| 1. |
- Gupta, Rahul, et al.
(författare)
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Strain Engineering of Epitaxial Pt/Fe Spintronic Terahertz Emitter
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Spin-based terahertz (THz) emitters, utilizing the inverse spin Hall effect, are ultra-modern sources for the generation of THz electromagnetic radiation. To make a powerful emitter having large THz amplitude and bandwidth, fundamental understanding in terms of microscopic models is essential. This study reveals important factors to engineer the THzemission amplitude and bandwidth in epitaxial Pt/Fe emitters grown on MgO and MgAl2O4 (MAO) substrates, where the choice of the substrate plays an important role. The THz amplitude and bandwidth are affected by the induced strain in the Fe spin source layer. On the one hand, the THz electric field amplitude is found to be larger when Pt/Fe is grown on MgO even though the crystalline quality of the Fe film is superior when grown on MAO. This is because of the larger defect density, smaller electron relaxation time, and lower electrical conductivity in the THz regime when Fe is grown on MgO. On the other hand, the bandwidth is found to be larger for Pt/Fe grown on MAO and is explained by the uncoupled/coupled Lorentz oscillator models. This study provides an insightful pathway to further engineer metallic spintronic THz emitters in terms of the proper choice of substrate and microscopic properties of the emitter layers.
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| 2. |
- Gupta, Rahul, et al.
(författare)
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Substrate Effect on Terahertz Emission in Fe/Pt Spintronic Emitters
- 2021
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Ingår i: 2021 46th International Conference On Infrared, Millimeter And Terahertz Waves (IRMMW-THZ). - : Institute of Electrical and Electronics Engineers (IEEE). - 9781728194240
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The choice of the substrate plays an important role for spintronic terahertz (THz) emitters (STEs). We have grown epitaxial Pt/Fe bilayer thin films on MgO and MgAl2O4 substrates. The THz electric field amplitude is found to be larger when Pt/Feis is grown on MgO even though the crystal quality of the Fe film is better when grown on MgAl2O4. This study indicates that the Fecrystal quality affects the THz emission in Pt/Fe STEs and points to the importance of a careful choice of the substrate to enhance the THz amplitude in STEs.
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| 3. |
- Konda, Srinivasa Rao, et al.
(författare)
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Influence of embedded NiO-nanoparticles on the nonlinear absorption of tungsten disulfide nanolayers
- 2023
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Ingår i: Optical materials (Amsterdam). - : Elsevier. - 0925-3467 .- 1873-1252. ; 138
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Tidskriftsartikel (refereegranskat)abstract
- 2D transition metal dichalcogenides possess fascinating properties due to their direct bandgap, strong spin-orbit coupling, and promising electronic/mechanical properties. In this work, we synthesized pure tungsten disulfide (WS2) nanolayers and NiO nanoparticles (NPs) decorated in few-layered WS2 and measured the third-order nonlinear optical properties using femtosecond Z-scan measurements. The open aperture Z-scan data illustrated that the inclusion of NiO nanoparticles into the WS2 layers increases the nonlinear absorption at 800 and 400 nm wavelengths. Furthermore, we observed the switchability of the nonlinear absorption from saturable absorption to two-photon absorption or reverse saturable absorption by changing the pump intensity. Thus, the embedded NiO NPs played a crucial role in the variation of intensity-dependent nonlinear absorption mechanism of WS2 nanolayers and thus can be helpful for various optical applications such as laser pulse compression and optical limiting to prevent over-exposure of protective photosensitive sensors by intense ultrashort laser pulses.
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| 4. |
- Mottamchetty, Venkatesh, et al.
