Colloidal nanoparticles are attractive optical materials for their low threshold nonlinear response and thus all-optical, nondestructive features which are important in biomedical optics and optical processing. We develop a theoretical scheme based on numerical solution of Nonlinear Schrödinger Equation and nonideal gas model of nonlinearity to investigate temporal analysis of optical bistability (OB) and modulation instability in colloidal nanoparticles. Our scheme determines the dependence of a nanosuspension system dynamic state on characteristic/control parameters including external feedback depth, nanosuspension length, and the initial density of nanoparticles as well as the optical input power. We show that these parameters are intensely correlated. We also indicate that the nonlinear response of nanosuspension may be saturated over a threshold of input power, and thus an unexpected procedure of system evolution toward stability rather than transition to chaos will occur. Consequently, provided that internal feedback is present inside the nanosuspension controlling chaos will be attainable by simply adjusting the optical input power as the control parameter in contrast to the other chaos control methods which require external injection. Finally, we propose an approach which gives a measure of switching time to optimize OB. The optimum results are obtained for the lowest taken values of characteristic/control parameters.
Quality testing of optics which is used in laboratories is one of the most important tasks and many procedures are proposed and used. These testing procedures are based on measurement of reflecting laser wavefront from optical component surfaces. By using the Shack-Hartmann method, we can measure a simple curved laser beam wavefront. For achieving this, firstly we reduce optical noise which may disturb our optical data. We improved peak location and sum location algorithms to introduce a simple new algorithm, based on adaptive thresholding. The proposed algorithm scans the image to identify the approximate location of focal spots by looking for local optical centers on CCD screen.
Fully coherent laser beams are very sensitive to the turbulence medium. Studies have shown that using partially coherent
beams is an effective method to reduce this unsatisfactory feature. Unfortunately partially coherent beams are more
expanded when they propagate thought turbulence medium. In this paper we have determined a special degree of global
coherency, which optimizes beam propagation with respect to limiting factors (sensitivity to the turbulence and broadening)
The quality factor of laser beams has attracted considerable attention and some different approaches have been reported to treat the problem. In this paper we analyze quality factor of laser beam and compare the effect of different aberrations on beam quality by expanding pure phase term of wavefront in terms of Zernike polynomials. Also we analyze experimentally the change of beam quality for different Astigmatism aberrations, and compare theoretical results with experimentally results. The experimental and theoretical results are in good agreement.
The switching time of an optically switched polarization- bistable laser diode between locked and free oscillating modes is studied by analytical and numerical methods based on rate equations. Dependencies of switching time on the detuning and power of optical input and injection current are analyzed. It is shown that larger detuning and power of optical input are effective in shortening the switching time as well as smaller injection current. By starting with linear stability analysis, analytical expressions are developed to predict the switching time. Our analytical results, in which the switching of optical output from locked to unlocked mode is shown to be composed of two relaxation processes with a short and long time constants, are in agreement with the numerical results showing fast and slow switching behaviors dependent on the locked state, in contrast to the dynamic behavior of carrier density dominated by a single relaxation process.