Showing papers on "Laser published in 2006"
TL;DR: In this paper, a systematic study of the ratio between the integrated intensities of the disorder-induced D and G Raman bands (ID∕IG) in nanographite samples with different crystallite sizes (La) and using different excitation laser energies is presented.
Abstract: This work presents a systematic study of the ratio between the integrated intensities of the disorder-induced D and G Raman bands (ID∕IG) in nanographite samples with different crystallite sizes (La) and using different excitation laser energies. The crystallite size La of the nanographite samples was obtained both by x-ray diffraction using synchrotron radiation and directly from scanning tunneling microscopy images. A general equation for the determination of La using any laser energy in the visible range is obtained. Moreover, it is shown that ID∕IG is inversely proportional to the fourth power of the laser energy used in the experiment.
2,161 citations
TL;DR: In this article, a high-quality electron beam with 1 GeV energy was achieved by channelling a 40 TW peak-power laser pulse in a 3.3 cm-long gas-filled capillary discharge waveguide.
Abstract: Gigaelectron volt (GeV) electron accelerators are essential to synchrotron radiation facilities and free-electron lasers, and as modules for high-energy particle physics. Radiofrequency-based accelerators are limited to relatively low accelerating fields (10–50 MV m−1), requiring tens to hundreds of metres to reach the multi-GeV beam energies needed to drive radiation sources, and many kilometres to generate particle energies of interest to high-energy physics. Laser-wakefield accelerators1,2 produce electric fields of the order 10–100 GV m−1 enabling compact devices. Previously, the required laser intensity was not maintained over the distance needed to reach GeV energies, and hence acceleration was limited to the 100 MeV scale3,4,5. Contrary to predictions that petawatt-class lasers would be needed to reach GeV energies6,7, here we demonstrate production of a high-quality electron beam with 1 GeV energy by channelling a 40 TW peak-power laser pulse in a 3.3-cm-long gas-filled capillary discharge waveguide8,9.
1,568 citations
TL;DR: An AlN PIN (p-type/intrinsic/n-type) homojunction LED with an emission wavelength of 210 nm, which is the shortest reported to date for any kind of LED, represents an important step towards achieving exciton-related light-emitting devices as well as replacing gas light sources with solid-state light sources.
Abstract: The development of a compact, solid-state light-emitting diode (LED) that emits at 210 nanometres — the shortest wavelength yet achieved for any type of LED — represents an important step towards achieving exciton-related light-emitting devices and replacing inefficient gas light sources with solid-state light sources. Compact high-efficiency ultraviolet solid-state light sources1—such as light-emitting diodes (LEDs) and laser diodes—are of considerable technological interest as alternatives to large, toxic, low-efficiency gas lasers and mercury lamps. Microelectronic fabrication technologies and the environmental sciences both require light sources with shorter emission wavelengths: the former for improved resolution in photolithography and the latter for sensors that can detect minute hazardous particles. In addition, ultraviolet solid-state light sources are also attracting attention for potential applications in high-density optical data storage, biomedical research, water and air purification, and sterilization. Wide-bandgap materials, such as diamond2 and III–V nitride semiconductors (GaN, AlGaN and AlN; refs 3–10), are potential materials for ultraviolet LEDs and laser diodes, but suffer from difficulties in controlling electrical conduction. Here we report the successful control of both n-type and p-type doping in aluminium nitride (AlN), which has a very wide direct bandgap11 of 6 eV. This doping strategy allows us to develop an AlN PIN (p-type/intrinsic/n-type) homojunction LED with an emission wavelength of 210 nm, which is the shortest reported to date for any kind of LED. The emission is attributed to an exciton transition, and represents an important step towards achieving exciton-related light-emitting devices as well as replacing gas light sources with solid-state light sources.
1,562 citations
Book•
01 Jan 2006
TL;DR: In this article, the authors present an overview of the current state of the art in the field of laser-induced breakdown spectroscopy (LIBS) and its application in various applications.
