Linear and nonlinear optical properties of gold nanoparticle-doped photonic crystal fiber

Faris H, Ahmed H, Mamdouh S, Thambiratnam K, Mohamed T. Using Femtosecond Laser Pulses to Explore the Nonlinear Optical Properties of Au NP Colloids That Were Synthesized by Laser Ablation

In this study, we experimentally investigated the nonlinear optical properties of Au nanoparticles (Au NPs) that were prepared in pure distilled water using the laser ablation method. The Au NPs were prepared using a nanosecond Nd:YAG laser with an ablation time of 5 or 10 min at a constant laser energy of 100 mJ. The structure and the linear optical properties of the Au NPs were investigated using a transmission electron microscope (TEM) and UV-visible spectrophotometer analysis, respectively. The TEM measurements showed that the average size of the Au NPs varied from 20.3 to 14.1 nm, depending on the laser ablation time. The z-scan technique was used to investigate the nonlinear refractive index (n2) and nonlinear absorption coefficient (γ) of the Au NPs, which were irradiated at different excitation wavelengths that ranged from 740 to 820 nm and at different average powers that ranged from 0.8 to 1.6 W. The Au NP samples exhibited a reverse saturable absorption (RSA) behavior that increased when the excitation wavelength and/or incident laser power increased. In addition, the Au NPs acted as a self-defocusing material whenever the excitation wavelength or incident power were modified.

Nano-Structured Optical Fibers Made of Glass-Ceramics, and Phase Separated and Metallic Particle-Containing Glasses

For years, scientists have been looking for different techniques to make glasses perfect: fully amorphous and ideally homogeneous. Meanwhile, recent advances in the development of particle-containing glasses (PCG), defined in this paper as glass-ceramics, glasses doped with metallic nanoparticles, and phase-separated glasses show that these “imperfect” glasses can result in better optical materials if particles of desired chemistry, size, and shape are present in the glass. It has been shown that PCGs can be used for the fabrication of nanostructured fibers—a novel class of media for fiber optics. These unique optical fibers are able to outperform their traditional glass counterparts in terms of available emission spectral range, quantum efficiency, non-linear properties, fabricated sensors sensitivity, and other parameters. Being rather special, nanostructured fibers require new, unconventional solutions on the materials used, fabrication, and characterization techniques, limiting the use of these novel materials. This work overviews practical aspects and progress in the fabrication and characterization methods of the particle-containing glasses with particular attention to nanostructured fibers made of these materials. A review of the recent achievements shows that current technologies allow producing high-optical quality PCG-fibers of different types, and the unique optical properties of these nanostructured fibers make them prospective for applications in lasers, optical communications, medicine, lighting, and other areas of science and industry.

Degenerate four-wave mixing for measurement of magnetic field using a nanoparticles-doped highly nonlinear photonic crystal fiber

A novel magnetic field sensor based on the degenerate four-wave mixing (DFWM) technique is theoretically proposed using a As₂S₃-core silica-cladding photonic crystal fiber (PCF). In order to enhance the sensitivity, we put forth a novel design of highly nonlinear PCF where the silica cladding is doped with either Au, Ag, or Al metallic nanoparticles. The effect of volume fraction of the nanoparticles within the cladding and the size of nanoparticles are considered as the control parameters in designing the magnetic field PCF sensor to obtain high sensitivity using this novel DFWM scheme. The PCF structure of the proposed sensor is optimized with the proposed pitch of 3 μm and air hole diameter of 2.78 μm. We consider a pumping pulsed laser light with a wavelength of 2100 nm in the mid-IR regime. It has been found that the optimized PCF with Al-SiO₂-cladding with small volume fraction and small nanoparticle size possess magnetic field sensitivity values of 2.74 and -0.058  nm/Oe for the Stokes and anti-Stokes gain lines.

Fabrication and optical characterization of silica optical fibers containing gold nanoparticles

Gold nanoparticles have been used since antiquity for the production of red-colored glasses. More recently, it was determined that this color is caused by plasmon resonance, which additionally increases the material's nonlinear optical response, allowing for the improvement of numerous optical devices. Interest in silica fibers containing gold nanoparticles has increased recently, aiming at the integration of nonlinear devices with conventional optical fibers. However, fabrication is challenging due to the high temperatures required for silica processing and fibers with gold nanoparticles were solely demonstrated using sol-gel techniques. We show a new fabrication technique based on standard preform/fiber fabrication methods, where nanoparticles are nucleated by heat in a furnace or by laser exposure with unprecedented control over particle size, concentration, and distribution. Plasmon absorption peaks exceeding 800 dB m(-1) at 514-536 nm wavelengths were observed, indicating higher achievable nanoparticle concentrations than previously reported. The measured resonant nonlinear refractive index, (6.75 ± 0.55) × 10(-15) m(2) W(-1), represents an improvement of >50×.

Laser-induced growth of nanocrystals embedded in porous materials

Space localization of the linear and nonlinear optical properties in a transparent medium at the submicron scale is still a challenge to yield the future generation of photonic devices. Laser irradiation techniques have always been thought to structure the matter at the nanometer scale, but combining them with doping methods made it possible to generate local growth of several types of nanocrystals in different kinds of silicate matrices. This paper summarizes the most recent works developed in our group, where the investigated nanoparticles are either made of metal (gold) or chalcogenide semiconductors (CdS, PbS), grown in precursor-impregnated porous xerogels under different laser irradiations. This review is associated to new results on silver nanocrystals in the same kind of matrices. It is shown that, depending on the employed laser, the particles can be formed near the sample surface or deep inside the silica matrix. Photothermal and/or photochemical mechanisms may be invoked to explain the nanoparticle growth, depending on the laser, precursor, and matrix. One striking result is that metal salt reduction, necessary to the production of the corresponding nanoparticles, can efficiently occur due to the thermal wrenching of electrons from the matrix itself or due to multiphoton absorption of the laser light by a reducer additive in femtosecond regime. Very localized semiconductor quantum dots could also be generated using ultrashort pulses, but while PbS nanoparticles grow faster than CdS particles due to one-photon absorption, this better efficiency is counterbalanced by a sensitivity to oxidation. In most cases where the reaction efficiency is high, particles larger than the pores have been obtained, showing that a fast diffusion of the species through the interconnected porosity can modify the matrix itself. Based on our experience in these techniques, we compare several examples of laser-induced nanocrystal growth in porous silica xerogels, which allows extracting the best experimental conditions to obtain an efficient particle production and to avoid stability or oxidation problems.

H2-induced copper and silver nanoparticle precipitation inside sol-gel silica optical fiber preforms

Ionic copper- or silver-doped dense silica rods have been prepared by sintering sol-gel porous silica xerogels doped with ionic precursors. The precipitation of Cu or Ag nanoparticles was achieved by heat treatment under hydrogen followed by annealing under air atmosphere. The surface plasmon resonance bands of copper and silver nanoparticles have been clearly observed in the absorption spectra. The spectral positions of these bands were found to depend slightly on the particle size, which could be tuned by varying the annealing conditions. Hence, transmission electron microscopy showed the formation of spherical copper nanoparticles with diameters in the range of 3.3 to 5.6 nm. On the other hand, in the case of silver, both spherical nanoparticles with diameters in the range of 3 to 6 nm and nano-rods were obtained.