Theoretical Transmittance Research Articles

Influence of germanium concentration on the microstructure and optical transparency of terbium gallium garnet ceramics

AbstractIn recent years, transparent terbium gallium garnet (TGG) ceramics have garnered significant interest for their application in high‐power Faraday isolators. However, challenges in achieving high transparency have led researchers to explore the addition of various sintering aids as a key strategy to enhance the optical quality of TGG ceramics. Through this work, the effect of germanium (Ge) addition on the microstructure and optical transparency of TGG magneto‐optical ceramics was investigated. TGG powders were synthesized by the co‐precipitation method, and the source Ge was Ge ethoxide added through a ball‐milling step. Transparent TGG ceramics were prepared by air pre‐sintering combined with hot isostatic pressing post‐treatment and subsequent annealing. The ceramics containing 200 ppm Ge exhibit optimal transmittance of 81.3% at 1064 nm (a value of theoretical transmittance), the Verdet constant was −133.0 rad·T−1·m−1 at 633 nm. When the addition of Ge reaches 600 ppm, a secondary phase can be observed on the surface of ceramic. Subsequently, TGG ceramics prepared from 1425°C to 1500°C with 200 ppm of Ge were analyzed, which revealed that the optimal pre‐sintering temperature is 1450°C.

Synchronous improvement in mechanical properties and dielectric performance of poly(silylene arylether arylacetylene) by introducing trifluoromethyl groups

AbstractPoly(silylene arylether arylacetylene) (PSEA) resin is a promising material for preparing an advanced wave‐transparent composite because of excellent thermal stability and good dielectric properties. Herein, a novel poly(silylene arylether arylacetylene) resin with trifluoromethyl groups (PSEAF) was synthesized by Grignard coupling reaction, and the effects of the incorporation of trifluoromethyl groups on various properties of PSEAF resin and quartz fiber reinforced composites were investigated. Compared to PSEA, the PSEAF resin exhibits better solubility and processability, and lower apparent activation energy for curing reactions. After thermal curing reactions, the PSEAF resin converts to an amorphous crosslinked network with the temperature at 5% weight loss (Td5) around 470 °C. The cured PSEAF resin possesses improved mechanical properties and dielectric properties. The flexural strength arrives at 64.4 MPa, and the dielectric constant (ε) and dielectric loss (tanδ) at 30 MHz are 2.75 and 4.3 × 10−3, respectively. Besides, the quartz fiber reinforced PSEAF composite simultaneously shows ε of 3.3, theoretical wave transmittance |T|2 of 91.4% at 7 GHz, and flexural strength of 350 MPa.

Highly transparent Ce:Nd:YAG ceramic with good light conversion capacity for solar-pumped solid-state lasers

Developing a high quality ceramic laser gain medium for solar directly pumped solid state lasers is essential, and yet the light conversion efficiency of the gain media for solar pumping remains a challenge. In this study, Ce and Nd ions, co-doped YAG transparent ceramics with theoretical transmittance and stable Ce3+ valent state were developed, and revealed that the absorbed visible light and light conversion efficiency in Ce,Nd:YAG ceramics were 3.98 times and 1.34 times higher than those in widely reported Cr,Nd:YAG ceramics, respectively. A concentration matching principle between Ce3+ and Nd3+ ions in YAG was established, and a higher Nd3+ ion doping concentration with a relatively low Ce3+ concentration was favorable to improve both the light conversion efficiency and emission intensity at 1064 nm of Ce,Nd:YAG ceramics. Energy transfer efficiency from Ce3+ to Nd3+ of the 0.3 at.%Ce,1.5at.%Nd:YAG ceramic reached as high as 61.71% at room temperature. Surprisingly, it was further promoted to 64.31% at a higher temperature of 473 K. More excited electrons at the upper energy level of Ce3+ ion under the high temperature accounted for this novel phenomenon. This study proposes a new design strategy of gain materials for solar directly pumped solid state lasers.