Abstract: Foreword. Preface. Acronyms, Constants, And Symbol.s 1. History. 1.1 Atomic optical emission spectrochemistry (OES). 1.2 Laser-induced breakdown spectroscopy (LIBS). 1.3 LIBS History 1960-1980. 1.4 LIBS History 1980-1990. 1.5 LIBS History 1990-2000. 1.6 Active Areas of Investigation, 2000-2002. References. 2. Basics of the LIBS plasma. 2.1 LIBS plasma fundamentals. 2.2 laser-Induced Breakdown. 2.3 laser ablation. 2.4 double or multiple pulse libs. 2.5 summary. References. 3. Apparatus fundamentals. 3.1 Basic LIBS apparatus. 3.2 Lasers. 3.3 Optical systems. 3.4 Methods of spectral resolution. 3.5 Detectors. 3.6 Detection system calibration. 3.7 Timing considerations. 3.8 Methods of LIBS deployment. References. 4. Determining LIBS analytical figures-of-merit. 4.1 Introduction. 4.2 Basics of LIBS measurements. 4.3 precision. 4.4 Calibration. 4.5 Detection limit. References. 5. Qualitative LIBS Analysis. 5.1 Identifying elements. 5.2 Material identification. 5.3 Process control. References. 6. Quantitative LIBS Analysis. 6.1 Introduction. 6.2 Geometric Sampling Parameters. 6.3 Other sampling considerations. 6.4. Particle size. 6.5 use of internal standardization. 6.6 Chemical Matrix effects. 6.7. Example of libs measurement: Impurities in Lithium Solutions. 6.8 Reported figures of merit for LIBS measurements. 6.9 Conclusions. References. Chapter 7. REMOTE LIBS MEASUREMENTS. 7.1 Introduction. 7.2 Conventional open path LIBS. 7.3 Stand-off LIBS using Femtosecond pulses. 7.4 Fiber optic LIBS. References 8. Examples of recent LIBS fundamental research, instruments and novel applications. 8.1 Introduction. 8.2 fundamentals. 8.3 calibration-free LIBS. 8.4 laser and spectrometer advances. 8.5 surface analysis. 8.6 Double pulse studies and applications. 8.7 Steel applications. 8.8 libs for biological applications. 8.9 nuclear reactor applications. 8.10 LIBS for space applications. References. 9. THE FUTURE OF LIBS. 9.1 Introduction. 9.2 Expanding the understanding and capability of the libs process. 9.3 Widening the universe of libs applications. 9.4 Factors that will speed the commercialization of Libs. 9.5 conclusion. References. APPENDIX A: Safety Considerations in LIBS. A.1. safety plans. A.2 Laser Safety. A.3 Generation of Aerosols. A.4 laser pulse induced ignition. APPENDIX B: LIBS Application Matrix. APPENDIX C: LIBS Detection Limits. C.1 detection limits from the literature. C.2 uniform detection limits. APPENDIX D: Major LIBS References. Index.
1,473 citations
TL;DR: In this paper, a number of consequences of relativistic-strength optical fields are surveyed, including wakefield generation, a relativistically version of optical rectification, in which longitudinal field effects could be as large as the transverse ones.
Abstract: The advent of ultraintense laser pulses generated by the technique of chirped pulse amplification (CPA) along with the development of high-fluence laser materials has opened up an entirely new field of optics. The electromagnetic field intensities produced by these techniques, in excess of ${10}^{18}\phantom{\rule{0.3em}{0ex}}\mathrm{W}∕{\mathrm{cm}}^{2}$, lead to relativistic electron motion in the laser field. The CPA method is reviewed and the future growth of laser technique is discussed, including the prospect of generating the ultimate power of a zettawatt. A number of consequences of relativistic-strength optical fields are surveyed. In contrast to the nonrelativistic regime, these laser fields are capable of moving matter more effectively, including motion in the direction of laser propagation. One of the consequences of this is wakefield generation, a relativistic version of optical rectification, in which longitudinal field effects could be as large as the transverse ones. In addition to this, other effects may occur, including relativistic focusing, relativistic transparency, nonlinear modulation and multiple harmonic generation, and strong coupling to matter and other fields (such as high-frequency radiation). A proper utilization of these phenomena and effects leads to the new technology of relativistic engineering, in which light-matter interactions in the relativistic regime drives the development of laser-driven accelerator science. A number of significant applications are reviewed, including the fast ignition of an inertially confined fusion target by short-pulsed laser energy and potential sources of energetic particles (electrons, protons, other ions, positrons, pions, etc.). The coupling of an intense laser field to matter also has implications for the study of the highest energies in astrophysics, such as ultrahigh-energy cosmic rays, with energies in excess of ${10}^{20}\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$. The laser fields can be so intense as to make the accelerating field large enough for general relativistic effects (via the equivalence principle) to be examined in the laboratory. It will also enable one to access the nonlinear regime of quantum electrodynamics, where the effects of radiative damping are no longer negligible. Furthermore, when the fields are close to the Schwinger value, the vacuum can behave like a nonlinear medium in much the same way as ordinary dielectric matter expanded to laser radiation in the early days of laser research.
