Spatiotemporal Instability of Femtosecond Pulses in Graded-Index Multimode Fibers

We study the spatiotemporal instability generated by a universal unstable attractor in normal dispersion graded-index multimode fiber for femtosecond pulses for the first time. Experimentally observed spatiotemporal instability sidebands are 91-THz detuned from the pump wavelength of 800 nm. Detailed analysis carried out numerically by employing coupled-mode pulse propagation model. Numerically obtained results are well-aligned with experimental observations. Spatial evolution of the total field and spatiotemporal instability sidebands is calculated numerically, and for the input pulses of 200-fs duration, formation and evolution of spatiotemporal instability are shown in both spatial and temporal domains. Our results present the unique features of spatiotemporal instability, such as remarkable frequency shift with inherited beam shape of instability sidebands. © 1989-2012 IEEE

Spatio-temporal evolution of ultrashort pulses in graded-index multimode fiber at normal dispersion

[No abstract available

CO2 laser polishing of conical shaped optical fiber deflectors

A novel method for polishing conical shaped optical fiber deflectors by modulated CO2 laser exposure is reported. The conical shaped fiber deflector geometry was first formed with rough mechanical polishing, then it was exposed to modulated CO2 laser operating with wavelength at 10.6 µm to achieve fine polish surfaces. The motivation of this work is to demonstrate that the modulated CO2 laser exposure approach allows a fiber surface roughness at a nanometer scale without modifying the conical shape of the fiber deflector. The average surface roughness of mechanically polished fiber deflectors with 30 and 9 µm lapping films was smoothed down to 20.4 and 4.07 nm, respectively, after CO2 laser polishing process. By combining mechanical and laser polishing techniques, fabrication of conical shaped optical fiber deflectors takes less time and it becomes laborer independent and easy to apply. © 2017, Springer-Verlag Berlin Heidelberg

1018 nm Yb-doped high-power fiber laser pumped by broadband pump sources around 915 nm with output power above 100 W

We demonstrate a 1018 nm ytterbium-doped all-fiber laser pumped by tunable pump sources operating in the broad absorption spectrum around 915 nm. In the experiment, two different pump diodes were tested to pump over a wide spectrum ranging from 904 to 924 nm by altering the cooling temperature of the pump diodes. Across this so-called pump wavelength regime having a 20 nm wavelength span, the amplified stimulated emission (ASE) suppression of the resulting laser was generally around 35 dB, showing good suppression ratio. Comparisons to the conventional 976 nm-pumped 1018 nm ytterbium-doped fiber laser were also addressed in this study. Finally, we have tested this system for high power experimentation and obtained 67% maximum optical-to-optical efficiency at an approximately 110 W output power level. To the best of our knowledge, this is the first 1018 nm ytterbium-doped all-fiber laser pumped by tunable pump sources around 915 nm reported in detail. © 2017 Optical Society of America

Optical electrophysiology: Femtosecond laser facilitated electrophysiological measurements from single cells

Summary form only given. One of the indispensable tools of electrophysiology is patch-clamp recording, which enables direct observation of ionic transport through cellular membranes. It is an invaluable research tool, providing experimental information related to cellular electrical metabolism, as well as various pathological conditions. While the inventors of patchclamp recording subsequently became Nobel laurates [1], still it can be considered as one of the most complicated experimental setups, due to the difficulty in puncturing cells using capillary microelectrodes with extreme precision. The throughput of the measurement is also considerably low. Thus, automatized planar patch-clamp systems depending on automatic suction of cells using special chips have emerged, considerably increasing the throughput of electrophysiological measurements for about a decade [2]. However, they are generally restricted to be used only with cultured cells, while they have a poor applicability when isolated cells are considered. Real-time observation of the cells for quality assessment, in terms of the measurement, is also not possible.Here, a novel laser assisted method for performing cellular electrophysiological measurements is suggested and experimentally demonstrated. Femtosecond lasers have previously been used to form nano-sized pores on cell membranes [3], and their effect on membrane electrical polarization was also investigated [4]; however, this study is their very first utilization in electrophysiology. In this study, femtosecond laser pulses, coupled to an optical microscope, are used to first form a micrometer sized pore on a thin polymer membrane separating two electrodes. Afterwards, the nearby cell is sucked on the pore, and a small hole on this cell is formed again with the femtosecond laser, revealing the membrane over the pocket for electrophysiological recording. This method could be utilized to increase the throughput of electrophysiological measurements substantially, while providing ultimate control to the researcher over the experiment, which is non-existent in planar systems

A twisted shaped cladding light stripper by CO2 laser processing for high power fiber lasers and amplifiers

