Wide Optical Window Research Articles

Diamond optomechanical crystals

Cavity-optomechanical systems realized in single-crystal diamond are poised to benefit from its extraordinary material properties, including low mechanical dissipation and a wide optical transparency window. Diamond is also rich in optically active defects, such as the nitrogen-vacancy (NV) and silicon-vacancy (SiV) centers, which behave as atom-like systems in the solid state. Predictions and observations of coherent coupling of the NV electronic spin to phonons via lattice strain has motivated the development of diamond nanomechanical devices aimed at realization of hybrid quantum systems, in which phonons provide an interface with diamond spins. In this work, we demonstrate diamond optomechanical crystals (OMCs), a device platform to enable such applications, wherein the co-localization of ~ 200 THz photons and few to 10 GHz phonons in a quasi-periodic diamond nanostructure leads to coupling of an optical cavity field to a mechanical mode via radiation pressure. In contrast to other material systems, diamond OMCs operating in the resolved-sideband regime possess large intracavity photon capacity (> 10$^5$) and sufficient optomechanical coupling rates to reach a cooperativity of ~ 20 at room temperature, allowing for the observation of optomechanically induced transparency and the realization of large amplitude optomechanical self-oscillations.

Role of reaction time in tuning the morphology and third order nonlinear optical properties of barium borate

Single crystalline nanoclusters and nanorods like structure of barium borate (β- BaB2O4) were synthesized by organic free hydrothermal method at various reaction times of 8, 24 and 48h. XRD shows the formation of pure and single phase of β- BaB2O4 with improved crystallinity at elevated reaction time. β- BaB2O4 crystallizes in hexagonal system with lattice parameter a=b=12.53Å and c=12.72Å. The surface morphology picturizes the formation of nanoclusters and rod structures with several micrometer length and nanometer diameter. By increasing the reaction time and due to prolonged pressure, aggregation followed by elongation resulted in the transformation of nanoclusters into rod like structure. The nanostructured barium borates possess strong UV absorbance and wide optical window. The nonlinear optical studies by Z– scan technique shows the material to possess saturable absorption and self-defocusing nature. A strong variation in third order nonlinear optical parameters with change in the morphology of β- BaB2O4 was observed. Also β- BaB2O4 rod like structure is identified to be more efficient optical limiters in the green regime of continuous wave lasers.

Elucidation of two photon absorption of ethylenediaminium (2,4-dinitrophenolate) crystals

Optical quality single crystals of ethylenediaminium (2,4-dinitrophenolate) [EDA(2,4)DNP] were grown by solvent evaporation method for optical limiting applications against intense ultrashot pulse lasers. Single crystal XRD showed that the material crystallizes in monoclinic system with centric space group P21/C. The crystal packing diagram was elucidated for the first time in literature and it revealed six hydrogen bonds played a very important role in stabilizing the structure. A bifurcated hydrogen bond was also observed between ethylenediamminium and dinitrophenolate ions. The formation of charge transfer complex during the reaction of ethylenediamine and 2,4-dinitrophenol was strongly evident through the vibrational spectroscopic studies. TG–DTA and DSC curves indicate that the material exhibited strong decomposition at 224 °C. Ground state absorption analysis showed that the grown crystals possess absorption maxima in UV region (270 nm, 346 nm) and wide optical transmittance window (480–1200 nm) in the entire visible and NIR region. Measurement of two photon absorption (2PA) and optical limiting response by Z-scan technique under nanosecond pulse excitation was reported. Hence EDA(2,4)DNP with high 2PA coefficient (0.79 ± 0.04 × 10−10 m/W) and low limiting threshold (2.40 ± 0.05 × 1012 W/m2) will be a potential candidate for optical limiting applications like eye and sensor protection against short pulse lasers that are well spread in human interactive sectors.