1,459 citations
TL;DR: In this paper, a simple theoretical model is developed to predict residual stress distributions in selective laser sintering (SLS) and selective laser melting (SLM), aiming at a better understanding of this phenomenon.
Abstract: Purpose – This paper presents an investigation into residual stresses in selective laser sintering (SLS) and selective laser melting (SLM), aiming at a better understanding of this phenomenon.Design/methodology/approach – First, the origin of residual stresses is explored and a simple theoretical model is developed to predict residual stress distributions. Next, experimental methods are used to measure the residual stress profiles in a set of test samples produced with different process parameters.Findings – Residual stresses are found to be very large in SLM parts. In general, the residual stress profile consists of two zones of large tensile stresses at the top and bottom of the part, and a large zone of intermediate compressive stress in between. The most important parameters determining the magnitude and shape of the residual stress profiles are the material properties, the sample and substrate height, the laser scanning strategy and the heating conditions.Research limitations/implications – All exper...
1,415 citations
TL;DR: An electrically pumped AlGaInAs-silicon evanescent laser architecture where the laser cavity is defined solely by the silicon waveguide and needs no critical alignment to the III-V active material during fabrication via wafer bonding is reported.
Abstract: An electrically pumped light source on silicon is a key element needed for photonic integrated circuits on silicon. Here we report an electrically pumped AlGaInAs-silicon evanescent laser architecture where the laser cavity is defined solely by the silicon waveguide and needs no critical alignment to the III-V active material during fabrication via wafer bonding. This laser runs continuous-wave (c.w.) with a threshold of 65 mA, a maximum output power of 1.8 mW with a differential quantum efficiency of 12.7 % and a maximum operating temperature of 40 degrees C. This approach allows for 100's of lasers to be fabricated in one bonding step, making it suitable for high volume, low-cost, integration. By varying the silicon waveguide dimensions and the composition of the III-V layer, this architecture can be extended to fabricate other active devices on silicon such as optical amplifiers, modulators and photo-detectors.
1,257 citations
TL;DR: The FDML laser is ideal for swept-source OCT imaging, thus enabling high imaging speeds and large imaging depths, and dynamic linewidths are narrow enough to enable imaging over a 7 mm depth with only a 7.5 dB decrease in sensitivity.
Abstract: We demonstrate a new technique for frequency-swept laser operation--Fourier domain mode locking (FDML)--and its application for swept-source optical coherence tomography (OCT) imaging. FDML is analogous to active laser mode locking for short pulse generation, except that the spectrum rather than the amplitude of the light field is modulated. High-speed, narrowband optical frequency sweeps are generated with a repetition period equal to the fundamental or a harmonic of cavity round-trip time. An FDML laser is constructed using a long fiber ring cavity, a semiconductor optical amplifier, and a tunable fiber Fabry-Perot filter. Effective sweep rates of up to 290 kHz are demonstrated with a 105 nm tuning range at 1300 nm center wavelength. The average output power is 3mW directly from the laser and 20 mW after post-amplification. Using the FDML laser for swept-source OCT, sensitivities of 108 dB are achieved and dynamic linewidths are narrow enough to enable imaging over a 7 mm depth with only a 7.5 dB decrease in sensitivity. We demonstrate swept-source OCT imaging with acquisition rates of up to 232,000 axial scans per second. This corresponds to 906 frames/second with 256 transverse pixel images, and 3.5 volumes/second with a 256x128x256 voxel element 3-DOCT data set. The FDML laser is ideal for swept-source OCT imaging, thus enabling high imaging speeds and large imaging depths.
1,026 citations
TL;DR: In this paper, the FLASH soft X-ray free-electron laser was used to reconstruct a coherent diffraction pattern from a nano-structured nonperiodic object, before destroying it at 60,000 K.
