Showing papers on "Femtosecond published in 2013"
TL;DR: In this article, a new field of direct femtosecond laser surface nano/microstructuring and its applications is reviewed, where the authors present a review of the current state-of-the-art in this field.
Abstract: This paper reviews a new field of direct femtosecond laser surface nano/microstructuring and its applications. Over the past few years, direct femtosecond laser surface processing has distinguished itself from other conventional laser ablation methods and become one of the best ways to create surface structures at nano- and micro-scales on metals and semiconductors due to its flexibility, simplicity, and controllability in creating various types of nano/microstructures that are suitable for a wide range of applications. Significant advancements were made recently in applying this technique to altering optical properties of metals and semiconductors. As a result, highly absorptive metals and semiconductors were created, dubbed as the “black metals” and “black silicon”. Furthermore, various colors other than black have been created through structural coloring on metals. Direct femtosecond laser processing is also capable of producing novel materials with wetting properties ranging from superhydrophilic to superhydrophobic. In the extreme case, superwicking materials were created that can make liquids run vertically uphill against the gravity over an extended surface area. Though impressive scientific achievements have been made so far, direct femtosecond laser processing is still a young research field and many exciting findings are expected to emerge on its horizon.
822 citations
TL;DR: In this paper, a unified formalism is presented for the betatron radiation of trapped and accelerated electrons in the so-called bubble regime, the synchrotron radiation of laser-accelerated electrons in usual meter-scale undulators, the nonlinear Thomson scattering from relativistic electrons oscillating in an intense laser field, and the Thomson backscattered radiation of a laser beam by laser accelerated electrons.
Abstract: Relativistic interaction of short-pulse lasers with underdense plasmas has recently led to the emergence of a novel generation of femtosecond x-ray sources. Based on radiation from electrons accelerated in plasma, these sources have the common properties to be compact and to deliver collimated, incoherent, and femtosecond radiation. In this article, within a unified formalism, the betatron radiation of trapped and accelerated electrons in the so-called bubble regime, the synchrotron radiation of laser-accelerated electrons in usual meter-scale undulators, the nonlinear Thomson scattering from relativistic electrons oscillating in an intense laser field, and the Thomson backscattered radiation of a laser beam by laser-accelerated electrons are reviewed. The underlying physics is presented using ideal models, the relevant parameters are defined, and analytical expressions providing the features of the sources are given. Numerical simulations and a summary of recent experimental results on the different mechanisms are also presented. Each section ends with the foreseen development of each scheme. Finally, one of the most promising applications of laser-plasma accelerators is discussed: the realization of a compact free-electron laser in the x-ray range of the spectrum. In the conclusion, the relevant parameters characterizing each sources are summarized. Considering typical laser-plasma interaction parameters obtained with currently available lasers, examples of the source features are given. The sources are then compared to each other in order to define their field of applications.
634 citations
TL;DR: In this article, the nonlinear optical properties of few-layer MoS${}_{2}$ two-dimensional crystals were studied using femtosecond laser pulses, which showed a polarization intensity dependence that directly revealed the underlying symmetry and orientation of the crystal.
Abstract: The nonlinear optical properties of few-layer MoS${}_{2}$ two-dimensional crystals are studied using femtosecond laser pulses. We observed highly efficient second-harmonic generation from the odd-layer crystals, which shows a polarization intensity dependence that directly reveals the underlying symmetry and orientation of the crystal. Additionally, the measured second-order susceptibility spectra provide information about the electronic structure of the material. Our results open up opportunities for studying the nonlinear optical properties in these two-dimensional crystals.
601 citations
TL;DR: This simultaneous XRD-XES study shows that the PS II crystals are intact during measurements at the LCLS, not only with respect to the structure of PS II, but also with regard to the electronic structure of the highly radiation-sensitive Mn4CaO5 cluster, opening new directions for future dynamics studies.
