Refractive Index Research Articles

Influence of Y2O3 Concentration on the Optical Properties of Multicomponent Glasses and Glass–Ceramics

The optical properties and structural characterization of multicomponent silicate glasses of low Al2O3 and different Y2O3 concentrations have been studied. These glasses have also been crystallized to obtain glass–ceramic materials, and their properties have been characterized. The obtained glasses were transparent and their refractive indexes increased with Y2O3 concentration. After a heat treatment at 930 °C for 10 min, these glasses maintained their transparency, but a brown color appeared, and after 30 min, those glasses with high Y2O3 concentrations turned opaque or white in color. These processes of crystallization for obtaining the new glass–ceramics have been studied by means of FTIR and Raman spectroscopies, and the crystallized materials were characterized with XRD and FE-SEM techniques. These glasses and glass–ceramics have also been characterized by means of UV–vis spectroscopy, and the corresponding optical properties (reflectance, color, band-gap) have been determined as a function of the Y2O3 concentrations and the structural properties.

Retrieval of refractive index and water content for the coating materials of aged black carbon aerosol based on optical properties: a theoretical analysis

Abstract. Water content in the coatings of aged black carbon (BC) aerosol can be reflected through the complex refractive index. In this study, the retrieval of the refractive index and water content for non-absorbing coatings of BC aerosol during hygroscopic growth (RH = 0 %–95 %) based on scattering and absorption properties is theoretically investigated. Optical properties of morphologically realistic fractal BC aerosols are simulated using the multiple-sphere T-matrix method (MSTM), the optical equivalent refractive index of coating material is retrieved based on the Mie theory, and the water content in coatings is further retrieved using effective medium theory. Results show that the scattering property performs best in retrieving the refractive index and water content. The retrieval errors of the refractive index of heavily aged BC aerosols are less than 10 % at high relative humidities (RHs), while partially coated BC and thinly coated BC have larger errors. The regularity of retrieved water content is similar to that of the refractive index retrieved, and the retrieved water content errors range from 2 % to 63 % for heavily coated BC. This study provides a helpful optical method to obtain the water content of BC coatings.

Effect of Al-, In-, and Mg-doping in the ZnO on the structural, electrical, and optical properties of ZnO/CH3NH3PbI3 heterostructure

The creation of ZnO/CH3NH3PbI3 heterostructures with Aluminum (Al), Magnesium (Mg), and Indium (In) doped ZnO serving as an electron transport layer is the aim of this work. A favorable orientation for the CH3NH3PbI3 absorber layer crystallizes in the tetragonal phase [220], while ZnO crystallizes in the hexagonal phase [100]. This information is yielded by x-ray diffraction analysis. Al, In, and Mg doping of the transport layer has a significant effect on the optical characteristics like absorption and extinction coefficients, optical gaps, and optical and electrical conductivity. The UV–visible characterization of the heterostructures reveals that n-type doping can raise ZnO gap energy from 3.15 to 3.42 eV. The band gap energy of CH3NH3PbI3 is around 1.53–1.55 eV. Additionally, the absorption coefficient of each sample is high, it exceeds 105 cm−1. The ZnO thin films, both undoped and doped (with Al, In and Mg) exhibit an increase in refractive index from 1.97 to 2.13. The best dopant is found to be In. The refractive index of films composed of CH3NH3PbI3 is 3.13.

DFT assessment on the future prospects of inorganic lead-free halide double perovskites Cs2ABI6 (AB: GeZn, SnBe) for energy conversion technologies