Abstract: Theory predicts that with an ultrashort and extremely bright coherent X-ray pulse, a single diffraction pattern may be recorded from a large macromolecule, a virus, or a cell before the sample explodes and turns into a plasma. Here we report the first experimental demonstration of this principle using the FLASH soft X-ray free-electron laser. An intense 25 fs, 4 x 10{sup 13} W/cm{sup 2} pulse, containing 10{sup 12} photons at 32 nm wavelength, produced a coherent diffraction pattern from a nano-structured non-periodic object, before destroying it at 60,000 K. A novel X-ray camera assured single photon detection sensitivity by filtering out parasitic scattering and plasma radiation. The reconstructed image, obtained directly from the coherent pattern by phase retrieval through oversampling, shows no measurable damage, and extends to diffraction-limited resolution. A three-dimensional data set may be assembled from such images when copies of a reproducible sample are exposed to the beam one by one.
957 citations
TL;DR: It is demonstrated that the injection and subsequent acceleration of electrons can be controlled by using a second laser pulse, and the electron beams obtained are stable and tuneable, and compatible with electron bunch durations shorter than 10 fs.
Abstract: In laser-plasma-based accelerators, an intense laser pulse drives a large electric field (the wakefield) which accelerates particles to high energies in distances much shorter than in conventional accelerators. These high acceleration gradients, of a few hundreds of gigavolts per metre, hold the promise of compact high-energy particle accelerators. Recently, several experiments have shown that laser-plasma accelerators can produce high-quality electron beams, with quasi-monoenergetic energy distributions at the 100 MeV level. However, these beams do not have the stability and reproducibility that are required for applications. This is because the mechanism responsible for injecting electrons into the wakefield is based on highly nonlinear phenomena, and is therefore hard to control. Here we demonstrate that the injection and subsequent acceleration of electrons can be controlled by using a second laser pulse. The collision of the two laser pulses provides a pre-acceleration stage which provokes the injection of electrons into the wakefield. The experimental results show that the electron beams obtained in this manner are collimated (5 mrad divergence), monoenergetic (with energy spread <10 per cent), tuneable (between 15 and 250 MeV) and, most importantly, stable. In addition, the experimental observations are compatible with electron bunch durations shorter than 10 fs. We anticipate that this stable and compact electron source will have a strong impact on applications requiring short bunches, such as the femtolysis of water, or high stability, such as radiotherapy with high-energy electrons or radiography for materials science.
738 citations
TL;DR: In this article, a high-speed velocimeter was built using off-the-shelf components developed for the telecommunications industry, including fiber lasers, high-bandwidth high-sample-rate digitizers, and fiber optic circulators.
Abstract: We have built a high-speed velocimeter that has proven to be compact, simple to operate, and fairly inexpensive. This diagnostic is assembled using off-the-shelf components developed for the telecommunications industry. The main components are fiber lasers, high-bandwidth high-sample-rate digitizers, and fiber optic circulators. The laser is a 2W cw fiber laser operating at 1550nm. The digitizers have 8GHz bandwidth and can digitize four channels simultaneously at 20GS∕s. The maximum velocity of this system is ∼5000m∕s and is limited by the bandwidth of the electrical components. For most applications, the recorded beat frequency is analyzed using Fourier transform methods, which determine the time response of the final velocity time history. Using the Fourier transform method of analysis allows multiple velocities to be observed simultaneously. We have obtained high-quality data on many experiments such as explosively driven surfaces and gas gun assemblies.
TL;DR: In this article, scaling laws derived from fluid models and supported by numerical simulations are used to accurately describe the acceleration of proton beams for a large range of laser and target parameters.
Abstract: The past few years have seen remarkable progress in the development of laser-based particle accelerators. The ability to produce ultrabright beams of multi-megaelectronvolt protons routinely has many potential uses from engineering to medicine, but for this potential to be realized substantial improvements in the performances of these devices must be made. Here we show that in the laser-driven accelerator that has been demonstrated experimentally to produce the highest energy protons, scaling laws derived from fluid models and supported by numerical simulations can be used to accurately describe the acceleration of proton beams for a large range of laser and target parameters. This enables us to evaluate the laser parameters needed to produce high-energy and high-quality proton beams of interest for radiography of dense objects or proton therapy of deep-seated tumours.
TL;DR: Reliable and reproducible laser-accelerated ion beams were achieved by intense laser irradiation of solid microstructured targets and Scalability studies show that, owing to their compact size and reasonable cost, such table-top laser systems with high repetition rates could contribute to the development of new generations of particle injectors that may be suitable for medical proton therapy.
