- 标题
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Zukunftsperspektiven des Femtosekundenlasers in der Vorderabschnittschirurgie; Future perspectives of the femtosecond laser in anterior segment surgery;
摘要： Around 12 years after its introduction laser cataract surgery (LCS) has enabled remarkable progress, such as extremely precise capsulotomy and lens fragmentation with reduced or no ultrasound energy at all (zero phako); however, another innovation push is necessary to bring this technology to its full potential. Among the many benefits that have not yet been fully explored are primary posterior laser capsulotomy (PPLC) and the use of the femtosecond laser in pediatric cataract patients. In the present collective of patients in whom a PPLC was carried out at the end of the operation, a clearly reduced prevalence of secondary cataract could be observed, whereas the short additional intervention was not associated with notable complications. The LCS in infants is best carried out as an off-label procedure, which has been rendered more precise by the Bochum formula. In the near future, postoperative laser fine tuning will enable the target refraction to be achieved in most patients. Laser-induced refractive index change (LIRIC) will enable very exact refraction alterations on an already implanted intraocular lens (IOL), on a contact lens and on a treatment native cornea. A new version of the Scheimpflug camera will be used just prior to surgery to analyze the morphology and kernel density of the lens opacity and to carry out a real-time grading of lens hardness. Based on this categorization, where the system classifies the results into five different density grades, the surgeon is automatically provided with an individualized fragmentation pattern defined preoperatively by the operator. A further innovation of the same system involves microcorneal incisions for fine tuning of residual refractive deficits.
关键词： Femtosecond laser-assisted cataract surgery,Bochum formula,Postoperative refractive enhancement/fine tuning,Primary posterior laser capsulotomy,Laser-induced refractive index change
更新于2025-09-23 15:19:57
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Effect of applied electric field on the nonlinear optical properties of modulation-doped GaAs/Al Ga1-As double quantum well
摘要： In the present study, the effects of varying doping concentration and applied electric field on the intersubband-related optical absorption and relative refractive index change coefficients in modulation-doped GaAs/AlxGa1?xAs double quantum wells are theoretically investigated. The allowed energy levels and the corresponding wave-functions are calculated by solving the Schr?dinger and Poisson equations self-consistently within the framework of the effective-mass and parabolic band approximations. The optical coefficients are evaluated using the compact density matrix formalism within an iterative procedure. The numerical results are presented for two different doping concentration and several values of the electric field. They show that both the peak position and the magnitude of the calculated total optical absorption coefficients and refractive index changes are significantly affected by the applied electric field and the doping concentration. The treatment is suitable to consider the general problem with different wells and barrier sizes, although the barrier width should preferably be small enough as to allow for an effective inter-well coupling.
关键词： Relative refractive index change,Modulation-doped QW,Absorption coefficient,self-consistent method
更新于2025-09-23 15:19:57
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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) - Analysis of Various Approaches for the Fabrication of Diffractive Optical Elements
摘要： Diffractive Optical Elements (DOEs) exist for a large range of applications. Usually DOEs are obtained by combining lithographic techniques and etching in order to achieve pre-determined phase patterns. That way, it is possible to shape or split laser beams with very high efficiencies. Indeed for binary element which consist of two phase levels (0 and π) the diffraction efficiency is around 75% and this efficiency can approach 100% for multilevel elements. Various illustrations of DOEs can be found in the literature for example using organic materials like photoresists or inorganic materials such as silica or chalcogenide layers. Recent work has shown that DOEs can also be recorded in the volume of photosensitive chalcogenide layers, but no precise comparison of this class of DOEs has ever been made with classical DOEs. In this paper we propose to study binary DOEs fabricated with conventional lithography (based on local control of the thickness) and similar one fabricated using photo-induced refractive index change in As2S3 layers.
关键词： etching,phase patterns,silica,laser beams,photo-induced refractive index change,photoresists,lithography,As2S3 layers,chalcogenide layers,Diffractive Optical Elements,diffraction efficiency
更新于2025-09-16 10:30:52
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Double-Track Waveguides inside Calcium Fluoride Crystals
摘要： Calcium Fluoride (CaF2) was selected owing to its cubic symmetry and excellent luminescence properties as a crystal of interest, and ultrafast laser inscription of in-bulk double-track waveguides was realized. The guiding properties of these waveguides in relation to the writing energy of the femtosecond pulse are presented. The modified double-track waveguides have been studied by systematic developments of beam propagation experiments and numerical simulations. Furthermore, an adapted model and concepts were engaged for the quantitative and qualitative characterization of the waveguides, particularly for the transmission loss measurements and the three-dimensional refractive index mappings of the modified zones. Additionally, polarization-dependent guiding was investigated.
关键词： Calcium Fluoride,quantitative phase imaging,waveguides,femtosecond lasers,cubic crystal,micro-processing,double-track,photonic device,direct laser writing (DLW),refractive index change
更新于2025-09-16 10:30:52
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Stress-induced refractive index changes in laser fibers and preforms
摘要： Refractive index profile of the core is a key design parameter in fiber lasers and amplifiers. During manufacturing, the initial information of the index profile is obtained from the preform, while ultimately the performance is defined by the index profile of the fiber. Depending on stresses and diffusion, the two profiles may be different. It is possible to predict more accurately the laser fiber refractive index when we apply a stress-induced index change model to the measured preform index profile data. The improved capability to predict the fiber index from preform increases the confidence in achieving the designed index profile in fiber, which enables faster process feedback and higher fiber yields.
关键词： laser fiber,tension,optical fiber,modelling,thermal stress,preform,Refractive index change,DND,stress
更新于2025-09-11 14:15:04
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Measurement of In-fiber Refractive Index Change Using a Mach-Zehnder Interferometer
摘要： We report, for the first time, the use of a fiber optic Mach-Zehnder interferometer to measure core refractive index changes written by an ultrafast laser irradiation. The core-offset interferometer was constructed by splicing a slightly misaligned stub of standard single mode fiber between lead-in and lead-out optical fibers. When the core refractive index of an in-fiber interferometer is altered, it changes the phase of the core light. Since the phase of light propagating in the cladding (reference arm) remains unchanged, the transmission fringe pattern of the interferometer observes a spectral shift. The spectral shift was used to quantify the effective core refractive index change in a standard single mode fiber. Measurement of effective refractive index changes as high as 0.01356 and as low as 0.000475 are reported in this work.
关键词： effective refractive index change,fiber-optic sensor,ultrafast laser,Mach-Zehnder interferometer,in-fiber refractive index measurement
更新于2025-09-04 15:30:14