High Energy Materials - Publications

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    Highly efficient difference-frequency generation in KTP
    ( 1996-01-01) Bhar, G. C. ; Rudra, A. M. ; Chaudhary, A. K. ; Sasaki, T. ; Mori, Y.
    A conversion efficiency as high as 22% from dye-laser radiation to the near infrared with difference-frequency mixing of Nd:YAG laser radiation and its second-harmonic-pumped dye laser in an only 5 mm long KTP crystal is reported for the generation of tunable near infrared radiation.
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    The generation of efficient tunable coherent near-IR radiation by temperature-tuned non-critical difference-frequency mixing in a LBO crystal
    ( 1996-05-14) Bhar, G. C. ; Rudra, A. M. ; Chaudhary, A. K.
    Efficient tunable near-infrared radiation (NIR) (1.1-2.2 μm) has been generated by temperature-tuned non-critical phase-matched (NCPM) difference-frequency mixing of Nd:YAG and tunable dye laser radiation (560-710 nm) in a 5 mm LBO crystal. Energy conversion efficiency of 11% at 1.54 μm has been achieved. A large angular and spectral bandwidth is observed. Temperature-tuned type-II non-collinear phase-matching has also been reported. Comparison with other NIR-generating crystals shows that temperature-tuned NCPM in LBO is superior to other methods.
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    Generation of widely tunable mid-infrared radiation by difference frequency mixing in KTP
    ( 1997-10-07) Bhar, G. C. ; Chatterjee, U. ; Rudra, A. M. ; Chaudhary, A. K.
    The crystal potassium titanyl phosphate (KTP) shows promise for generation of tunable infrared radiations throughout the range 2-4.5 μm. Widely tunable mid-infrared radiations have been generated by nonlinear difference frequency mixing of the Nd:YAG second harmonic and the same pumped tunable dye laser radiation (610-710 nm) in a KTP crystal. The system generates more than 14 W mid-infrared peak power at 3.27 μm by difference frequency generation.
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    Tunable infrared generation in KTA and applications
    ( 1999-01-01) Bhar, G. C. ; Kumbhakar, P. ; Chaudhary, A. K. ; Chatterjee, U.
    Noncollinear difference frequency mixing of dye laser and Nd:YAG second harmonic (fundamental) radiation from a commercial laser system is employed for the generation of 2.7-5.3 μm (1.6-1.7 μm) radiations in a flux-grown KTiOAsO4 crystal. The generated radiation is used to scan the methane absorption in the fundamental (v3) and its first overtone (2v3) band at pressure 90 torr in a laboratory made single pass gas cell of length 33 cm.
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    Generation of ultraviolet radiation with wide angular tolerance in cesium lithium borate crystal
    ( 2000-01-01) Bhar, Gopal C. ; Kumbhakar, Pathik ; Chaudhary, Anil K.
    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.
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    Study of laser induced damage threshold and effect of inclusions in some nonlinear crystals
    ( 2000-07-01) Bhar, G. C. ; Chaudhary, A. K. ; Kumbhakar, P.
    The paper reports the comparative studies on the laser-induced single-shot and multiple-shot surface damage thresholds of nonlinear crystals, viz. Urea, 3-methyl-4-nitropyridine-1 oxide (POM), L-arginine phosphate (LAP) and β-barium borate (BBO) crystals. The measurements were made using radiation of 1064 nm and its second harmonic generation, i.e. 532 nm from a Q-switched Nd:YAG laser of pulse width 10 ns. In addition, the effect of Na+ impurity incorporated during growth in BBO crystal in different concentration (wt.%) has also been studied, and attempted to be correlated with various factors. We also measured the absorption coefficients of these crystals at different wavelengths. The Scanning Electron Microscope coupled with Energy Dispersive X-Ray Analyzer (SEM-EDX) has been employed to study the inclusions/impurities present in the crystals.
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    Tunable near-infrared radiation by difference frequency mixing in a lithium tetraborate crystal
    ( 2001-01-01) Chatterjee, U. ; Kumbhakar, P. ; Chaudhary, A. K. ; Bhar, G. C.
    The non-collinear difference frequency mixing (DFM) in lithium tetraborate (LB4) crystal was analyzed to study the generation of near-infrared radiations. The phase-matching characteristics for the generation of ultraviolet radiations by second harmonic generation were also studied. The LB4 crystal was polished on all four side faces for experimental verification. The analysis suggested that the use of high intensity input beams increased the efficiency of radiation generation for high threshold damage of the crystal.
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    Type-I walk-off compensated second and fourth harmonic generation of Nd: YAG laser radiation from a Li
    ( 2001-02-07) Bhar, G. C. ; Chaudhary, A. K. ; Kumbhakar, P. ; Rudra, A. M.