Abstract: Particle acceleration based on high intensity laser systems (a process known as laser-plasma acceleration) has achieved high quality particle beams that compare favourably with conventional acceleration techniques in terms of emittance, brightness and pulse duration. A long-term difficulty associated with laser-plasma acceleration--the very broad, exponential energy spectrum of the emitted particles--has been overcome recently for electron beams. Here we report analogous results for ions, specifically the production of quasi-monoenergetic proton beams using laser-plasma accelerators. Reliable and reproducible laser-accelerated ion beams were achieved by intense laser irradiation of solid microstructured targets. This proof-of-principle experiment serves to illuminate the role of laser-generated plasmas as feasible particle sources. Scalability studies show that, owing to their compact size and reasonable cost, such table-top laser systems with high repetition rates could contribute to the development of new generations of particle injectors that may be suitable for medical proton therapy.
TL;DR: Quasi-monoenergetic laser-driven C5+ ions with a vastly reduced energy spread are reported, which may enable significant advances in the development of compact MeV ion accelerators, new diagnostics, medical physics, inertial confinement fusion and fast ignition.
Abstract: Acceleration of particles by intense laser-plasma interactions represents a rapidly evolving field of interest, as highlighted by the recent demonstration of laser-driven relativistic beams of monoenergetic electrons. Ultrahigh-intensity lasers can produce accelerating fields of 10 TV m(-1) (1 TV = 10(12) V), surpassing those in conventional accelerators by six orders of magnitude. Laser-driven ions with energies of several MeV per nucleon have also been produced. Such ion beams exhibit unprecedented characteristics--short pulse lengths, high currents and low transverse emittance--but their exponential energy spectra have almost 100% energy spread. This large energy spread, which is a consequence of the experimental conditions used to date, remains the biggest impediment to the wider use of this technology. Here we report the production of quasi-monoenergetic laser-driven C5+ ions with a vastly reduced energy spread of 17%. The ions have a mean energy of 3 MeV per nucleon (full-width at half-maximum approximately 0.5 MeV per nucleon) and a longitudinal emittance of less than 2 x 10(-6) eV s for pulse durations shorter than 1 ps. Such laser-driven, high-current, quasi-monoenergetic ion sources may enable significant advances in the development of compact MeV ion accelerators, new diagnostics, medical physics, inertial confinement fusion and fast ignition.
TL;DR: In this paper, a photonic crystal nanocavity laser with response times as short as a few picoseconds resulting from 75-fold spontaneous emission rate enhancement in the cavity was demonstrated.
Abstract: Spontaneous emission is not inherent to an emitter, but rather depends on its electromagnetic environment. In a microcavity, the spontaneous emission rate can be greatly enhanced compared with that in free space. This so-called Purcell effect can dramatically increase laser modulation speeds, although to date no time-domain measurements have demonstrated this. Here we show extremely fast photonic crystal nanocavity lasers with response times as short as a few picoseconds resulting from 75-fold spontaneous emission rate enhancement in the cavity. We demonstrate direct modulation speeds far exceeding 100 GHz (limited by the detector response time), already more than an order of magnitude above the fastest semiconductor lasers. Such ultrafast, efficient, and compact lasers show great promise for applications in high-speed communications, information processing, and on-chip optical interconnects.
TL;DR: Photon correlation measurements show a transition from a thermal to a coherent light state proving that lasing action occurs at ultralow thresholds, and it is demonstrated that very few quantum dots as a gain medium are sufficient to realize a photonic-crystal laser based on a high-quality nanocavity.
Abstract: We demonstrate that very few (2\char21{}4) quantum dots as a gain medium are sufficient to realize a photonic-crystal laser based on a high-quality nanocavity. Photon correlation measurements show a transition from a thermal to a coherent light state proving that lasing action occurs at ultralow thresholds. Observation of lasing is unexpected since the cavity mode is in general not resonant with the discrete quantum dot states and emission at those frequencies is suppressed. In this situation, the quasicontinuous quantum dot states become crucial since they provide an energy-transfer channel into the lasing mode, effectively leading to a self-tuned resonance for the gain medium.
TL;DR: A novel technique for reliable electrical injection into single semiconductor nanowires for light-emitting diodes and lasers is presented, demonstrated by constructing the first zinc oxide single-nanowire light- Emitting diode at room temperature.
