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These studies are aimed to investigate influences of Ga dopant and As dopant on the optical properties of silicene. Silicene, a silicon analog of graphene, is expected to be better suited than graphene for the electronics industry, which is currently still dominated by silicon. In order to expand its application, its properties must be controllable. The development of the properties can be done by doping or applying external electric fields and stress. Like carbon, silicon also belongs to group IV of the periodic table. Ga (elements from group III) and As (element from group V) can play the role of dopant donor or acceptor in silicene. Therefore, the Density Functional Theory (DFT) calculations were carried out using a general gradient approach in order to investigate the influence of Ga atoms and Al atoms on the optical properties of silicon dioxide. The optical properties studied include refraction, reflection, and absorption. The results show that Ga doping, As doping, and Ga-As codoping reduce the value of the linear optical properties. The ability to control and exploit its optical properties shed light on designing silicene-based electronic and spintronics materials.

Air quality decreases due to the increase in air pollutants generated by motor vehicles that have a negative impact on human health. Generally, the pollutants can be gaseous and particulate matter. PM2.5 are particulate matters having diameters less than 2.5 µm, respectively. This research was aimed to design a measurement system of PM2.5 concentration. A PM NOVA SDS011 and a microcontroller ATmega328P were used as the sensor and the processing system. The principle of the sensor was based on the change of the particulate concentration to a voltage. The particulate PM2.5 concentration was displayed on an LCD. The system was completed by a LoRa SX1278 module to data communication. The performance of the system was tested based on the ability to measuring PM2.5 concentration and data communication in a varied distance. The result showed that the system worked well in measuring the PM2.5 concentration in the range of 0-1000 µg/m3. The resolution was 1 µg/m3. The system can be used to measure PM2.5 with a distance of up to 200 meters.

The Zinc oxide is well known as a direct wide bandgap semiconductor material with many promising properties for blue/UV optoelectronics, transparent electronics, spintronic devices and sensor applications. Controllable bandgap tuning is important to widen its possible applications. In the present work, we applied density functional theory to study bandgap tuning of ZnO by introducing Na atom and Cl atom. Sodium acts as p-type doping, while chlorine acts as n-type doping for ZnO. The effect of Na and Cl doping in the study was calculated using the Density Functional Theory (DFT) method. The results indicate that ZnO, which is a natural n type semiconductor when doped with p type, has an increase in bandgap, on the contrary, doping with n type decreased its bandgap

A pressure gradient method for spectral broadening of intense-femtosecond laser pulses in gas-filled hollow fiber is proposed. The simulations using input energy of 6 mJ and pulse duration of 40 fs have shown that using the same value of ∫ p(x)dx, the energy transmittance can be enhanced by a factor of 25% compared to that of using constant gas pressure while the global spatial phase is also improved.

We present results from interaction of helium with intense, femtosecond laser pulses. Using spectral methodfor selecting the harmonics, it can be shown that under certain condition, a single femto or subfemtosecondharmonic pulses as well as train of attosecond pulses can be generated from femtosecond intense driving field.

We investigate the possibility of optical pulse compression of high energy ultrashort laser pulses in an argon-filled planar waveguide, based on two level coupled mode theory and the full 3D nonlinear Schrödinger equation. We derive general expressions for controlling the spatial beam profile and the extent of the spectral broadening. The analysis and simulations suggest that the proposed method should be appropriate for optical pulse compression of ultrashort laser pulses with energies as high as 600 mJ.

A proposal for spectral broadening of tens milli Joule femtosecond laser pulses in an argon-filled hollow fiber is presented. The simulation results show that themethod could be useful under conditions where ionization plays a greater role and that it can be used to control plasma-induced spectral broadening.

The application of a Herriot multiple-pass cell (MPC) filled with neon for spectral broadening of a femtosecond, intense laser field has been studied theoretically. The simulation using 50 mJ, 60 fs laser pulses with a center wavelength of 780 nm has shown that relevant spectral broadening can be obtained after 10 passes of the pulse, yielding a compressed pulse with a width of 4.5 fs and an energy of 25 mJ.

We present a systematic study of filamentary ultrashort laser pulses in air, through numerical solutions of the nonlinear Schrödinger equation for various contributions of the delayed Kerr nonlinearity. The results show that a relatively larger contribution of the delayed Kerr nonlinearity will lead to a longer stable filament. This is explained from the transfer of the nonlinear contributions from the frontier part to the back of the pulse and the counterbalanced action of the negative plasma induced nonlinearity by the delayed Kerr nonlinearity in the trailing part of the pulses. Furthermore, effect of ionization on the stability of the filament is investigated. Two formulas are used to generate the data of the ionization, i.e., the Perelemov, Popov, and Terent'ev (PPT) and the Ammosov, Delone, and Krainov formula. It is found that simulation with higher ionization rate (PPT) could generate a more stable and longer filament.

The nonlinear susceptibility of atomic hydrogen interacting with an intense laser field has been investigated using a numerical solution of the time-dependent Schr\"odinger equation. It was shown that the behavior of the nonlinear susceptibility strongly depends on the intensity; it increases linearly in the low-intensity regime (Kerr regime), then saturates at a higher intensity. Furthermore, it was also shown that the nonlinear susceptibility is substantially induced by the ionization, whose magnitude is simply related to the density of the ionized electrons. By analyzing the calculated refractive index, it was found that the refractive index induced by ionization is 7--20 % smaller than that derived from the plasma frequency.