    A type-I walk-off compensation (WOC) arrangement has been made for the second harmonic generation (SHG) and the fourth harmonic generation (FOHG) of commercially available Q-switched Nd: YAG laser radiation, for the first time, using two identically cut Li2B4O7 crystals. The enhancement of the conversion efficiencies has been realized in the WOC arrangement by a factor of 2.71 for the SHG and 2.65 for the FOHG relative to the double-crystal non-walk-off arrangement. The absolute values of the conversion efficiencies obtained for WOC SHG and FOHG are 3.52% and 3.56% respectively, applying input power densities for the fundamental and second harmonic of the Nd: YAG laser beam at only 28.3 MW cm-2 and 11.7 MW cm-2, respectively. © 2001 IOP Publishing Ltd.
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    Tunable mid-infrared generation in cesium lithium borate crystal
    ( 2001-02-15) Chatterjee, U. ; Kumbhakar, P. ; Chaudhary, A. K. ; Bhar, G. C.
    Generation of tunable mid-infrared radiation has been done in a cesium lithium borate (CsLiB6O10, CLBO) crystal for the first time employing type-I noncollinear difference frequency mixing of Q-switched Nd:YAG (or its second harmonic) and the tunable dye-laser radiation (0.605-0.725 μm). In the process a quantum conversion efficiency of approximately 5.5% has been realized for the generation of 1.85 μm in only a 5 mm long crystal when the used peak power density of the pump dye-laser (0.675 μm) beam is as low as 12.7 MW/cm2.
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    Tunable mid-infrared spectrometer based on KTA crystal to study fundamental v
    ( 2001-05-01) Bhar, G. C. ; Kumbhakar, P. ; Chaudhary, A. K.
    Tunable mid-infrared radiation in the range 3-3.5 μm have been generated by difference frequency mixing in a biaxial potassium titanyl arsenate (KTA) crystal. The fundamental input radiations are the second harmonic of a commercially available Nd:YAG laser radiation (i.e. 532 nm) and the same pumped visible dye laser radiation. Using the generated tunable radiation the room temperature absorption spectra of R-branch of the v3 band of methane at 120 mbar pressure have been studied. Pressure dependent absorption of P(7) line of the v3 band of methane have also been studied. The absorption measurements have been performed in an indigenously built single pass gas cell of length 33 cm.
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    Highly efficient deep ultraviolet generation by sum-frequency mixing in a BBO crystal pair
    ( 2002-01-01) Bhar, Gopal C. ; Kumbhakar, Pathik ; Chatterjee, Udit ; Chaudhary, Anil K. ; Kokh, Alexander
    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.
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    Generation of UV radiation in a lithium tetraborate crystal by walk-off compensated Type I sum-frequency mixing
    ( 2002-08-29) Bhar, G. C. ; Kumbhakar, P. ; Chaudhary, A. K.
    Ultraviolet radiation is generated in two lithium tetraborate (Li2B4O7 or LB4) crystals by Type I walk-off compensated sum-frequency mixing (SFM) of the commonly available Nd:YAG laser radiation and radiation from a dye laser pumped by the second harmonic of the same YAG laser. In the walk-off compensated configuration, an enhancement in the conversion efficiency by a factor of 3.8 relative to the single pass generation is realised.
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    A comparative study of laser-induced surface damage thresholds in BBO crystals and effect of impurities
    ( 2004-01-01) Bhar, G. C. ; Chaudhary, A. K. ; Kumbhakar, P. ; Rudra, A. M. ; Sabarwal, S. C.
    The paper reports the laser induced single shot and multiple shot surface damage thresholds along with absorption characteristics studies of different types of BBO crystals using 1064 and 532 nm wavelengths of Nd:YAG laser. In addition different types of inclusions/impurities present in these crystals have also been investigated using scanning electron microscope coupled with energy dispersive X-ray analyzer (SEM-EDXA). The obtained damage data are correlated with the inclusions/impurities to study their effect on crystal quality. © 2004 Elsevier B.V. All rights reserved.
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    Low-limit photo-acoustic detection of solid RDX and TNT explosives with carbon dioxide laser
    ( 2006-03-01) Chaudhary, A. K. ; Bhar, G. C. ; Das, S.
    We report the absorption spectra of RDX and TNT explosive samples in solid form at room temperature using a carbon dioxide laser-based photo-acoustic technique. A continuous wave 12C16O2 laser, tunable between the 9.25-10.74 μm wavelength region, was used as an energy source. Interference-free limits of detection of solid RDX and TNT in simulated samples are estimated to be 10.0 and 16.5 ppbw, respectively. ©2006 Springer Science+Business Media, Inc.
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    Generation of tunable infrared radiation in rubidium titanyl phosphate crystal for the optical measurement of number density, absorption cross-section of methane gas
    ( 2006-03-01) Chaudhary, A. K. ; Bhar, G. C. ; Kumbhakar, P.
