Advanced Centre of Research in High Energy Materials (ACRHEM)

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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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    A comparative study of thermal stability of TNT, RDX, CL20 and ANTA explosives using UV 266 nm-time resolved photoacoustic pyrolysis technique
    ( 2019-03-15) Rao, K. S. ; Ganesh, D. ; Yehya, F. ; Chaudhary, A. K.
    The paper reports the potential use of UV based pulsed photoacoustic spectroscopy to study the thermal stability of some well-known premier explosives such as TNT, RDX, CL20, and ANTA between 30 and 350 °C range. The thermal PA spectra of samples were recorded using fourth harmonic wavelength i.e. 266 nm of pulse duration 7 ns and repetition rate 10 Hz obtained from Q-switched Nd: YAG laser system. Under the influence of UV radiation, the explosive molecules in vapor phase follow the photodissociation process and converted into their byproducts such as NO, NO2 and N2O etc. due to π* ← n transitions, which are responsible for the generation resultant PA signal at 266 nm wavelength. The results obtained from PA spectra as a function of temperature are cross verified with Thermo gravimetric-differential thermal analysis (TG-DTA) to ascertain the thermal stability of these samples. The comparative PA spectra of samples were analyzed and shown the behavior of acoustic modes with respect to incident laser energy, and data acquisition time. Finally, the thermal quality factor “Q” is measured to test the stability of reported explosives.
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    A low-cost LIBS detection system combined with chemometrics for rapid identification of plastic waste
    ( 2020-11-01) Junjuri, Rajendhar ; Gundawar, Manoj Kumar
    We present, rapid and efficient identification of ten different types of post-consumer plastics obtained from a local recycling unit by deploying a low cost, compact CCD spectrometer in laser-induced breakdown spectroscopy (LIBS) technique. For this investigation, spectral emissions were collected by an Echelle spectrograph equipped with an intensified charge-coupled device (ES-ICCD) as well as a non-gated Czerny Turner CCD spectrometer (NCT-CCD). The performance is evaluated by interrogating the samples in a single-shot as well as accumulation mode (ten consecutive laser shots). The results from principal component analysis (PCA) have shown excellent discrimination. Further, the artificial neural network (ANN) analysis has demonstrated that individual identification accuracies/rates up to ~99 % can be achieved. The data acquired with ES-ICCD in the accumulation of ten shots have shown average identification accuracies ~97 %. Nevertheless, similar performance is achieved with the NCT-CCD spectrometer even in a single shot acquisition which reduces the overall analysis time by a factor of ~15 times compared to the ES-ICCD. Furthermore, the detector/collection system size, weight, and cost also can be reduced by ~10 times by employing a NCT-CCD spectrometer. The results have the potential in realizing a compact and low-cost LIBS system for the rapid identification of plastics with higher accuracies for the real-time application.
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    A novel investigation of the thermal decomposition mechanism of (MTNI) and (KNO
    ( 2013-01-31) Yehya, F. ; Chaudhary, A. K.
    We report a novel approach based on time resolved pulsed photoacoustic (PA) technique to study the thermal decomposition mechanism of 1-methyl-2,4,5- trinitroimidazole (MTNI) and potassium nitrite (KNO2). The technique is based on the detection of free -NO2 molecules which is released due to thermal decomposition from these samples. The second harmonic i.e. λ = 532 nm pulses of 7 ns width at repetition rate 10 Hz obtained from Q-switched Nd:YAG laser is employed to record the PA spectrum. The recorded PA spectrums show the presence of first five even longitudinal acoustic modes i.e. 2nd, 4th, 6th, 8th and 10th with different intensities and frequency shift. In addition, the thermal decomposition mechanism of MTNI and KNO2 is crossed examined by TG-DTA technique which provides direct information of weight loss and heat flow thermal zones. The PA based temperature study is carried out for MNTI and KNO2 separately. We have obtained several highly resolved thermal zones which clearly demonstrate the process of thermal decomposition. Finally, the effect of pressure and input laser energy on PA signal has also been studied. © 2012 Elsevier B.V.
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    Acoustic shock wave emissions from laser induced breakdown of materials
    (University of Hyderabad, 2018-07-30) Manikanta, Elle ; Prem Kiran, P
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    An approach to reduce the sample consumption for LIBS based identification of explosive materials
    ( 2017-01-01) Anubham, S. K. ; Junjuri, R. ; Myakalwar, A. K. ; Gundawar, M. K.
