Shashi Prakash

An experimental investigation on Nd:YAG laser microchanneling on polymethyl methacrylate submerged in water:

In this research work, an experimental investigation has been carried out on underwater laser microchanneling on polymethyl methacrylate, using a pulsed Nd:YAG laser system. The underwater laser processing has been used to minimize the heat-affected zone, microcracking and burr formation around the microchannel. The process parameters that have been taken into consideration are lamp current, pulse frequency, pulse width and cutting speed. The microchannel characteristics that have been taken into account as responses are microchannel width, microchannel depth, burr width and burr height. Response surface methodology has been used to develop the mathematical relationships between the process parameters and microchannel characteristics. The adequacies of the models have been tested using analysis of variance. The interaction effects of process parameters on the microchannel characteristics have been analyzed and discussed. In addition to that, single-objective and multiobjective optimization of the process parameters have been performed to obtain desired values of microchannel characteristics.

Automated collimation testing using a temporal phase shifting technique in Talbot interferometry.

We propose a quantitative approach toward the detection of collimation of a coherent optical beam. For detection of collimation position of the collimator, a temporal phase shifting technique has been incorporated into Talbot interferometry. The slope of the phase maps depicts the collimation position of the collimator. This technique offers high precision, accuracy, and provides automated output.

Fabrication of microchannels: A review

Microchannels are primarily used in biomedical devices and microfluidic applications. Fabrication of microchannels has always been a tough task using conventional manufacturing technologies. Various types of materials are in use for fabricating microchannels in different types of applications including metals, polymers and ceramics. A number of methods are in use for fabricating different types of microchannels. These processes include both conventional and nonconventional fabrication techniques such as micromilling, lithography, embossing processes and laser ablation processing. During the recent years, some hybrid techniques have also been developed for fabrication of microchannels. This survey of various literatures reveals a broad spectrum of different processes used for fabricating microchannels. Currently, laser micromachining has been evolved as a potential technology for fabricating microchannels. Laser processing has been proved to be the most time efficient and clean. In this article, fabrication processes for creating microchannels have been reviewed with special emphasis on laser micromachining. This article mostly addresses the fabrication techniques for creating surface microchannels.

Profile and depth prediction in single-pass and two-pass CO2 laser microchanneling processes

Polymer based microfluidic channels are used in many chemical and biological devices. Polymethylmethacrylate (PMMA) has emerged as a key material for such devices owing to its high optical transparency and mechanical strength. The use of CO2 laser processing for fabricating microchannels on PMMA has been proved as an efficient and cost effective method. In this work, theoretical models for predicting microchannel profile and depth have been proposed. A model for single-pass laser processing has been proposed based on energy balance. A two-pass laser process for microchannel fabrication produces smoother microchannels with better surface topography and reduced bulging around the microchannel edges. An energy balance based model has also been proposed for two-pass processing. The experimental verification of the proposed models was conducted. Spectroscopic tests were carried out to determine the absorptivity, and simultaneous thermogravimetric analysis/differential scanning calorimetry (TGA/DSC) tests were performed to determine the thermo-physical properties of the PMMA used in the proposed model. The results predicted using the model were found to be in close agreement with the actual values.

Automated collimation testing by incorporating the Fourier transform method in Talbot interferometry

In this paper, we report an automated technique for collimation testing by incorporating Fourier fringe analysis of the recorded interferograms in Talbot interferometry. The triangular profile of Talbot interferometric fringes has been recorded using a CCD and computer system. The interferograms corresponding to the in-focus, at-focus, and out-of-focus positions of the collimating lens have been recorded. Direct phase measurement using the Fourier transform method has been used for detection of collimation positions. Good accuracy and precision in measurement have been achieved.

Collimation testing by use of the Lau effect coupled with moiré readout

We present an easy, simple, and inexpensive technique for checking the quality of the collimation of optical beams using the Lau effect combined with moiré readout. The experimental arrangement consists of a modified Lau-based interferometer in which a white-light incoherent source illuminates a set of two gratings. A collimating lens is placed between the two gratings such that the self-images of the second grating are formed. The third grating is positioned at one of the self-imaging planes forming moiré fringes. The type of the moiré fringe demonstrates the quality of collimation of the optical beam. The necessary theoretical background is presented and the results of our experimental investigation are reported. The technique can also be used for accurate determination of the focal length of a collimating lens using low-cost components.

