P K Gupta
Articles written in Pramana – Journal of Physics
Volume 64 Issue 2 February 2005 pp 229-238
In this paper, we report the development of experimental set-up for time-gated optical imaging through turbid media using stimulated Raman scattering. Our studies on the contrast of time-gated images show that for a given optical thickness, the image contrast is better for sample with lower scattering coefficient and higher physical thickness, and that the contrast improves with decreasing value of anisotropy parameters of the scatterers. These results are consistent with time-resolved Monte Carlo simulations.
Volume 82 Issue 2 February 2014 pp 191-195 Contributed Papers
In a thermally birefringence-compensated linear cavity configuration, ∼160 W of average green power by intracavity frequency doubling of AO Q-switched Nd:YAG/LBO-based laser is demonstrated. The corresponding optical to optical conversion efficiency is estimated to be ∼12.7%. The pulse repetition rate is 20 kHz with the individual pulse duration of 73 ns. The beam quality parameter is measured to be 18.
Volume 82 Issue 2 February 2014 pp 197-202 Contributed Papers
We present our studies on dual wavelength operation using a single Nd:YVO4 crystal and its intracavity sum frequency generation by considering the influence of the thermal lensing effect on the performance of the laser. A KTP crystal cut for type-II phase matching was used for intracavity sum frequency generation in the cavity at an appropriate location for efficient and stable yellow output power. More than 550 mW of stable CW yellow-orange beam at 593.5 nm with beam quality parameter ($M^2$) ∼ 4.3 was obtained. The total pump to yellow beam conversion efficiency was estimated to be 3.83%.
Volume 82 Issue 2 February 2014 pp 243-248 Contributed Papers
In a plethora of microfabrication processes available now-a-days, one needs to choose the best possible option suitable for the job on-hand. This paper discusses three versatile approaches to fabricate microchips for lab-on-chip (LOC) applications in general and uranium analysis in water samples as a specific case. Laser-direct patterning succeeded by soft lithography, laser micropatterning followed by HF etching and micromilling have been demonstrated which not only suit the objective of uranium detection but also for most of the LOC applications. The different techniques elaborated enable development of LOCs in polymers as well as glass with a depth ranging from few microns to 100 𝜇m or higher while squeezing the reaction lengths of ∼10 cm on a 20 mm × 32 mm chip. This development equips one to design and develop more complicated LOC devices to take advantage of their hastened reaction cycle with minimal waste in terms of capital and maintenance cost.
Volume 82 Issue 2 February 2014 pp 433-437 Contributed Papers
We report the development of an optoelectronic tweezers set-up which works by lightinduced dielectrophoresis mechanism to manipulate microparticles. We used thermal evaporation technique for coating the organic polymer, titanium oxide phthalocyanine (TiOPc), as a photoconductive layer on ITO-coated glass slide. Compare to the conventional optical tweezers, the technique requires optical power in 𝜇W range and provides a manipulation area of a few mm2. The set-up was used to manipulate the polystyrene microspheres and red blood cells (RBCs). The RBCs could be attracted or repelled by varying the frequency of the applied AC bias.
Volume 95, 2021
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