    An experimental design based on spectral construction, which has potential to minimise the sample consumption, the number of laser shots and time required to collect the data from laser induced breakdown spectroscopy for identification of the explosive materials is reported in the study. This approach is an ideal solution in the field of hazardous material detection, where the availability of the sample can be a serious limiting factor. The experimental data recorded on a set of five high energy materials has been considered to test the performance of the proposed methodology. Multiple spectra are constructed by assuming a normal distribution at each wavelength of the spectrum, where random numbers are generated using the mean and standard deviations obtained from arbitrarily chosen five experimental spectra from each class. The newly generated spectra are called as synthetic spectra. The correct classification obtained from - K - nearest neighbour combined with principal component analysis and partial least square - discriminant analysis demonstrated very promising results. The correct classification rates differed by only 4 per cent - 7 per cent as compared to conventional approach where experimental spectra alone are considered for the analysis. Further, when RDX is excluded, the obtained results are almost identical with conventional approach.
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    Bulk crystal growth, crystalline perfection and optical homogeneities of 2AP4N single crystals for second and third order frequency conversion and terahertz (THz) device applications
    ( 2021-08-01) Karuppasamy, P. ; Kamalesh, T. ; Senthil Pandian, Muthu ; Ramasamy, P. ; Sunil, Verma ; Chaudhary, A. K.
    Bulk size organic 2AP4N single crystals were grown by a point seed rotation technique using methanol solvent. The lattice dimensions of the grown crystal and their various crystalline planes have been analyzed by XRD measurement and also the lattice strain was calculated. The lattice perfection was examined by HRXRD and found to be extremely good. The optical transparency and cut-off value of the grown crystal were analyzed by the UV–Vis NIR measurement. The crystalline homogeneity has been confirmed by the birefringence and Mach-Zehnder interferometry techniques. The SHG measurement has been carried out with different particles. The refractive indices of grown crystal have been measured in different wavelengths by prism coupling technique and the Sellmeier's co-efficient has been calculated. The Type-I and Type-II phase-matching angles were determined and the crystal was cut along the phase-matching angles. The third order nonlinear optical parameters were analyzed by Z-scan technique. In addition, the crystal shows potential to generate pulsed Terahertz (THz) radiation by optical rectification using 800 nm wavelength at 140 fs, obtained from Ti: Sapphire Laser. The generated THz spectrum is extended up to 3.0 THz. The maximum conversion efficiency of the generated signal is of the order of 0.64 × 10−5%.
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    Classification of challenging Laser-Induced Breakdown Spectroscopy soil sample data - EMSLIBS contest
    ( 2020-07-01) Vrábel, Jakub ; Képeš, Erik ; Duponchel, Ludovic ; Motto-Ros, Vincent ; Fabre, Cécile ; Connemann, Sven ; Schreckenberg, Frederik ; Prasse, Paul ; Riebe, Daniel ; Junjuri, Rajendhar ; Gundawar, Manoj Kumar ; Tan, Xiaofeng ; Pořízka, Pavel ; Kaiser, Jozef
    We present results of the classification contest organized for the EMSLIBS 2019 conference. For this publication, we chose only the five best approaches and discussed their algorithm in detail. The main focus of the contest reflected both recent and long-term challenges of Laser-Induced Breakdown Spectroscopy (LIBS) data processing. The contest was designed with a purpose to raise a challenge in handling and processing a very large dataset, containing high-dimensional elemental spectra. For the contest, 138 samples were measured using a lab-based LIBS system. In total, the data set consisted of 70,000 spectra, separated into 12 classes according to their elemental composition. Due to its extensivity and complexity, the data set is unique within the LIBS community. The central idea was to simulate the so-called “out-of-sample” classification (i.e. according to similar elemental composition), implying various real-world applications. Even more, it reflects the current level of expertise in the LIBS community and the capability of the LIBS method itself.
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    Comparative study of temperature dependent generation of tunable terahertz radiation in ppln crystal using ultrafast laser pulses
    ( 2014-07-21) Rao, K. S. ; Venkatesh, M. ; Chaudhary, A. K.
    We ascertain the effective lengths and grating periods for temperature tuned terahertz generation using 40, 150 fs pulses of 800 nm and 30 ps pulses of 1064 nm in PPLN crystals.
