Surface Modification of Polymer Materials Induced by Laser Irradiation

We report on the surface modification effects using allyl‐diglycol CR39 polymer induced by laser irradiation at 157 nm F2 laser (VUV) and 248 nm KrF laser. The motivation is to investigate the ablation effects on this polymer in optical waveguides application the ablation effects on this polymer in optical waveguides. Fabrication of waveguides has been observed using continuous wave (CW) at 244 nm argon ion laser. Ablation effects on the surface of this polymer have been characterized including ablation threshold at different wavelengths from the assorted depth of craters formed from UV pulsed laser. Application of this polymer in optical waveguide application is corroborated by the refractive index value on the CR39 channels that varied as fluences changed when using the continuous wave UV irradiation. A limit for upper fluence at the point where laser ablation originates on this polymer has also been determined

157nm F₂laser characterization and application to polymer ablation

The work in this thesis focuses on applications and characterization studies of the vacuum ultra-violet (VUV) 157nm F2 laser. The laser ablation properties of various polymeric materials, namely polydimethylsiloxane (PDMS), the photo-resist SU-8, nylon 66, ultra-high molecular weight polyethylene (UHMWPE), Lexan polycarbonate and CR-39 polymer have been investigated. The main priority was given to Lexan polycarbonate and CR-39 polymer as new potential materials to explore using this laser.A considerable component of the work is directed at gaining a better understanding of the underlying physics of the laser interaction in relation to surface modification, in particular the possible limitations on surface roughness set by mode coherence effects. White light interferomety, and optical and scanning electron microscopy (SEM) measurements are carried out to identify the processing conditions for micron scale size structures (cones) produced on the surface, and the realization of 'smooth' and in some instances intentionally 'roughened' surfaces after ablation. It is shown that exceptionally well defined conical structures can be formed on Lexan polycarbonate and CR-39 polymer with certain laser processing conditions. These cones produce a circular interference fringe system with submicron period adjacent to their base as a result of walls reflections. An ablation model is used to analyse these fringes, and from the range of fringe visibility it is shown possible to estimate the spatial coherence properties of the F2 laser beam.A preliminary investigation of ablating CR-39 that had been exposed to an alpha particle source is described. This polymer is widely used for detecting ionizing particles by use of chemical etching to reveal their damage tracks. 157nm laser ablation of chemically etched, radiation exposed samples showed the etched track 'pores' tended to be smoothed by ablation and also appeared to act as nucleation sites for cones.A fluorescence technique using Lumilass G9 glass plate and a CCD camera was applied in this work to analyze the VUV laser beam. This required knowledge of using optical systems, a CCD camera, and capturing and analyzing bmp images for analysis in MathCAD. Measurements made in this way permit divergence to be found for the direct and the weakly focussed (asymmetric) laser output beam. Spatial coherence derived in this way is shown to be in reasonable agreement with that based on the cone interference result. The fluorescence method is also applied to characterizing small-scale beam fluctuations on the direct F2 laser output beam. These are found to have a magnitude of a few %, a value that compares quite well earlier theoretical predictions and a simulation of spatial mode fluctuations in the narrow line-width, highly multimode F2 laser

Controllable Core Size of Au@TiO2 through Al(NO3)3 Addition and Its Effects on DSSC Performance

It is known that plasmonic nanoparticles in dye-sensitized solar cells (DSSC) could enhance efficiency through improvement in light absorbance and electron dynamics. Herein we investigated various sizes of AuNP through spontaneous Al(NO3 )3 addition. Core-Shell Au@TiO2 was prepared with various Al(NO3 )3 concentrations of 0.25 mM, 0.5 mM, 0.75 mM and 1 mM. The Au@TiO2 volume fraction of 1% was further added to TiO2 photoanode. Based on the particle size analyzer (PSA) characteristics, the synthesized AuNP’s size was within a range of 34.62 nm – 139.5 nm. The highest efficiency of DSSC was obtained for the sample with the largest AuNP ’s diameter, i.e., 0.0313%, which is about three times higher than pristine DSSC. The increase in efficiency was in accord with Metallic Nanoparticle Boundary Element Method (MNPBEM) simulation, UV-vis spectroscopy, and Incident Photon to Current Conversion Efficiency (IPCE) analysis largest Au core diameter contributes to the strong absorbance and hence the short circuit curren