Abstract: Intense femtosecond x-ray pulses produced at the Linac Coherent Light Source (LCLS) were used for simultaneous x-ray diffraction (XRD) and x-ray emission spectroscopy (XES) of microcrystals of photosystem II (PS II) at room temperature. This method probes the overall protein structure and the electronic structure of the Mn4CaO5 cluster in the oxygen-evolving complex of PS II. XRD data are presented from both the dark state (S1) and the first illuminated state (S2) of PS II. Our simultaneous XRD-XES study shows that the PS II crystals are intact during our measurements at the LCLS, not only with respect to the structure of PS II, but also with regard to the electronic structure of the highly radiation-sensitive Mn4CaO5 cluster, opening new directions for future dynamics studies.
383 citations
TL;DR: Lasers with ultrashort pulses are shown to be particularly useful tools for the production of nanocluster films and the important question of the film stoichiometry relative to that of the target will be thoroughly discussed in relation to the films reported in the literature.
Abstract: Laser ablation of dielectrics by ultrashort laser pulses is reviewed. The basic interaction between ultrashort light pulses and the dielectric material is described, and different approaches to the modeling of the femtosecond ablation dynamics are reviewed. Material excitation by ultrashort laser pulses is induced by a combination of strong-field excitation (multi-photon and tunnel excitation), collisional excitation (potentially leading to an avalanche process), and absorption in the plasma consisting of the electrons excited to the conduction band. It is discussed how these excitation processes can be described by various rate-equation models in combination with different descriptions of the excited electrons. The optical properties of the highly excited dielectric undergo a rapid change during the laser pulse, which must be included in a detailed modeling of the excitations. The material ejected from the dielectric following the femtosecond-laser excitation can potentially be used for thin-film deposition. The deposition rate is typically much smaller than that for nanosecond lasers, but film production by femtosecond lasers does possess several attractive features. First, the strong-field excitation makes it possible to produce films of materials that are transparent to the laser light. Second, the highly localized excitation reduces the emission of larger material particulates. Third, lasers with ultrashort pulses are shown to be particularly useful tools for the production of nanocluster films. The important question of the film stoichiometry relative to that of the target will be thoroughly discussed in relation to the films reported in the literature.
377 citations
TL;DR: In this paper, a seeded free-electron laser with a two-stage harmonic upshift configuration provided tunable and coherent soft-X-ray pulses with energies of tens of microjoules and a low pulse-to-pulse wavelength jitter at wavelengths of 10.8 nm and below.
Abstract: A seeded free-electron laser with a two-stage harmonic upshift configuration provided tunable and coherent soft-X-ray pulses. The configuration produced single-transverse-mode, narrow-spectral-bandwidth femtosecond pulses with energies of several tens of microjoules and a low pulse-to-pulse wavelength jitter at wavelengths of 10.8 nm and below.
356 citations
TL;DR: Three-dimensional imaging of the generation and subsequent evolution of coherent acoustic phonons on the picosecond time scale within a single gold nanocrystal by means of an x-ray free-electron laser is reported, providing insights into the physics of this phenomenon.
Abstract: Key insights into the behavior of materials can be gained by observing their structure as they undergo lattice distortion. Laser pulses on the femtosecond time scale can be used to induce disorder in a "pump-probe" experiment with the ensuing transients being probed stroboscopically with femtosecond pulses of visible light, x-rays, or electrons. Here we report three-dimensional imaging of the generation and subsequent evolution of coherent acoustic phonons on the picosecond time scale within a single gold nanocrystal by means of an x-ray free-electron laser, providing insights into the physics of this phenomenon. Our results allow comparison and confirmation of predictive models based on continuum elasticity theory and molecular dynamics simulations.
271 citations
TL;DR: In this paper, a simple, rapid and inexpensive nanolithography technique is demonstrated that exploits nonlinear feedback mechanisms to tightly regulate the formation of nanostructures induced by femtosecond laser pulses.
Abstract: A simple, rapid and inexpensive nanolithography technique is demonstrated that exploits nonlinear feedback mechanisms to tightly regulate the formation of nanostructures induced by femtosecond laser pulses. The nonlocal nature of the feedback allows the nanostructures to be seamlessly stitched, resulting in large-area nanostructuring whose periodicity is uniform on a subnanometre scale.
269 citations
TL;DR: It is demonstrated that direct laser irradiation is in fact not essential for ultrafast demagnetization, and that electron cascades caused by hot electron currents accomplish it very efficiently.