In this study, we employed density functional theory (DFT) calculations to investigate the structural, elastic, electronic, optical, and thermoelectric properties of Cs2ABI6 (AB: GeZn, SnBe) halide double perovskites (HDPs). We employed the full-potential linear augmented plane-wave (FP-LAPW) method, incorporating the generalized gradient approximation (GGA) and Tran-Blaha modified Becke-Johnson (TB-mBJ) approach for the exchange-correlation potential. We found that the HDPs are stable in a cubic structure (space group Fm-3m), as indicated by phase stability analysis, formation energies, tolerance factor, and elastic constants. The compounds exhibits ductile behavior, as assessed by Poisson's and Pugh's ratios. The electronic band structures of Cs2GeZnI6 and Cs2SnBeI6 exhibit indirect band gaps (X-L) of 1.124 eV and 1.551 eV, respectively, as calculated using the TB-mBJ approximation. Optical spectra were evaluated over the 0–13 eV energy range, including the dielectric functions, extinction coefficient, electron energy loss, refractive index, optical conductivity, reflectivity, and absorption coefficient. Additionally, we calculated thermoelectric parameters across a range of chemical potentials and temperatures to assess their suitability for thermoelectric applications. Our results suggest that these compounds are highly promising candidates for both optoelectronic and thermoelectric devices.

Influencing factors of self-aligned imaging in near-field lithography for the Fabry–Perot cavity effect

In near-field lithography, the Fabry–Perot (F-P) cavity enhancement effect can significantly improve image quality and resolution. This paper considers changes in the refractive index and air distance in self-aligned imaging. Simulation results demonstrate that the Fabry–Perot resonator effect achieves effective self-alignment in 3D imaging. The proposed structure builds on traditional near-field imaging structures and F-P resonator research, suggesting a Cu/SiO2 structure as the front layer. Rigorous coupled wave analysis (RCWA), finite element method (FEM), and finite-difference time-domain (FDTD) methods were employed to verify the self-alignment effect on single gratings and rectangular hole arrays. The results indicate that the self-alignment lithography method based on the F-P effect not only enhances lithography contrast and normalized image log-slope (NILS) but also shows robust performance against variations in air distance and complex refractive index. Notably, for the rectangular aperture array structure, with changes in air distance and complex refractive index within a certain range, the NILS remains stable above 2.8, and the contrast stays near 0.70. These simulation results confirm that the F-P resonator-based scheme is viable for plasma imaging lithography with small critical dimensions.

Merging bound states in the continuum-driven ultrahigh sensing figure of merit in all-dielectric metasurfaces.

Radiation-free photonic bound states in the continuum (BIC) in metasurfaces allow ultrahigh quality (Q) factor and strongly confined mode volume, which are extremely advantageous in the development of ultrasensitive microcavity sensors. However, the conventional isolated BICs are susceptible to failure due to symmetry breaking caused by fabrication imperfection and nonzero incident angle. Here, we propose a silicon nitride-based metasurface with multiple BIC merging. The merging of accidental BIC and symmetry-protected BIC can increase the Q-factor near the Brillouin zone Γ point and thus robustly induces a figure of merit (FOM) of refractive index sensing at small incident angles two orders of magnitude higher than that in isolated BIC configuration. Specifically, the FOM in merging BIC reaches 108 at a 2° incident angle. The BIC merging can be universally achieved in square lattices with C4 symmetry, and slower decay of Q-factor and higher FOM can further occur in hexagonal lattices benefiting from higher-order topological charges. The advantage of merging BIC is also maintained when considering in-plane and out-of-plane symmetry breaking. These results offer a unique design path for high-performance metasurface sensors and can be extended to other high-Q applications such as low-threshold lasers, nonlinear frequency conversion, and low-loss waveguides.

Comprehensive honey analysis: A novel HPLC-DAD method for hydroxymethylfurfural quantification and quality evaluation via diastase activity and sugar profile determination

