In this work we demonstrate comprehensive studies on graphene oxide (GO) and reduced graphene oxide (rGO) based saturable absorbers (SA) for mode-locking of Er-doped fiber lasers. The paper describes the fabrication process of both saturable absorbers and detailed comparison of their parameters. Our results show, that there is no significant difference in the laser performance between the investigated SA. Both provided stable, mode-locked operation with sub-400 fs soliton pulses and more than 9 nm optical bandwidth at 1560 nm center wavelength. It has been shown that GO might be successfully used as an efficient SA without the need of its reduction to rGO. Taking into account simpler manufacturing technology and the possibility of mass production, GO seems to be a good candidate as a cost-effective material for saturable absorbers for Er-doped fiber lasers.
Graphene family materials have unique properties, which make them valuable for a range of applications. The antibacterial properties of graphene have been reported; however, findings have been contradictory. This study reports on the antimicrobial proprieties of three different graphene materials (pristine graphene (pG), graphene oxide (GO), and reduced graphene oxide (rGO)) against the food-borne bacterial pathogens Listeria monocytogenes and Salmonella enterica. A high concentration (250 μg/mL) of all the analyzed graphenes completely inhibited the growth of both pathogens, despite their difference in bacterial cell wall structure. At a lower concentration (25 μg/mL), similar effects were only observed with GO, as growth inhibition decreased with pG and rGO at the lower concentration. Interaction of the nanoparticles with the pathogenic bacteria was found to differ depending on the form of graphene. Microscopic imaging demonstrated that bacteria were arranged at the edges of pG and rGO, while with GO, they adhered to the nanoparticle surface. GO was found to have the highest antibacterial activity.
We demonstrate generation of linearly polarized pulses from a passively Q-switched Erbiumdoped fiber laser. The cavity was designed using only polarization maintaining (PM) fibers and components, resulting in linearly polarized output beam with degree of polarization (DOP) at the level of 97.6%. Reduced graphene oxide (rGO) was used as a saturable absorber for Q-switched operation. The laser was capable of delivering 1.85 µs pulses with 125 nJ pulse energy at 115 kHz repetition rate.Graphene, due to its unique nonlinear optical properties, has been widely used as a saturable absorber (SA) for various types of lasers. Since the demonstration of a mode-locked fiber laser [1], many setups were presented, utilizing erbium-[1-4], ytterbium- [5,6] and thulium-doped fibers [7]. Thanks to the high modulation depth, broad operation range and ultrafast recovery time, graphene may be used to generate ultrashort pulses (e.g. 174 fs [4]) from passively mode-locked lasers. Recently, also passive Q-switching with graphene-SA has been demonstrated [8][9][10][11]. In a passively Q-switched laser, the cavity losses are automatically modulated by the saturable absorber, so there is no need of placing an active component (e.g. acoustooptic modulator) inside the resonator. The repetition rates of such lasers are lower and the pulses are longer in comparison to mode-locked lasers, but the achieved pulse energies usually exceed those which are achievable from mode-locked oscillators. Recent reports have shown the possibility of achieving 40 nJ pulses from graphene Q-switched Er-doped lasers [8]. Nevertheless, all previous reports on graphene Q-switched lasers were related to non-polarization maintaining cavities. Therefore, the polarization state of the output beam was undetermined. Such setups require polarization controllers (PC) placed in the laser cavity in order to induce the pulsed operation. In many practical applications (industrial or scientific) it is extremely important to maintain the linear polarization state of the laser output. In general, the saturable absorption in graphene is a polarization-independent process, which was verified experimentally by Zhang et al. [12]. It means, that graphene-based saturable absorbers may be used in PM cavities with only one, well-defined polarization state, without affecting the saturable absorption. This opens a possibility to generate scalar solitons in mode-locked lasers [13,14] or linearly polarized pulses from Q-switched lasers, with the DOP near to 100%.Up till now, many various methods were used to fabricate graphene saturable absorbers. For example, Bao et. al and Zhang et. al [1,2] demonstrated the usage of chemical vapor deposition (CVD) to synthetize graphene on Ni films. Also mechanical exfoliation of graphene from bulk graphite may lead to efficient fiber laser mode-locking [15]. Wet chemistry offers a wide spectrum of techniques of preparing flake graphene and its derivatives. Among them two methods are most attractive and efficient. The first is direct exfoliation of gra...
The carbon-based nanomaterial family consists of nanoparticles containing allotropes of carbon, which may have a number of interactions with biological systems. The objective of this study was to evaluate the toxicity of nanoparticles comprised of pristine graphene, reduced graphene oxide, graphene oxide, graphite, and ultradispersed detonation diamond in a U87 cell line. The scope of the work consisted of structural analysis of the nanoparticles using transmission electron microscopy, evaluation of cell morphology, and assessment of cell viability by Trypan blue assay and level of DNA fragmentation of U87 cells after 24 hours of incubation with 50 μg/mL carbon nanoparticles. DNA fragmentation was studied using single-cell gel electrophoresis. Incubation with nanoparticles containing the allotropes of carbon did not alter the morphology of the U87 cancer cells. However, incubation with pristine graphene and reduced graphene oxide led to a significant decrease in cell viability, whereas incubation with graphene oxide, graphite, and ultradispersed detonation diamond led to a smaller decrease in cell viability. The results of a comet assay demonstrated that pristine graphene, reduced graphene oxide, graphite, and ultradispersed detonation diamond caused DNA damage and were therefore genotoxic in U87 cells, whereas graphene oxide was not.
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