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    Comparative Study of Ultraviolet Laser-Based Time-Resolved Photoacoustic Fingerprint Spectra and Thermal Decomposition Mechanisms of Energetic 1,2,3-1H-Triazole Derivatives Under Controlled Pyrolysis
    ( 2017-07-01) Rao, Konda Srinivasa ; Chaudhary, Anil Kumar
    We report the comparative study of photoacoustic (PA) fingerprint spectra, thermal decomposition, and stability mechanism of some phenyl and bis series energetic compounds named 1-(2-methoxy,-3,5-dinitrophenyl)-1H-1,2,3-triazole (S5), 1-(3-methoxy, 2, 6 dinitrophenyl) 1H-1, 2, 3 triazole (S10), 1-(4-nitrophenyl)-1H-1,2,3-triazole (S8), and 2,6-bis ((4-(nitromethyl)-1H-1,2,3-triazol-1-yl)methyl) pyridine (S9). Fourth harmonic wavelength, i.e., 266 nm of pulse duration 7 ns and 10 Hz repetition rate obtained from Q-switched Nd: YAG laser, was used to record the thermal PA spectra of these compounds under controlled pyrolysis condition in the range of 30–350 ℃. The PA fingerprint spectra are produced due to entire molecule vapor along with principal functional byproduct NO2 molecule. NO2 molecule is a major gas released during thermal decomposition due to weakest nature of C–NO2 bond. Further, NO2 molecules are involved in photodissociation process due to π*←n transition and converted into NO molecules inside the PA cell due to excitation by 266 nm wavelength. The combined results of PA and gas chromatography–mass spectrometry (GC-MS) spectra along with thermo gravimetric–differential thermal analysis (TG-DTA) data confirm the thermal decomposition mechanism process that can be completed in multiple steps. In addition, GC-MS spectra also confirm the release of NO and NO2 molecules. The effect of incident laser energy and data acquisition time has been carried out for understanding the behavior of acoustic modes. Finally, the thermal quality factor “Q” is measured to test the stability of compounds.
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    Computational study of energetic materials under Hydrostatic compression
    (UNIVERSITY OF HYDERABAD, 2016-02-20) Yedukondalu, Neelam ; Vaitheeswaran, G.S
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    Correlation between discrete probability and reaction front propagation rate in heterogeneous mixtures
    ( 2017-09-01) Naine, Tarun Bharath ; Gundawar, Manoj Kumar
    We demonstrate a very powerful correlation between the discrete probability of distances of neighboring cells and thermal wave propagation rate, for a system of cells spread on a one-dimensional chain. A gamma distribution is employed to model the distances of neighboring cells. In the absence of an analytical solution and the differences in ignition times of adjacent reaction cells following non-Markovian statistics, invariably the solution for thermal wave propagation rate for a one-dimensional system with randomly distributed cells is obtained by numerical simulations. However, such simulations which are based on Monte-Carlo methods require several iterations of calculations for different realizations of distribution of adjacent cells. For several one-dimensional systems, differing in the value of shaping parameter of the gamma distribution, we show that the average reaction front propagation rates obtained by a discrete probability between two limits, shows excellent agreement with those obtained numerically. With the upper limit at 1.3, the lower limit depends on the non-dimensional ignition temperature. Additionally, this approach also facilitates the prediction of burning limits of heterogeneous thermal mixtures. The proposed method completely eliminates the need for laborious, time intensive numerical calculations where the thermal wave propagation rates can now be calculated based only on macroscopic entity of discrete probability.
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    DAST crystal based terahertz generation and recording of time resolved photoacoustic spectra of N
    ( 2016-07-01) Rao, K. S. ; Chaudhary, A. K. ; Venkatesh, M. ; Thirupugalmani, K. ; Brahadeeswaran, S.
    We report the THz generation using optical rectification process in an indigenously grown organic salt 4-N, N-dimethylamino-4′-N′-methyl-stilbazoliumtoyslate (DAST). A 60 fs, 1 kHz optical parametric amplifier, tunable between 0.8 and 1.6 μm range was employed to generate THz radiation. It is observed that the THz signal is accompanied with weak second harmonic signal of pump wavelength. The conversion efficiency (η) of generated THz is 0.0161%. The radiation generated from DAST crystal is only THz signal, which is confirmed theoretically by choosing the crystal thickness is equivalent to be its optimum coherence length. In addition, we have selected two rotational lines i.e. J = 19, 58 of pure N2O gas by using 0.5 and 1.5 THz band pass filters for recording the time resolved photoacoustic (PA) spectra at 1 atm pressure for the first time.
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    Dependence of radiation decay constant of laser produced copper plasma on focal position
    ( 2019-12-01) Junjuri, Rajendhar ; Rashkovskiy, Sergey A. ; Gundawar, Manoj Kumar
    Laser-induced copper plasma is investigated experimentally and theoretically. Laser-induced plasma on the surface of the copper sample is generated by focusing a nanosecond (∼7 ns) laser pulse. The experiment is performed in the ambient atmosphere at three different focal positions (lens to sample distances). The main objective of this work is to investigate the effect of the focal position on the radiation decay constant of the plasma. Experimental data are used for estimating the plasma temperature, electron density, ablated mass, and radiation decay constant. It is shown that these parameters essentially depend on the focal position with respect to the sample surface. The theory of relaxation of radiation is considered for the kinetic evolution of the plasma. The results of the theory are compared with the obtained experimental data.
