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Investigation of the structure and optical absorption of silicon coated with a chromium film after femtosecond laser irradiation
摘要： Microstructured silicon (Si) doped with chromium (Cr) has been produced by femtosecond laser pulses. Microstructured surfaces were produced after laser irradiation at different fluence values. The dependence of its absorptance on laser fluence and thermal annealing were investigated. Microstructured Si that was fabricated at lower laser fluences exhibited perfect absorption below the Si bandgap as well as better thermal stability. The crystal structures of samples obtained before and after thermal annealing were characterized by Raman spectroscopy. The mechanism of absorption below the bandgap of Si is discussed in detail based on the results from Raman spectroscopy and optical absorption.
关键词： femtosecond laser,microstructured silicon,chromium doping,infrared absorption
更新于2025-09-11 14:15:04
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Boson Band Vibrations Aid Refractive Index Mapping of Waveguides in High Index Chalcogenide Glass
摘要： The boson band mapping of waveguides fabricated by femtosecond laser inscription was used for the first time to identify and understand the material densification profile in chalcogenide glasses. The refractive index mapping of waveguides in high refractive index dielectrics is problematic as there are no known techniques. Refracted near field technique cannot be carried out in glasses with refractive index higher than 1.6 due to the lack of availability or toxic nature of the index matching oil. Though other techniques based on holographic and phase microscopies are available, sample preparation steps compatible with reliable measurement are tedious and in some cases, like diamond, is almost impossible. In this work, using the information obtained from the Bosonic band vibrations, we explain waveguide formation in Gallium Lanthanum Sulphide (GLS) glass. The boson peak shows up in any amorphous material regardless of its constituents or stoichiometry and is observed in the low frequency region between 0 – 100 cm-1. Their origin is a well debated and controversial topic. Here we make use of its response to the physical properties of the material.
关键词： refractive index mapping,waveguides,boson band vibrations,chalcogenide glass,femtosecond laser inscription
更新于2025-09-11 14:15:04
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Accelerated inactivation of <i>M13</i> bacteriophage using millijoule Femtosecond Lasers
摘要： Irradiation of femtosecond (fs) pulse lasers in the visible and near-infrared ranges have been proposed as a promising candidate for inactivating viruses. However, in order to achieve significant virus inactivation, past works have required relatively long irradiation times (1 hour or longer), even for small volumes. Given its advantages compared with other techniques, there is an urgent need to shorten the time required to inactivate viruses using fs laser technology. In this study, we investigate the inactivation of purified M13 bacteriophage in phosphate-buffered saline with large active volume (1 cm3), and short exposure time (several minutes), using lasers with 20 mJ/pulse energy at various wavelengths (800 nm, 400 nm or both 800 nm and 400 nm combined). For an exposure time of 15 min and 2 min, the use of a 400 nm wavelength laser results in a high load reduction of 5.8 ± 0.3 and 2.9 ± 0.15, respectively, on the log10 scale of viability. We show that virus inactivation using the 400 nm laser is much more efficient compared with that using 800 nm laser, or the simultaneous irradiation of 400 nm and 800 nm lasers. Higher pathogen inactivation is observed for lasers with shorter pulse duration, whereas at longer pulse durations, the inactivation is reduced. For millijoule-energy fs laser irradiation, the M13 bacteriophage inactivation, via the reduction of the functionality of M13 bacteriophages, is accompanied with relatively small amounts of genetic damage.
关键词： femtosecond laser,inactivation,M13 bacteriophage,load reduction
更新于2025-09-11 14:15:04
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[IEEE 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Paris, France (2019.9.1-2019.9.6)] 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Generation of a Few Cycle Terahertz Pulse in Aperiodically Poled Lithium Niobate by Sequence of Pump Pulses
摘要： It is shown that chirped aperiodically poled lithium niobate crystal is capable to generate powerful THz pulses with controllable number of THz field oscillations (from nearly single- to multi-cycles), when it is pumped by sequence of femtosecond laser pulses with chirped delays between adjacent pulses. The peak electric field strength of about 0.3 MV/cm (for non-focused THz beam) is predicted if intensity of each pump pulse in the sequence is 20 GW/cm2.