Abstract: We present a novel technique for reliable electrical injection into single semiconductor nanowires for light-emitting diodes and lasers. The method makes use of a high-resolution negative electron-beam resist and direct electron-beam patterning for the precise fabrication of a metallic top contact along the length of the nanowire, while a planar substrate is used as a bottom contact. It can be applied to any nanowire structure with an arbitrary cross section. We demonstrate this technique by constructing the first zinc oxide single-nanowire light-emitting diode. The device exhibits broad sub-bandgap emission at room temperature.
TL;DR: A modelocked ytterbium (Yb)-doped fiber laser that is designed to have strong pulse-shaping based on spectral filtering of a highly-chirped pulse in the cavity is demonstrated.
Abstract: A modelocked Yb-doped fiber laser without an anomalous dispersive segment is demonstrated. Pulse-shaping is based on spectral filtering of a highly-chirped pulse in the cavity. The laser generated 170-fs pulses with 3-nJ pulse energy. Article not available.
TL;DR: It is shown that polyelectrolyte-multilayer capsules containing metallic nanoparticles in their walls can be remotely activated to release encapsulated materials inside living cells and this approach is ideally suited to applications where precise control is necessary.
Abstract: Drug delivery into biological cells is an important and growing area of application. Among other systems, such as gels, polymeric micelles, liposomes, and colloids, nanoengineered polyelectrolyte multilayer microcapsules offer a unique opportunity to combine surface multifunctionality with design flexibility for the delivery of encapsulated materials into designated compartments and cells. Furthermore, microcapsules can be arranged in arrays for imaging, could be appropriate candidates for a cell-sorting system, and serve as fluorescence markers for the characterization of cells by fluorescence-activated cell sorting (FACS). The capsules are fabricated using the layer-bylayer (LbL) method by alternately adsorbing oppositely charged polymers on colloidal templates followed by core dissolution. In this regard, proteins and biocompatible polymers have also received increased interest. The main advantage of such a method is the precise control over the chemical composition of the surfaces. In the area of biomedical applications, polyelectrolytemultilayer capsules are envisioned for the delivery of encapsulated materials into biological cells. Recently, we have presented the real-time monitoring and remote release of encapsulated materials from polyelectrolyte-multilayer capsules on the single-capsule level. Such an approach is different from the studies reported by other research groups in that it is performed on a single-capsule level, which is the method ideally suited to applications where precise control is necessary. In addition, the distinctive feature reported in reference [10b] is the measurement of the temperature rise induced locally by absorption of laser light by nanoparticles. In general, nanoparticles are becoming ubiquitous components that link chemistry and physics with biology and biochemistry. They can be embedded in the walls of capsules to provide functionality, and they are also finding increasing interest for biological imaging. Herein, we show that polyelectrolyte-multilayer capsules containing metallic nanoparticles in their walls can be remotely activated to release encapsulatedmaterial inside living cells. Fluorescently labeled polymers were chosen as a model system for encapsulated materials. The remote-release experiments were conducted according to the following scheme. The polyelectrolyte-multilayer shells were doped with metal nanoparticles, which served as absorption centers for energy supplied by a laser beam. These absorption centers cause local heating that disrupts the local polymer matrix and allows the encapsulated material to leave the interior of the capsule. When using lasers with biological objects, it is important to minimize the absorption of laser light by cells and tissue. This can be accomplished by choosing the laser wavelength in the biologically “friendly” window—the near-infrared (NIR) part of the spectrum. Usually the spectral properties of water serve as a good criterion, as it constitutes 80–85% of eukaryotic cells. Indeed, in water the temperature rise in the focus of a laser diode with wavelength 850 nm and operating at optical powers up to 100 mW during less than 1 s exposure time was reported to be under 1 K. Other important parameters that control the interaction of laser light with the absorption centers are the size of the nanoparticles and their concentration on the microcapsules. The concentration of metal nanoparticles plays an important role for two reasons: 1) when the distance between the two adjacent nanoparticles is of the order of their size, the thermal effects produced by [*] Dr. A. G. Skirtach, Dr. O. Kreft, K. K hler, Prof. Dr. H. M hwald, Prof. Dr. G. B. Sukhorukov Institut f+r Grenzfl-chen Max-Planck-Institut f+r Kolloidund Grenzfl-chenforschung Am M+hlenberg 1, 14424 Golm/Potsdam (Germany) Fax: (+49)331-567-9202 E-mail: andre.skirtach@mpikg-golm.mpg.de
TL;DR: The marriage of UltraFast and UltraStable lasers was brokered mainly by two international teams and became exciting when a special "designer'' microstructure optical fiber was shown to be nonlinear enough to produce white light from the femtosecond laser pulses, such that the output spectrum embraced a full optical octave as mentioned in this paper.