157nm F₂laser characterization and application to polymer ablation

The work in this thesis focuses on applications and characterization studies of the vacuum ultra-violet (VUV) 157nm F2 laser. The laser ablation properties of various polymeric materials, namely polydimethylsiloxane (PDMS), the photo-resist SU-8, nylon 66, ultra-high molecular weight polyethylene (UHMWPE), Lexan polycarbonate and CR-39 polymer have been investigated. The main priority was given to Lexan polycarbonate and CR-39 polymer as new potential materials to explore using this laser. A considerable component of the work is directed at gaining a better understanding of the underlying physics of the laser interaction in relation to surface modification, in particular the possible limitations on surface roughness set by mode coherence effects. White light interferomety, and optical and scanning electron microscopy (SEM) measurements are carried out to identify the processing conditions for micron scale size structures (cones) produced on the surface, and the realization of 'smooth' and in some instances intentionally 'roughened' surfaces after ablation. It is shown that exceptionally well defined conical structures can be formed on Lexan polycarbonate and CR-39 polymer with certain laser processing conditions. These cones produce a circular interference fringe system with submicron period adjacent to their base as a result of walls reflections. An ablation model is used to analyse these fringes, and from the range of fringe visibility it is shown possible to estimate the spatial coherence properties of the F2 laser beam. A preliminary investigation of ablating CR-39 that had been exposed to an alpha particle source is described. This polymer is widely used for detecting ionizing particles by use of chemical etching to reveal their damage tracks. 157nm laser ablation of chemically etched, radiation exposed samples showed the etched track 'pores' tended to be smoothed by ablation and also appeared to act as nucleation sites for cones. A fluorescence technique using Lumilass G9 glass plate and a CCD camera was applied in this work to analyze the VUV laser beam. This required knowledge of using optical systems, a CCD camera, and capturing and analyzing bmp images for analysis in MathCAD. Measurements made in this way permit divergence to be found for the direct and the weakly focussed (asymmetric) laser output beam. Spatial coherence derived in this way is shown to be in reasonable agreement with that based on the cone interference result. The fluorescence method is also applied to characterizing small-scale beam fluctuations on the direct F2 laser output beam. These are found to have a magnitude of a few %, a value that compares quite well earlier theoretical predictions and a simulation of spatial mode fluctuations in the narrow line-width, highly multimode F2 laser

Investigation of nonlinear optical properties on structures of silver micro-flowers

In this report, we investigated nonlinear optical properties of silver microstructures in flowers like shape (AgMFs). These structures have been fabricated on indium–tin–oxide substrate applying electrochemical deposition technique using three different time depositions of Ag (NH3)2OH to produce different sizes of Ag structures in micron scale size. The nonlinear optical property of the material was investigated by a Z-scan technique using femtosecond laser pulses at 800 nm. The AgMFs with higher Ag concentration show a greater enhancement in magnitude and sharpness of the plasmon resonance band. We found out that AgMFs exhibit highly enhanced surface plasmon resonance sensitivity than previous work reported using Ag nanoparticles (AgNPs) structures as comparison due to the arbitrarily structures of micro-like flowers. The Z-scan measurement using pulse laser showed that the nonlinear absorption of AgMFs is as high as 3.7 × 10−9 cm2 W−1 compared to AgNPs as ~2 × 108 cm2 W−1

Manipulating of nanometer spacing dual-wavelength by controlling the apodized grating depth in microring resonators

We propose a passive photonic design for an optically pumped laser system and tunable dual-wavelength generation application by employing optical nonlinear mode coupling of two coupled III–V semiconductor microring resonators, which is connected to a pump and drop waveguide buses. One of the two rings contains a grating, whereas the other has a planar surface. The mechanism underlying the dual-wavelength generation can be explained via the resonance detuning of the spectra that results in nonlinear mode mixing. The tunability of the wavelengths can be achieved by altering the grating depth of the microring resonator and the power coupling coefficients. In the grating design of the microring resonators, we have selected a trapezoidal-profiled apodized grating to obtain low reflectivity at the sidelobes. A time-domain traveling wave (TDTW) analysis yields an InGaAsP core refractive index of 3.3. This core is surrounded by a grating InP cladding with a refractive index of 3.2. We further confirm that the propagation of a Gaussian pulse input with a power of 10 mW and a bandwidth of 0.76 ps is well confined within the system mode propagation. The results show a 2:1 fan-out of two spectrally separate signals, which can be employed for compact and high functional sources on chips

TE-like mode analysis of microsystem InGaAsP/InP semiconductor resonator generating 20 GHz repetition rate pulse trains

