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Dive into the research topics where Debasis Swain is active.

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Featured researches published by Debasis Swain.


Applied Physics Letters | 2012

Ultrafast excited state dynamics and dispersion studies of nonlinear optical properties in dinaphthoporphycenes

Debasis Swain; P.T. Anusha; T. Shuvan Prashant; Surya P. Tewari; Tridib Sarma; Pradeepta K. Panda; S. Venugopal Rao

Ultrafast excited state dynamics of dinaphthoporphycenes were investigated using femtosecond and picosecond degenerate pump-probe techniques at 600 nm and 800 nm, respectively. Femtosecond pump-probe data indicated photo-induced absorption at 600 nm resulting from two-photon/single photon excitation, whereas picosecond pump-probe data demonstrated photo-bleaching which was a consequence of three-photon absorption. The fastest lifetimes (100–120 fs) observed are attributed to the intramolecular vibrational relaxation, the slower ones (1–3 ps) to internal conversion, and the slowest components (7–10 ps) to non-radiative decay back to ground state. Z-scan studies in the 560–600 nm range were also carried out.


Journal of Materials Chemistry C | 2014

Sterically demanding zinc(II) phthalocyanines: synthesis, optical, electrochemical, nonlinear optical, excited state dynamics studies

Debasis Swain; Radhakant Singh; Varun Kumar Singh; Narra Vamsi Krishna; Lingamallu Giribabu; Soma Venugopal Rao

Two novel sterically demanding zinc phthalocyanines were synthesized and characterized. Their optical and electrochemical properties were investigated in detail. The emission spectra were recorded in different solvents and the fluorescence yields obtained were in the range of 0.2–0.3 while time-resolved fluorescence data revealed radiative lifetimes of typically few ns. Nonlinear optical (NLO) properties were also evaluated at wavelengths of 600, 640, 680, and 800 nm using picosecond (∼1.5 ps) pulses and further studies with femtosecond (∼140 fs) pulses at 800 and 780 nm were also performed. Two-photon absorption (2PA) and saturable absorption (SA) were the dominant nonlinear absorption mechanisms observed with ps/fs excitation at different wavelengths in the visible spectral region. NLO coefficients were extracted from ps/fs closed and open aperture Z-scan measurements. Large two-photon absorption cross-sections of ∼14 000 GM and n2 values in the range of 1–7 × 10−16 cm2 W−1 were retrieved for these molecules from the ps Z-scan data. The excited state decay dynamics were investigated using degenerate pump-probe experiments with ∼70 fs pulses near 600 nm. Double exponential fits of the pump-probe data suggested two decay times for both molecules investigated.


Journal of Materials Chemistry C | 2014

Enhanced optical limiting and carrier dynamics in metal oxide-hydrogen exfoliated graphene hybrids

Benoy Anand; Adarsh Kaniyoor; Debasis Swain; Tessy Theres Baby; S. Venugopal Rao; S. Siva Sankara Sai; S. Ramaprabhu; Reji Philip

Hydrogen exfoliated graphene (HEG) is an interesting class of few-layer graphene, which is synthesized via hydrogen induced simultaneous exfoliation-reduction of graphite oxide. HEG exhibits strong optical limiting (OL) due to defect states arising from a large number of structural defects as well as oxygen functionalities present on its surface. Recently, we have shown that OL in HEG can be improved by simple acid functionalization, as it results in an increased number of defects. In the present study, we demonstrate that the OL performance of functionalized HEG (f-HEG) can be further improved, in both the short-pulse (nanosecond) and ultrafast (femtosecond) laser excitation regimes, using hybrids of f-HEG with transition metal oxide nanoparticles (NPs) such as CuO. The enhancement in the OL efficiency of the hybrid arises from strong nonlinear absorption in CuO NPs, which is determined mostly by interband and intraband transitions. The presence of defect states in the samples is confirmed using ultrafast pump–probe measurements, which reveal a delayed carrier relaxation due to carrier trapping by these states. Furthermore, we show that the occurrence of induced thermal scattering is minimal in these water dispersed systems, such that OL occurs predominantly due to nonlinear absorption.