Abstract: Irradiating a ferromagnet with a femtosecond laser pulse is known to induce an ultrafast demagnetization within a few hundred femtoseconds. Here we demonstrate that direct laser irradiation is in fact not essential for ultrafast demagnetization, and that electron cascades caused by hot electron currents accomplish it very efficiently. We optically excite a Au/Ni layered structure in which the 30 nm Au capping layer absorbs the incident laser pump pulse and subsequently use the X-ray magnetic circular dichroism technique to probe the femtosecond demagnetization of the adjacent 15 nm Ni layer. A demagnetization effect corresponding to the scenario in which the laser directly excites the Ni film is observed, but with a slight temporal delay. We explain this unexpected observation by means of the demagnetizing effect of a superdiffusive current of non-equilibrium, non-spin-polarized electrons generated in the Au layer.
262 citations
TL;DR: It is demonstrated that quantitative concentration determination of cholesterol in the presence of interfering chemical species can be achieved with sensitivity down to 4 mM, and it is shown that mammalian cell SRS hyperspectral imaging reveals the spatially inhomogeneous distribution of saturated lipids, unsaturatedlipids, cholesterol, and protein.
Abstract: Raman microscopy is a quantitative, label-free, and noninvasive optical imaging technique for studying inhomogeneous systems. However, the feebleness of Raman scattering significantly limits the use of Raman microscopy to low time resolutions and primarily static samples. Recent developments in narrowband stimulated Raman scattering (SRS) microscopy have significantly increased the acquisition speed of Raman based label-free imaging by a few orders of magnitude, at the expense of reduced spectroscopic information. On the basis of a spectral focusing approach, we present a fast SRS hyperspectral imaging system using chirped femtosecond lasers to achieve rapid Raman spectra acquisition while retaining the full speed and image quality of narrowband SRS imaging. We demonstrate that quantitative concentration determination of cholesterol in the presence of interfering chemical species can be achieved with sensitivity down to 4 mM. For imaging purposes, hyperspectral imaging data in the C–H stretching region is...
247 citations
TL;DR: This work combines the emittance-spoiler technique with a magnetic chicane in the undulator section to control the pulse duration and relative delay between two intense x-ray pulses and uses differently tuned canted pole undulators such that the two pulses have different wavelengths as well.
Abstract: With an eye toward extending optical wave-mixing techniques to the x-ray regime, we present the first experimental demonstration of a two-color x-ray free-electron laser at the Linac Coherent Light Source. We combine the emittance-spoiler technique with a magnetic chicane in the undulator section to control the pulse duration and relative delay between two intense x-ray pulses and we use differently tuned canted pole undulators such that the two pulses have different wavelengths as well. Two schemes are shown to produce two-color soft x-ray pulses with a wavelength separation up to $\ensuremath{\sim}1.9%$ and a controllable relative delay up to 40 fs.
TL;DR: The results demonstrate the complex decay routes in such hybrid systems and that, contrary to expectations, the lower polariton is intrinsically long-lived.
Abstract: We present a comprehensive experimental study of the photophysical properties of a molecule-cavity system under strong coupling conditions, using steady-state and femtosecond time-resolved emission and absorption techniques to selectively excite the lower and upper polaritons as well as the reservoir of uncoupled molecules. Our results demonstrate the complex decay routes in such hybrid systems and that, contrary to expectations, the lower polariton is intrinsically long-lived.
TL;DR: In this article, the effect of time on the wettability of metallic alloys was investigated, and it was shown that the change from hydrophilicity to hydrophobicity occurred over time and is due to surface chemistry modifications.
TL;DR: This work studies in detail the effect of femtosecond laser irradiation process parameters (fluence and scanning speed) on the hydrophobicity of the resulting micro/nano-patterned morphologies on stainless steel, particularly those possessing the triple roughness pattern that exhibited low contact angle hysteresis.
