Ternary 2D materials, potential candidates for next generation technology showcase boundless opportunities by providing greater degree of freedom through integration of various elements with compositional variety. GeSeTe is a chalcogenide compound with great environmental stability and phase changing feature, making it eligible for many advanced photonics and optoelectronics devices such as ultrafast optical switching, optical modulator, parametric amplifier to name some. In this work, Ternary 2D GeSeTe nanosheets were synthesized employing facile LPE method, followed by extensive characterization have been conducted to comprehend various features of the prepared nanosheets such as thickness, optical absorption etc. Then, the NLO responses of the prepared nanosheets under NIR regime have been realized employing Zscan methods. The obtained nonlinear absorption coefficient varies from -73 ~ -4.5 cm/GW and -220 ~ -35 cm/GW at 1062 nm and 1560 nm wavelengths respectively indicating superior SA characteristics of GeSeTe nanosheets. The sample nanosheets switched its nonlinear absorption from SA to RSA with increased input intensity enabling potential opportunities for GeSeTe in optical limiting devices. Furthermore, the nonlinear refraction n2 was recorded to be -9.5×10- 4 cm2/GW and -5×10-4 cm2/GW at 1062 nm and 1560 nm respectively. To the authors' best knowledge, it is the very first time the NLO responses of GeSeTe nanosheets have been investigated and the achieved responses confirms the superior NLO features of GeSeTe that could be widely utilized in various photonics and optoelectronics devices.
Modern optoelectronic technologies rely heavily on UV photodetectors, which transform UV light stimuli into electrical signals and are used to measure UV radiation levels useful in military communication, medicine and biology. In this work, we report a novel approach to mitigate dark current in Gr-GaS heterojunction by utilizing van der Waals contacted Au electrodes. The all van der Waals photodetector shows self-powered characteristics with rectification ratio of ~102, sub femto ampere dark currents and excellent photo response properties under illumination at 375nm. With detection ability of sub microwatt per square centimeter light of 375 nm at zero bias voltage, the device shows a self-powered responsivity of 16.21mA/W and specific detectivity of 2.12X1012 Jones with appreciable response times (rise/ fall) of 201.99ms/220.44ms with a linear dynamic range of 53.15dB. Such high-performance Gr-GaS-Au all van der Waals UV photodetector presented in this work is comparable to previously reported results, suggesting that it has great potential for UV-A band detection for weak light signals.
Localized surface plasmon resonance (LSPR) shows great promise in optoelectronic devices, solar steam generation, and medical treatment owing to its strong enhancement of light-matter interactions. Herein, for the first time, 1D-2D metallic MWCNTs and HfTe2 van der Waals (vdW) heterostructure are used for demonstrating the LSPR to enhance the temperature of a solar absorber. The proposed vdW heterostructure is synthesized by a facile self-grown hydrothermal method and grown on top of a copper (Cu) foam. The HRTEM image and EDS spectrum confirm the formation of the vdW heterostructure on the Cu foam. The synergic effect of Te-based TMD with MWCNT provides a broadband absorbance of approximately 92% weighted by the standard air mass 1.5 global solar spectrum and takes full advantage of LSPR to confine heat in a small area. Moreover, the ultrathin nature of MWCNT endows them with the super permeability of water vapor. The solar-driven steam generation performance of the prepared vdW heterostructure demonstrates an excellent evaporation efficiency of 87.43% and an increment of the surface temperature to 79.8 °C in less than 20 mins under 1 kWm–2 solar illumination. Therefore, the proposed vdW heterostructure can be realized in high-temperature steam generation applications.
Two-dimensional (2D) materials are getting a lot of attention in the nonlinear optics research due to their excellent structural characteristics and nonlinear effects. Here, the layered dependent second harmonic generation (SHG) of 2D-gallium sulfide (GaS) nanosheets are demonstrated for the first time. According to the obtained findings, SHG signal was identified exclusively for the odd layer GaS-nanosheets due to the existence of broken inversion symmetry. The even layer, on the other hand, generated no SHG signal due to its centrosymmetric structure. Moreover, the layered dependent damaged threshold of the prepared sample is also discussed here.
Photon management of perovskite solar cells (PSCs) is studied by the use of nanohole front contact, which allows improving the JSC of the PSC by providing an improved light incoupling. The front contact integrated with spherical nanocone shaped holes represent a refractive index grating allowing for light incoupling approaching unity while minimizing reflection losses. Besides, the front contact has a comparable refractive index (n~2.5) with the perovskite absorber, which minimizes the front reflections in PSC. Optics and optimization of front contact and solar cell are investigated by three-dimensional (3D) finite-difference time-domain (FDTD) simulations whereas finite element method simulations are used to study the electrical response of the device. Investigations reveal a maximum light incoupling enhancement of 10~12% for the optimized PSC, leading to 10 to 27% JSC enhancement with respect to the planar reference PSC.