Journal of Porphyrins and Phthalocyanines | 2014

Optical, electrochemical, third-order nonlinear optical, and excited state dynamics studies of thio-zinc phthalocyanine

Debasis Swain; Varun Kumar Singh; Narra Vamsi Krishna; Lingamallu Giribabu; S. Venugopal Rao

Zinc phthalocyanine with S-aryl groups at α-positions have been synthesized and its optical, emission, electrochemical and third-order nonlinear optical properties were investigated. Both the Soret and Q-bands were red-shifted and obeyed Beer–Lamberts law. Electrochemical properties indicated that both oxidation and reduction processes were ring centered. Emission spectra were recorded in different solvents and the fluorescence yields obtained were in the range of 0.02 while time-resolved fluorescence data revealed lifetimes of typically few ns. Excited state dynamics in this novel thio-zinc phthalocyanine molecule has been investigated using femtosecond (fs) degenerate pump-probe spectroscopy. Nonlinear optical properties of this molecule have been examined using the Z-scan technique with picosecond (ps) and fs pulses. Both open and closed aperture Z-scan curves were recorded with ~2 ps/~150 fs laser pulses at a wavelength of 800 nm and nonlinear optical coefficients were extracted from both the studies. Degenerate pump-probe data performed at 600 nm suggested a single long lifetime of ~300 ps, possibly originating from the non-radiative decay of S1 state.


Proceedings of SPIE, the International Society for Optical Engineering | 2010

Pump-probe experiments with sub-100 femtosecond pulses for characterizing the excited state dynamics of phthalocyanine thin films

S. Venugopal Rao; Debasis Swain; Surya P. Tewari

We present our results on the characterization of ultrafast excited state dynamics of two phthalocyanines in thin film form studied using femtosecond pump-probe technique. One was a symmetric Zinc phthalocyanine (SPc) while the other was an unsymmetrical Zinc phthalocyanine (USPc). The femtosecond (fs) pulses at 800 nm were characterized using a single shot autocorrelator. The pump probe measurements were carried out with 590/610 nm pulses emanating from an optical parametric amplifier. SPc demonstrated an excited lifetime of ~30 ps while the ASPc exhibited ~60 ps lifetime. The potential applications of these molecules are discussed briefly.


RSC Advances | 2015

Optical, electrochemical, third order nonlinear optical, and excited state dynamics studies of bis(3,5-trifluoromethyl)phenyl-zinc phthalocyanine†

Narra Vamsi Krishna; Varun Kumar Singh; Debasis Swain; Soma Venugopal Rao; Lingamallu Giribabu

A zinc phthalocyanine with bis(3,5-trifluoromethyl)phenyl groups at peripheral positions has been synthesized and its optical, emission, electrochemical and third-order nonlinear optical properties were investigated. Both the Soret and Q bands were red-shifted and obeyed Beer–Lamberts law. Electrochemical properties indicated that both oxidation and reduction processes were ring centred. Emission spectra were recorded in different solvents and the fluorescence yields obtained were in the range of 0.29 to 0.10, while the time-resolved fluorescence data revealed lifetimes of typically a few ns. Nonlinear optical coefficients were retrieved from the Z-scan measurements using picosecond and femtosecond pulses. Excited state lifetime was deduced from the femtosecond degenerate pump–probe measurements. Our data suggests that this compound has potential for applications in the field of photonics.


Proceedings of SPIE | 2011

Ultrafast nonlinear optical properties and excited state dynamics of phthalocyanine thin films

S. Venugopal Rao; P.T. Anusha; T. Shuvan Prashant; Debasis Swain; Surya P. Tewari

We have investigated the nonlinear optical properties, optical limiting thresholds, and figures of merits for five different phthalocyanine thin films, achieved through doping in PMMA, using the Z-scan technique at 800 nm with 2 ps laser pulses. From the open-aperture Z-scan data we established that these molecules exhibit strong two photon absorption (2PA) with the nonlinear coefficients in the range of 15-200 cm/GW. We have also estimated the sign and magnitude of real part of third order nonlinearity through the closed aperture scans. Preliminary femtosecond pump-probe data suggests that the lifetimes of excited states are in the sub-100 ps regime for all the molecules in film form. Our studies provide tangible evidence that these phthalocyanines are potential candidates for multi-photon imaging and optical limiting applications.