Abstract: This work studies in detail the effect of femtosecond laser irradiation process parameters (fluence and scanning speed) on the hydrophobicity of the resulting micro/nano-patterned morphologies on stainless steel. Depending on the laser parameters, four distinctly different nano-patterns were produced, namely nano-rippled, parabolic-pillared, elongated sinusoidal-pillared and triple roughness nano-structures. All of the produced structures were classified according to a newly defined parameter, the laser intensity factor (LIF); by increasing the LIF, the ablation rate and periodicity of the asperities increase. In order to decrease the surface energy, all of the surfaces were coated with a fluoroalkylsilane agent. Analysis of the wettability revealed enhanced superhydrophobicity for most of these structures, particularly those possessing the triple roughness pattern that also exhibited low contact angle hysteresis. The high permanent superhydrophobicity of this pattern is due to the special micro/nano-structure of the surface that facilitates the Cassie-Baxter state.
TL;DR: In this article, the authors demonstrate that the ionization-limited attainable intracavity peak intensity increases with decreasing pulse duration, which can be used for high-order harmonic generation in a gas, with repetition rates around 100 MHz.
Abstract: Coherently enhancing laser pulses in a passive cavity provides ideal conditions for high-order harmonic generation in a gas, with repetition rates around 100 MHz (refs 1,2,3). Recently, extreme-ultraviolet radiation with photon energies of up to 30 eV was obtained, which is sufficiently bright for direct frequency-comb spectroscopy at 20 eV (ref. 4). Here, we identify a route to scaling these radiation sources to higher photon energies. We demonstrate that the ionization-limited attainable intracavity peak intensity increases with decreasing pulse duration. By enhancing nonlinearly compressed pulses of an Yb-based laser and coupling out the harmonics through a pierced cavity mirror, we generate spatially coherent 108 eV (11.45 nm) radiation at 78 MHz. Exploiting the full potential of the demonstrated techniques will afford high-photon-flux ultrashort-pulsed extreme-ultraviolet sources for a number of applications in science and technology, including photoelectron spectroscopy, coincidence spectroscopy with femtosecond to attosecond resolution5,6 and characterization of components and materials for nanolithography7. Spatially coherent 11.45 nm radiation is produced by outcoupling the harmonics of cavity-enhanced nonlinearly compressed pulses from a Yb-based laser through a pierced cavity mirror. This technique may lead to high-photon-flux ultrashort-pulse extreme-ultraviolet sources for use in a wide range of applications.
TL;DR: In this article, the instantaneous field of an unknown pulse is imprinted onto the deflection of the attosecond extreme ultraviolet pulse using an all-optical set-up with a bandwidth up to 1 PHz.
Abstract: The time-dependent field of an electromagnetic pulse can be measured if there is a fast enough gate. For terahertz radiation, femtosecond photoinjection of free carriers into a semiconductor in the presence of the terahertz radiation can serve as the gate1. For visible or infrared radiation, attosecond photoionization of a gas target in the presence of the optical field is a direct analogue2,3,4,5,6,7,8. Here, we show that nonlinear optical mixing9,10,11,12,13 in a medium in which attosecond pulses are being generated can also be used to measure the time-dependent field of an optical pulse. The gate is the phase accumulated by the recollision electron during the subcycle time interval between ionization and recombination. We show that the instantaneous field of an unknown pulse is imprinted onto the deflection of the attosecond extreme ultraviolet pulse using an all-optical set-up with a bandwidth up to 1 PHz. A new laser-field measurement technique is demonstrated that exploits nonlinear optical mixing in a gas in which attosecond pulses are being generated. The instantaneous field of an unknown pulse is imprinted onto the deflection of an attosecond pulse using an all-optical set-up with a bandwidth of up to 1 PHz.
TL;DR: In this article, an ultra-intense, phase-stable terahertz laser field was applied to ferromagnetic cobalt films to imprint the laser's phase and field-strength characteristics onto the magnetization response.
Abstract: Off-resonant femtosecond magnetization dynamics are observed after applying an ultra-intense, phase-stable terahertz laser field to ferromagnetic cobalt films. The laser's phase and field-strength characteristics are directly imprinted onto the magnetization response. The off-resonant magnetization removes the speed limitation caused by the cooling process, providing new opportunities for ultrafast data storage.
