• Pathik Kumbhakar

      Articles written in Pramana – Journal of Physics

    • Third harmonic generation of CO2 laser radiation in AgGaSe2 crystal

      Gopal C Bhar Pathik Kumbhakar D V Satyanarayana N S N Banerjee U Nundy C G Chao

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      Generation of third harmonic of CO2 laser radiation has been obtained in a type-II, ϑ=57° cut 9 mm thick AgGaSe2 crystal for the first time by sum-frequency-mixing of the fundamental with its second harmonic, the latter being obtained using another type-I, ϑ=55° cut 11 mm thick AgGaSe2 crystal. The energy conversion efficiencies obtained for second harmonic and third harmonic generations are 6.3% and 2.4% respectively with the input fundamental pump power density of 5.9 MW/cm2 only. The wavelength of the fundamental CO2 laser radiation used for the generation of harmonics is 10.6 µm, P(20) line. A compact TEA CO2 laser source has been built in the laboratory.

    • Generation of ultraviolet radiation with wide angular tolerance in cesium lithium borate crystal

      Gopal C Bhar Pathik Kumbhakar Anil K Chaudhary

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      Tangential phase-matching has been realised in cesium lithium borate (CLBO) crystal for the first time for the generation of fourth harmonic (266 nm) of Nd:YAG and third harmonic (226.7 nm) of a dye laser radiation by second harmonic generation and sum-frequency mixing with the angular tolerance as large as 22 mrad and 21 mrad respectively, over one of the interacting beams. An energy conversion efficiency of 15% for fourth harmonic generation is obtained with a 5.5 mm thick crystal and with the average pump powers only 170 and 70 mW. A set of Sellmeier dispersion equations for the CLBO crystal have also been formulated.

    • Highly efficient deep ultraviolet generation by sum-frequency mixing in a BBO crystal pair

      Gopal C Bhar Pathik Kumbhakar Udit Chatterjee Anil K Chaudhary Alexander Kokh

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      Generation of deep ultraviolet radiation at 210 nm by Type-I third harmonic generation is achieved in a pair of BBO crystals with conversion efficiency as high as 36%. The fundamental source is the dye laser radiation pumped by the second harmonic of a Q-switched Nd: YAG laser. A walk-off compensated configuration with the BBO crystal pair has enabled us to realize such a high conversion efficiency in the interaction.

    • Observation of two-photon absorption at UV radiation in ZnS quantum dots

      Manajit Chattopadhyay Pathik Kumbhakar Udit Chatterjee

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      Research studies on quantum dots (QDs) of semiconductor materials are of potential interest in present days having promising applications in different optoelectronic devices. Among other materials, ZnS is a direct bandgap semiconductor material having a wide bandgap of 3.6 eV for its cubic phase at room temperature and it shows excellent optical properties. However, here the nonlinear optical (NLO) properties of chemically synthesized ZnS QDs of average size of ∼ 1.5 nm have been reported which are measured by using an indigenously developed Z-scan technique. The pump radiation is 355 nm which is the third harmonic of the Q-switched Nd:YAG laser radiation having pulsed duration of 10 ns with the repetition rate of 10 Hz. The measured experimental data have been analysed by using analytical models and two-photon absorption coefficients of the ZnS QDs at 355 nm have been extracted.

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