Publications by authors named "Pritam Khan"

9 Publications

  • Page 1 of 1

HVD-LSTM based recognition of epileptic seizures and normal human activity.

Comput Biol Med 2021 Sep 27;136:104684. Epub 2021 Jul 27.

Faculty of Engineering and Information Technology, University of Technology Sydney, Ultimo, NSW, 2007, Australia. Electronic address:

In this paper, we detect the occurrence of epileptic seizures in patients as well as activities namely stand, walk, and exercise in healthy persons, leveraging EEG (electroencephalogram) signals. Using Hilbert vibration decomposition (HVD) on non-linear and non-stationary EEG signal, we obtain multiple monocomponents varying in terms of amplitude and frequency. After decomposition, we extract features from the monocomponent matrix of the EEG signals. The instantaneous amplitude of the HVD monocomponents varies because of the motion artifacts present in EEG signals. Hence, the acquired statistical features from the instantaneous amplitude help in identifying the epileptic seizures and the normal human activities. The features selected by correlation-based Q-score are classified using an LSTM (Long Short Term Memory) based deep learning model in which the feature-based weight update maximizes the classification accuracy. For epilepsy diagnosis using the Bonn dataset and activity recognition leveraging our Sensor Networks Research Lab (SNRL) data, we achieve testing classification accuracies of 96.00% and 83.30% respectively through our proposed method.
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http://dx.doi.org/10.1016/j.compbiomed.2021.104684DOI Listing
September 2021

Direct visualization of phase-matched efficient second harmonic and broadband sum frequency generation in hybrid plasmonic nanostructures.

Light Sci Appl 2020 22;9:180. Epub 2020 Oct 22.

Department of Physics and Bernal Institute, University of Limerick, Limerick, Ireland.

Second harmonic generation and sum frequency generation (SHG and SFG) provide effective means to realize coherent light at desired frequencies when lasing is not easily achievable. They have found applications from sensing to quantum optics and are of particular interest for integrated photonics at communication wavelengths. Decreasing the footprints of nonlinear components while maintaining their high up-conversion efficiency remains a challenge in the miniaturization of integrated photonics. Here we explore lithographically defined AlGaInP nano(micro)structures/AlO/Ag as a versatile platform to achieve efficient SHG/SFG in both waveguide and resonant cavity configurations in both narrow- and broadband infrared (IR) wavelength regimes (1300-1600 nm). The effective excitation of highly confined hybrid plasmonic modes at fundamental wavelengths allows efficient SHG/SFG to be achieved in a waveguide of a cross-section of 113 nm × 250 nm, with a mode area on the deep subwavelength scale ( /135) at fundamental wavelengths. Remarkably, we demonstrate direct visualization of SHG/SFG phase-matching evolution in the waveguides. This together with mode analysis highlights the origin of the improved SHG/SFG efficiency. We also demonstrate strongly enhanced SFG with a broadband IR source by exploiting multiple coherent SFG processes on 1 µm diameter AlGaInP disks/AlO/Ag with a conversion efficiency of 14.8% MW which is five times the SHG value using the narrowband IR source. In both configurations, the hybrid plasmonic structures exhibit >1000 enhancement in the nonlinear conversion efficiency compared to their photonic counterparts. Our results manifest the potential of developing such nanoscale hybrid plasmonic devices for state-of-the-art on-chip nonlinear optics applications.
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http://dx.doi.org/10.1038/s41377-020-00414-4DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7582155PMC
October 2020

Excitation of coherent optical phonons in iron garnet by femtosecond laser pulses.

J Phys Condens Matter 2019 Jul 5;31(27):275402. Epub 2019 Apr 5.

Department of Physics, Kyushu University, Fukuoka 819-0395, Japan. Department of Physics and Bernal Institute, University of Limerick, V94 T9PX Limerick, Ireland.

We employed femtosecond pump-probe technique to investigate the dynamics of coherent optical phonons in iron garnet. A phenomenological symmetry-based consideration reveals that oscillations of the terahertz T mode are excited. Selective excitation by a linearly polarized pump and detection by a circularly polarized probe confirm that impulsive stimulated Raman scattering (ISRS) is the driving force for the coherent phonons. Experimental results obtained from ISRS measurements reveal excellent agreement with spontaneous Raman spectroscopy data, analyzed by considering the symmetry of the phonon modes and corresponding excitation and detection selection rules.
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http://dx.doi.org/10.1088/1361-648X/ab1665DOI Listing
July 2019

Tuning nanosecond transient absorption in a-Ge₂₅As₁₀Se₆₅ thin films via background illumination.

Opt Lett 2015 Oct;40(19):4512-5

In this Letter, we report for the first time, to the best of our knowledge, continuous-wave laser background illumination (BGI) as a simple and yet useful tool to tune nanosecond transient absorption (TA) in a-Ge25As10Se65 thin films. In our experiments, we observed remarkable blueshift in TA as a function of the BGI intensity. Strikingly, relaxations of TA in background-illuminated samples are much faster than the as-prepared samples. This observation provides new insights into the bond-breaking mechanism. Further, decay time constants of TA are wavelength dependent, which signifies that excited carriers have a longer lifetime in deep traps than in shallow traps.
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http://dx.doi.org/10.1364/OL.40.004512DOI Listing
October 2015

First observation of the temperature-dependent light-induced response of Ge(25)As(10)Se(65) thin films.