TL;DR: Femtosecond x-ray diffraction measurements unveil the response of copper to laser shock-compression at peak normal elastic stresses of ~73 gigapascals (GPa) and strain rates of 109 per second, and capture the evolution of the lattice from a one-dimensional elastic to a 3D plastically relaxed state within a few tens of picoseconds.
Abstract: The ultrafast evolution of microstructure is key to understanding high-pressure and strain-rate phenomena. However, the visualization of lattice dynamics at scales commensurate with those of atomistic simulations has been challenging. Here, we report femtosecond x-ray diffraction measurements unveiling the response of copper to laser shock-compression at peak normal elastic stresses of ~73 gigapascals (GPa) and strain rates of 10 9 per second. We capture the evolution of the lattice from a one-dimensional (1D) elastic to a 3D plastically relaxed state within a few tens of picoseconds, after reaching shear stresses of 18 GPa. Our in situ high-precision measurement of material strength at spatial (
TL;DR: In this paper, the authors reported femtosecond time-resolved X-ray absorption near-edge spectroscopy (XANES) measurements of a spin-crossover system, iron(II) tris(2,2′-bipyridine) in water.
Abstract: X-ray free electron lasers (XFELs) deliver short (<100 fs) and intense (∼1012 photons) pulses of hard X-rays, making them excellent sources for time-resolved studies. Here we show that, despite the inherent instabilities of current (SASE based) XFELs, they can be used for measuring high-quality X-ray absorption data and we report femtosecond time-resolved X-ray absorption near-edge spectroscopy (XANES) measurements of a spin-crossover system, iron(II) tris(2,2′-bipyridine) in water. The data indicate that the low-spin to high-spin transition can be modeled by single-exponential kinetics convoluted with the overall time resolution. The resulting time constant is ∼160 fs.
TL;DR: It is discussed possible experiments that employ attosecond X-ray pulses to probe the quantum coherence and correlations of valence electrons and holes, rather than the charge density alone, building on the analogy with existing studies of vibrational motions using femtosecond techniques in the visible regime.
Abstract: New free-electron laser and high-harmonic generation X-ray light sources are capable of supplying pulses short and intense enough to perform resonant nonlinear time-resolved experiments in molecules. Valence-electron motions can be triggered impulsively by core excitations and monitored with high temporal and spatial resolution. We discuss possible experiments that employ attosecond X-ray pulses to probe the quantum coherence and correlations of valence electrons and holes, rather than the charge density alone, building on the analogy with existing studies of vibrational motions using femtosecond techniques in the visible regime.
TL;DR: A new light source of a two-colour double-pulse (TCDP) XFEL in hard X-rays using variable-gap undulators is shown, which realizes a large and flexible wavelength separation of more than 30% with an ultraprecisely controlled time interval in the attosecond regime.
Abstract: To study the dynamics of materials and biological samples at ultrafast time scales it is beneficial to use two short laser pulses, ideally at different energies. Here, the authors demonstrate the generation of two femtosecond hard X-ray laser pulses in a free electron laser, with more than 30% energy separation.
TL;DR: These results merge two fields, femtosecond magnetism in metals and band insulators, and non-equilibrium phase transitions of strongly correlated electrons, in which local interactions exceeding the kinetic energy produce a complex balance of competing orders.
