• A K Chaudhary

      Articles written in Pramana – Journal of Physics

    • Measurement of refractive index of biaxial potassium titanyl phosphate crystal plate using reflection spectroscopic ellipsometry technique

      A K Chaudhary A Molla A Asfaw

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      The paper reports the measurement of refractive indices and anisotropic absorption coefficients of biaxial potassium titanyl phosphate (KTP) crystal in the form of thin plate using reflection ellipsometry technique. This experiment is designed in the Graduate Optics Laboratory of the Addis Ababa University and He–Ne laser ($\lambda = 632.8$ nm), diode laser ($\lambda = 670.0$ nm) and temperature-tuned diode laser ($\lambda = 804.4$ and 808.4 nm), respectively have been employed as source. The experimental data for $n_{x}$, $n_{y}$ are fitted to the Marquardt–Levenberg theoretical model of curve fitting. The obtained experimental data of refractive indices are compared with different existing theoretical and experimental values of KTP crystals and found to be in good agreement with them.

    • Low-limit detection of NO2 by longitudinal mode selection in a photoacoustic resonant system

      F Yehya A K Chaudhary

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      The paper reports the pulsed laser-based photoacoustic (PA) spectroscopy of NO2 in a resonant PA cavity with special filters made of stainless steel. The PA cell along with special types of sound filters are designed and fabricated to excite only the second-order longitudinal mode inside the cavity. The second harmonic, i.e. $\lambda = 532$ nm pulse width, of 7 ns obtained from $Q$-switched Nd:YAG laser at 10 Hz repetition rate has been used to study the saturation behaviour of the PA signal and absorption coefficient with respect to the input laser energy. Generally, the $Q$-factor of longitudinal modes in the acoustic cavities is quite low. However, by modifying the design of the cell and the filter, we can achieve high value of $Q = 30$. The combination of special filter along with the experimental data acquisition technique helped us to achieve the minimum detection concentration of NO2 of the order of 9 ppbV which is much better than the previous value of the same PA cell without filter [Yehya and Chaudhary, Appl. Phys. B 106, 953 (2012)].

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