The pressing need for knowledge of the detailed wavefront properties of ultra‐bright and ultra‐short pulses produced by free‐electron lasers has spurred the development of several complementary ...characterization approaches. Here a method based on ptychography is presented that can retrieve high‐resolution complex‐valued wavefunctions of individual pulses without strong constraints on the illumination or sample object used. The technique is demonstrated within experimental conditions suited for diffraction experiments and exploiting Kirkpatrick–Baez focusing optics. This lensless technique, applicable to many other short‐pulse instruments, can achieve diffraction‐limited resolution.
Understanding the wavefront of ultra‐bright and ultra‐short pulses of X‐ray free‐electron lasers is both important and challenging. A method based on ptychography that can retrieve full high‐resolution complex‐valued wave functions of individual pulses is presented.
The present paper explores the generalized third-order nonlinear Schrödinger (GTONLS) equation which is used to model ultra-short pulses in optical fibers. The analysis is carried out systematically ...by adopting a complex transformation for reducing the GTONLS equation to a couple of nonlinear ordinary differential equations (NLODEs) with specific conditions such that the resulting NLODEs can be solved through the use of well-designed techniques such as the expa -function and unified methods. As an outcome, different wave structures including dark and bright solitons as well as Jacobi elliptic solutions to the model are formally constructed.
Investigations on nonlinear optics are active, with the applications in the modulators, fiber lasers, optical sensors, etc. In this paper, we focus our attention on a system for the ultra-short ...pulses in an inhomogeneous multi-component nonlinear optical medium. Starting from the existing Lax pair and one-fold Darboux transformation (DT), we construct the N-fold DT of that system, which involves N distinct spectral parameters, where N is a positive integer. The N-fold generalized DT with one spectral parameter is obtained through resorting to the Taylor-series-expansion coefficients of a special solution to that Lax pair. Double-pole soliton solutions of that system are derived via that N-fold generalized DT with N=2. With the aid of the N-fold DT, an N-fold Darboux matrix is constructed, based on which the multi-pole soliton solutions in the determinant form with respect to the electromagnetic field E are determined. Graphically, we find that those double-pole soliton solutions are a kind of the bound-state soliton solutions which represent the elastic interactions between the two solitons. Effects of the coefficients in that system on the double-pole soliton are shown via choosing the trigonometric, linear and quadratic functions. Furthermore, we present the triple-pole soliton and quadruple-pole soliton with respect to E. Our results might be useful in understanding the ultra-short pulses in the nonlinear optical media.
A novel approach for machining of cylindrical hard materials and arbitrary shapes is presented. Alumina-toughened zirconia dental implants with complex geometry are manufactured with femtosecond ...quasi-tangential laser ablation. This rapid prototyping approach for small-scale production decreases the development-time cycle tremendously and trumps conventional approaches. Moreover, a comprehensive parameter study for radial and tangential ablation with single- and multi-pulse is presented. A process achieving an ablation rate of 1 mm3 min−1 with a surface roughness Ra of 0.2 μm is introduced. The meta-stable tetragonal phase of the ceramic persists and is assessed via Raman spectroscopy. The small heat-affected zone is subsequently ablated with a radial laser process step. Hence, high-precision dental implants are producible with a mean error of smaller 5 μm over the complete contour.
This work presents the development of a new sub-THz source for the generation of trains of coherent high-power ultra-short pulses at 263 GHz via passive mode-locking of two coupled helical gyro-TWTs. ...For the first time, it is shown that the operation of such passive mode-locked helical gyro-TWTs in the hard excitation regime is of particular importance to reach the optimal coherency of the generated pulses. This could be of particular interest for some new time-domain DNP-NMR methods.
Display omitted
•Laser ablation of copper with ultra-short burst pulses was optically investigated.•The evolution of the ablation clouds in time was imaged for 1, 2 and 3 pulses.•After a single ...pulse, a dense cloud expands with a velocity of approximately 200 m/s.•A second pulse applied 12.2 ns after the first results in suppression of ablation.•A third pulse applied after the first pulse ablates a higher amount of mass.
Investigations on the ablation of copper with ultra-short laser pulses using single pulses and bursts of two or three pulses are presented in this paper. On the basis of shadowgraphic experiments, it is shown that the material ablated by the first pulse is shielding the second pulse of a burst. In addition, material is re-deposited, which significantly counteracts the ablation process. Adding a third pulse to the burst again leads to ablation of material, but with an ablation cloud containing more material than the one generated by a single pulse.