Fabrication and spectral performance of Ndx:(La0.05Lu0.05Gd0.05Y0.05)Ca0.8-xF2.2+x High-entropy transparent fluoride ceramics

In this study, Ndx:(La0.05Lu0.05Gd0.05Y0.05)Ca0.8-xF2.2+x (x = 0.0–0.012) high-entropy transparent ceramics were prepared by the vacuum hot pressing method. The crystal structure, microstructure, elemental distribution and spectral properties of Ndx:(La0.05Lu0.05Gd0.05Y0.05)Ca0.8-xF2.2+x, as well as the impact of Nd3+ content on these properties was systematically examined. The material demonstrates high optical transparency, achieving a maximum on-line transmittance of nearly 90 % at 1200 nm, which is very close to the theoretical CaF2 transmittance (92%–94 %). Porosity and grain size are identified as the primary scattering factors. The EDX analysis revealed that the prepared transparent ceramics exhibited a high level of density and uniform distribution of elements. The highest luminescence intensity is observed at a Nd3+ concentration of 1 at.%, the fluorescence lifetime decays relatively slowly with increasing concentration of doped Nd3+ ions.

Dynamically tunable multiple plasmon-induced transparency effect based on monolayer graphene structure system with rectangular defect cavities

In this article, a dynamically tunable multiple plasmon-induced transparency (PIT) effect in monolayer graphene structure system with rectangular defect cavities is investigated both theoretically and numerically. Because the graphene of our structure exists in a continuous form, the Fermi level of the graphene can be dynamically tuned by simply applying a bias voltage. The expressions of the theoretical transmittance are correctly deduced, and the fitting theoretical results are very consistent with the numerical simulation data. When the Fermi level of the graphene is increased from 0.8 eV to 1.2 eV, the group index of the dual-PIT system is controlled between 383 and 766. Alternatively, the group index of the triple-PIT system is maintained between 445 and 812. Moreover, the maximum group index can reach 812 at 1.2 eV, which shows that it can be designed as an excellent slow light device. Therefore, the proposed structures and results may provide strong guidance towards multichannel optical filters, dynamically tunable and excellent slow light and light storage devices.

A tunable graphene-based dual PIT device with dual-polarization excitation capability

A simple dual plasmon induced transparency (PIT) device based on “Z” type and “circle-strip” combination is designed, which is composed of monolayer graphene. This structure has the capability to excite double PIT simultaneously in the x polarization and y polarization directions. The polarization direction of the incident light will change the resonance frequency of the horizontal and vertical bands, but the resonance frequency of the circular graphene in the middle is not affected by the polarization direction of the light. After comparing the transmission spectra of the single structure and the combined structure, combined with the analysis of the surface electric field, it is determined that the structure adopts the coupling method of bright-bright-bright mode to realize the double PIT function. In both x and y polarization directions, the three components of the device are capable of inducing dipole resonance. Additionally, simulation results fit well with the theoretical transmittance calculations. When the device is utilized as a light sensor, it has been observed that sensitivity tends to increase alongside Fermi level elevation. Specifically, under x polarization, sensitivity can reach 1.888THz/RIU with a maximum FOM of 9.28 when the refractive index of the analyte is 1.7. Meanwhile, under y polarization, sensitivity can reach 1.943THz/RIU with a maximum FOM of 7.61 when the refractive index of the analyte is 1.3. In its capacity as an optical switch, the device has demonstrated a maximum modulation depth of 80.6 % at 2.64THz under x polarization, and 73.29 % at 1.92THz under y polarization. All modulations are achieved by adjusting the Fermi level.

Effects of ZrO2 concentration on the properties of pressureless-sintered highly transparent Er2O3 ceramics

Erbium oxide (Er2O3) transparent ceramics were successfully fabricated with different contents of zirconia (ZrO2) additive sintered at 1850 °C for 8 h in vacuum. The effects of ZrO2 concentration on microstructure, optical, mechanical, and thermal properties of Er2O3 transparent ceramics were systematically investigated in this study. With the concentration of ZrO2 increasing from 0 to 4 at.%, the average grain size of Er2O3 transparent ceramics decreased from 166.6 to 4.7 μm. Also, the Vickers hardness and fracture toughness were increased from 7.6 ± 0.3 to 10.1 ± 0.3 GPa and 0.69 ± 0.05 to 1.09 ± 0.03 MPa m1/2, respectively. However, the thermal diffusion coefficient and thermal conductivity reduced slightly after the doping of ZrO2. The in-line transmittance of 4 at.% ZrO2-doped Er2O3 ceramics with the excellent optical quality reached 77% in the visible range and 78% at 1100 nm, which were 95% and 96% of the theoretical in-line transmittance of Er2O3 single crystal, respectively. There were absorption peaks at 1500 nm and in the visible light range of 4 at.% ZrO2-doped Er2O3 ceramics. The Er2O3 ceramics developed in this study can be potential candidates for application in solid-state lasers.