Effect of crystal violet dye on the structural, optical, mechanical and piezoelectric properties of ADP single crystal

Single crystals of pure and crystal violet (CV) dye doped (0.05mol%) ammonium dihydrogen phosphate (ADP) were grown and characterized. Structural and compositional studies were carried out using XRD, EDAX and FTIR. In UV⿿vis-NIR measurements, characteristic absorption at 590nm was observed for CV dye, with increased transmittance, wider optical window and increased band gap from 5.80eV to 6.0eV. In photoluminescence studies, CV doping resulted in partial quenching of blue emission at 440nm. The piezoelectric charge coefficient was also enhanced from 1.82 pC/N to 2.78 pC/N. In micro-hardness studies, CV doped crystals exhibited better mechanical strength. The distribution of hardness number was statistically analyzed using Weibull statistics. The values of transition point, critical load, etc. were evaluated for both the crystals. Raman studies revealed that no structural phase transformations were observed after indentation for both the samples.

Chalcogenide glass fibers: Optical window tailoring and suitability for bio-chemical sensing

Glassy materials based on chalcogen elements are becoming increasingly prominent in the development of advanced infrared sensors. In particular, infrared fibers constitute a desirable sensing platform due to their high sensitivity and versatile remote collection capabilities for in-situ detection. Tailoring the transparency window of an optical material to the vibrational signature of a target molecule is important for the design of infrared sensor, and particularly for fiber evanescent wave spectroscopy. Here we review the basic principles and recent developments in the fabrication of chalcogenide glass infrared fibers for application as bio-chemical sensors. We emphasize the challenges in designing materials that combine good rheological properties with chemical stability and sufficiently wide optical windows for bio-chemical sensing. The limitation in optical transparency due to higher order overtones of the amorphous network vibrations is established for this family of glasses. It is shown that glasses with wide optical window suffer from higher order overtone absorptions. Compositional engineering with heavy elements such as iodine is shown to widen the optical window but at the cost of lower chemical stability. The optical attenuations of various families of chalcogenide glass fibers are presented and weighed for their applications as chemical sensors. It is then shown that long-wave infrared fibers can be designed to optimize the collection of selective signal from bio-molecules such as cells and tissues. Issues of toxicity and mechanical resistance in the context of bio-sensing are also discussed.

In situ soft x-ray fluorescence and absorption microspectroscopy: A study of Mn-Co/polypyrrole electrodeposition

This paper reports the development and application of a novel thin-layer electrochemical microcell for in situ soft x-ray fluorescence and absorption microspectroscopy. The microcell, fabricated using ultraviolet lithography, is an improved version of concepts previously developed in our group, featuring a wide optical window that allows the extension of the range of accessible in situ microspectroscopy and imaging methods, including those requiring small emission take-off angles. The three-electrode design implemented in the cell enables optimal electrochemical control. The first in situ experiment employing this new cell explores the electrochemical growth of a novel Mn-Co/polypyrrole composite that is a prospective electrocatalyst for Pt replacement in air cathodes. Morphological, compositional, and chemical-state distributions of Mn and Co codeposited with polypyrrole are subsequently performed in situ as a function of time and position, yielding otherwise unachievable information regarding the electrodeposition process.

Optical transmission radiation damage and recovery stimulation of DSB: Ce3+ inorganic scintillation material

Recently, a new scintillation material DSB: Ce3+ was announced. It can be produced in a form of glass or nano-structured glass ceramics with application of standard glass production technology with successive thermal annealing. When doped with Ce3+, material can be applied as scintillator. Light yield of scintillation is near 100 phe/MeV. Un-doped material has a wide optical window from 4.5eV and can be applied to detect Cherenkov light. Temperature dependence of the light yield LY(T) is 0.05% which is 40 times less than in case of PWO. It can be used for detectors tolerant to a temperature variation between -20° to +20°C.Several samples with dimensions of 15x15x7 mm3 have been tested for damage effects on the optical transmission under irradiation with γ-quanta. It was found that the induced absorption in the scintillation range depends on the doping concentration and varies in range of 0.5-7 m−1. Spontaneous recovery of induced absorption has fast initial component. Up to 25% of the damaged transmission is recuperated in 6 hours. Afterwards it remains practically constant if the samples are kept in the dark. However, induced absorption is reduced by a factor of 2 by annealing at 50°C and completely removed in a short time when annealing at 100°C. A significant acceleration of the induced absorption recovery is observed by illumination with visible and IR light. This effect is observed for the first time in a Ce-doped scintillation material. It indicates, that radiation induced absorption in DSB: Ce scintillation material can be retained at the acceptable level by stimulation with light in a strong irradiation environment of collider experiments.

