We have investigated laser ablation in InSb in the fluence regime of 8.5 J/cm2 to 21 J/cm2 by studying the
crater morphology. Crater morphology shows a non linear change in depth, volume and roughness at fluence of 14.5
J/cm2 (Fcr) and above. These non linear variations with presence of several micro-cavities at the crater bottom (potential
bubble nucleation sites) suggest a different material removal mechanism at Fcr and above. The results have been
explained in light of various ablation theories which support explosive boiling as a possible mass removal mechanism at
Fcr and above. Thermal melting model for laser ablated InSb is in good agreement with the experimental results.
Planar multilayer optical waveguides consisting of thin dielectric films with metal cladding have been investigated as TM-mode absorption polarizers. Two types of structure are analyzed. In the first one, the guided-mode losses were calculated as a function of the thicknesses of the buffer layer and the metal. Another polarizer, utilizing a MgF2/metal/MgF2 overlayer, is discussed. It is observed that in this configuration TM absorption losses are enhanced and thus we get a better extinction ratio. The polarizer has also been fabricated and characterized on ion exchange optical planar waveguides with a MgF2/Ag/MgF2 overlayer.
The waveguiding properties of SC-450 photoresist films are presented. The basic waveguiding properties such as refractive index, propagation losses, thickness, and birefringence of photoresist film are optimized. The effect of dye doping and UV exposure on photoresist film is also observed. The film shows excellent transmission (above 90%) in the wavelength range of 500 to 1500 nm. The present results suggest that photoresist films may be the good option to be used as an optical component.
The entrance and exit surface damage has been observed in newly developed Neodymium doped phosphate laser glasses viz. Potassium Barium Aluminium Phosphate (KBAP), Lanthanum Potassium Barium Aluminium Phosphate (LKBAP), Yttrium Aluminium Phosphate (YAP) under Q switched Nd:YAG laser irradiation at 1.06 μm wavelength near normal incidence. The YAP glass is suitable for low repetition rate system such as range finders while KBAP and LKBAP find applications for high repetition rate systems which are used in material processing and electro-optic counter measures. The difference between the entrance and exit surface damage thresholds has been explained using electromagnetic effects. The comparison of the morphological features of the KBAP and LKBAP suggest the role of metallic inclusion in the samples whereas in the case of YAP sample, the damage is governed by the intrinsic physical properties of this glass.
Evolution of laser damage morphology has been studied in 112 oriented, mirror polished Indium Antimonide(InSb)samples as a function of increasing energy, pulse repetition rate and number of pulses using a Nd:Cr:GSGG laser of 1.06 μm wavelength having a pulse width of 20ns. Scanning Electron Microscope (SEM) investigations of the irradiated samples have been done to understand the evolution of damage morphology. Damage morphology is consistent with surface melting and solidification along with an evidence of subsurface overheating. Temperature profiles calculated at different fluence levels confirm substantial subsurface heating. Multiple pulse damage seen at 20Hz with increasing fluence levels is mainly thermal damage. Thermal modeling has been done to explain different morphological features.
Polyvinyl alcohol (PVA)-based thin film optical waveguides are fabricated and characterized. Various waveguide parameters, namely, refractive index, propagation losses and depth, birefringence, and polarization conversion properties of dip-coated thin film optical waveguides are evaluated. The effective refractive index of PVA film is found to be between 1.506 and 1.531 for various concentrations. The propagation losses are 2.35 to 0.30 dB/cm for various thicknesses. The propagation loss reduces when the thickness of the film is increased. The low propagation losses, birefringence insensitivity, high transmission in the aged and annealed waveguides, control over film refractive index, the good adhesiveness of the film and good compatibility with substrate show that PVA-based waveguides are promising candidates for the optoelectronic field.
Negative photoresist films (HNR-80 and HNR-120) are fabricated and characterized for waveguiding purpose. Various waveguiding parameters, namely, refractive index, thickness, propagation losses, and birefringence of the photoresist films are evaluated. Propagation losses are optimized to the value of 0.29 dB/cm for both materials. These photoresist materials show excellent transmission with almost no absorption in the wavelength range of 400 to 900 nm. The waveguides are polarization insensitive for various temperatures. Considering these properties, these materials offer a good option to use as waveguiding materials in integrated optics.
Evolution of damage in mirror polished samples of HgCdTe, CdTe & CdZnTe has been studied for three fluence regimes-Damage Threshold (Fth), Five Times Damage Threshold (5Fth), Ten Times Damage Threshold (10Fth) with multiple pulses of a Q-switched 1.06 μm Nd:YAG laser of 20ns pulse duration. Damage morphology observed under Scanning Electron Microscope (SEM) seem to evolve almost in similar fashion with increasing number of pulses as well as incident energy in HgCdTe and CdZnTe on account of uniform heating through a significant depth through the sample surface whereas in case of CdTe, effect of subsurface superheating is evident. Thermal modeling has been done to explain the evolution of laser damage.
We report on the investigation of a series of polyaniline based conjugated polymers with rather different backbone structure and energy gap in order to explore the effect of their molecular
architecture on nonlinear optical properties. In particular, we report on the dispersion of x(3) in the spectral range covering the rising slope of the optical absorption as well as in off resonance conditions.
Pits formation during the laser induced damage with GaAs surface either for picosecond or for femtosecond laser pulses, shows that defects always play an important role in damage morphology of GaAs surface, as previously these pits formation have also been seen for micro and nanosecond laser pulses. The nature of these pits gives an important information about the morphological features of damaged GaAs surface in picosecond and femtosecond regime. In this paper we report a comparative study of laser induced damage morphology of GaAs surface based on the nature of these pits formation.
Polymeric Optical Waveguides have attracted a lot of attention with a view to their flexibility for fabrication and their cost effectiveness. In the search for new materials recently the study of Styrene Acrylonitrile (SAN) thin film optical waveguides has been reported. SAN exhibits a considerable transmission (80-90%) in the visible and infrared regions, which is important for integrated optical devices. But the propagation loss is a major drawback of SAN based waveguides. Here we report 4-layer waveguides with Glass plus SAN plus Polystyrene plus air, structure. With the help of this multilayer structure we were able to reduce propagation loss by 30% in comparison to single layer SAN based waveguides. We also present the other basic properties like index profile, guide thickness, birefringence.
Polymer thin film devices are fast emerging as efficient active elements for processing of optical signals for using civil, space and military applications. The requirements for a thin film material to be used in optical processing and communication are the high second and third order non-linear susceptibilities, low propagation loss and variable depth, propagation to allow the same device operate at different wavelength.
A systematic study of the fabrication and characterization of planar optical waveguides in Z-LiNbO3, fabricated by the proton exchange technique using orthophosphoric acid is reported. The guides are fabricated by immersing lithium niobate substrates in orthophosphoric acid for different durations. The results are compared with those for guides fabricated using benzoic acid under similar conditions. The data are analyzed to calculate the value of the diffusion coefficients. The surface index and the depth produced using the orthophosphoric acid proton exchange process is marginally higher.
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