Sintering of lixiviated nano glass-ceramics: An original route to elaborate transparent ceramics

We report the elaboration of translucent ZnGa2O4 ceramics by an innovative process, the sintering by Spark Plasma Sintering (SPS) of spinel ceramic powder obtained by the lixiviation of glass-ceramics. Indeed, a selective dissolution of the silica-rich glass matrix allows isolating ZnGa2O4 nanocrystals embedded in the silicate glass-ceramic. This glass-ceramic is elaborated from the parent glass of composition 55 SiO2 - 5 Na2O - 17 ZnO - 23 Ga2O3 (%mol) that undergoes a subsequent heat-treatment at 1100 °C under air leading to the crystallization of zinc gallate spinel nanocrystals with size in the 20–60 nm range. Lixiviated nanocrystals are collected and sintered by SPS to get a bulk ceramic. While the transmittance of this ceramic is only 60% at 4.5 µm, which is lower than the theoretical transmittance (82.5%), these first results are still promising and pave the way to new transparent ceramic processing route. Indeed, glass crystallization combined with selective lixiviation process is a powerful, non-conventional elaboration process that can further allow the stabilization and isolation of metastable crystalline phases with interesting functional properties.

Measurement of Nd:Y2O3 broad band near infra-red transmittance using FTIR system

We report on the measurement of transmittance in Nd:Y2O3 using a homemade Fourier transform infrared (FTIR) spectroscopy measurement system. The transmittance of Nd:Y2O3 samples in the 850–1100 nm band was measured and compared with the theoretical transmittance. A figure of merit (FOM) was defined to assess the proximity of the measured value to the theoretical value. The maximum FOM obtained was 240, corresponding to 99.6% of the theoretical transmittance at a wavelength of 1078 nm. Our results demonstrate the high accuracy and precision of the FTIR system for measuring transmittance in Nd:Y2O3 samples within the near-infrared wavelength range.

Multifrequency on-off modulation and slow light characterization of the patterned black phosphorus metamaterial based on dual plasmon-induced transparency.

We present a monolayer patterned black phosphorus (BP) metamaterial for generating a tunable dual plasmon-induced transparency (PIT). We have derived the expression for the theoretical transmittance by introducing the coupled mode theory (CMT), and the calculated results of the expression highly overlap with the simulation results. The quarterly frequency synchronous switch with two different operating bands is designed by the carrier density and scattering rate on the dual PIT modulation effect. Two parameters were selected as important markers to show the performance of the optical switch: the modulation depth (MD) and the insertion loss (IL). The theoretical analysis of this structure shows that the higher modulation depth (5.45d B<M D<12.06d B) and lower insertion loss (0.60d B<I L<0.22d B) of these switches are of good application. In addition, we found the slow light properties of the structure were excellent with a group index of up to 219. This work provides a theoretical basis to prepare multifrequency optical switch and optical buffer devices.

Effect of the Electrodeposition Potential on the Physical Properties of Rapid Thermal Processing‐Annealed CuInSe2 Films

Herein, the effect of the bath reference potential during the one‐step electrodeposition process of chalcopyrite CuInSe2 (CIS) films on “ITO‐coated glass” substrate is reported. Electrodeposited films are annealed by rapid thermal processing (RTP) under argon atmosphere. The deposition potential ranges between −0.85 and −0.65 V. The surface morphology and crystalline structure are investigated by scanning electron microscopy and X‐ray diffraction (XRD), respectively. Obtained results from XRD are supported by cyclic voltammetric measurements. Values of the extinction coefficient and refractive index are determined by fitting curves of theoretical reflectance and transmittance to experimental ones using the Fresnel matrix method. Results show that the deposition potential affects the physical properties of electrodeposited CIS films. Furthermore, using the Mott–Schottky analysis, it is shown it is possible to grow n‐ or p‐type CIS semiconductor by adjusting the cathodic voltage. This switching can be attributed to the effect of a metastable hole trap in CIS films.

