Papers by mohammad jaberi
Stimulated Brillouin scattering in an inhomogeneous plasma with broad-bandwidth thermal noise
The Physics of Fluids, 1983
Stimulated Brillouin scattering in a plasma containing broad-bandwidth thermal noise was consider... more Stimulated Brillouin scattering in a plasma containing broad-bandwidth thermal noise was considered. Plasma profiles which are inhomogeneous (for example, because of a velocity gradient) were studied. At each point in the profile, a different electromagnetic wave can be resonant with the pump wave and a local ion acoustic wave, and can thus be amplified from its noise level. Some difficult points of the linear theory of this process are first examined. Then a nonlinear equation is derived, which governs the decrease of the incident-wave amplitude as it propagates toward the critical density surface. Solutions of this equation predict a maximum value of the absorbed intensity, Imax. For incident laser intensities Iin, higher than this value, only a fraction Imax/Iin is absorbed.
Control of SBS pulse compression by interaction geometrical parameters
Optics Communications
Effect of Interaction Geometry on the Stimulated Brillouin Scattering
Optics and Photonics Society of Iran, 2019
Optics and Photonics Society of Iran, 2019
In this paper, the effect of the presence of Ag nanoparticles in an organic medium on stimulated ... more In this paper, the effect of the presence of Ag nanoparticles in an organic medium on stimulated Brillouin scattering stokes pulse duration and pulse compression has been investigated experimentally. Presence of the nanoparticles in the scattering medium can be resulted in stimulated Mie-Bragg scattering and changes in the Brillouin scattering response of the medium. The results show that the backward stokes pulse duration decreases and pulse compression increases by increasing the concentration of Ag nanoparticles. Also, pulse compression can be controlled by changing the nanoparticles concentration.
Micro- and nanostructures formation on glass surface with different parameters of excimer laser irradiation
Optical Engineering, 2018
Abstract. We present the formation of micro- and nanostructures on glass surfaces by 15-ns 193-nm... more Abstract. We present the formation of micro- and nanostructures on glass surfaces by 15-ns 193-nm ArF laser irradiation during the laser irradiation. The effect of laser fluence and pulse number on the micro- and nanostructure formation is studied. The scanning electron microscopy images of the irradiated surfaces show that the shape and density of the microstructures change with different laser parameters. Our results show that the microstructure formation is a characteristic feature of the ablation threshold of the glass surface at 15-ns ArF laser irradiation. The ordered microstructures are obtained with 500 pulses at 350 mJ / cm2 laser fluence. Also, the nanostructures can be formed at subthreshold laser fluence. The micro-Raman analysis of the glass surfaces before and after the laser irradiation shows that no phase change has occurred during surface structuring. The obtained compact and ordered micro- and nanostructures or multiscale structured surface can be applied in photonics and surface science.
Optics and Photonics Society of Iran, Mar 15, 2015
In this paper, the spectral behavior of a two-cell phase conjugated mirror (PCM) with a two-pass ... more In this paper, the spectral behavior of a two-cell phase conjugated mirror (PCM) with a two-pass Nd:YAG amplifier has been analyzed experimentally and theoretically and compared to the conventional mirror. For this purpose, amplifier input intensity for the two different states of laser oscillator with two and more longitudinal modes have been investigated. Results of the Fourier analysis of the amplified intensity show considerable differences between Fourier amplitudes of the amplifier equipped with PCM and a two-pass amplifier with a conventional turning mirror under the same output energy. The amplifier with PCM has a completely filtered and different spectral behavior with clearly reduction of the beating between Fourier components of the input optical field.