关键词： Optical rectification,Aperiodically poled lithium niobate,Terahertz pulse,Femtosecond laser pulses
更新于2025-09-11 14:15:04
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Femtosecond Laser Double Pulses Nanofabrication on Silicon
摘要： The temporal shaping femtosecond (fs) laser is realized by dividing a fs laser pulse into two identical sub-pulses. The double-pulse fs laser can be used to effectively control the initial free electron state such as electron temperature, capacity and density, etc. to improve the surface morphology quality. In this experiment, silicon was fabricated using the double-pulse fs laser. It was found that the average diameter of ablated micro- or nanoholes decreases with the increasing pulse delay (up to 1.5 ps) under the same laser fluence and the phenomenon was explained quantitatively by the plasma model. Furthermore, nanoholes were achieved using the double-pulse fs laser, which cannot be obtained by single pulse laser, and the processing size can be reduced to below 200 nm.
关键词： femtosecond laser,silicon,plasma model,double pulses,nanofabrication
更新于2025-09-11 14:15:04
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Comparison of clinical outcomes between manual and femtosecond laser techniques for intrastromal corneal ring segment implantation
摘要： The purpose was to compare the visual, refractive and aberrometric results of intrastromal corneal ring segments implantation with manual dissection and femtosecond laser–assisted surgery. This is a multicentre study, which included consecutive patients with paracentral keratoconus, in which the difference between the axes of the topographic flattest and the coma aberration was <60°, who had Ferrara-type intrastromal corneal ring segment implantation using manual dissection or femtosecond laser technique. LogMAR uncorrected (uncorrected distance visual acuity) and corrected (corrected distance visual acuity) distance visual acuity, refractive errors and the root mean square for corneal coma-like aberration were recorded before and at 6 months after surgery. The study included 84 and 110 eyes in the manual group and in the femtosecond group, respectively. After surgery, there was a statistically significant improvement in uncorrected distance visual acuity and corrected distance visual acuity for both groups (p < 0.0001), and there were no statistically significant differences between groups (p > 0.3). For both groups, there was a reduction in spherical equivalent after intrastromal corneal ring segment implantation (p < 0.0001). There were no statistically significant differences between groups in the magnitude of spherical equivalent reduction (p = 0.34) The magnitude of the root mean square coma-like reduction was 0.93 ± 0.76 and 0.83 ± 0.80 μm in the manual and femtosecond group, respectively (p = 0.2). While in the femtosecond laser group no complications were reported, in the manual group, the intraoperative or postoperative complications rate was 13.09%. Although both surgical techniques provide comparable visual, refractive and aberrometric outcomes, it should be noted that the femtosecond laser is a safer surgical procedure, with no complications reported.
关键词： intracorneal ring segments,femtosecond laser surgery,manual surgery,Keratoconus
更新于2025-09-11 14:15:04
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Plasmonic layer-selective all-optical switching of magnetization with nanometer resolution
摘要： All-optical magnetization reversal with femtosecond laser pulses facilitates the fastest and least dissipative magnetic recording, but writing magnetic bits with spatial resolution better than the wavelength of light has so far been seen as a major challenge. Here, we demonstrate that a single femtosecond laser pulse of wavelength 800 nm can be used to toggle the magnetization exclusively within one of two 10-nm thick magnetic nanolayers, separated by just 80 nm, without affecting the other one. The choice of the addressed layer is enabled by the excitation of a plasmon-polariton at a targeted interface of the nanostructure, and realized merely by rotating the polarization-axis of the linearly-polarized ultrashort optical pulse by 90°. Our results unveil a robust tool that can be deployed to reliably switch magnetization in targeted nanolayers of heterostructures, and paves the way to increasing the storage density of opto-magnetic recording by a factor of at least 2.
关键词： femtosecond laser pulses,plasmon-polariton,storage density,magnetic recording,all-optical magnetization reversal
更新于2025-09-11 14:15:04
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[IEEE 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Paris, France (2019.9.1-2019.9.6)] 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Femtosecond Laser Processing and Evaluation of Broadband THz Anti-Reflection Structures
摘要： We fabricate terahertz anti-reflection structures on the surface of high-resistivity silicon via femtosecond laser processing. We measure its spectral properties by terahertz time-domain spectroscopy, and find a broadband increase in transmissivity over 0.3 - 2.5 THz. We investigate the observed spectral characteristics of this transmission by using numerical simulation. We successfully reproduce the observed result for all frequencies, including a previously undocumented high-frequency drop-off, when the model includes additional material losses. We believe these effects to be induced by the laser-ablation fabrication process.