Design of a transparent and flexible broadband omnidirectional antenna using characteristic mode analysis

An optically-transparent, mechanically flexible, monopole-radiation-characteristic, broadband omnidirectional antenna is proposed in this work. The radiator layer of the sandwich-structured antenna consists of a circular central patch with 16 circular satellite patches, and the characteristic mode analysis (CMA) was used to guide the detailed design process. We first analyzed the different modes of the 3×3 circular patch array, further reduced the size of the surrounding patch to increase the required omnidirectional mode bandwidth, further reduced the cross-polarization by adjusting the distance between the four corner patch and the central patch, and finally increased the number of surrounding patches to increase the bandwidth and gain. The entire analysis and optimization process uses the CMA. The antenna was excited by a single probe, with good omnidirectionality, low cross-polarization, and broad operating bandwidth in (5-12.7) GHz, achieving 87% relative bandwidth and peak gain of 4.1 dBi. The antenna has a radius of 27 mm and a thickness of 4.5 mm. A transparent and flexible antenna sample was fabricated on a flexible polydimethylsiloxane (PDMS) substrate using electrohydrodynamic (EHD) printing technology. The optical transmittance of the horseshoe-structured metal grids fabricated by EHD was investigated, as well as the equivalent surface resistance evaluation method. The theoretical optical transmittance of the horseshoe-structured single-layer silver grid on the PDMS substrate was 81.2%, versus 80.8% measured value, with an equivalent surface resistance of roughly 5 Ω/◻. The proposed antenna was bent on a 50 mm-radius cylinder surface and retained excellent omnidirectionality.

Optical properties and Faraday magneto-optical effects of highly transparent novel Tb2Zr2O7 fluorite ceramics

A novel magneto-optical transparent Tb2Zr2O7 ceramic with a high in-line transmittance of ∼76.2% at 635 nm (∼98.2% of the theoretical transmittance of perfect Tb2Zr2O7 single crystal) was successfully fabricated by vacuum sintering from its solid-phase reactive fluorite particle. In the visible region, the Tb2Zr2O7 bulk material was found to have a high refractive index of around 2.10 ± 0.03 and an optical basicity of 0.985 ± 0.015 while the electronic polarizability of the O2− anion in the Tb2Zr2O7 system generally remained constant at 2.45 ± 0.06 Å3. The Faraday effect results revealed that the transparent Tb2Zr2O7 ceramic had Verdet constants of −400 ± 4, −260 ± 4, and −62 ± 2 rad·T−1·m−1 at 515, 635, and 1064 nm, respectively, which were roughly 1.9-fold higher than the commercial Tb3Ga5O12 single crystal. Our outcomes demonstrated that the developed optical functional Tb2Zr2O7 ceramic has potential application as an excellent magneto-optical material.

Perfluorocyclobutyl aryl ether-based poly(silylene arylacetylene)s with a low dielectric constant for advanced wave-transparent composites

A high-performance matrix with good mechanical properties, low dielectric constant as well as high thermal stability for advanced composites is in demand for the aerospace industry. In this study, novel perfluorocyclobutyl aryl ether-based poly(silylene arylacetylene)s (PSFCBs) were synthesized, which can be converted to amorphous crosslinked networks via thermal crosslinking reactions at a low temperature. The thermal decomposition temperature at 5 wt% loss (Td5) of cured PSFCBs is around 440 °C and there is no glass transition temperature (Tg) below 380 °C. Among them, the cured PSFCB-P with the phenylmethylsilylene structure displays the optimal comprehensive performance. Dielectric constant (ε) and dielectric loss (tanδ) are respectively 2.45 and 1.5 × 10-3 at 30 MHz, and the theoretical transmittance |T|2 arrives at 95.1 %. The flexural strength of the cured PSFCB-P reaches 52.5 MPa. Quartz fiber cloth/PSFCB-P composites show good dielectric properties (ε of 3.22) in the high-frequency range (7 GHz to 17 GHz) and high mechanical properties (flexural strength of 324.5 MPa, ILSS of 30.5 MPa). Positron annihilation lifetime spectroscopy (PALS) indicates that the cured PSFCB-P has a high free volume beneficial to the decrease of the ε.