Optical limiting behavior of β-BaB2O4 nanoparticles in pulsed and continuous wave regime

Barium borate (β-BaB2O4) nanoparticles were prepared by a hydrothermal technique using barium chloride and boric acid as starting materials. Powder x-ray diffraction confirms the pure single phase formation of β-BaB2O4. Fourier transform infrared spectroscopy spectra shows the presence of BO3 units which extend themselves to form (B3O6)3− anionic groups in β-BaB2O4. Scanning electron microscopy imaging shows the two-dimensional undulating particle surface with particle size in the range of 45–170 nm. β-BaB2O4 has strong absorption in the UV region and it possesses a wide optical transmittance window (201 to 1100 nm). The optical band gap of the β-BaB2O4 nanoparticle is estimated to be 5.9 eV. In the photoluminescence spectra the presence of self trapped excitonic state (347 nm) was identified. The third order optical nonlinearity of the sample excited in two different pumping regimes, short pulse excitation (532 nm, 5 ns) and continuous wave laser (532 nm, 50 mW) was studied. The material shows limiting behavior due to two photon absorption in the pulsed laser regime and self defocusing in the continuous wave regime.

Ethylenediaminium di(4-nitrophenolate): A third order NLO material for optical limiting applications

Single crystals of ethylenediaminium di(4-nitrophenolate) [EDA4NP] were grown by slow evaporation solution growth technique using ethanol as solvent at constant temperature. It crystallizes in monoclinic centrosymmetric space group C2/c with cell dimension a=11.326Ǻ, b=7.264Ǻ, c=20.036Ǻ; β=93.55°. Fourier Transform Infra Red (FT-IR) spectrum was recorded to identify various functional groups present in EDA4NP. Nuclear Magnetic Resonance (NMR) spectral studies were performed to confirm the functional groups. Thermogravimetric analysis and differential thermal analysis showed that the compound melts at 142.9°C. The material possesses a wide optical transparency window in the visible and near IR region (500–1200nm). The nonlinear refractive index, nonlinear absorption coefficient and third-order nonlinear susceptibility of EDA4NP were estimated to be n2=5.46×10−8cm2W−1, β=0.65×10−3cmW−1 and χ(3)=2.96×10−6esu respectively. The limiting behavior observed with the sample is attributed mainly to nonlinear refraction.

Large-Area p-i-n Photodiode With High-Speed and High-Efficiency Across a Wide Optical Operation Window (0.85 to 1.55 μm)

We demonstrate novel InP based photodiodes, which eliminate the degradation in speed and efficiency under short wavelength (0.85 μm) operation and have a enlarged device diameter as compared to that of GaAs based PDs for the same desired speed performance. By inserting a p-type In $_{0.52}$ Al $_{0.32}$ Ga $_{0.16}$ As layer with an intermediary bandgap value (1.2 eV) between In $_{0.52}$ Al $_{0.48}$ As (1.47 eV) window and In $_{0.53}$ Ga $_{0.47}$ As (0.75 eV) absorption layers, the huge surface absorption (recombination), which would lead to efficiency degradation, under short wavelength excitation can be diluted. The slow hole transport in our structure can also be diminished due to the p-type doping in these absorption layers. Furthermore, the trade-offs between RC-limited bandwidth (device size) and carrier transient time in GaAs based PDs can be further released due to the excellent electron transport characteristic in the In $_{0.53}$ Ga $_{0.47}$ As (collector) layer. These devices with a large diameter as 62 μm, which is the usual size of 10 Gbit/s InP based PDs, can achieve wide 3-dB bandwidths; varying from 25 to 17 GHz when the operating wavelengths changes from 0.85 to 1.55 μm. A constant and high external efficiency (∼74%) with a clear eye-opening at around 40 Gbit/s has also been achieved over this wide optical window.