Real-time slope mapping and defect detection in bent plates using Talbot interferometry

We demonstrate a simple method for obtaining slope contours of bent plates using Talbot interferometry. The technique has been used to map slope contours of polymethyl methacrylate specimens of different shapes. The Talbot image of a coarse grating is projected onto a specimen such that the self-image is backreflected onto the same grating again. As a Talbot interferometer is basically a grating shearing interferometer, it results in the generation of characteristic slope maps of the specimen under test. Results of the investigation match well with other slope-mapping techniques. Validation of experimental results with theoretical predictions in the case of a cantilever beam specimen has been undertaken. Accuracy of about 4.7% with respect to theoretical predictions is obtained.

Slope measurement of bent plates using double grating shearing interferometry

A grating-based shearing interferometeric setup for slope measurement of bent plates has been proposed. The specimen under test is illuminated by a collimated beam from the laser. Light reflected from the specimen passes through two identical holographic gratings placed in tandem. The grating frequency has been so chosen that the diffracted orders from each grating are separated out distinctly. Two first-order beams diffracted from each of the gratings superpose in space. In the resulting interferogram, the fringes due to slope information of the object are visualized. Mathematical formulation for experimental determination of slope values has been undertaken. Validation of the experimental results with theoretical predictions in case of cantilever beam provides good correlation. The main advantage of the technique has been the realization of very compact geometry without the need for spatial filtering arrangement commonly associated with the grating-based techniques used to date.

Efficient resource provisioning using traffic balancing in multidomain optical networks

Summary In multidomain optical networks (MDONs) the emerging multimedia, multivendor applications–based scheduled traffic (ST) is periodic and repeated day by day. The traffic is heavy during the working hours and slack during the non-office hours. This results in the scarcity of network resources during the working hours, leading to the increased blocking of requests, even though there remains relatively large underused capacity during the non-office hours. To use the network resources uniformly and efficiently, the demands may be slided within or shifted along the time zones/windows. In this paper, we first propose a heuristic algorithm, time-aware routing and wavelength assignment (TA-RWA), which allocates resources without traffic balancing (TB) for the ST in MDON. Time-aware routing and wavelength assignment policy is then used as a benchmark for comparison with the 3 different TB solutions (named as P1-TB, P2-TB, and P3-TB), in which the network load is redistributed by rescheduling the intradomain and interdomain demands. We performed extensive simulation experiments in MATLAB environment and compared the proposed policies with the existing ordering policies. From the results, it can be inferred that the proposed TB policies outperform the TA-RWA, and the existing strategies of the blocking probability, resource utilization ratio (RUR), and percentage of intradomain and interdomain connections established. The best performance is achieved using P3-TB strategy, in which requests are slided within, and shifted, along different time windows. The strategy shows about 70% reduction in the percentage blocking probability with respect to the TA-RWA and the existing strategies.

Setting sensitivity in collimation testing using Lau interferometry

An improved method for testing the collimation of an incoherent optical beam using Lau interferometry is presented. The experimental setup consists of a white light source and a set of three identical gratings. A source grating G1 is placed in front of a collimating lens. Beyond the collimating lens gratings G2 and G3 are so aligned that the lines of the gratings make a small but equal and opposite angle with the vertical. The self-image of grating G2 is superimposed on the grating G3, resulting in the generation of moire fringes. Decollimation of the optical beam results in a change in the dimensions of the self-image. This change is detected using the magnification effect of the moire method. The horizontal moire fringes are indicative of collimation of the optical beam. Deviation from the horizontal inclination of the moire fringes indicates setting in of decollimation. Theoretical and experimental investigations to determine the sensitivity achievable in this collimation testing technique are undertaken and results of the investigations are reported. Experimental results are in close agreement with the theoretical predictions.