Balance PCE, AVT and CRI for good eye comfort semi-transparent organic photovoltaics via Ga2O3 or In2O3 electron collection layers

One of the promising applications for semi-transparent organic solar cells (ST-OSCs) is using as photovoltaic glass windows due to their suitable transparency, comfortable and adjustable color. However, it is difficult to achieve good eye comfort ST-OSCs with suitable average visible transmittance (AVT), power conversion efficiency (PCE) and color rendering index (CRI) because the three factors affect and restrict mutually. To realize ST-OSCs with high performance, theoretical transmittance spectra of ST-OSCs are obtained using the finite-difference time-domain (FDTD) simulation, and then the theoretical optimized structural parameters with appropriate AVT and CRI are achieved. The experimental ST-OSCs output is analyzed under the guidance of theory, and PM6:Y6-based ST-OSCs with Ga 2 O 3 or In 2 O 3 electron collection layers (ECLs) demonstrate outstanding power-generating and chromatic parameters. The PCE for devices with Ga 2 O 3 ECL gets up to 12.6% with an AVT of 22.5% and a CRI of 86.94, and the PCE for devices with In 2 O 3 ECL reaches up to 12.7% with an AVT of 21.5% and a CRI of 88.29. Apparently, the two deep-blue devices guarantee comfortable visual sensations when seeing through the devices, and this work offers a simple approach to achieve power-generating glass with good eye comfort color in energy-saving skyscrapers. • Good eye comfort ST-OSCs were optimized using finite-difference time-domain. • Ga 2 O 3 and In 2 O 3 were utilized as ECLs for good eye comfort OSCs, respectively. • Ga 2 O 3 -based devices show a PCE of 12.6% with an AVT of 22.5% and a CRI of 86.9. • In 2 O 3 -based devices show a PCE of 12.7% with an AVT of 21.4% and a CRI of 88.3.

Fabrication of Highly Transparent Y2O3 Ceramics via Colloidal Processing Using ZrO2-Coated Y2O3 Nanoparticles

An easy approach is described for the preparation of ZrO2-coated Y2O3 nanopowder from a solution of zirconium nitrate with commercial Y2O3 nanopowder. The evolution process of the ZrO2 coating layer upon calcination, such as the phase and microstructure of the particles’ surface, was studied. Calcination of the powder at 700 °C resulted in ZrO2-coated Y2O3 nanopowder. The rheological properties of the suspensions of ZrO2-coated Y2O3 powders were studied. A well-dispersed suspension with a solid loading of 35.0 vol% using ZrO2-coated Y2O3 nanopowder was obtained. The consolidated green body obtained by the centrifugal casting method showed improved homogeneity with a relative density of 50.2%. Transparent ceramic with high transparency and an average grain size of 1.7 µm was obtained by presintering at 1500 °C for 16 h in air, followed by post-HIP at 1550 °C for 2 h under 200 MPa pressure. The in-line transmittance at the wavelength of 1100 nm (1.0 mm thick) reached 81.4%, close to the theoretical transmittance of Y2O3 crystal.

Optical, thermal, and mechanical properties of (Y1−xScx)2O3 transparent ceramics

Sesquioxides such as Y2O3 and Sc2O3 are important optical materials, but the fabrication of their transparent ceramics remains a challenge due to the ultra-high melting point of over 2400 °C. In this work, a series of (Y1−xScx)2O3 transparent ceramics were successfully fabricated by a simple vacuum sintering process without any sintering additives, and the effect of scandium (Sc) content (x) on the crystal structure and optical/thermal/mechanical properties was evaluated. Y2O3 and Sc2O3 form a complete solid solution with a cubic bixbyite structure. The formation of (Y1−xScx)2O3 solid solution promotes the densification of ceramics, leading to the realization of high transparency close to the theoretical transmittance over a wide wavelength range of 0.35–8 µm. In particular, the in-line transmittance in the range of 0.6–6 µm remains above 80% for (Y1−xScx)2O3 with x = 0.23–0.31, while the pristine Y2O3 and Sc2O3 are opaque. Moreover, the mechanical properties including Vickers hardness (HV), fracture toughness (KIC), and biaxial flexural strength (δb) are evidently enhanced due to the solid solution strengthening, while the thermal conductivity (k) is reduced due to the reduction of photon free path. This study demonstrates that forming of solid solution is a facile and universal approach for preparing sesquioxide transparent ceramics with high optical and mechanical quality.