Abstract: Four long-running currents in laser technology met and merged in 1999--2000. Two of these were the quest toward a stable repetitive sequence of ever-shorter optical pulses and, on the other hand, the quest for the most time-stable, unvarying optical frequency possible. The marriage of UltraFast and UltraStable lasers was brokered mainly by two international teams and became exciting when a special ``designer'' microstructure optical fiber was shown to be nonlinear enough to produce ``white light'' from the femtosecond laser pulses, such that the output spectrum embraced a full optical octave. Then, for the first time, one could realize an optical frequency interval equal to the comb's lowest frequency, and count out this interval as a multiple of the repetition rate of the femtosecond pulse laser. This ``gear-box'' connection between the radio frequency standard and any/all optical frequency standards came just as Sensitivity-Enhancing ideas were maturing. The four-way Union empowered an explosion of accurate frequency measurement results in the standards field and prepares the way for refined tests of some of our cherished physical principles, such as the time-stability of some of the basic numbers in physics (e.g., the ``fine-structure'' constant, the speed of light, certain atomic mass ratios etc.), and the equivalence of time-keeping by clocks based on different physics. The stable laser technology also allows time-synchronization between two independent femtosecond lasers so exact they can be made to appear as if the source were a single laser. By improving pump/probe experiments, one important application will be in bond-specific spatial scanning of biological samples. This next decade in optical physics should be a blast.
TL;DR: A broad-bandwidth optical frequency comb is coherently coupled to a high-finesse optical cavity that acts as the sample chamber and sensitive intracavity absorption information is simultaneously available across 100 nanometers in the visible and near-infrared spectral regions.
Abstract: We demonstrate highly efficient cavity ringdown spectroscopy in which a broad-bandwidth optical frequency comb is coherently coupled to a high-finesse optical cavity that acts as the sample chamber. 125,000 optical comb components, each coupled into a specific longitudinal cavity mode, undergo ringdown decays when the cavity input is shut off. Sensitive intracavity absorption information is simultaneously available across 100 nanometers in the visible and near-infrared spectral regions. Real-time, quantitative measurements were made of the trace presence, the transition strengths and linewidths, and the population redistributions due to collisions and the temperature changes for molecules such as C2H2, O2, H2O, and NH3.
TL;DR: A theory for nonlinear, multidimensional plasma waves with phase velocities near the speed of light is presented, appropriate for describing plasma waves excited when all electrons are expelled out from a finite region by either the space charge of a short electron beam or the radiation pressure of an intense laser.
Abstract: We present a theory for nonlinear, multidimensional plasma waves with phase velocities near the speed of light. It is appropriate for describing plasma waves excited when all electrons are expelled out from a finite region by either the space charge of a short electron beam or the radiation pressure of a short intense laser. It works very well for the first bucket before phase mixing occurs. We separate the plasma response into a cavity or blowout region void of all electrons and a sheath of electrons just beyond the cavity. This simple model permits the derivation of a single equation for the boundary of the cavity. It works particularly well for narrow electron bunches and for short lasers with spot sizes matched to the radius of the cavity. It is also used to describe the structure of both the accelerating and focusing fields in the wake.
TL;DR: In this article, a review of recent results of the studies of double laser pulse plasma and ablation for laser induced breakdown spectroscopy applications is presented, where the authors demonstrate that the maximum effect is obtained at some optimum separation delay time between pulses, which depends on several factors, such as the target material, the energy level of excited states responsible for the emission, and the type of enhancement process considered.
TL;DR: Buffered Fourier domain mode locking (FDML), a technique for tailoring the output and multiplying the sweep rate of FDML lasers, is described and the role of the laser source in dynamic range versus sensitivity performance in optical coherence tomography (OCT) imaging is investigated.
Abstract: We describe buffered Fourier domain mode locking (FDML), a technique for tailoring the output and multiplying the sweep rate of FDML lasers. Buffered FDML can be used to create unidirectional wavelength sweeps from the normal bidirectional sweeps in an FDML laser without sacrificing sweep rate. We also investigate the role of the laser source in dynamic range versus sensitivity performance in optical coherence tomography (OCT) imaging. Unidirectional sweep rates of 370 kHz over a 100 nm range at a center wavelength of 1300 nm are achieved. High-speed, swept-source OCT is demonstrated at record speeds of up to 370,000 axial scans per second.