Dynamic Analysis of High-Efficiency InP-Based Photodiode for 40 Gbit/s Optical Interconnect Across a Wide Optical Window (0.85 to 1.55 μm)

The detailed dynamic analysis of novel high-speed InP-based photodiodes (PDs) has been performed. Such device can sustain an invariable high external efficiency (∼74%; no antireflection coating) across a wide optical operation window (0.85 to 1.55 μm). Furthermore, compared with the traditional GaAs-based high-speed PD for optical interconnect applications, our proposed device structure can offer an enlarged device active diameter and eliminate the degradation in responsivity performance when the desired speed performance is increased. This is because the strong photoabsorption process and the elimination of slow hole drift in the In0.53Ga0.47As based collector layer at 0.85-μm wavelength operation. By measuring the dynamic performance of PDs with different active diameters across such wide optical window, we can accurately extract the electron drift-velocity under different wavelengths excitations in the In0.53Ga0.47As collector layer. This result indicates that at short-wavelength (0.85 μm) operation, the photogenerated electron in the In0.53Ga0.47As collector suffers from significant intervalley scattering effect due to its high excess energy. By using such device with diameter of optical window as large as 40 μm, 40 Gbit/s error-free transmissions have been successfully demonstrated through 5-km single-mode (SMF-28) and 0.1-km multimode (OM4) fibers at long- and short-wavelengths operations with reasonable sensitivity, respectively.

Strategies for the selective volume sintering of ceramics

Abstract

Second- and third-order optical studies of 4-Bromoanilinium hydrogen phthalate single crystal for nonlinear optical device applications

A new organic NLO material 4-Bromoanilinium hydrogen phthalate was grown by slow evaporation technique. The solubility and metastable zone width were determined. The crystal belongs to monoclinic system with space group C2. Optical transmittance spectrum confirms the wide optical window. Absorption coefficient and band gap were calculated from transmittance. The thermal stability, laser-induced surface damage threshold and mechanical behaviour were analysed. The particle size-dependent second harmonic generation efficiency was evaluated by Kurtz–Perry powder method and existence of phase matching. The third-order optical study was measured by Z-scan studies. The dispersion of birefringence behaviour was studied.

Studies on crystal growth, vibrational, optical, thermal and dielectric properties of new organic nonlinear optical crystal: Bis (2,3-dimethoxy-10-oxostrychnidinium) phthalate nonahydrate single crystal

In this paper, we report the synthesis, growth and characterization of a new organic NLO single crystal of Bis (2,3-dimethoxy-10-oxostrychnidinium) phthalate nonahydrate, for the first time. The single crystal XRD study reveals that the crystal belongs to monoclinic system. The molecular structure and the nature of the vibrations were identified by vibrational and NMR spectroscopic studies. The UV absorption edge was found to be 330nm with a wide optical transmittance window covering the visible region. The crystal exhibits physicochemical stability upto 90.56°C. Various thermodynamic parameters were calculated from the TG data. The Kurtz powder second harmonic generation revealed that the SHG efficiency of the grown crystal was about 2.8 times that of KDP and was found to be phase matchable. The measured low value of birefringence indicates its suitability for NLO devices. The PL spectrum exhibited two peaks (355 and 406nm) due to the donation of protons from carboxylic acid to quartenium nitrogen. The dielectric behavior of the grown crystal was analyzed for different frequencies at different temperatures.

Growth, optical, thermal, dielectric and microhardness characterizations of melaminium bis (trifluoroacetate) trihydrate single crystal

Single crystals of melaminium bis (trifluoroacetate) trihydrate (MTFA) of dimensions (8×8×4mm3) have been grown successfully by slow evaporation technique. The unit cell dimensions and morphology have been identified from X-ray powder diffraction analysis. The UV absorption edge is found to be 345nm with a wide optical transmittance window covering the visible region and the direct optical band gap is calculated as 4.59eV. The various optical properties such as reflectance, extinction coefficient, refractive index, optical conductivity have been calculated and their dependence with incident photon energy has also been discussed. Further, the thermal stability has been investigated by TG/DTA techniques. Microhardness measurements along three different planes show that there exists considerable anisotropy. The dielectric response of the crystal has been analyzed in the frequency range from 50Hz to 5MHz at different temperatures and the results are discussed.