Abstract: Magnetic order in a manganite can be switched during femtosecond photo-excitation via coherent superpositions of quantum states; this is analogous to processes in femtosecond chemistry where photoproducts of chemical and biochemical reactions can be influenced by creating suitable superpositions of molecular states. Today's magnetic memory and logic devices operate at gigahertz switching speeds. To achieve the even faster terahertz regime will require new technologies, and ultrafast all-optical magnetic switching using coherent spin manipulation is a leading contender. Ilias Perakis and colleagues demonstrate a development of this technique that achieves femtosecond all-optical switching of the magnetic state through the establishment of a 'colossal' magnetization component from an antiferromagnetic ground state. The switch to ferromagnetic ordering in Pr0.7Ca0.3MnO3 occurs within a mere 120 femtoseconds, a remarkably short time interval for a non-equilibrium magnetic phase transition. This is a new principle in magnetic switching, analogous to processes in femtochemistryin which photoproducts of chemical and biochemical reactions can be influenced by creating suitable superpositions of molecular states. This work is also of relevance to the fields of spin-chemistry, quantum biology and spin-electronics. The technological demand to push the gigahertz (109 hertz) switching speed limit of today’s magnetic memory and logic devices into the terahertz (1012 hertz) regime underlies the entire field of spin-electronics and integrated multi-functional devices. This challenge is met by all-optical magnetic switching based on coherent spin manipulation1. By analogy to femtosecond chemistry and photosynthetic dynamics2—in which photoproducts of chemical and biochemical reactions can be influenced by creating suitable superpositions of molecular states—femtosecond-laser-excited coherence between electronic states can switch magnetic order by ‘suddenly’ breaking the delicate balance between competing phases of correlated materials: for example, manganites exhibiting colossal magneto-resistance suitable for applications3,4. Here we show femtosecond (10−15 seconds) photo-induced switching from antiferromagnetic to ferromagnetic ordering in Pr0.7Ca0.3MnO3, by observing the establishment (within about 120 femtoseconds) of a huge temperature-dependent magnetization with photo-excitation threshold behaviour absent in the optical reflectivity. The development of ferromagnetic correlations during the femtosecond laser pulse reveals an initial quantum coherent regime of magnetism, distinguished from the picosecond (10−12 seconds) lattice-heating regime characterized by phase separation without threshold behaviour5,6. Our simulations reproduce the nonlinear femtosecond spin generation and underpin fast quantum spin-flip fluctuations correlated with coherent superpositions of electronic states to initiate local ferromagnetic correlations. These results merge two fields, femtosecond magnetism in metals and band insulators1,7,8,9, and non-equilibrium phase transitions of strongly correlated electrons10,11,12,13,14,15,16,17, in which local interactions exceeding the kinetic energy produce a complex balance of competing orders.
TL;DR: In this paper, the coherent dynamic of phonons in crystalline materials was observed using X-ray free-electron (XFED) laser pulses, which could provide insight into low energy collective excitations in solids and how they interact at a microscopic level to determine the material's macroscopic properties.
Abstract: Femtosecond pulses from X-ray free-electron lasers offer a powerful method for observing the coherent dynamic of phonons in crystalline materials, it is now shown. This time-resolved spectroscopic tool could provide insight into low-energy collective excitations in solids and how they interact at a microscopic level to determine the material’s macroscopic properties.
TL;DR: A femtosecond fiber laser system comprising four coherently combined large-pitch fibers as the main amplifier and an excellent beam quality and efficiency have been obtained.
Abstract: We report on a femtosecond fiber laser system comprising four coherently combined large-pitch fibers as the main amplifier. With this system, a pulse energy of 1.3 mJ and a peak power of 1.8 GW are achieved at 400 kHz repetition rate. The corresponding average output power is as high as 530 W. Additionally, an excellent beam quality and efficiency of the combination have been obtained. To the best of our knowledge, such a parameter combination, i.e., gigawatt pulses with half a kilowatt average power, has not been demonstrated so far with any other laser architecture.
TL;DR: It is demonstrated for the first time the possibility to generate long plasma channels up to a distance of 1 km, using the terawatt femtosecond T&T laser facility.
Abstract: We demonstrate for the first time the possibility to generate long plasma channels up to a distance of 1 km, using the terawatt femtosecond T&T laser facility. The plasma density was optimized by adjusting the chirp, the focusing and beam diameter. The interaction of filaments with transparent and opaque targets was studied.
TL;DR: In this paper, induced tracks in fused silica using scanning electron microscopy (SEM) with nm resolution were analyzed and it was shown that nanostructures are porous nanoplanes with an av- erage index lower than typical silica.