Phase control of optical bistability via spin coherence in a quantum well waveguide
Journal of the Optical Society of America B
Increasing the laser damage threshold of the Nd:YAG crystal by ArF laser irradiation
The European Physical Journal Plus, 2014
ABSTRACT
Optical and Quantum Electronics, 2014
A thin disc Nd:YAG crystal sample was irradiated with 500 pulses of XeCl laser (λ = 308 nm, τ = 2... more A thin disc Nd:YAG crystal sample was irradiated with 500 pulses of XeCl laser (λ = 308 nm, τ = 20 ns) at ∼ 100 mJ/cm 2 laser fluence and 25 Hz repetition rate. The UV-Vis-NIR and additional absorption spectra of the sample showed that optical transmission of the Nd:YAG crystal increased in ultraviolet and visible regions due to elimination of some oxygen vacancies of the crystal following the irradiation. Increase in laser damage threshold of the Nd:YAG crystal sample subsequent to annihilation of oxygen vacancies was obtained by the laser damage threshold experiment. The laser damage thresholds of the irradiated and un-irradiated crystals were measured using 30 ns, 1,064 nm single longitudinal mode, TEM 00 pulses of a passively Q-switched Nd:YAG laser. The laser damage threshold of the irradiated crystal (after dividing by √ 3 to scale for pulse duration of 10 ns) was obtained to be 501 ± 50 J/cm 2. It is nearly five times as high as that of un-irradiated Nd:YAG crystal, which was found to be 102 ± 15 J/cm 2. Keywords Laser damage threshold • Nd:YAG crystal • XeCl laser 1 Introduction Laser irradiation can cause damage to optical materials and instruments. Damage of optical surfaces used in high power laser systems is a serious problem that limits power output of
Optics Communications, 2015
In this paper, the spectral behavior of two-cell phase conjugating mirror (PCM) with a two-pass N... more In this paper, the spectral behavior of two-cell phase conjugating mirror (PCM) with a two-pass Nd:YAG amplifier has been analyzed experimentally and theoretically. For this purpose, input intensity with single and multi-longitudinal modes has been investigated. The numerical model is based on focused geometry model (1 þ 1 dimension) equations of Stokes back-scattered intensity and acoustic waves, for two-cell generator-amplifier phase conjugating mirror with proper boundary conditions that are solved simultaneously with the rate equations of Nd:YAG optical amplifier. Results of the Fourier analysis of the amplified intensity show considerable differences between Fourier amplitudes of the amplifier equipped with PCM and a two-pass amplifier with a conventional mirror under the same output energy. The amplifier with PCM has a completely filtered and different spectral behavior with clearly reduction of the beating between Fourier components of input optical field. Calculations show that the filtering of Fourier components by a PCM is done more effectively with lower pumping energy.
Nitrogen lasers, optical devices of variable gain coefficient: Theoretical considerations
Optics Communications, 2010
ABSTRACT Based on our previous measurements on the gain values by employing an oscillator amplifi... more ABSTRACT Based on our previous measurements on the gain values by employing an oscillator amplifier (OSC–AMP) N2-laser system of variable AMP electrode lengths, a calculation has been made for evaluation of the gain coefficient using rate equations. It is shown both numerically and analytically that small signal gain, g0, is following our experimental observations of g0=m+n/lAMP, where m and n are some constants, and lAMP is the length of the amplifier. For simplifying the calculation in the OCS–AMP circuit, an experimental condition of imposing the OSC-open-circuit operation has been applied, where the voltage waveforms from the relevant sections of the Blumlein circuit have been used for evaluation of the circuit parameters. Due to the fact that during the past years different cross-sections for the electron-impact excitations from the ground to the upper, N2(C), and lower, N2(B), have been introduced, our experimental observations have also been applied to examine the effect of introduced electron impact-excitation cross-sections on the g0(lAMP) behavior.
Journal of the Optical Society of America B, 2013
Optical bistability and multistability behaviors are investigated in a tripod four-level atomic c... more Optical bistability and multistability behaviors are investigated in a tripod four-level atomic configuration, including a unidirectional ring cavity. We find that optical bistability and multistability can be obtained by changing the relative phase of the driven fields and the intensity of the microwave field. In addition, we can switch optical bistability to optical multistability by adjusting the relative phase of the driven fields or vice versa, and the threshold can be controlled via changing the parameters of the scheme.
Effect of the Electron Spin-Relaxation on Optical Bistability via the Heavy-Hole and the Light-Hole
Modern Physics Letters B, 2014
In this paper, the influence of the spin-relaxation on the optical bistability via a nonradiative... more In this paper, the influence of the spin-relaxation on the optical bistability via a nonradiative coherence between the heavy-hole and the light-hole in a GaAs quantum well inside a unidirectional ring cavity is studied. In the present theoretical model, spin-relaxation was considered as a source for decoherence and it was found that the spin-relaxation leads to the change of optical bistability behavior, including increase in threshold intensity and hysteresis loop. Furthermore, in the presence of spin-relaxation, the transition from optical bistability to optical multistability can be obtained by tuning the applied field.
Journal of Physics: Conference Series, 2014
This paper presents increase in laser damage threshold of the Nd:YAG crystal subsequent to annihi... more This paper presents increase in laser damage threshold of the Nd:YAG crystal subsequent to annihilation of oxygen vacancies in the crystal structure at low dose of XeCl laser irradiation. A Nd:YAG crystal was irradiated with 500 pulses of XeCl laser (λ=308nm, τ=20 ns) at the fluence of ~100 mJ/cm 2 and 25 Hz repetition rate. The optical absorptions of the Nd:YAG crystal reduced in ultraviolet and visible regions due to elimination of some color centres indicated by UV-Vis-NIR spectra. We measured the laser damage threshold of the irradiated and un-irradiated crystals using 30 ns, 1064 nm single longitudinal mode, TEM 00 pulses of a passively Q-switched Nd:YAG laser. The laser damage threshold of the irradiated crystal (after dividing by √3 to scale for pulse duration of 10 ns) was obtained to be 501±50 mJ/cm 2. It is nearly 5 times as high as that of un-irradiated Nd:YAG crystal, which was found to be 102±15 J/cm 2. The present results are very important for using Nd:YAG crystals as the laser amplifier media.
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Papers by mohammad jaberi