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Nonlinear optical measurements of the material showed strong saturable absorption and nonlinear optical extinctions induced by Mie scattering over broad temporal and wavelength ranges. Through comparative studies in thermal-optic switching, the researchers demonstrated that the biomaterial tellurium (Bio-Te) provided definite improvements in the thermal-optic decaying lifetime compared to the materials WS2 and graphene. Professor Werner J. Blau of Trinity College Dublin said that the biologically generated tellurium nanorods could be especially suitable for photonic device applications in the mid-infrared range. “This wavelength region is becoming a hot technological topic as it is useful for biomedical, environmental, and security-related sensing, as well as laser processing and for opening up new windows for fiber optical and free-space communications,” he said. While most optical materials are chemically synthesized, using a biologically based nanomaterial proved less expensive and less toxic, the team said. The team will continue to expand the biomaterial’s potential for use in all-optical telecom switches, and believes the material could be useful for expanding broadband capacity. “We need greater bandwidth and switching speeds,” University of Houston professor Seamus Curran said. “We need all-optical switches to do that.”

For more information:
https://doi.org/10.1038/s41467-019-11898-z

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We demonstrate antenna-coupled spintronic terahertz (THz) emitters excited by 1550 nm, 90 fs laser pulses. Antennas are employed to optimize THz outcoupling and frequency coverage of ferromagnetic/nonmagnetic metallic spintronic structures. We directly compare the antenna-coupled devices to those without antennas. Using a 200 lm H-dipole antenna and an ErAs:InGaAs photoconductive receiver, we obtain a 2.42-fold larger THz peak-peak signal, a bandwidth of 4.5 THz, and an increase in the peak dynamic range (DNR) from 53 dB to 65 dB. A 25 lm slotline antenna offered 5 dB larger peak DNR and a bandwidth of 5 THz. For all measurements, we use a comparatively low laser power of 45mW from a commercial fiber-coupled system that is frequently employed in table-top THz time-domain systems.

Schematic of THz emission from photoexcited FMANM bilayers, plain and microstructured. (a) A femtosecond laser pulse triggers ultrafast spin transport from the FM into the NM layer where the spin current js flowing along the z axis is converted into a charge current jc along the y direction, acting as a source of THz radiation. The direction of the in-plane magnetization of the FM layer is set along the x axis by an external magnetic field Bext. (b) Current distribution in an unstructured (plain) bilayer and (c) the STE bilayer embedded in the gap of an antenna. Note that THz current generation by the ISHE is independent of emitter type and antenna choice

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Congratulations to our new paper”Control of nonlinear refractive index of AuNPs doped with nematic liquid crystal under external electric field” by H. Mbarak, A. K. Kodeary, S. M. Hamidi, E. Mohajarani, Y. Zaatar

In the present work, the nonlinear refractive index of gold nanoparticles (NP) doped with nematic liquid crystal (NLC) is determined using Z-scan technique. The gold NPs were synthesized by laser ablation (Nd: YAG laser at 1064 nm) dispersed in liquid deionized water. This work was especially done using a close aperture placed in front of the detector to show the effect of the nematic liquid crystal (E7) on the nonlinear refractive index of the Au NPs under an external electric field. It’s found experimentally, that the nonlinear refractive index of the gold nanoparticles doped with E7 can be varied by changing both the compositional percentage of gold NPs and NLC molecules. The obtained nonlinear refractive index of the samples showed that nematic liquid crystal (E7) can act as a good material for controlling the third order nonlinear coefficient due to its large nonlinear optical properties.

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Congratulations to our new paper”Two-Dimensional Plasmonic Biosensing Platform: Cellular Activity Detection under Laser Stimulation” by Sajede Saeidifard, Foozieh Sohrabi, Mohammad Hossein Ghazimoradi, Seyedeh Mehri Hamidi, Shirin Farivar, Mohammad Ali Ansari

