International Journal of

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Larger width of P-cladding layer in p-i-n waveguide of traveling wave electroabsorption modulator (TWEAM) results in lower resistance and microwave propagation loss which provides an enhanced high speed electro-optical response. In this paper, a fullvectorial finite-difference-based optical mode solver is presented to analyze mushroom-type TWEAM for the first time. In this analysis, the discontinuities of the normal components of the electric field across abrupt dielectric interfaces which are known as the limitations of scalar and semivectorial approximation methods are considered. The optical field distributions in mushroom-type TWEAM and conventional ridge-type TWEAM of the same active region for 1.55 μm operation are presented. The important parameters in the high-frequency TWEAM design such as optical effective index which defines optical velocity and transverse mode confinement factor are calculated. The modulation response of mushroom-type TWEAM is calculated by considering interaction of microwave and optical fields in waveguide and compared to that of conventional ridge-type TWEAM. The calculated 3dB bandwidths for ridge-type and mushroom-type TWEAM are about 139 GHz and 166 GHz for 200 μm and 114 GHz and 126 GHz for 300 μm waveguide length, respectively.

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Time resolved laser induced incandescence (LII) technique is used to measure size distribution of soot nanoparticles of candle's flame. Pulsed Nd:YAG laser is used to heat nanoparticles to incandescence temperature and the resulting signal is measured. Mass and energy balance equations are numerically solved to calculate temperature of soot particles in low fluence regime. Assuming Plank black body radiation and lognormal size distribution for soot particles, the intensity of LII signals are calculated. Using Levenberg-Marquart nonlinear regression algorithm and numerical and experimental LII signals, mean particle size and distribution width of soot nanoparticles are obtained.

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Micro size craters were created by interaction of nanosecond laser beam with titanium target in liquid media. The dimension of crater i.e. depth and width is important in some applications such as micromachining. When the interaction occurs in liquid environment, the ablated materials from the target expand into the liquid. The ablated material can affect the interaction process if the ablated material concentration increases. In this paper, we study the effect of ablated materials in liquids on the crater width. The crater dimension was characterized by using an optical microscope. The results show that not only the type of environment liquid is important in the final size of the created craters, but also the laser fluence and the liquid depth in which the interaction takes place is important in the crater size.

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In this paper, considering optical feedback as an optical injection, and taking in to account round-trip time role in the external cavity, a standard small signal analysis is applied on laser rate equations. By considering the relaxation oscillation (f2) and external cavity frequencies (f) ratio for semiconductor laser, field amplitude response gain, optical phase and carrier number for long external cavities (LEC) and short external cavities (SEC) are obtained. Laser output intensity and resonance peak dynamics have been shown by bifurcation diagrams. Furthermore, the effects of some control parameters, such as enhancement factor, pumping current and feedback strength, on response gain have been discussed in short and long external cavities. As a result, in optical injection, for SEC, compared to LEC, more varied dynamics are observed. Also, higher values of the response gain peak in SEC, in comparison with LEC, make SEC to be affected more by the injected beam. SEC provides greater bandwidth, and also better performance in the range of compared to LEC.

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In this paper, an ideal cylindrical metamaterial invisibility cloak with infinite-length which its electric permittivity and magnetic permeability mapped to the Drude dispersion model is simulated. The sinusoidal plane waves with microwave frequencies used as sources. To this end, the dispersive finite-difference time-domain method (FDTD) used with Convolutional Perfectly Matched Layered (CPML) absorbing boundaries conditions. A comparison performed between scattering of cloaked and non-cloaked PEC cylinder. And finally, the influence of incident wave frequency, thickness of cloak and observer angle relative to the propagation line to performance of cloak, was surveyed.

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In this paper, the dynamic behavior of laser induced optical breakdown in impure water was studied by using a pump- probe technique. The plasma was induced by a 1064 nm Nd:YAG laser pulse (with pulse duration ~10 ns) in distilled water with two types of impurities: (I) a solution (highly diluted salt water as a conductor) and (II) a colloidal (TiO₂ in colloidal nanoparticle form as a dielectric); and finally the results were compared. The results show that, for both liquids, the probe beam transmission is reduced with pump laser intensity. Our results also show that, impurity size and type of conductivity can influence on plasma time evolution and transmissivity. 

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In this paper, we have investigated the dependence of the spectral entanglement and indistinguishability of photon pairs produced by the spontaneous parametric down-conversion (SPDC) procedure on the bandwidth of spectral filters used in the detection setup. The SPDC is a three-wave mixing process which occurs in a nonlinear crystal and generates entangled photon pairs and utilizes as one of the most useful resources in a variety of fields such as quantum computation, quantum cryptography, and quantum communication. The amount of the spectral entanglement and the indistinguishability of photon pairs are the two critical characteristics of the photon pairs determining their potential applications. The degree of the spectral entanglement of a quantum system, i.e. photon pairs, is determined by the entanglement entropy which is a measure of the system disorder. First, we derive the eigenvalue equation of reduced density operator of the signal and the idler photons in terms of the bandwidth of spectral filters. Then, by numerically solving the eigenvalue equation, we calculate the Schmidt coefficients for different values of the bandwidth of spectral filters. Finally, by calculating the entropy operator one can obtain the dependence of spectral entanglement of the photon pairs on filter bandwidth. The amount of indistinguishability of the photon pairs is measured by the visibility of the HOM diagram. Since the whole spectral information of the photon pairs exists in their two-photon mode function, using this function and the presented model we calculate the amount of indistinguishability by obtaining the visibility of the HOM diagram for different values of the bandwidth of the spectral filters. In this way, the dependence of the indistinguishability of the photon pairs on this quantity is reported.

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In this paper, design and fabrication of an internal resonant enhanced frequency doubling of the continuous-wave ytterbium-doped fiber laser at 1064nm using a Fabry-Perot bow tie cavity inside the fiber laser cavity is presented. The 3.5W power coupled into the enhancement cavity is amplified to 163W by the intracavity passive locking technique. By placing an LBO crystal within this resonant enhancement cavity, conversion efficiency of the second harmonic generation of the laser in continuous regime is increased from 0.023% to 51.42% (i.e. about 2200 times) which results to generation of 1.8W light at 532nm.

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Propagation of ion acoustic solitary waves (IASWs) in electronegative plasma containing positive and negative ions, trapped and non-thermal electrons are investigated. Using the Sagdeev pseudopotential method and investigation of the energy integral, the existence of propagation regions for these waves is analyzed. It is shown that the Mach number, positive and negative ions densities ratio and the trapping parameter can lead to change the pseudopotential amplitude and also it is shown that the lower limit of the Mach number increases with the density and mass ratios of positive and negative ions, but the upper limit of the Mach number does not depend on the densities ratio. The results show that for this kind plasma, there is only compressive IASW. This research will be helpful in understanding of physical phenomena concerned in plasmas in which the effects of trapped electrons control the dynamics of wave.

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The modification of cell surface structures has become a focal point in cell biology, with methods like drugs, chemicals, and non-destructive techniques such as laser light exposure being utilized. In particular, exposure to femtosecond laser pulses has been found to increase cell permeability to formulations without causing thermal damage. This study aimed to observe and document the changes in the structure of Staphylococcus aureus bacteria when they were optically trapped and subjected to femtosecond laser pulses, along with the application of a medicinal substance, over 20 minutes. The research successfully determined the optimal power and exposure time of the laser light on the bacterial surface and demonstrated the ability of femtosecond laser pulses to enhance the efficacy of the medicinal substance.