of ethical corporate culture as mediating variable. After careful observation and attention to appearance and capabilities relevant for comprehensive examination process, it was decided that the above named student passed the comprehensive examination as one of the requirements to obtain a Bachelor of Economics in the faculty of Economics and Business Syarif
CERTIFICATION OF COMPREHENSIVE EXAMS SHEET Today, Monday July 27 th 2020, we have administered a ... more CERTIFICATION OF COMPREHENSIVE EXAMS SHEET Today, Monday July 27 th 2020, we have administered a comprehensive test examination to: 1. Name Lamin Jassey 2. Student Number 11160820000122 3. Department Accounting 4. Thesis Title Factors determining employee fraud: the role of ethical corporate culture as mediating variable. After careful observation and attention to appearance and capabilities relevant for comprehensive examination process, it was decided that the above named student passed the comprehensive examination as one of the requirements to obtain a Bachelor of Economics in the faculty of Economics and Business Syarif
Study of the formation and evolution of large scale, ordered structures is an enduring theme in s... more Study of the formation and evolution of large scale, ordered structures is an enduring theme in science. Generation, evolution and control of large sized magnetic domains are challenging tasks, given the complex nature of competing interactions in a magnetic system. Here, we demonstrate large scale non-coplanar ordering of spins, driven by picosecond, megagauss magnetic pulses derived from a high intensity, femtosecond laser. Our studies on a specially designed yttrium iron garnet (YIG) dielectric/metal film sandwich target, show the creation of complex, large, concentric, elliptical shaped magnetic domains which resemble the layered shell structure of an onion. The largest shell has a major axis over hundreds of micrometers, in stark contrast to sub micrometer scale polygonal, striped or bubble shaped magnetic domains in magnetic materials, or large dumbbell shaped domains produced in magnetic films irradiated with accelerator based relativistic electron beams. Micromagnetic simula...
Study of the formation and evolution of large scale, ordered structures is an enduring theme in s... more Study of the formation and evolution of large scale, ordered structures is an enduring theme in science. Generation, evolution and control of large sized magnetic domains are challenging tasks, given the complex nature of competing interactions in a magnetic system. Here, we demonstrate large scale non-coplanar ordering of spins, driven by picosecond, megagauss magnetic pulses derived from a high intensity, femtosecond laser. Our studies on a specially designed yttrium iron garnet (YIG) dielectric/metal film sandwich target, show the creation of complex, large, concentric, elliptical shaped magnetic domains which resemble the layered shell structure of an onion. The largest shell has a major axis over hundreds of micrometers, in stark contrast to sub micrometer scale polygonal, striped or bubble shaped magnetic domains in magnetic materials, or large dumbbell shaped domains produced in magnetic films irradiated with accelerator based relativistic electron beams. Micromagnetic simula...
pulses generate relativistic electron pulses,important for many applications[?]. In this paper, w... more pulses generate relativistic electron pulses,important for many applications[?]. In this paper, we present a femtosecond time-resolved and micrometer space resolved giant magnetic fields generated by 10 19 W cm −2 , 800 nm, 30 fs, high intensity contrast laser pulses in using pump-probe Cotton Mouton polarimetry[?]. The space and time resolved maps of the magnetic fields at the front and rear of targets reveal turbulence in the magnetic fields [?]. We also present data from shadowgraphy and Cherenkov emission along with model calculations to build up a picture of the transport process.
pulses generate relativistic electron pulses,important for many applications[?]. In this paper, w... more pulses generate relativistic electron pulses,important for many applications[?]. In this paper, we present a femtosecond time-resolved and micrometer space resolved giant magnetic fields generated by 10 19 W cm −2 , 800 nm, 30 fs, high intensity contrast laser pulses in using pump-probe Cotton Mouton polarimetry[?]. The space and time resolved maps of the magnetic fields at the front and rear of targets reveal turbulence in the magnetic fields [?]. We also present data from shadowgraphy and Cherenkov emission along with model calculations to build up a picture of the transport process.
The basic understanding of high-intensity femtosecond laser absorption in a solid is crucial for ... more The basic understanding of high-intensity femtosecond laser absorption in a solid is crucial for high-energy-density science. This multidimensional problem has many variables like laser parameters, solid target material, and geometry of the excitation. This is important for a basic understanding of intense laser-matter interaction as well for applications such as `plasma mirror'. Here, we have experimentally observed high-intensity, high-contrast femtosecond laser absorption by an optically polished fused silica target at near-relativistic laser intensities ($\sim$10$^{18}$ W/cm$^2$). The laser absorption as a function of angle of incidence and incident energy is investigated for both $p$- and $s$-polarized pulses in detail, providing a strong indication of the presence of collisionless processes. At an optimum angle of incidence, almost as large as 80% of the laser ($p$-polarized) energy gets absorbed in the target. Such a high percentage of absorption at near-relativistic inte...
The basic understanding of high-intensity femtosecond laser absorption in a solid is crucial for ... more The basic understanding of high-intensity femtosecond laser absorption in a solid is crucial for high-energy-density science. This multidimensional problem has many variables like laser parameters, solid target material, and geometry of the excitation. This is important for a basic understanding of intense laser-matter interaction as well for applications such as `plasma mirror'. Here, we have experimentally observed high-intensity, high-contrast femtosecond laser absorption by an optically polished fused silica target at near-relativistic laser intensities ($\sim$10$^{18}$ W/cm$^2$). The laser absorption as a function of angle of incidence and incident energy is investigated for both $p$- and $s$-polarized pulses in detail, providing a strong indication of the presence of collisionless processes. At an optimum angle of incidence, almost as large as 80% of the laser ($p$-polarized) energy gets absorbed in the target. Such a high percentage of absorption at near-relativistic inte...
