Sharif Digital Repository

We have performed an analysis of harmonic contents of the optical output power for a diode laser and described the results in details. In the first step the absolute value of power for each harmonic is obtained in terms of various diode laser parameters, and the variations of external parameters such as modulation current, bias current and frequency are discussed. The analysis is done by direct solution of rate equations of an arbitrary diode laser for carrier and photon densities. We conclude that the maximum power occurs at isolated peaks and their loci have been investigated and shown to be predictable by theory. It is known that the optical power has a nonlinear dependence on frequency,... 

Conversion of CH4 molecule into higher hydrocarbons using two different wavelengths of 248 nm KrF laser and 355 nm of third harmonic of Nd:YAG laser is studied experimentally and theoretically. The stable products are analyzed and the effect of pressure on conversion of methane is measured. The detected reaction products are C2H2, C2H4, and C2H6. The conversion efficiency of 33.5% for 355 nm in comparison to 2.2% conversion for 248 nm for C2H2 is achieved. The potential of laser parameters as an important variable in controlling of final products is investigated  

Progress of carbon nanotube (CNT) research and development in terms of published papers and patents is reported. Developments concerning CNT structures, synthesis, and major parameters, in terms of the published documents are surveyed. Publication growth of CNTs and related fields are analyzed for the period of 2000-2010. From the explored search term, "carbon nanotubes", the total number of papers containing the CNT concept is 52,224, and for patents is 5,746, with a patent/paper ratio of 0.11. For CNT research in the given period, an annual increase of 8.09% for paper and 8.68% for patents are resulted. Published papers for CNT, CVD and CCVD synthesis parameters for the period of 2000-2010... 

Laser assisted machining (LAM) is a promising technology for machining hard to cut materials. In most experimental cases, LAM is undergone in two stages; first, the temperature at the material removal point (Tmr) is tuned by adjusting laser parameters and next, the cutting tool is engaged. Introduction of highly localized heat energy to the workpiece makes the modeling of this process very complicated. Hence, an analytical model for the first stage of the process - rather than multiple experiments or FE modelling - would be beneficial. This article presents an analytical solution to the transient, temperature field in a rotating cylinder subject to a localized laser heat source. The... 

In this study, high harmonic generation from a multi-atomic nitrous oxide molecule was investigated. A comprehensive three-dimensional calculation of the molecular dynamics and electron trajectories through an accurate time-dependent density functional theory was conducted to efficiently explore a broad harmonic plateau. The effects of multi-electron and inner orbitals on the harmonic spectrum and generated coherent attosecond pulses were analyzed. The role of the valence electrons in controlling the process and extending the harmonic plateau was investigated. The main issue of producing a super-continuum harmonic spectrum via a frequency shift was considered. The time-frequency...