TL;DR: The acceleration of high-energy ion beams (up to several tens of mega-electron-volts per nucleon) following the interaction of short (t 1018 W˙cm-2˙μm-2) laser pulses w...
Abstract: The acceleration of high-energy ion beams (up to several tens of mega-electron-volts per nucleon) following the interaction of short (t 1018 W˙cm-2˙μm-2) laser pulses w...
TL;DR: By introducing the second-harmonic component of the white light in the laser-induced plasma as a local oscillator, coherent detection of broadband THz waves with ambient air is demonstrated for the first time.
Abstract: We report the experimental results and theoretical analysis of broadband detection of terahertz (THz) waves via electric-field-induced second-harmonic generation in laser-induced air plasma with ultrashort laser pulses. By introducing the second-harmonic component of the white light in the laser-induced plasma as a local oscillator, coherent detection of broadband THz waves with ambient air is demonstrated for the first time. Our results show that, depending on the probe intensity, detection of THz waves in air can be categorized as incoherent, hybrid, and coherent detection. Coherent detection is achieved only when the tunnel ionization process dominates in gases.
TL;DR: The method consists of irradiating silicon wafers with femtosecond laser pulses and then coating the surfaces with a layer of fluoroalkylsilane molecules, which creates a surface morphology that exhibits structure on the micro- and nanoscale.
Abstract: We present a simple method for fabricating superhydrophobic silicon surfaces. The method consists of irradiating silicon wafers with femtosecond laser pulses and then coating the surfaces with a layer of fluoroalkylsilane molecules. The laser irradiation creates a surface morphology that exhibits structure on the micro- and nanoscale. By varying the laser fluence, we can tune the surface morphology and the wetting properties. We measured the static and dynamic contact angles for water and hexadecane on these surfaces. For water, the microstructured silicon surfaces yield contact angles higher than 160° and negligible hysteresis. For hexadecane, the microstructuring leads to a transition from nonwetting to wetting.
TL;DR: In this paper, a surface plasmon device composed of a resonant optical antenna integrated on the facet of a commercial diode laser, termed a Plasmonic Laser antenna, was demonstrated.
Abstract: The authors have demonstrated a surface plasmon device composed of a resonant optical antenna integrated on the facet of a commercial diode laser, termed a plasmonic laser antenna. This device generates enhanced and spatially confined optical near fields. Spot sizes of a few tens of nanometers have been measured at a wavelength ∼0.8μm. This device can be implemented in a wide variety of semiconductor lasers emitting in spectral regions ranging from the visible to the far infrared, including quantum cascade lasers. It is potentially useful in many applications including near-field optical microscopes, optical data storage, and heat-assisted magnetic recording.
Patent•
20 Sep 2006
TL;DR: In this paper, a laser hair removal device is described, having a base unit and a hand held laser wand, which generates light pulses of sufficient energy and duration to damage papilla of each hair follicle in the path of the beam.
Abstract: A laser hair removal device (10) is disclosed, having a base unit (12) and a hand held laser wand (14). Laser (18) generates light pulses of sufficient energy and duration to damage papilla of each hair follicle in the path of the beam. The device (10) includes one or more safety features to prevent accidental misuse of the device. In particular the device incorporates a high intensity LED (24) which makes looking at the potential path of the laser uncomfortable thus promoting a blinking reflex. Additionally the device may incorporate a skin contact/proximity sensor (26) to prevent use of the laser away from the skin, and/or one or more locking means to prevent accidental powering of the laser.
TL;DR: In this article, the authors review the mechanisms of and techniques for bulk modification of transparent materials using femtosecond laser pulses and discuss the fabrication of photonic and other structures in transparent materials, including waveguides, couplers, gratings, diffractive lenses, optical data storage and microfluidic channels.
Abstract: When a femtosecond laser pulse is focused inside a transparent material, the optical intensity in the focal volume can become high enough to induce permanent structural modifications such as a refractive index change or the formation of a small vacancy. Thus, one can micromachine structures inside the bulk of a transparent material in three dimensions. We review the mechanisms of and techniques for bulk modification of transparent materials using femtosecond laser pulses and discuss the fabrication of photonic and other structures in transparent materials, including waveguides, couplers, gratings, diffractive lenses, optical data storage, and microfluidic channels.