(författare)
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Application of vector beams for enhanced high-order harmonics generation in laser-induced plasmas
- 2022
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Ingår i: Optics Express. - : Optica Publishing Group. - 1094-4087. ; 30:10, s. 17080-17093
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Tidskriftsartikel (refereegranskat)abstract
- High-order harmonics driven by phase- and polarization-structured femtosecond pulses are unique sources of the extreme ultraviolet vortex and vector beams, which have various applications. Here, we report the generation of intense high-order harmonics during propagation of the polarization-structured vector beams (radially polarized beam, azimuthally polarized beam, and their superposition) through the laser-induced plasmas (In, C, CdS, Zns, Ag2S). Low-order harmonics became stronger with radially polarized and azimuthally polarized driving beams compared with the linearly polarized beams, which is explained on the basis of phase matching and specific properties of vector beams. Contrary to that, the resonance-enhanced harmonic generated in the indium plasma in the case of radially polarized and azimuthally polarized beams was twice weaker compared with the harmonic generated by the LP beam due to modification in the resonant transition selection rules leading to a decrease of the oscillator strength of ionic transitions. Harmonic cut-off and intensity in the case of superposition of the radially and azimuthally polarized beams were lesser compared with the cases of the individual (radially polarized and azimuthally polarized) beams. (C) 2022 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement
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| 5. |
- Mottamchetty, Venkatesh, et al.
(författare)
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Direct evidence of terahertz emission arising from anomalous Hall effect
- 2023
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Ingår i: Scientific Reports. - : Springer Nature. - 2045-2322. ; 13:1
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Tidskriftsartikel (refereegranskat)abstract
- A detailed understanding of the different mechanisms being responsible for terahertz (THz) emission in ferromagnetic (FM) materials will aid in designing efficient THz emitters. In this report, we present direct evidence of THz emission from single layer Co0.4Fe0.4B0.2 (CoFeB) FM thin films. The dominant mechanism being responsible for the THz emission is the anomalous Hall effect (AHE), which is an effect of a net backflow current in the FM layer created by the spin polarized current reflected at the interfaces of the FM layer. The THz emission from the AHE-based CoFeB emitter is optimized by varying its thickness, orientation, and pump fluence of the laser beam. Results from electrical transport measurements show that skew scattering of charge carriers is responsible for the THz emission in the CoFeB AHE-based THz emitter.
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| 6. |
- Mottamchetty, Venkatesh, et al.
(författare)
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High-Order Harmonics Generation in MoS2 Transition Metal Dichalcogenides : Effect of Nickel and Carbon Nanotube Dopants
- 2023
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Ingår i: International Journal of Molecular Sciences. - : MDPI. - 1661-6596 .- 1422-0067. ; 24:7
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Tidskriftsartikel (refereegranskat)abstract
- The transition metal dichalcogenides have instigated a lot of interest as harmonic generators due to their exceptional nonlinear optical properties. Here, the molybdenum disulfide (MoS2) molecular structures with dopants being in a plasma state are used to demonstrate the generation of intense high-order harmonics. The MoS2 nanoflakes and nickel-doped MoS2 nanoflakes produced stronger harmonics with higher cut-offs compared with Mo bulk and MoS2 bulk. Conversely, the MoS2 with nickel nanoparticles and carbon nanotubes (MoS2-NiCNT) produced weaker coherent XUV emissions than other materials, which is attributed to the influence of phase mismatch. The influence of heating and driving pulse intensities on the harmonic yield and cut-off energies are investigated in MoS2 molecular structures. The enhanced coherent extreme ultraviolet emission at similar to 32 nm (38 eV) due to the 4p-4d resonant transitions is obtained from all aforementioned molecular structures, except for MoS2-NiCNT.
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| 7. |
- Mottamchetty, Venkatesh, et al.
(författare)
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Terahertz emission from epitaxial α-W/Co60Fe40 spintronic emitters
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- We report efficient terahertz (THz) generation in epitaxial α-W/Co60Fe40 spintronic emitters. Two types of emitters have been investigated; epitaxial α-W(110)/Co60Fe40(110) and α-W(001)/Co60Fe40(001) deposited on single crystalline Al2O3(11-20) and MgO(001) substrates, respectively. The generated THz radiation is about 10% larger for α-W(110)/Co60Fe40(110) grown on single crystalline Al2O3(11-20), which is explained by the fact that the α-W(110)/Co60Fe40(110) interface for this emitter is more transparent to the spin current due to the presence of Ångström-scale interface intermixing at the W/CoFe interface. Our results also reveal that the generation of THz radiation is larger when pumping with the laser light from the substrate side, which is explained by a larger part of the laser light due to interference effects in the film stack being absorbed in the ferromagnetic Co60Fe40 layer in this measurement configuration.
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