    Tunable near-infrared radiation has been generated in a rubidium titany1 phosphate (RTP) crystal by employing non-collinear difference-frequency mixing (DFM) technique. The input radiation sources are Nd:YAG laser radiation and its second harmonic pumped dye laser radiation. For the generation of 2.0 radiation, the maximum value of the conversion efficiency (quantum) obtained in the process is 49% from the dye (0.6945 μm) to the infrared (2.0 μm) radiation in the 7.9-mm-long crystal. The generated tunable mid-infrared radiation has been used to measure the number density, absorption cross-section and minimum detectable concentration of methane gas in its 2ν3 band in a multi-pass cell at 30.075 Torr pressure. The number density and column density of the methane molecules are found to be 1.068 × 1018 cm-3 and 3.02 × 1021 cm-2, respectively, whereas the minimum still-detectable concentration at 1.658 μm wavelength is estimated to be 4.523 × 1017/cm3. © 2005 Elsevier Ltd. All rights reserved.
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    Generation of coherent tunable deep UV radiation for detection and absorption studies of explosives RDX and TNT
    ( 2007-07-01) Chaudhary, A. K. ; Rudra, A. M. ; Kumbhakar, P. ; Bhar, G. C.
    We report a technique for the efficient generation of tunable coherent deep UV radiation and its application in studies of RDX and TNT at the ppm level on the basis of their absorption characteristics. The obtained experimental absorption data are compared with conventional spectrophotometric data. The UV radiation in the range 200-260 nm has been generated by the type-I noncollinear third harmonic of the dye laser radiation (600-700 nm) and also by sum frequency mixing (SFM) of Nd:YAG output (1064 nm) with the second harmonic of the dye laser in β-barium borate (BBO) crystal. The maximum conversion efficiency of the generated signal is estimated to be 57.5% at λ = 218.9 nm wavelength. Apart from measurements of the absorbance of RDX and TNT at different concentrations in their respective solutions, the minimum detection concentrations have also been ascertained. The estimated minimum detectable concentration of RDX is 8.47•10-9 M, whereas that for TNT is 35.7•10-9 M. The data were obtained using only ∼100 μJ/pulse of laser energy. © 2007 Springer Science+Business Media, Inc.
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    Non-linear absorption and second harmonic imaging of Zn-BaTiO
    ( 2008-07-31) Fasasi, A. Y. ; Maaza, M. ; Theron, Ch ; Neethling, P. ; Buttner, U. ; Leitch, A. ; Chaudhary, A. K.
    Zinc-doped barium titanate samples have been prepared on Corning glass as well as on silicon wafer by laser ablation. Samples on glass having different deposition time and varying zinc oxide content have been studied by Z-scan technique at a wavelength of 540 nm and laser intensity of 20 GW while samples on silicon have been characterized by second harmonic (SH) imaging as a function of zinc content. The result on Z-scan measurements shows that films doped with 1 wt.% ZnO and deposited for a period of 80, 100 and 180 min respectively exhibit non-linear absorption with the maximum non-linear absorption coefficient (βmax) of 800 cm/GW. The undoped as well as samples of BaTiO3 doped with 3, 4 and 5 wt.% ZnO with deposition time of 60 min each exhibit non-linear saturation with the sample containing 5 wt.% ZnO having the lowest value of - 5.9 × 102 cm/GW, which signifies that an increase in zinc oxide content leads to a reduction in the observed bleaching effect. In addition, it is also suggested that switching from non-linear absorption to non-linear saturation is probably due to thickness effect. The SH imaging has shown the location dependence of the films, which we assume may be due to the geometry of the deposition module and crystal growth through the formation of small crystallites as the building block of the films. © 2007 Elsevier B.V. All rights reserved.
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    Measurement of refractive index of biaxial potassium titanyl phosphate crystal plate using reflection spectroscopic ellipsometry technique
    ( 2009-10-01) Chaudhary, A. K. ; Molla, A. ; Asfaw, A.
    The paper reports the measurement of refractive indices and anisotropic absorption coeffcients 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 (λ = 632:8 nm), diode laser (λ = 670:0 nm) and temperature-tuned diode laser (λ = 804:4 and 808.4 nm), respectively have been employed as source. The experimental data for nx, ny 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.
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    Generation of THz radiation from Bow tie Photoconductive antennas based on Semi insulating Gallium Arsenide
    ( 2012-01-01) Venkatesh, M. ; Rao, K. S. ; Abhilash, T. S. ; Tewari, S. P. ; Chaudhary, A. K.
    The generation and detection of THz radiation ranging 0.1- 2 THz using indigenously designed Semi Insulating -GaAs photoconductive bow tie antennas with ultra-short laser pulses (140 fs, 800 nm) was discussed. © 2012 OSA.