OPTICS: PHENOMENA, MATERIALS, DEVICES, AND CHARACTERIZATION: OPTICS 2011: International Conference on Light | 2011

Multiphoton Absorption Studies in Porphycenes Using Picosecond and Femtosecond Pulses

Debasis Swain; P.T. Anusha; T. Shuvan Prashant; Surya P. Tewari; Tridib Sarma; Pradeepta K. Panda; S. Venugopal Rao

We present our results obtained from the Z‐scan measurements in porphycenes performed using ∼2 picosecond (ps) and ∼40 femtosecond (fs), 800 nm pulses with a repetition rate of 1 kHz delivered by amplified Ti:sapphire laser systems. Open aperture Z‐scan data demonstrated interesting multi‐photon absorption properties for these molecules. In the ps regime these compounds exhibited two‐photon absorption (2PA) at lower peak intensities whereas three‐photon absorption (3PA) was dominant mechanism observed at higher peak intensities. In the fs regime saturable absorption was the mechanism detected. Closed aperture data was collected to evaluate the nonlinear refractive indices of these molecules in both the time domains. The magnitude of n2 was ∼10−17 cm2/W in the fs regime and ∼10−15 cm2/W in the ps regime.


Proceedings of SPIE | 2012

Ultrafast nonlinear optical studies of 3,8,13,18-Tetrachloro-2,7,12,17-tetramethoxyporphyrin and its derivatives

Debasis Swain; Anup Rana; Pradeepta K. Panda; S. Venugopal Rao

Recently we synthesized 3,8,13,18-tetrachloro-2,7,12,17-tetramethoxyporphyrin and its metallo-derivatives [1]. The free-base molecule is unique owing to the presence of an electron donating methoxy group and electron withdrawing chloro group on the adjacent β- positions of each pyrrole moiety. We could synthesize these molecules through two different routes; the first route provided pure isomer, albeit in low yield, whereas the second route provided mixture of isomers with higher yield [1]. Herein we report the third-order nonlinear optical properties of these porphyrins obtained from Z-scan measurements using ~40 fs, 800 nm pulses. Open aperture data confirmed the presence of saturable absorption whereas the closed aperture data indicated a positive nonlinearity. We have compared the data of the pure isomer with that of the mixture of isomers.


Proceedings of SPIE | 2012

Ultrafast nonlinear optical studies of cyclo[4]naphthobipyrroles

P.T. Anusha; Debasis Swain; Tridib Sarma; Pradeepta K. Panda; Venugopal Rao

Expanded porphyrins belong to the class of porphyrinoids, where the core of the porphyrin macrocycle is increased either by incorporating additional pyrrolic units, or by increasing the number of bridging carbon atoms from more than four, or a combination of both. The significance of these classes of compounds lies in their novel photophysical and nonlinear optical properties. Superior nonlinear optical coefficients are usually observed for aromatic expanded porphyrins with large number of π-electrons owing to their distinct structural features. In this regard, cyclo[8]pyrrole is unique, owing to its large planar 30-π core macrocyclic ring in its diprotonated state. Here, all the eight pyrrole units are directly linked to each other through their á-positions. Recently, we have synthesized, cyclo[4]naphthobipyrroles, a unique class of cyclo[8]pyrroles, where alternate pyrrole units are fused with naphthalene moieties. This adds more rigidity to the resultant cyclo[8]pyrrole while further extending the resultant π-conjugation. Herein, we present some of our results from the picosecond nonlinear optical studies of a â-octa-isopropyl-cyclo[4]naphthobipyrrole. The nonlinear optical coefficients were extracted from the Z-scan measurements. The values of two-photon cross-sections obtained for these molecules were in the range of 104 GM.

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P.T. Anusha

University of Hyderabad

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Lingamallu Giribabu

Indian Institute of Chemical Technology

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Tridib Sarma

University of Hyderabad

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Narra Vamsi Krishna

Indian Institute of Chemical Technology

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Varun Kumar Singh

Indian Institute of Chemical Technology

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