Combing biosensors and nanoscience as a growing technique provides great advantages such as a label-free and real time analysis, high sensitivity, low limit of detection, small size and integration to other systems. That is why plasmonics finds various applications in drug detection, food safety, agriculture, photothermal therapy, etc. In this paper, we have fabricated a two-dimensional plasmonic grating biosensor using soft lithography technique, which has eliminated some disadvantages of conventional plasmonic structures like expensive fabrication cost, inflexibility and lack of mass production. On the other hand, we benefited from infrared neural stimulation for regulating membrane depolarization, which is based on photothermal mechanism and provides a contact-free and high spatial/temporal resolution. Eventually, membrane depolarization of two different cell-types of Herpg Hodode (Hep G2) and Mesenchymal stem cell cultured on two-dimensional plasmonic has been investigated under infrared neural stimulation. After preparing the soft plasmonic crystal, its reflection spectra and respective ellipsometry parameters were analyzed before and after cell culture with/without stimulation (near-infrared immune region ~1450 nm). By comparing the obtained ellipsometry results for HEP G2 and mesenchymal stem cells, it is observed that the behavior of two cell types with respect to IR stimulation is the same besides providing us the possibility of distinguishing the level of membrane depolarization under various stimulating frequency.
The strength point of this integrated system for membrane depolarization detection has been shown experimentally which can open new avenues toward neuroplasmonic application in the future.

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Congratulations to our new paper “Signature of plasmonic nanoparticles in multi-wavelength low power random lasing” by S. F. Haddawi, Hammed R. Humud, S. M. Hamidi 

A multi-wavelength plasmonic random lasing is attained by core-shell nanoparticles and the mixture of metallic nanoparticles in the host dye medium. The plasmonic nanoparticles, fabricated using laser ablation in liquid, were mixed in the corresponding dye medium and pumped with green nano-second pulsed laser. Due to this optical pumping process of plasmonic nanoparticles, amplification of the fluorescence and the lasing activity took place due to the localized surface plasmon resonance and scattering of each nanoparticle, core-shell and mixture nanoparticles. Our results show efficient coherent random lasing due to the interface between two different metallic nanoparticles in the middle part of the visible spectral region considering its applicability in the design and fabrication of compact and miniaturized random laser sources.

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Congratulations to our new paper “Bi:YIG@Au Magneto-Plasmonic Core-Shell Nano-Grating with Robust, High Magneto-Optical Figure of Merit” by Somayeh Sadeghi, Seyedeh Mehri Hamidi

We numerically examine the role of Fano resonance for enhanced magneto-optical effect in an arrayed magneto-plasmonic core-shell structure composed of Bi:YIG cores as a magneto-optical active medium and Au sells as plasmonic ones. The optical and magneto-optical behavior of the magneto-plasmonic core-shell grating structure sustaining Fano resonance is investigated by means of Lumerical software based on the finite-difference time-domain solver. In the proposed structure, Fano resonance arises from the interplay between the guided mode and the surface plasmon resonance which results in enhanced magneto-optical Faraday effect. In addition, the Fano resonance and correspond enhanced magneto-optical effect can be tuned by changing the array period of the structure. The obtained results can be of interest in miniaturized and advanced magneto-optical devices.

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Congratulations to our new paper  ” One dimensional photonic crystal as an efficient tool for in-vivo optical sensing of neural activity ” by Foozieh Sohrabia, Seyedeh Mehri Hamidia,*, Nasrin Asgaria, Mohammad Ali Ansari, Roya Gachilooa

In this paper, we recorded optically the neural/neuromuscular activity of alive worm via phase-sensitive measurement while stimulating it optically using infrared laser. By supporting Tamm plasmon mode, our fabricated
multilayer structure of Glass/(TiO2/SiO2)12/Au was used as a sensing platform. By fixing an earth worm to the gold side of the structure and using open optic measurements, the amplitude ratio (Ψ) and phase shift (Δ) of reflections under s- and p-polarized incident lights have been recorded for different frequencies and pulse duration of IR laser. By increasing the pulse duration to 17ms, Δ and Ψ values of Tamm Plasmon Polariton resonance for different frequencies have been splitted considerably in a regular trend. We hope that the combination of plasmonics and Tamm plasmon mode can open new insights into non-invasive neural/neuromusular stimulation and recording.

