الفهرس 
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Abstract
The purpose of the current study is to enhance the performance parameters of optical fiber sensor for detection of lead ions in water. Optical fiber sensing is an important sensing technique where combining the advantage of using new materials such as graphene and the features of the optical fibers. Previously, the sensing probes were prepared by different methods such as sputtering; we are seeking for a new, easy, low cost and not complicated method with superior advantages over other methods. In this work, sputtering method was used to prepare gold probe (Au/core). Also, gold nanoparticles probe (AuNPs/core), graphene probe (Gn/core), graphene /gold probe (Gn/Au/core), and graphene / goldnanoparticles probe (Gn/AuNPs/core) were prepared by dip coating method. The structures of these probes were examined via Scanning Electron Microscope (SEM), optical microscopy and Raman spectroscopy. Lead ions in water with different concentrations were detected via optical fiber surface plasmon resonance (SPR) with the prepared probes mentioned above. where the fiber mounted along flow cell, with flow rate (5.5 mL/sec). The performance parameters of different probes increased noticeably as the probe change from Au, AuNPs, Gn/core, Gn/Au/core to Gn/AuNPs/core. The Gn/AuNPs/core probe shows a superior sensitivity (Sn), Figure of Merit (FOM), Signal to noise ratio (SNR), and Limit of detection (LOD) among other sensors, which make it available for chemical and biological applications. Also in this thesis, the sensing probes of graphene-gold nanoparticles
composite (Gn-AuNPs/core) were fabricated by dip coating method on the unclad fiber followed by laser irradiation (980 nm, 1.5W) at different times (0, 2, 5, and10 min). The prepared and irradiated probes were characterized by SEM and Raman spectroscopy. Raman spectra and SEM of prepared probes confirm the deposition of graphene gold nanocomposite on the bare core and indicate the surface of probes becomes more roughness and homogeneity distribution of nanoparticles after laser treatment. The resonant wavelengths of SPR spectra were red shifted to 52, 55, 60 and 63 nm for 0, 2, 5, and 10 min respectively for the irradiated Gn-AuNPs composite/core probe for the analyte range (0-200 ppm). Laser sensitization has enhance the sensor performance with superior sensitivity 0.725 nm/ppm and lowest limit of detection (0.13 ppm) for 10 min irradiated probes, the sensitivity was enhanced 129٪ with respect to before laser treatment. The laser sensitization of dip-coated graphene gold nanocomposite is a promising method for enhancing performance parameters of optical fiber sensors.