We demonstrate an interesting modulation of fast electron temperature and yield as a function of ... more We demonstrate an interesting modulation of fast electron temperature and yield as a function of the thickness of nanocrystalline coating on a dielectric target, in femtosecond, intense laser interaction with a solid target. We measure the fast electron energy spectrum for fused silica targets coated with ultrathin, nanocrystalline Cu films with thickness ranging from 30 to 100 nm and compare them with those from a planar, uncoated polished silica surface. The fast electron temperature exhibits an unexpected dependence on the film thickness, peaking at 30 and 45 nm and falling off for films with higher thicknesses. During these experiments, the size of the Cu nanograins was kept constant and only the film thickness was varied. We find that—in the low thickness limit—the target thickness acts as an additional length scale, independent of the surface topography, and needs to be separately optimized for maximizing the generation of fast electrons from high-intensity, ultrashort laser–matter interaction.
We demonstrate an interesting modulation of fast electron temperature and yield as a function of ... more We demonstrate an interesting modulation of fast electron temperature and yield as a function of the thickness of nanocrystalline coating on a dielectric target, in femtosecond, intense laser interaction with a solid target. We measure the fast electron energy spectrum for fused silica targets coated with ultrathin, nanocrystalline Cu films with thickness ranging from 30 to 100 nm and compare them with those from a planar, uncoated polished silica surface. The fast electron temperature exhibits an unexpected dependence on the film thickness, peaking at 30 and 45 nm and falling off for films with higher thicknesses. During these experiments, the size of the Cu nanograins was kept constant and only the film thickness was varied. We find that—in the low thickness limit—the target thickness acts as an additional length scale, independent of the surface topography, and needs to be separately optimized for maximizing the generation of fast electrons from high-intensity, ultrashort laser–matter interaction.
We present ultrafast pump-probe reflectivity and Doppler spectrometry of a silicon target at rela... more We present ultrafast pump-probe reflectivity and Doppler spectrometry of a silicon target at relativistic laser intensity. We observe an unexpected rise in reflectivity to a peak approximately $9 ps after the main pulse interaction with the target. This occurs after the reflectivity has fallen off from the initially high "plasma-mirror" phase. Simultaneously measured time-dependent Doppler shift data show an increase in the blue shift at the same time. Numerical simulations show that the aforementioned trends in the experimental measurements correspond to a strong shock wave propagating back toward the laser. The relativistic laser-plasma interaction indirectly heats the cool-dense (n e ! 10 23 cm À3 and T e $ 10 eV) target material adjacent to the corona, by hot electron induced return current heating, raising its temperature to around 150 eV and causing it to explode violently. The increase in reflectivity is caused by the transient steepening of the plasma density gradient at the probe critical surface due to this explosive behavior.
We present ultrafast pump-probe reflectivity and Doppler spectrometry of a silicon target at rela... more We present ultrafast pump-probe reflectivity and Doppler spectrometry of a silicon target at relativistic laser intensity. We observe an unexpected rise in reflectivity to a peak approximately $9 ps after the main pulse interaction with the target. This occurs after the reflectivity has fallen off from the initially high "plasma-mirror" phase. Simultaneously measured time-dependent Doppler shift data show an increase in the blue shift at the same time. Numerical simulations show that the aforementioned trends in the experimental measurements correspond to a strong shock wave propagating back toward the laser. The relativistic laser-plasma interaction indirectly heats the cool-dense (n e ! 10 23 cm À3 and T e $ 10 eV) target material adjacent to the corona, by hot electron induced return current heating, raising its temperature to around 150 eV and causing it to explode violently. The increase in reflectivity is caused by the transient steepening of the plasma density gradient at the probe critical surface due to this explosive behavior.
Remote manipulation (triggering and guiding) of lightning in atmospheric conditions of thundersto... more Remote manipulation (triggering and guiding) of lightning in atmospheric conditions of thunderstorms has been the subject of intense scientific research for decades. High power, ultrashort-pulse lasers are considered attractive in generating plasma channels in air that could serve as conductors/diverters for lightning. However, two fundamental obstacles, namely the limited length and lifetime of such plasma channels prevented their realization to this date. In this paper, we report decisive experimental results of our multi-element broken wire concept that extends the generated plasma channels to the required tens of meters range. We obtain 13-meter-long plasma wire, limited only by our current experimental setup, with plasma conditions that could be sufficient for the leader initiation. This advance, coupled with our demonstrated method of laser heating for long time sustenance of the plasma channel, is a major, significant step towards controlling lightning.
Remote manipulation (triggering and guiding) of lightning in atmospheric conditions of thundersto... more Remote manipulation (triggering and guiding) of lightning in atmospheric conditions of thunderstorms has been the subject of intense scientific research for decades. High power, ultrashort-pulse lasers are considered attractive in generating plasma channels in air that could serve as conductors/diverters for lightning. However, two fundamental obstacles, namely the limited length and lifetime of such plasma channels prevented their realization to this date. In this paper, we report decisive experimental results of our multi-element broken wire concept that extends the generated plasma channels to the required tens of meters range. We obtain 13-meter-long plasma wire, limited only by our current experimental setup, with plasma conditions that could be sufficient for the leader initiation. This advance, coupled with our demonstrated method of laser heating for long time sustenance of the plasma channel, is a major, significant step towards controlling lightning.
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Papers by Deep Sarkar