Shadowgraphic imaging technique is used to study the dynamics of cavitation bubbles produced during the pulsed laser ablation of a silver target in water. Ablation of a solid target immersed in liquid with a pulsed laser beam is a popular technique for the synthesis of colloidal nanoparticles. To understand the highly complex mechanism involved in nanoparticle formation, estimation of the thermodynamical parameters within the bubble, where the nucleation of the nanoparticles occur, is extremely important. The dynamics of the bubble studied using a fast gated CCD camera reveal that the bubble expands initially and then reaches its maximum size after which it starts compressing. The range of temperature and pressure values within the bubble is analytically assessed using two known models, the Rayleigh-Plesset and the van der Waals model.
If a zonal wavefront sensor such as the Shack-Hartmann wavefront sensor is used to measure the surface profile, the sensing scheme apart from the test wavefront requires a reference wavefront. In order to switch between the two there is a need to replace the test surface by a reference surface such as a mirror. This often introduces inaccuracies in the measurement. In this paper, we introduce an experimental arrangement comprising wave plates and polarizing beam splitters where both the reference and the test wavefronts can be simultaneously present or one can easily switch from reference wavefront to test wavefront.
Grating array based zonal wavefront sensor (GAZWFS), using an array of gratings implemented with a liquid crystal spatial light modulator (LCSLM) to display the gratings, offers a flexible measurement approach. But the wavefront with a large slope may not accurately be sensed by the sensor like any Shack- Hartmann type sensor. In this paper, we propose a zone wise scanning method to improve the dynamic range of GAZWFS by blocking and unblocking the individual gratings. The estimation of the wavefront and expansion of the dynamic range of GAZWFS by the zone wise scanning method is demonstrated by numerical simulation and a proof-of-principle experimental implementation.
Laser induced breakdown at copper-water interface was used to synthesize Copper@CopperOxide nanocomposites
in the colloidal form. The antibacterial activities of these nanoparticles were studied using UV-Vis and Raman
spectroscopy.
We propose the use of square arrays of multiple atomic lenses, produced by interference of four nearly collinear optical beams in atom lithography using dipole force. Simulated lithographic patterns are reported for collimated as well as divergent rubidium atomic beam traveling in such square arrays of optical channels. The proposed configuration has the ability to write large numbers of periodic structures in square arrays in a single step.
Polarization interferometry is normally not a regular topic in the class room at graduate level. Therefore a polarization heterodyne interferometer similar to a Michelson interferometer using polarizing components is discussed in this paper to demonstrate the interference of two orthogonal polarized beams. The measurement of the phase shift as a result of orientation of polarizer is performed by recording corresponding fringe shift. The theoretical expression is also presented using Jones calculus for the fringe shift as a function of azimuth of the polarizer. The experimental set-up is simple and can be very well incorporated in the teaching laboratory.
Lasers have made the revolution in the modern optical technologies but there is hardly any efforts to take up the basic understanding of laser Physics via laboratory classes at graduate and undergraduate level. In this paper, a simple experiment for studying the life time of the upper laser level under lasing condition, the relaxation oscillations, measurement of threshold current and variation of laser power as a function of current in a laser diode is presented. The experiment utilizes the readily available low cost components, a key chain laser and some of the electronics instrument normally available at any undergraduate laboratory of science and engineering department.
A sandwiched M tech program is proposed for Photonics. The course structure is designed carefully so as to provide a thorough base in the subject simultaneously students are trained well to meet the present and the future market challenges at par with any conventional technology based program.
We report the generation of 2D hexagonal array geometry of equally illuminating light spots using the interference of eight beam. Geometry and size of the arrays can be easily controlled by appropriate orientation of the optical components in the reported configuration.
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