The propagation dynamics of intense femtosecond laser pulses in argon have been investigated theoretically and the results are compared with experimental data. It was found that in the initial stage the pulse propagates with the focal point moving ahead of the original one. The central beam of the trailing part experiences defocusing owing to ionization by the leading part and then regains self-focusing provided by power from the outer part. On propagating further, a quasistable balance is established between self-focusing and defocusing due to ionization-induced nonlinearity and diffraction, causing the beam to propagate in a self-guided mode. Furthermore, it was shown that the front of the split pulse decays faster, while the trailing edge experiences self-focusing and self-defocusing until a self-guided propagation mode is achieved. Multiple pulse splitting and shortening as a result of the dynamics near the focal point were also observed.

We report on the compression of intense ultrashort laser pulses for the purpose of producing few-cycle optical pulses at the multimillijoule level by using a planar waveguide (PWG). The PWG is composed of two parallel glass slabs separated by a gap of 100 microm and mounted in a gas chamber filled with a noble gas. In comparison with the conventional hollow-fiber-based pulse compression technique, the use of a PWG enables the injection of high-energy ultrashort pulses, because the input laser beam is confined only in the lateral direction perpendicular to the waveguide plane. Using this technique, we demonstrate the generation of 12 fs, 2 mJ laser pulses in an argon-filled PWG.

We have demonstrated the generation of 5 fs, 0.5 TW pulses at 1 kHz repetition rate using a pulse compression technique in a hollow fiber with a pressure gradient. Owing to the excellent beam quality by passing through the hollow fiber, the beam after pulse compression could be focused to a nearly diffraction-limited spot size. We obtained for the first time a peak intensity as high as 5x10(18) W/cm(2) in the 2-cycle regime.

We have investigated the nonlinear susceptibility of atoms induced by high intensity, ultrashort laser pulses using a numerical solution of the time-dependent Schrodinger equation. We found that the instantaneous nonlinear susceptibility becomes saturated at high intensity. We also found that the saturation is closely linked to depletion of the ground state. Based on the numerical results, a simple model that generalizes the nonlinear susceptibility of atoms for high intensity, ultrashort laser pulses is proposed. We also investigated the ionization-induced dipole moment and found that the amplitude of the dipole moment induced by an ionized electron is, in general, smaller than that induced by a free-electron, and is attributable to a residual interaction between the ionized-electron and its parent ion.

We investigated the possibility of plasma-induced spectral broadening of high-energy ultrashort laser pulses in a helium-filled multipass cell (MPC) through a series of full numerical simulations of the extended nonlinear Schrodinger equation. It was found that the gas pressure must be set low so that the propagation dynamics can be controlled only by plasma defocusing. Simulations using 100 mJ, 40 fs laser pulses in the MPC, which is 6 m long and has a mirror of 3.1 m radius at each end, showed that if the gas pressure is set within the range of 40-130 Pa, then the relevant spectral broadening can be obtained after five passes, yielding compressed pulses of a 4.7-6.4 fs width. The ratio of the energy of the compressed pulse to the output pulse is found to be within 58-88%.

A proposal for spectral broadening of an intense laser pulse with energy 15 mJ and a pulse duration of 40 fs in an argon-filled hollow fiber, using conjugate pressure-gradient method, is presented. The design, to be referred as conjugate pressure-gradient method, shall consist of a pair of hollow-fiber segments, each with gas pressure that increasingly and decreasingly varies, respectively. It is expected that the occurrence of early self-focusing can be avoided, as well as the elimination of the additional nonlinear processes at hollow fiber exit. Simulation using 15 mJ, 40 fs laser pulses shows that, in the intensity regime where ionization is important, excellent spectral broadening and spectral phase of the pulses can be obtained using the proposed conjugate pressure gradient method. The method therefore shall be useful for the spectral broadening of high-energy, ultrashort laser pulses.

We investigate the dynamics of femtosecond laser pulses propagating in a hollow fiber filled with argon, through a full numerical solution of the nonlinear Schrodinger equation. The simulation results show that, if the intensity is low and no ionization takes place, the spatial profile of the beam does not change very much so that its propagation model may be simplified to a one-dimensional model. If the intensity is high and ionization takes place, the spatial dynamics as well as temporal dynamics become very complicated because of self-focusing and defocusing. It is found that, for the same value of the B integral, self-focusing inside a hollow fiber can be substantially suspended by a differential gas pressure technique, where the gas pressure is set to be a minimum at the entrance and then increased with the propagation distance. Numerical simulations show that using such a technique, the energy transmitted during propagation inside hollow fiber is significantly enhanced, and the spatial phase is also improved.

The spatiotemporal dynamics of high-intensity femtosecond laser pulses propagating in argon have been investigated experimentally and the results compared with numerical calculations. After the beam expands and refocuses, the pulse splits in two. While the subcomponent expands immediately, the main component propagates as a filament. The pulse duration of the main component is less than half the initial pulse duration and the spectrum is broadened by a factor of two.

We investigate the energy scaling of high-order harmonics in Ar, using a loosely focused beam in a phase-matched condition. Adjusting the argon gas density and the pump laser focusing condition produces a total output harmonic energy as high as 0.7 μJ in the spectral region 34.8–25.8 nm (the corresponding orders of the 23rd–31st harmonics); 27th-order harmonic (29.6-nm) energy attained is as high as 0.3 μJ with an almost perfect spatial profile. High efficiency and good spatial quality are achieved simultaneously.