Abstract: A type of glass modifications occurring after femto- second laser irradiation gives rise to strong (10 −2 ). This form birefringence is thought to be related to index nanostructure (called nanogratings). Analyzing induced tracks in fused silica using scanning electron microscopy (SEM) with nm resolution shows that nanostructures are porous nanoplanes with an av- erage index lower than typical silica (� n ∼ -0.20). Their origin is explained as arising from fast decomposition of the glass un- der localized, high-intensity femtosecond laser radiation where strong nonlinear, multiphoton-induced photoionization leads to plasma generation. Mechanistic details include Coulom- bic explosions characteristic of strong photoionization and the production of self-trapped exciton (STE). Rapid relaxation of these STE prevents recombination and dissociated atomic oxy- gen instead recombines with each other to form molecular oxygen pointed out using Raman microscopy. Some of it is dissolved in the condensed glass whilst the rest is trapped within nanovoids. A chemical recombination can only occur at 1200 ◦ C for many hours. This explains the thermal stability
TL;DR: In this article, a review of the evolution of the self-focus phenomenon in light beams is presented, and the current status of this rapidly growing area of nonlinear optics and laser physics is discussed.
Abstract: 2012 marked the 50th anniversary of the first published prediction of the self-focusing phenomenon in light beams. The recent revived interest in the subject is due to advances in high-power femtosecond laser technology and due to the possibility they provided of creating extended filaments of high light field intensity in gases and condensed media. This review shows in retrospect how our understanding of the self-action of light evolved from the self-focusing of laser beams in the 1960s to the filamentation of femtosecond laser pulses at present. We also describe the current status of this rapidly growing area of nonlinear optics and laser physics. Finally, we discuss, in general terms, what the phenomena of laser beam self-focusing and laser pulse filamentation have in common and how they differ.
TL;DR: A fiber-optic Fabry-Perot interferometric pressure sensor with its external diaphragm surface thinned and roughened by a femtosecond laser, which makes the sensor immune to variations in the ambient refractive index.
Abstract: In this Letter, we report on a fiber-optic Fabry-Perot interferometric pressure sensor with its external diaphragm surface thinned and roughened by a femtosecond laser. The laser-roughened surface helps to eliminate outer reflections from the external diaphragm surface and makes the sensor immune to variations in the ambient refractive index. The sensor is demonstrated to measure pressure in a high-temperature environment with low-temperature dependence.
TL;DR: In this paper, the formation of laser-induced periodic surface structures (LIPSS) on titanium upon irradiation with linearly polarized femtosecond (fs) laser pulses (τ=30,fs, λ=790,nm) in an air environment is studied experimentally and theoretically.
Abstract: The formation of laser-induced periodic surface structures (LIPSS) on titanium upon irradiation with linearly polarized femtosecond (fs) laser pulses (τ=30 fs, λ=790 nm) in an air environment is studied experimentally and theoretically. In the experiments, the dependence on the laser fluence and the number of laser pulses per irradiation spot has been analyzed. For a moderate number of laser pulses (N<1000) and at fluences between ∼0.09 and ∼0.35 J/cm2, predominantly low-spatial-frequency-LIPSS with periods between 400 nm and 800 nm are observed perpendicular to the polarization. In a narrow fluence range between 0.05 and 0.09 J/cm2, high-spatial-frequency-LIPSS with sub-100-nm spatial periods (∼λ/10) can be generated with an orientation parallel to the polarization (N=50). These experimental results are complemented by calculations based on a theoretical LIPSS model and compared to the present literature.
TL;DR: In this article, a femtosecond laser microfabrication was used to realize super-hydrophobic patterned polydimethylsiloxane (PDMS) surfaces with tunable adhesion by a femto-conditional laser.
Abstract: We present a rapid, facile, and simple method to realize superhydrophobic patterned polydimethylsiloxane (PDMS) surfaces with tunable adhesion by a femtosecond laser. These surfaces are composed of superhydrophobic laser-induced structures and hydrophobic unstructured square array. The femtosecond laser structured domain shows superhydrophobicity with ultralow water adhesion, while the nonstructured flat PDMS shows ordinary hydrophobicity with ultrahigh water adhesion. By adjusting the relative area fraction of laser structured and nonstructured domains, the as-prepared superhydrophobic surfaces show tunable water adhesion that ranges from ultralow to ultrahigh, on which the sliding angle can be controlled from 1° to 90° (a water droplet cannot slide down even when the as-prepared surface is vertical or turned upside down). The tunable adhesive superhydrophobic surfaces achieved by femtosecond laser microfabrication may be potentially used in microfluidic systems to modulate the mobility of liquid droplets.