Designing high efficiency asymmetric polarization converter for blue light: a deep reinforcement learning approach.

Conventional polarization converters selectively preserve the required polarization state by absorbing, reflecting or refracting light with unwanted polarization state, leading to a theoretical transmittance limit of 0.5 for linearly polarized light with unpolarized light incidence. In the meanwhile, due to the high-dimensional structure parameters and time-consuming numerical simulations, designing a converter with satisfactory performance is extremely difficult and closely relies on human experts' experiences and manual intervention. To address these open issues, in this paper, we first propose an asymmetric polarization converter which shows both high transmittance for one linearly polarized light and high transmittance for the orthogonal linearly polarized light with 90° rotation in blue wavelength region. To maximize the performance of the proposed structure, a deep reinforcement learning approach is further proposed to search for the optimal set of structure parameters. To avoid overly long training time by using the numerical simulations as environment, a deep neural network is proposed to serve as the surrogate model, where a prediction accuracy of 96.6% and 95.5% in two orthogonal polarization directions is achieved with micro-second grade simulation time respectively. With the optimized structure, the average transmittance is larger than 0.5 for the wavelength range from 444 to 466 nm with a maximum of 0.605 at 455 nm, which is 21% higher than the theoretical limit of 0.5 of conventional polarization converters.

Optical properties and energy transfer performances in high quality Cr,Nd: YAG transparent laser ceramics for solar pumped lasers.

Realizing a high solar light conversion magnitude in Cr,Nd: YAG transparent ceramic is crucial to its applications in solar pumped solid state lasers. In this study, high quality Cr,Nd:YAG transparent laser ceramics with homogeneous microstructure and theoretical transmittance were fabricated, and an efficient laser oscillation of watt-level was realized by pumping ceramic at 808 nm. There were no any characteristic absorptions corresponding to Cr2+ or Cr4+ ions detected, even when the Cr3+ ion doping concentration reached 0.6 at.%. Increasing Cr3+ and Nd3+ doping concentrations significantly enhanced the emission intensity of ceramics at 1.06 µm, and energy transfer efficiency of the 0.3 at.% Cr,Nd: YAG ceramics was increased from 14.9% to 36.9% when increasing Nd3+ ion concentration from 0.3 at.% to 1.0 at.%, with an increasing magnitude of 247.6%. The results indicated that Cr,Nd: YAG transparent ceramic is a promising gain medium for solar pumped solid state lasers.

Study on the optical and thermal properties of a new mid-infrared TeO2-Ta2O5-La2O3 glass

A new mid-infrared tellurite ternary glass with small glass formation area was prepared by modified melt quenching. A high-throughput, simple and fast glass melting process is realized by erecting the tube furnace sideways. The forming range of glass can be quickly and efficiently explored. Moreover, the equipment is convenient for stirring in the melting process, and can effectively reduce bubbles and stripes in the molten glass, thus preparing the matrix glass with excellent performance. The maximum phonon energy of the glass is 765 cm−1, and the appropriate phonon energy is beneficial to achieve intense mid-infrared luminescence or laser. The density of glass is 5.385 g/cm3, indicating high refractive index of this new glass. The glass transition temperature is 428 °C, and there is no obvious crystallization thermal effect before the glass melts. The thermal expansion coefficient of TeO2-Ta2O5-La2O3 (TTL) glass is 12.5 × 10−6K−1 (25–300 °C). The refractive index of glass is 2.01 and the Abbe number is 21.48. The maximum transmittance in the near infrared range is between 76.44% and 80.85%, while the theoretical transmittance is 80.08% (2700 nm). Therefore, this glass is a promising laser glass matrix material in the 2.0–2.7 μm band.