In microsystem technologies, the microring resonators (MRRs) can be used as a filter device. A wavelength-selective modified add-drop MRR filter is used for adding and dropping a particular wavelength in order to control the light propagation within the system. The spectrum of the mode-locked laser could be generated using a fiber laser loop consisting of active gain medium, EDF, Lumics 980 nm laser diode (LD), wavelength division multiplexer (WDM), isolator, a polarization controller (PC) and carbon nanotube (CNT). The multi-mode-locked laser could be generated at the through and drop port of the system after the mode-locked pulse from the fiber laser circulate within the MRR filter. Here, the mode-locking relies on a fiber laser setup, where the MRR filter has been modeled using the Fimmwave and PICWave softwares. We present this photonic circuits simulator based on the time-domain traveling wave (TDTW) method, provides modeling both active and passive photonic circuits. The pulse bandwidth and repetition of the train mode-locked pulses generated by the fiber laser setup are 0.65 ps and 30 MHz respectively. Using the MRR filter, the drop port output pulses show the FSR and FWHM of 172 pm (20 GHz) and 8.3 pm respectively. The finesse and the Q-factor are approximately 20.72 and 1.9 × 105 respectively

Sonochemical synthesis of reduced graphene oxide uniformly decorated with hierarchical ZnS nanospheres and its enhanced photocatalytic activities

Reduced graphene oxide (rGO) decorated with zinc sulphide nanospheres (ZnSNSs) was synthesized through the simple ultrasonic irradiation of an aqueous solution containing zinc acetate dihydrate (Zn(CH3COO)2·2H2O), thioacetamide (C2H5NS), and graphene oxide (GO). The results of X-ray diffraction, Fourier-transform infrared transmission spectroscopy, X-ray photoelectron spectroscopy and Raman spectroscopy confirmed the simultaneous formation of cubic-phase ZnSNSs and the reduction of GO through the ultrasonic irradiation process. Field emission scanning electron microscope images showed that the size and number density of the nanoparticles could be tuned by adjusting the precursor amounts. Transmission electron microscopy images showed that the spherical ZnS nanoparticles were comprised of small nanoparticles with an average size of ∼5 nm aggregated together. The result of photoluminescence spectroscopy and Brunauer–Emmett–Teller (BET) measurement demonstrated that the incorporation of reduced graphene oxide (rGO) sheets with ZnSNSs suppressed the electron–hole recombination and increased the surface area of the composite. Hence, a significant enhancement in the photocatalytic degradation of methylene blue (MB) was observed with the ZnSNSs–rGO nanocomposite, compared to the bare ZnS particles

One-pot sonochemical synthesis of reduced graphene oxide uniformly decorated with ultrafine silver nanoparticles for non-enzymatic detection of H2O2 and optical detection of mercury ions

Reduced graphene oxide (rGO) uniformly decorated with silver nanoparticles (AgNPs) was synthesized through the simple ultrasonic irradiation of an aqueous solution containing a silver ammonia complex (Ag(NH3)2OH) and graphene oxide (GO). The results of X-ray diffraction, Fourier-transform infrared transmission spectroscopy, X-ray photoelectron spectroscopy and Raman spectroscopy confirmed the simultaneous formation of cubic-phase AgNPs and the reduction of GO through an ultrasonication process. The size of the nanoparticles could be tuned by adjusting the volume ratio of the precursors and the ultrasonic irradiation time. Transmission electron microscopy images showed a uniform distribution of ultrafine spherical AgNPs with a narrow size distribution on the rGO sheets, which could only be achieved using the silver ammonia complex, rather than silver nitrate, as the precursor. The average particle size of the silver with the narrowest size distribution was 4.57 nm. The prepared AgNPs–rGO modified glassy carbon electrode exhibited notable electrocatalytic activity toward the non-enzymatic detection of H2O2 with a wide linear range of 0.1–70 mM (R2 = 0.9984) and a detection limit of 4.3 μM. Furthermore, the prepared AgNPs–rGO composite was employed for the spectral detection of Hg2+ ions and showed a detection limit of 20 nM

Fabrication and simulation studies on D-shaped optical fiber sensor via surface plasmon resonance

This paper describes simulation and experimental methods for designing a D-shaped surface plasmon resonance (SPR) fibre sensor. The sensor consists of two set-up approaches. Finite element method is used in simulation on the fibre sensor device. Two experimental methods for detecting relative intensity are used by varying the wavelength of the optical signal sources and the thickness of gold layer coated on the D-shaped fibre. In the first method, the sensor device works by detecting the relative intensity of two optical signal sources having different wavelengths. In the second set-up, the relative intensity between two D-shaped fibres coated with different thicknesses of gold is measured when a single signal source is launched at the input. The difference in intensities of the signal outputs is used to estimate the refractive index at the sensing region. A prototype SPR D-shaped fibre sensor has been fabricated and the experimental results show good agreement with simulation