Growth and anisotropic studies on potential nonlinear optical crystal imidazole–imidazolium picrate monohydrate (IIP) in different orientations for NLO device fabrications

A new organic NLO material Imidazole–imidazolium picrate monohydrate (IIP) was grown by the slow evaporation technique using acetonitrile as a solvent. The solubility and meta stable zone width was determined. The IIP crystal belongs to orthorhombic system with noncentrosymmetric space group P212121. The morphology of the IIP crystal was studied. Optical transmittance spectrum confirms a wide optical window exhibited by IIP crystal. The transmittance of IIP crystal was used to calculate the extinction coefficient (k) and absorption coefficient (α). The thermal stability of the crystal was determined using TG-DTA studies. The laser induced surface damage threshold and mechanical behavior of the IIP crystal were analyzed in different planes at different temperatures. The second harmonic generation (SHG) effective nonlinearity of IIP is 3.6 times that of standard reference material potassium dihydrogen phosphate (KDP) crystal.

Optical, thermal and microhardness studies on dichloridobis(1-ethyl-2,6-dimethylpyridinium-4-olate-κO) zinc(II)

A newly engineered host–guest hydrogen bonded metal–organic coordination compound, dichloridobis(1-ethyl-2,6-dimethylpyridinium-4-olate-κO)zinc(II) (EDMPZC), [C18H26Cl2N2O2Zn] has been designed and synthesized. Single crystals of dimensions (5 × 5 × 2 mm3) have been grown by slow evaporation technique. The unit cell dimensions and morphology are identified from single crystal XRD analysis. Further, it has been characterized by FT-IR absorption, FT-NMR spectroscopy, elemental analyses (CHN and XRF) and their thermal stability investigated following TG/DTA and DSC techniques. The thermal transport properties, thermal effusivity (e), thermal diffusivity (α), thermal conductivity (K) and heat capacity (Cp) have been measured by the photopyroelectric technique at room temperature. The laser damage threshold of the grown crystal was measured using Q-switched Nd:YAG laser (1064 nm, 10 ns, 10 Hz). The mechanical stability of the crystal has been studied from the Vicker's microhardness measurement. The UV absorption edge is 262 nm with a wide optical transmittance window covering the UV–Vis–NIR region and the optical band gap of the compound is found to be 3.5 eV.

Enhanced ultraviolet response using graphene electrodes in organic solar cells

We demonstrate enhanced ultraviolet (UV) response in organic photovoltaic devices using few-layer graphene as the transparent and conducting electrode. This is compared to the same device stack fabricated on a conventional indium tin oxide (ITO) electrode. The enhanced UV response was confirmed by examining the photocurrent spectra over a wide spectral range and is consistent with the excellent UV transmittance of graphene over ITO. The results render the graphene electrode a promising alternative to ITO to enable applications for UV photodetectors or other optoelectronic devices with a wider optical window.

Modeling of a compact and completely non-blocking 4 × 4 multimode interference switch for optical communication applications

Modelling of a compact and completely non-blocking 4×4 optical switch utilizing integrated multi-mode interference (MMI) waveguides with a channel profile of Ti-indiffused Lithium Niobate is described. Design novelty lies in its satisfactory operation for two wide optical windows (100 nm each), with center wavelengths (λcentre) of 1.3 and 1.55 µm, possessing low losses. For either of these windows, the average value of propagation losses are maintained lower than 1 dB with a vacillation of extremely low polarization dependent losses ( ≤ 0.15 dB). Index tuned regions are optimized to achieve average crosstalk levels better than −19 and −12 dB for its operation in the wavelength range of 1.25 to 1.35 µm and 1.50 to 1.60 µm, respectively. It is also observed that switch possess absolute loss uniformity (of the range of 0.5% to 1.6%) with a maximum of ±2.5% tolerance in the structural parameters.

Composition dependence of optical band gap of the Se–Ge–Te far infrared transmitting glasses

A systematic series of Se x Ge 25 −x Te 75 ( x=0, 5, 10, 15, 20 at%) far infrared transmitting glasses were prepared by traditional melt-quenching method. Physical, thermal and optical properties of the glass system were analyzed. The allowed indirect transition of samples was calculated according to the classical Tauc equation. The results show the density increases with the substitution of Ge by Se and a maximum Τ g value of 175 °C was obtained for the Se 15Ge 10Te 75 glass. The energy band gap of Se 15Ge 10Te 75 glass is 1.25 eV, possessing the largest metallization criterion value (0.25) and the lowest refractive index (3.16). When the dissolved amount of Se increased from 0 to 15 at%, the values of indirect optical band gap were in the range from 0.573 to 0.679 eV. A wide optical transparent window with a cut-off wavelength beyond 18 μm was shown.