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    Detection of Explosives and Non-explosive Materials from a Soil Matrix Using 0.5 and 1.5 THz Radiation
    ( 2021-01-01) Naveen Kumar, P. ; Ganesh, D. ; Nagaraju, M. ; Reshma, B. ; Chaudhary, A. K.
    We present the absorption coefficients and refractive indices of explosive and nonexplosive molecules such as TNT, RDX, CL20 and glucose, salt, sugar and milk powder mixed in a soil matrix by using 0.5 and 1.5 THz radiation.
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    Development of picosecond standoff libs system for the identification of the metals and alloys
    ( 2019-12-01) Prakash, Gummadi Arun ; Junjuri, Rajendhar ; Gundawar, Manoj Kumar
    We report the development and optimization of a standoff laser-induced breakdown spectroscopy (ST-LIBS) system for identification of metals and alloys. A simple convex lens and low-cost portable CCD spectrometer were utilized as collection system instead of conventional big telescope coupled to ICCD. Good signal to noise ratio has been achieved with minimum pulse energy of 2.5 mJ at a standoff distance of 6 m. This is the first report on picosecond ST-LIBS combined with compact detection system to the best of our knowledge. The developed system can work as a promising tool for process control and defense applications.
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    Effect of electron-phonon interaction and valence band edge shift for carrier-type reversal in layered ZnS/rGO nanocomposites
    ( 2021-03-15) Natarajan, Vanasundaram ; Naveen Kumar, P. ; Ahmad, Muneer ; Sharma, Jitender Paul ; Chaudhary, Anil Kumar ; Sharma, Praveen Kumar
    The artificial stacking of nanohybrid films helps to enhance their properties and thus intrigues researchers to explore this possibility in emerging technologies. The layer-by-layer approach was used to fabricate samples of zinc sulfide/reduced graphene oxide (ZnS/rGO) by using spin coating technique. The structure and optoelectronic properties has been extensively studied by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), UV–VIS-NIR spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and Hall measurements. Raman spectrum elucidates the phonon contribution of ZnS and breathing mode of κ-point phonons and sp2 bonds of carbon atoms of rGO. The electron-phonon interactions reveal reduction in electron mobility and enhancement in holes contribution with rGO content leading to surface charge transfer doping (SCTD). XPS results explain the valence band edge and conduction band edge to form type-I band alignment to reconfirm carrier-type reversal. A change in the dispersion of refractive indices along with a small rise in the value of absorption coefficient in terahertz (THz) region for ZnS/rGO nanocomposite films has been observed. These results will open up new opportunities to furthering the science of this technologically important class of materials for future electronics.
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    Effect of Heat Loss on Propagation Limits of Combustion Fronts in Heterogeneous Mixtures
    ( 2020-03-03) Tarun Bharat, Naine ; Mishra, Debi Prasad ; Gundawar, Manoj Kumar
    The effect of heat loss on the propagation limits of combustion front is studied by considering one-dimensional chain of discrete point sources using two systems, namely (i) periodic and (ii) disordered. Each point source in the system is characterized by heat loss parameter (β). Unstable modes of combustion front propagation in periodic system have been detected with the manifestation of bifurcation patterns for different value of heat loss. Combustion front rate, quenching of combustion front for periodic and several disordered systems are investigated theoretically at different value of heat loss. It has been found that the heat loss in the nonadiabatic system does not affect the burn rate, although it plays a vital role in deciding the combustion limit. Theoretical results of combustion limit and burn rate have been compared with available experimental data.
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    Effects of disordered microstructure and heat release on propagation of combustion front
    ( 2016-01-01) Naine, Tarun Bharath ; Gundawar, Manoj Kumar
    Numerical experiments for diagnosis of combustion of actual heterogeneous systems are performed on a one-dimensional chain. The internal microstructure of actual heterogeneous systems is apriori unknown, various distributions like uniform, beta, and normal have been considered for distributing neighboring reaction cells. Two cases, for the nature of distribution of heat release of reaction cells are taken into account, one with identical heat release and the other with disordered heat release. Role of different random distributions in describing heterogeneous combustion process is established in present paper. Particularly, the normal distribution of arranging neighboring reaction cells has been found to be powerful methodology in explaining the combustion process of an actual heterogeneous system at higher ignition temperatures for both cases of distributing heat release. Validation of the developed model with the experimental data of combustion of the CMDB propellants, gasless Ti + xSi system, and different thermite mixtures is performed. Our results show that the experimental burning rates at higher ignition temperatures (ε > 0.32) of the heterogeneous system are better reproduced theoretically with the present model. We have also shown that different combustion limits for different thermite systems are the consequences of disordered heat release. Experimental data for thermite systems that have lower inflammability limits are analyzed in the view of disordered heat releases of cells. The model developed in the view of disordered heat releases reproduces the experimental burn rates and experimental combustion limit.