Image sensing technology has a great impact on our daily life as well as the entire society, such as health, safety and security, communication systems, and entertainment. The conventional optical color sensors consist of side by side arranged optical filters for three basic colors (blue, green, and red). Hence, the efficiency of such optical color sensors is limited by only 33%. In this study, a vertically stacked color sensor is investigated with perovskite alloys, which has the potential to provide the efficiency approaching 100%. The proposed optical sensor will not be limited by color Moire error or color aliasing. Perovskite materials with suitable bandgaps are determined by applying the energy shifting model and the optical constants are used for further investigations. Quantum efficiencies and spectral responsivities of the described color sensors are investigated by three-dimensional electromagnetic simulations. Investigated spectral sensitivities are further analyzed for the
The invited paper explains the transmission properties of a range of near-, mid-, and far-IR optical fibres for their
applications in chemical and biological sensing. Methods for the fabrication of single and multiple-core mid-IR fibres are
discussed in view of controlling the thermal and viscosity properties for fibre drawing. In particular, the need for
removing impurity bands in the 5000 to 1000 cm-1 range is explained. The importance of engineering multi-core fibres
is also discussed for simultaneous measurements of Raman, IR and surface plasmon enhanced modes together with say,
temperature using a mid-IR transmitting tellurite fibre e.g. in a chemical process. The paper explains the principles and
advantages of evanescent wave coupling of light at the resonant frequency bands for chemical sensing using a fibre
evanescent wave spectroscopic sensor having a GeTeSe chalcogenide fibre. Using fibre based techniques, measurements
for Cr6+ ions in solution and As3+ and As5+ in solids have been characterized at visible and mid-IR regions, respectively.
In this paper we also explain the importance of using mid-IR fibres for engineering novel laser and broadband sources
for chemical sensing.
We present efficient CW lasing Tm3+/Ho3+/Yb3+-triply-doped tellurite fibre at ~2.1 μm. Two different pump schemes
have been demonstrated for this laser: a 1.088 μm
Yb3+-doped silica fibre laser simultaneously pumping the Tm3+: 3H5,
Ho3+: 5I6 and Yb3+: 2F5/2 levels, and a 1.6 μm
Er3+/Yb3+-doped silica fibre laser directly pumping the Tm3+: 3F4 level. For
the 1.6 μm pumping, a slope efficiency of 62% has been achieved in a 76 cm long fibre which is close to the Stokes
efficiency limit of ~75%. An output power of 160 mW has also been achieved, but with no signs of saturation or fibre
damage suggesting that higher output powers should be possible. For the 1.088 μm pumping there is very strong pump
ESA resulting in bright blue (480 nm) and near-IR (800 nm) fluorescence due to the 1G4 → 3H6 and 3H4 →
3H6
transitions of Tm3+, respectively, and this limits the achievable slope efficiency, which in this case was a maximum of
25% for a 17 cm long fibre. With this pump scheme, the highest observed output power was 60 mW, and further power
scaling was limited due to the intense ESA and thermal damage to the pump end of the fibre. We also present results on
the active Q-switching of the 1.6 μm pumped fibre laser using a mechanical chopper operating at 19.4 kHz. Average
powers of 26 mW and pulse energies of 0.65 μJ were measured with pulse widths in the range 100-160 ns.
Near- and mid-infrared fibre lasers find many applications in areas such as remote and chemical sensing, lidar and
medicine, and tellurite fibres offer advantages over other common fibre glasses such a lower phonon energy and higher
rare-earth ion solubility than silicate glasses, and greater chemical and environmental stability than fluoride glasses. Rate
equation modelling is a very useful tool for the characterisation and performance prediction of new rare earth transitions
in these novel fibre materials. We present the numerical rate equation modelling results for a ~2 μm Tm3+-doped tellurite
fibre laser when pumped with a 1.6 μm Er3+/Yb3+-doped double-clad silica fibre laser. A maximum slope efficiency of
76% with respect to launched pump power was achieved in the experimental fibre laser set up with a 32 cm long fibre.
The high slope efficiency is very close to the Stokes efficiency limit of ~82% which is due to the in-band pumping
scheme employed and the lack of pump excited state absorption. The two-level rate equations involving absorption and
emission between the Tm3+: 3H6 and 3F4 levels have been solved iteratively using a fourth-order Runge-Kutta algorithm
and the results compared with the experimental results. For the 32 cm fibre with output coupler reflectivities of 12%,
50%, 70% and 90%, the respective theoretical slope efficiencies of 73%, 64%, 53% and 29% are in very good agreement
with the experimentally measured values of 76%, 60%, 48% and 33%.