Ψ parameter for pulse duration time of (a) 3ms (b) 5ms (c) 8ms (d) 17ms for IR frequencies of 3 Hz, 5.5 Hz and 7 Hz at θ=30°.
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Congratulations to our new paper “Bio-compatible and highly sensitive two-dimensional plasmonic sensor ” by A.S. Nasiri, S. M. Hamidi

We propose a novel bio-compatible two dimensional plasmonic sensor with array of ring and the hole structure on an optically thick gold film for biochemical sensing. We use finite-difference time-domain simulation for design and calculation of sensitivity in the Near-Infrared Region. The bio-compatible and cheap plasmonic Glycerol sensor with high sensitivity by interferometer style as a motif in the sensor’s structure. The proposed sensor can be applied as highly sensitivity sensor with a good linear response under different glycerol concentrations.

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Congratulations to our new paper ” Electrically driven flexible two dimensional plasmonic structure based on nematic liquid crystal ” by Hossein Mbarak, Seyedeh Mehri Hamidi, Ezeddin Mohajerani and Z Zattar

A novel two dimensional active plasmonic grating based on liquid crystal (LC) infiltration is demonstrated by combining the plasmonic properties of the gold nanostructure and the optical properties of the liquid crystal. In this structure, a thin layer of E7 liquid crystal was typically injected onto a gold nanostructure, deposited on a PDMS substrate, using nanoimprint lithography method. The surface plasmon resonance (SPR) of the fabricated plasmonic structure can be controlled by changing the refractive index of LC, which was achieved with an external electric field. LC molecules confined between the gold nanostructure and an indium–tin-oxide (ITO) glass are randomly aligned, and they can exhibit a reversible refractive index, depending on their orientation under the external voltage and the polarization of the incident light. Results demonstrates that the wavelength of the resonance peak can be red shifted by the electric field-dependent refractive index of liquid crystal. This experimental work provides us an active control of surface plasmon resonance using liquid crystal which can act as an ideal active medium for different applications such as low voltage sensor with the sensitivity of 0.4375nm/V.

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Recognizing special molecules is crucial in many biochemical processes, and thus, highly enhanced sensing methods are in high demand. In this work, we designed a microrod array metasurface with a SiO2-loaded subwavelength lithium niobate waveguide as a unique platform for enhanced experimental fingerprint detection of lactose. The metasurface could lead to strong surface wave modes due to the near-field coupling of the spoof localized surface plasmon, which also could provide a stronger interaction length between light and matter. The selectivity was remarkable in the transmission spectrum at an intrinsic characteristic frequency of 0.529 THz with a thin layer of lactose, while it was faint while transmitting terahertz (THz) waves normally through a lactose layer of the same thickness. Together with the ability to freely design the shape of the metasurface and the electromagnetic properties, we believe that this platform can function as an elegant on-chip-scale enhanced THz sensing platform.

(a) Schematic of THz detection of an analyte using a microrod array metasurface
as an on-chip sensor. A column of y-polarized dipoles located inside the LN
waveguide is used to excite THz waves (blue oscillation signal). The thickness of
the SiO2 layer is h¼2 lm. The inset shows the detailed design parameters: p, a,
l and g are 20, 10, 55, and 15 lm, respectively. (b) Enhanced field confined to the
surface of the composite structure. (c) and (d) Distribution of the field components
Ey and Ez at f¼0.529 THz.

In summary, we show the potential of a platform relying on a microrod array metasurface with a SiO2-loaded LN subwavelength waveguide as a generic design for THz sensing. Remarkable selectivity can be seen from the experimental and simulated transmission spectra with a minute amount of the analyte. The stronger confinement of surface wave modes owing to near-field SLSP coupling and the longer interaction length along the waveguide would effectively increase the molecular absorption, thereby enabling detection of a thin lactose layer. Meanwhile, the results agree well with each other. This is difficult to distinguish with normally incident THz waves transmitting through a lactose of the same thickness without a metasurface. The myriad of geometries for the composite structure provides engineers with enormous flexibility to design sensing platforms that operate over a broad range of frequencies. We believe that this platform is truly simple and efficient while providing a versatile method for enhanced fingerprint detection in the THz regime. This would bring THz sensing benefits to mainstream applications.

For more information: doi: 10.1063/1.5087609


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