Publications by authors named "Konda Srinivasa Rao"

3 Publications

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Resonance-enhanced high harmonic in metal ions driven by elliptically polarized laser pulses.

Opt Lett 2021 May;46(10):2372-2375

Resonance enhancement of a single order harmonic has been a main attractive feature in high-harmonic generation from laser ablated plumes of metals. Although it has been extensively investigated experimentally and theoretically, studies so far have focused only on linearly polarized driving fields. In this Letter, we study the dependence of the resonant harmonic yield in tin ions on the driving laser ellipticity. We find that the resonance leads to a less rapid decay of the harmonic yield as a function of driving ellipticity, and it is qualitatively reproduced by quantum mechanical simulations. To the best of our knowledge, our findings provide a new type of evidence for supporting previously proposed mechanisms for enhancement.
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http://dx.doi.org/10.1364/OL.425495DOI Listing
May 2021

Nonlinear Optical Studies of Gold Nanoparticle Films.

Nanomaterials (Basel) 2019 Feb 19;9(2). Epub 2019 Feb 19.

The Guo China-US Photonics Laboratory, State Key Laboratory of Applied Optics, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, Changchun 130033, China.

Gold films are widely used for different applications. We present the results of third- and high-order nonlinear optical studies of the thin films fabricated from Au nanoparticle solutions by spin-coating methods. These nanoparticles were synthesized by laser ablation of bulk gold in pure water using 200 ps, 800 nm pulses. The highest values of the nonlinear absorption coefficient (9 × 10 cm W), nonlinear refractive index (3 × 10 cm² W), and saturation intensity (1.3 × 10 W cm) were achieved using 35 fs, 400 nm pulses. We also determined the relaxation time constants for transient absorption (220 fs and 1.6 ps) at 400 nm. The high-order harmonic generation was studied during propagation of 35 fs, 800 nm pulses through the plasma during the ablation of gold nanoparticle film and bulk gold. The highest harmonic cutoff (29th order) was observed in the plasma containing gold nanoparticles.
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http://dx.doi.org/10.3390/nano9020291DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6409993PMC
February 2019

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.

Appl Spectrosc 2017 Jul 27;71(7):1481-1493. Epub 2017 Mar 27.

Advanced Center of Research in High Energy Materials (ACRHEM), University of Hyderabad, Hyderabad, India.

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 ( S), 1-(3-methoxy, 2, 6 dinitrophenyl) 1H-1, 2, 3 triazole ( S), 1-(4-nitrophenyl)-1H-1,2,3-triazole ( S), and 2,6-bis ((4-(nitromethyl)-1H-1,2,3-triazol-1-yl)methyl) pyridine ( S). 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 NO molecule. NO molecule is a major gas released during thermal decomposition due to weakest nature of C-NO bond. Further, NO 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 NO 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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http://dx.doi.org/10.1177/0003702817698147DOI Listing
July 2017