Opt Lett 2015 Apr;40(7):1559-62

Ge-rich ternary chalcogenide glasses (ChGs) exhibit photobleaching (PB) when illuminated with bandgap light. This effect originates from the combined effects of intrinsic structural changes and photo-oxidation. In a sharp contradiction to previous observations, in this Letter, we demonstrate, for the first time, that Ge-rich Ge(25)As(10)Se(65) ChG thin films exhibit photodarkening (PD) at 20 K and PB at 300 and 420 K after having been continuously illuminated for ∼3 hours. The temporal evolution of PD/PB shows distinct characteristics at the temperature of illumination, and provides valuable information on the light-induced structural changes. Furthermore, structure-specific far-infrared (FIR) absorption measurements give direct evidence of different structural units involved in PD/PB at the contrasting temperatures. By comparing the light-induced effects in vacuum and air, we conclude that intrinsic structural changes dominate over photo-oxidation in the observed PB in Ge(25)As(10)Se(65) ChG thin films.
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http://dx.doi.org/10.1364/OL.40.001559DOI Listing
April 2015

Tailoring between network rigidity and nanosecond transient absorption in a-Ge(x)As(35-x)Se₆₅ thin films.

Opt Lett 2015 Mar;40(5):768-71

In this Letter, we report the first observation of dramatic decrease in nanosecond (ns) pulsed laser-induced transient absorption (TA) in a-Ge(x)As(35-x)Se₆₅ thin films by tuning the amorphous network from floppy to rigid. Our results provide the direct experimental evidence of a self-trapped exciton mechanism, where trapping of the excitons occurs through bond rearrangements. Taken together, a rigid amorphous network with more constraints than degrees of freedom are unable to undergo any such bond rearrangements and results in weaker TA. However, we also demonstrate that excitation fluence can be effectively utilized as a simple tool to lift up enough constraints to introduce large TA even in rigid networks. Apart from this, we also show that TA is tunable with network rigidity as it blueshifts when the mean coordination is increased from 2.35 to 2.6.
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http://dx.doi.org/10.1364/OL.40.000768DOI Listing
March 2015

Nanosecond light induced, thermally tunable transient dual absorption bands in a-Ge₅As₃₀Se₆₅ thin film.

Sci Rep 2014 Oct 10;4:6573. Epub 2014 Oct 10.

Department of Physics, Indian Institute of Science Education and Research, Bhopal 462023, India.

In this article, we report the first observation of nanosecond laser induced transient dual absorption bands, one in the bandgap (TA₁) and another in the sub-bandgap (TA₂) regions of a-Ge₅As₃₀Se₆₅ thin films. Strikingly, these bands are thermally tunable and exhibit a unique contrasting characteristic: the magnitude of TA₁ decreases while that of TA₂ increases with increasing temperature. Further, the decay kinetics of these bands is strongly influenced by the temperature, which signifies a strong temperature dependent exciton recombination mechanism. The induced absorption shows quadratic and the decay time constant shows linear dependence on the laser beam fluence.
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http://dx.doi.org/10.1038/srep06573DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4192641PMC
October 2014

Role of Ge:As ratio in controlling the light-induced response of a-Ge(x)As(35-x)Se65 thin films.

Sci Rep 2014 Feb 7;4:4029. Epub 2014 Feb 7.

Department of Physics, Indian Institute of Science Education and Research, Bhopal 462023, India.

In this paper, we present interesting results on the quantification of photodarkening (PD), photobleaching (PB) and transient PD (TPD) in a-Ge(x)As(35-x)Se65 thin films as a function of network rigidity. Composition dependent light-induced responses of these samples indicate that there exist two parallel competing mechanisms of instantaneous PD arising from the As part of the network, and PB arising from the Ge part of the network. Raman spectra of the as-prepared and illuminated samples provide first direct evidence of the light-induced structural changes: an increase in AsSe3/2 pyramidal and GeSe4/2 corner-sharing tetrahedra units together with new Ge-O bond formation and decrease in energetically unstable edge sharing GeSe4/2 tetrahedra. Importantly, for a fixed Se concentration, Ge:As ratio plays the critical role in controlling the net light-induced response rather than the much believed rigidity of the glassy network.
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http://dx.doi.org/10.1038/srep04029DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3916963PMC
February 2014

Coexistence of fast photodarkening and slow photobleaching in Ge19As21Se60 thin films.

Opt Express 2012 May;20(11):12416-21

Department of Physics, Indian Institute of Science Education and Research, Bhopal 462023, India.

We experimentally demonstrate the coexistence of two opposite photo-effects, viz. fast photodarkening (PD) and slow photobleaching (PB) in Ge(19)As(21)Se(60) thin films, when illuminated with a laser of wavelength 671 nm. PD appears to begin instantaneously upon light illumination and saturates in tens of seconds. By comparison, PB is a slower process that starts only after PD has saturated. Both PD and PB follow stretched exponential dependence on time. Modeling of overall change as a linear sum of two contributions suggests that the changes in As and Ge parts of glass network respond to light effectively independent of each other.
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http://dx.doi.org/10.1364/OE.20.012416DOI Listing
May 2012
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