Applications of high power lasers and amplifiers have been increasing because of its superior properties such as high wall-plug efficiency, excellent beam quality, and reliability [1]. Despite advances in high power fiber components, there is still component reliability based challenges on extraction process of unwanted cladding light [2]. There are several techniques to extract the cladding light from the fiber laser system such as high index polymer coating that of working principle is violating the total internal reflection [2], roughened cladding surface which uses the scattering to eliminate the cladding light [3], soft metal coating to absorb the cladding light [4] and CO2 laser processing of cladding to disturb the light path with the structural manipulations and strip the unwanted light from these structures. There are some limitations for each case. The high index polymer CLS are limited by the thermal degradation of recoated polymer [4]. For the roughened or etching CLS, even though very high attenuations levels were achieved, the roughing or etching process decrease the fiber strength. This could create undesired problems such as heat localization and microcrack formation on cladding wall. Here, we present novel method for practical, robust, compact, and all glass cladding light stripper fabrication on Ytterbium (Yb) doped octagonally shaped double clad fiber (DCF)

Surface treatment of conical-shaped optical fiber deflectors by using CO2 laser

[No abstract available

Bio-based polymer nanocomposites based on layered silicates having a reactive and renewable intercalant

Soybean oil-based polymer nanocomposites were synthesized from acrylated epoxidized soybean oil (AESO) combined with styrene monomer and montmorillonite (MMT) clay by using in situ free radical polymerization reaction. Special attention was paid to the modification of MMT clay, which was carried out by methacryl-functionalized and quaternized derivative of methyl oleate intercalant. It was synthesized from olive oil triglyceride, as a renewable intercalant. The resultant nanocomposites were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The effect of increased nanofiller loading in thermal and mechanical properties of the nanocomposites was investigated by thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA). The nanocomposites exhibited improved thermal and dynamic mechanical properties compared with neat acrylated epoxidized soybean oil based polymer matrix. The desired exfoliated nanocomposite structure was achieved when the OrgMMT loading was 1 and 2 wt % whereas partially exfoliated nanocomposite was obtained in 3 wt % loading. It was found that about 400 and 500% increments in storage modulus at glass transition and rubbery regions, respectively were achieved at 2 wt % clay loading compared to neat polymer matrix while the lowest thermal degradation rate was gained by introducing 3 wt % clay loading. © 2013 Wiley Periodicals, Inc

Synthesis of colloidal 2D/3D MoS2 nanostructures by pulsed laser ablation in an organic liquid environment

Two-dimensional MoS2 nanosheets (2D MoS2 NS) and fullerene-like MoS2 nanostructures (3D MoS2 NS) with varying sizes are synthesized by nanosecond laser ablation of hexagonal crystalline 2H-MoS2 powder in organic solution (methanol). Structural, chemical, and optical properties of MoS2 NS are characterized by optical microscopy, scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and Raman and UV-vis-near infrared absorption spectroscopy techniques. Results of the structural analysis show that the obtained MoS2 NS mainly present a layered morphology from micrometer to nanometer sized surface area. Detailed analysis of the product also proves the existence of inorganic polyhedral fullerene-like 3D MoS2 NS generated by pulsed laser ablation in methanol. The possible factors which may lead to formation of both 2D and 3D MoS2 NS in methanol are examined by ab initio calculations and shown to correlate with vacancy formation. The hexagonal crystalline structure of MoS2 NS was determined by XRD analysis. In Raman spectroscopy, the peaks at 380.33 and 405.79 cm-1 corresponding to the E1 2g and A1g phonon modes of MoS2 were clearly observed. The colloidal MoS2 NS solution presents broadband absorption edge tailoring from the UV region to the NIR region. Investigations of MoS2 NS show that the one-step physical process of pulsed laser ablation-bulk MoS2 powder interaction in organic solution opens doors to the formation of two scaled micrometer- and nanometer-sized layered and fullerene-like morphology MoS2 structures. © 2014 American Chemical Society

Chirped-pulse oscillators: a unified standpoint

A completely analytical and unified approach to the theory of chirped-pulse oscillators is presented. The approach developed is based on the approximate integration of the generalized nonlinear complex Ginzburg-Landau equation and demonstrates that a chirped-pulse oscillator is controlled by only two parameters. It makes it easy to trace spread of the real-world characteristics of both solid-state and fiber oscillators operating in the positive dispersion regime.Comment: 12 pages, 11 figures, 5 tables; the mathematical apparatus is described in detail in http://info.tuwien.ac.at/kalashnikov/genNCGLE.htm