• SK Sharma

      Articles written in Pramana – Journal of Physics

    • An alternative approach to determine the spot-size of a multi-mode laser beam and its application to diode laser beams

      Rakesh Kapoor PK Mukhopadhyay Jogy George SK Sharma

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      An alternative approach is suggested to determine the spot-size of a multi-mode laser beam. It has been shown by simulations that the suggested approach can give the beam quality factor and characteristic radius with less than 5% error. Unlike the power content method, the proposed method is applicable to the beams even with diameter one tenth of the CCD size. The new approach has been applied to a multi-mode diode laser output and it is shown that the ABCD matrix analysis can be used for beam propagation, with the measured parameters of the laser.

    • Measurement of στ product of solid state laser materials by an alternative method: Application to Nd3+ doped YVO4 crystal for 4F3/24I11/2 transition

      PK Mukhopadhyay Jogy George SK Sharma Rakesh Kapoor TPS Nathan

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      In this paper an alternative approach for measurement of στ product for 4F3/24I11/2 transition of Nd3+ doped YVO4 crystal is reported. In this method a microchip laser is formed by keeping a small piece of the sample in plane-plane resonator and a diode laser (808 nm) is used for pumping. The pump power induced thermal lensing effect is used to make the cavity stable. The cavity mode area is estimated by measuring the thermal lens focal length at the threshold and the average pump area is measured by Gaussian fit to the intensity profiles of the pump beam. The value of στ product of Nd:YVO4 crystal obtained by this method is within 10% of the reported values. The advantage of this method is that it is a simple method for direct measurement of στ product of laser crystals.

    • Effect of absorbed pump power on the quality of output beam from monolithic microchip lasers

      Pranab K Mukhopadhyay K Ranganathan Jogy George SK Sharma TPS Nathan

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      The dependence of the beam propagation factor (M2 parameter) with the absorbed pump power in the case of monolithic microchip laser under face-cooled configuration is extensively studied. Our investigations show that the M2 parameter is related to the absorbed pump power through two parameters (α and β) whose values depend on the laser material properties and laser configuration. We have shown that one parameter arises due to the oscillation of higher order modes in the microchip cavity and the other parameter accounts for the spherical aberration associated with the thermal lens induced by the pump beam. Such dependency of M2 parameter with the absorbed pump power is experimentally verified for a face-cooled monolithic microchip laser based on Nd3+ -doped GdVO4 crystal and the values of α and β parameters were estimated from the experimentally measured data points.

    • Effect of Nd3+ concentration on CW and pulsed performance of fiber-coupled diode laser pumped Nd:YVO4 laser at 1064 nm

      Pranab K Mukhopadhyay K Ranganathan Jogy George SK Sharma TPS Nathan

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      The effect of Nd3+ concentration on the CW and Q-switched laser performances at 1064 nm from Nd: YVO4 has been studied under diode laser pumping in identical laser configuration. The Nd3+ concentrations used were 1, 2 and 3 at.% in YVO4 crystals. Under the CW operations we have compared the thermal lensing effect, slope efficiencies and also the beam quality at the fourth-order degeneracy configuration. Q-switching was done with the help of an acousto-optic modulator and we have compared the pulses obtained from Nd: YVO4 laser with different doping concentration. It was found that the 1 at.%-doped crystal is the best, offering highest optical-to-optical conversion efficiency (55%), lowest fractional heat load (24%), highest pulse energy (80 µJ) and shortest pulse width (20 ns). It was also found that there was not much difference in performances for 2 and 3 at.%-doped crystals both in CW and Q-switched configurations.

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