Abstract
In this work, we describe an interferometric method to generate ultra-short pulses below the Fourier limit. It is done by extending concepts first developed in the spatial domain to achieve ...sub-diffractive beams through the addition of a spatial chirp in one of the arms of a Michelson interferometer using a spherical mirror. To experimentally synthesize sub-Fourier pulses, we replace the spherical mirror with a water cell, since it produces chirp in the temporal domain. We also present an alternative procedure, based on asymmetrical interference between the widened pulse and the original pulse where the peaks of both pulses exhibit a temporal delay achieving the narrowing of ultra-short pulses with sub-Fourier scales. To characterize the performance of the system, we performed a preliminary assessment considering the percentage of full width at half-maximum shrinking obtained for each scheme. By means of a symmetrical configuration, 7% and 12% pulse reductions were verified, both experimentally and analytically, while for the non-symmetrical configuration, 10% and 24% reductions were achieved corresponding to main lobe to side-lobe ratios of 10% and 30%. The experimental setup scheme is simple, versatile and able to work with high-power laser sources and ultra-short pulses with a broad bandwidth at any central wavelength. The results presented in this work are promising and help to enlighten new routes and strategies in the design of coherent control systems. We envision that they will become broadly useful in different areas from strong field domain to quantum information.
Abstract
For our model material aluminum, the influence of laser pulse duration in the range between 0.5 and 16 ps on the ablation depth is investigated in a computational study with a hybrid ...approach, combining molecular dynamics with the well known two-temperature model. A simple, yet expedient extension is proposed to account for the delayed thermalization as well as ballistic transport of the excited electrons. Comparing the simulated ablation depths to a series of our own experiments, the extension is found to considerably increase the predictive power of the model.
Laser processing with ultra-short double pulses has gained attraction since the beginning of the 2000s. In the last decade, pulse bursts consisting of multiple pulses with a delay of several 10 ns ...and less found their way into the area of micromachining of metals, opening up completely new process regimes and allowing an increase in the structuring rates and surface quality of machined samples. Several physical effects such as shielding or re-deposition of material have led to a new understanding of the related machining strategies and processing regimes. Results of both experimental and numerical investigations are placed into context for different time scales during laser processing. This review is dedicated to the fundamental physical phenomena taking place during burst processing and their respective effects on machining results of metals in the ultra-short pulse regime for delays ranging from several 100 fs to several microseconds. Furthermore, technical applications based on these effects are reviewed.
A novel approach for machining of cylindrical ultra-hard materials with a highly defined contour is presented. Diamond grinding tools with complex geometry are manufactured with picosecond orthogonal ...and quasi-tangential laser ablation. Hitherto, laser manufacturing required a special axis configuration and optical beam deflection devices are utilized. Here, strategies and processes on a scanhead-free configuration using ultra-short pulsed laser are discussed enabling straight-forward implementation in industry. This rapid and flexible approach for the production of master tools for industrial grinding processes reveals benefits compared to conventional techniques. The manufacturing time is comparable to standard processes, however, increased grain protrusion is attained with the presented laser sharpening strategy. An ablation study for maximal material-removal rate reveals the impact of wavelength, strategy, and repetition rate at high average power up to 100 W. A combined laser manufacturing routine enables an ablation rate of 35 mm3 min−1 and a maximal geometric deviation of 3 μm after finishing. The final grinding tools are sharpened by a radial laser process preferentially removing the metal-based binding material. Hence, high-precision diamond grinding wheels with a mean error of smaller 1 μm over millimeter-sized contours can be manufactured. The meta-stable diamond structure persists and is assessed via Raman spectroscopy studies at laser cut grains.
Display omitted
•All-in-one laser conditioning process for super-abrasive grinding tools including profiling, truing, and sharpening.•High-precision laser manufacturing with tangential strategies using 100 W average power enables a 3μm tolerance band.•Scanhead-free laser processes with mechanical axes and a spindle allow an industrial implementation on existing machine tools.•The diamond phase persists proven by Raman spectroscopy and set-free cutting edges facilitate high-speed grinding.
PDF