关键词： anti-reflection,high-resistivity silicon,femtosecond laser processing,terahertz time-domain spectroscopy,terahertz
更新于2025-09-11 14:15:04
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Growth Promotion of Targeted Crystal Face by Nano-Processing via Laser Ablation
摘要： Control of crystal shape is an indispensable step for various applications of crystalline products. However, obtaining the desired crystal shape by conventionally tuning environmental conditions (temperature, additives, etc.) cannot always be reached. Recently, we have developed an innovative approach for spatiotemporal control of crystal growth of proteins and amino acids by locally modifying crystal structure (e.g., formation of screw dislocations) via femtosecond (fs) laser ablation. In this work, to clarify the appropriate laser condition for controlling the shape of single crystals with minimized damage, we first systematically investigated the dependence of pulse duration on laser ablation and crystal growth of L-phenylalanine (L-Phe). By using a laser system with tunable pulse durations from fs to nanosecond (ns), we found fs laser ablation can offer nanometer-sized, sharp etching of which diameter was smaller than the diffraction limit. By utilizing such nano-processing via fs laser ablation for promoting the growth of a targeted crystal face, we successfully demonstrated the preparation of a bulky crystal of L-Phe, which are difficult to be obtained by conventional crystallization methods.
关键词： L-phenylalanine,nano-processing,single crystal growth,crystal shape control,femtosecond laser ablation
更新于2025-09-11 14:15:04
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Comparison of 9.0 and 9.2?mm Flap Diameter Options of Femtosecond Laser In-Situ Keratomileusis for Hypermetropia and Hypermetropic Astigmatism
摘要： Aim. To compare the postoperative one-year outcomes of asphericity (Q) and high order aberration (HOA) values of 9.0 and 9.2 mm diameter ?ap groups in hypermetropia and hypermetropic astigmatism subjects who underwent femtosecond laser in-situ keratomileusis (LASIK). Materials and Methods. The study included 68 eyes of 34 patients. A femtosecond laser platform (Allegrato Wave, Wavelight AG, Erlangen, Germany) was used for ?ap cutting. Corneal stroma was ablated using Wavelight EX500 with wavefront-optimized pro?le (WaveLight GmbH, Erlangen, Germany). 9.0 mm ?ap diameter was randomly chosen for one eye, and 9.2 mm ?ap diameter was chosen for the fellow eye. Two eyes of the patients who used two di?erent ?ap diameters were enrolled into two di?erent groups. Corneal stroma was ablated using Wavelight EX500 with wavefront-optimized pro?le (WaveLight GmbH, Erlangen, Germany). Postoperative one-year outcomes of Q and HOA values of 9.0 and 9.2 mm diameter ?ap groups were compared statistically. Results. The preoperative manifest refraction spherical equivalents of the 9.0 and 9.2 mm diameter ?ap groups were 1.86 ± 1.81 D and 1.69 ± 1.99 D (p ? 0.754). No intraoperative or postoperative complications were observed. At postoperative one-year, Q values were 0.98 ± 0.13 D and 0.91 ± 0.15 D (p ? 0.029). HOAs including horizontal and vertical coma, horizontal and vertical trefoil, spherical aberration, and second order vertical coma were not signi?cantly di?erent (p > 0.05 for all). Total HOA values were 1.62 ± 0.14 and 1.40 ± 0.16, in the 9.0 and 9.2 mm diameter ?ap groups, respectively (p < 0.001). Conclusion. Both the 9.0 and 9.2 mm diameter ?ap options in femtosecond LASIK are equally safe and e?ective. Many of the HOA values are similar in both options, and better results were provided in terms of total HOA and Q values with the 9.2 mm diameter ?ap option. This study was registered with trial registration number 118-011.
关键词： hypermetropic astigmatism,asphericity,femtosecond laser,LASIK,high order aberration,hypermetropia,flap diameter
更新于2025-09-11 14:15:04