We report the active Q-switching of a Yb:Er:YVO4 laser for the first time. A Yb:Er:YVO4 crystal was end pumped by a
quasi-continuous wave laser diode emitting at 967 nm with a peak power of up to 48 W. The laser cavity was actively Qswitched
using the spinning disc technique. At a repetition rate of 19.2 kHz, the Q-switched slope efficiency and
threshold were 4 % and 62 mJ respectively. In comparison, the same system had a slope efficiency of 5% and a threshold
of 75 mJ without mechanical Q-switching. Single pulse of energy up to 90 μJ and duration as short as 110 ns were
obtained for the single output pulse per pump pulse operation.
The first demonstration of a pulsed Nd:YCOB laser at 1060 nm is reported, with results for both gain switching and Qswitching
presented. Active Q-switching is achieved using the spinning disc technique pulses of 50 ns duration with
pulse energies up to 0.6 mJ are obtained. Optimisation is performed for both pulse energy and slope efficiency of the
laser. A Q-switched slope efficiency of 56% is achieved.
Various lengths of Yb:Er:YVO4 were end pumped by a quasi-continuous wave 967 nm diode laser. The best slope
efficiency with respect to absorbed pump power for gain switched operation was 8 % for a 5 mm long crystal.
Co:MgAl2O4 saturable absorbers of 98 % and 93 % initial transmission were used to passively Q-switch the cavity. For
the 98 % initial transmission absorber, average pulses energies of 44 µJ were measured. The average pulse width and
repetition rate were ~256 ns and 36 kHz, respectively. For the 93% initial transmission absorber, a single output pulse of
37 µJ energy and 22 ns duration per pump pulse was measured when the crystal was pumped for a pumping duration of
1.7 ms.
We report a Tm3+/Yb3+-doped tellurite fibre laser operating at wavelengths in the range 1879 - 1994 nm. Two different pump schemes have been demonstrated for this laser: a 1088 nm Yb3+-doped silica fibre laser simultaneously pumping the Tm3+: 3H5 and Yb3+: 2F5/2 levels, and a 1610 nm Er3+/Yb3+-doped silica fibre laser directly pumping the Tm3+: 3F4 upper laser level. For the 1610 nm pumping, a slope efficiency of 76% has been achieved in a 32 cm long fibre which is very close to the Stoke efficiency limit of ~80%. An output power of 283 mW has also been achieved, but with no signs of saturation or fibre damage suggesting that higher output powers should be possible. For the 1088 nm pumping there is very strong pump ESA resulting in bright blue (480 nm) and near-IR (800 nm) emission and this limits the achievable slope efficiency, which in this case was a maximum of 10% for a 16 cm long fibre. With this pump scheme, the highest observed output power was 67 mW, and further power scaling was limited due to the intense ESA and thermal damage to the pump end of the fibre. Lasing has been achieved in <10 cm lengths of this fibre making this material a promising candidate for ultra compact medium power mid-IR laser sources for range-finding, medical and atmospheric monitoring and sensing applications.
Wavelengths around 1.15 μm, 1.3 μm and 1.7 μm can be used to pump Dy-doped ZBLAN fibre in order to generate ~3
μm with high efficiency. Previously the generation of 2.9 μm from the Dy-ZBLAN fibre was demonstrated by pumping
with 1.1 μm Yb-silica fibre laser sources. The laser slope efficiency and lasing threshold demonstrated was about ~5%
and ~1.78 W. In this investigation, the longer wavelength absorption band (6H9/2 , 6F11/2) centred at 1.3 μm of Dy3+-doped
ZBLAN is utilised and the lasing transition around ~3 μm takes places from 6H13/2 → 6H15/2. With this pumping scheme
the Stokes' efficiency is expected to be up to ~45%. A quasi-continuous wave Dy3+-ZBLAN fibre laser pumped by a
~1.3 μm Nd:YAG laser and operating at 2.96 μm with a bandwidth (FWHM) of ~14 nm has been demonstrated. For a
60cm fibre length, a threshold of 0.5W and a slope efficiency of ~20% with respect to the absorbed pump power was
observed. The overall pump absorption in the fibre was around 84%. The cavity reflectivities at 2.9 μm were 99% and
50%. The demonstrated slope efficiency was 45% of the Stokes' limit. The slope efficiency was around four times
higher and the threshold around 3.6 times lower than the previous performance demonstrated by using the 1.1 μm Yb
fibre laser pumping scheme. The higher performance achieved compared to the 1.1 μm pump scheme is due to the higher
Stokes' limit, lower pump ESA losses and higher cavity reflectivity. About 590 cm-1 Raman Stokes shift has also
detected by using 514.5 nm and 488 nm Ar ion laser as excitation pump sources.
Intracavity second harmonic generation (ISHG) of a continuous wave, diode-pumped, broadband Yb-doped fibre laser has been investigated. Frequency doubling of the fibre output and of the residual diode pump light, and sum frequency mixing (SFM) between the fibre output and the pump light were achieved simultaneously, resulting in three colour operation in the blue-green region.
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