Ensuring the authenticity and quality of honey is essential to safeguarding consumer health and combating food fraud. The primary analyses for honey quality involve determining diastase activity (DA), 5-hydroxymethylfurfural (HMF), and carbohydrate composition. A new high-performance liquid chromatography coupled with diode array detection (HPLC-DAD) method was developed, for the precise quantification of HMF, a key marker of honey quality and degradation. Utilizing a Phenomenex Kinetex RP-18 column (5 µm, 150 × 4.6 mm i.d.), with a mobile phase containing water and methanol (95:5, v/v) in gradient mode, at a flow rate of 1 mL/min, and UV detection at 284 nm, the method achieved rapid and efficient separation within 10 minutes, with a low detection limit of 0.03 mg L−1, and demonstrated good linearity, precision and recovery rates. The carbohydrate composition of honey, specifically glucose, fructose, saccharose, and maltose, was analysed using a HPLC with refractive index detection (HPLC-RI) method, using a Phenomenex Luna Omega Sugar column (3 µm, 250 ×4.6 mm i.d.), with a mobile phase composed of acetonitrile and water (85:15, v/v). This analytical protocol, incorporating the quantification of maltose, a critical yet often overlooked sugar, significantly bolsters the standard evaluation framework for honey authenticity. DA, a crucial enzymatic indicator, was assessed via the Schade method, providing additional insights into the enzymatic integrity and freshness of the honey samples. The methods were applied to analyse 65 commercial Spanish honey samples, revealing significant compliance with EU regulatory standards, yet also uncovering situations of potential adulteration. This research adds to the ongoing discussions on food safety by offering improved and dependable techniques for thoroughly assessing honey samples.

Design and Optimization of Encoded and Tunable Graphene-Silver Metasurface Surface Plasmon Resonance Sensor for Detection of Low Refractive Index Variation in Terahertz Regime

Design and Optimization of Encoded and Tunable Graphene-Silver Metasurface Surface Plasmon Resonance Sensor for Detection of Low Refractive Index Variation in Terahertz Regime

Polarization-selective metamaterial absorber using tailored Y-shaped SRR for UWB device and Doppler navigation aids applications

In this paper, we present an unprecedented metamaterial absorber design exhibiting exceptional characteristics in electromagnetic wave absorption. The proposed bent Y-shaped structure, fabricated on an FR-4 substrate with copper patches, showcases remarkable performance across a diverse frequency spectrum. Through exhaustive simulations in CST, this design manifests eight distinct resonant frequencies, achieving absorption rates exceeding 90 % at each resonance. The resonances, strategically spanning from L-band (3.728 GHz) through S-band, C-band, X-band, Ku-band, and K-band up to 22.664 GHz, signify unparalleled versatility and efficacy in mitigating electromagnetic radiation. It investigates the equivalent circuit parameters of a proposed metamaterial absorber design, focusing on inductance (L), capacitance (C), and resistance (R). This paper investigates the applications of UWB devices at 3.728 GHz and Doppler navigation aids at the 13.4 GHz frequency as regulated by the Federal Communications Commission. It includes a discussion on near-zero refractive Index Metamaterials (NZRIM), highlighting their potential utilization in achieving extraordinary control over wave behaviour. Notably, the absorber's inherent polarization insensitivity fortifies its adaptability in various applications. Additionally, the metamaterial exhibits near-zero or negative permittivity, altering electric response, while simultaneously demonstrating permeability absolute zero throughout all frequency bands sparking new avenues for exploration and challenging conventional electromagnetic theories.

Hydration behavior of L-proline in the presence of mono, bis, tris-(2-hydroxyethyl) ammonium acetate protic ionic liquids: Thermophysical properties

The hydration behavior of amino acids, essential for biological macromolecules, is influenced by ammonium biomaterials. The protic ionic liquids (PILs) are gaining attention in the food and pharmaceutical industries due to their nontoxicity and adjustable properties. Thus, study of the amino acids, such as L-proline, in the presence of PILs is crucial for understanding their hydration behavior. In this work, the effect of PILs, including mono, bis, tris (2-hydroxyethyl)ammonium acetate protic ionic liquids that might be naturally produced in human body, on L-proline hydration behavior was studied using COSMO calculations and thermophysical measurements. Measurements were the density, speed of sound, viscosity, and refractive index data of the solutions (L-proline + PILs + water) at various PIL concentrations at temperatures (298.15 to 318.15) K and under atmospheric pressure. The study indicates L-proline has weaker interactions with water compared to PILs ([2-HEA][Ac], [bis-2-HEA][Ac], and [tris-2-HEA][Ac]) due to its compact structure and lower negative dielectric energy. PILs interact more strongly with water through hydrogen bonding. Increasing temperature affects L-proline’s hydration layer, releasing more water molecules compared to PIL solutions. This effect is more pronounced with [tris-2-HEA][Ac], likely due to its larger size and complex structure. While L-proline promotes an ordered water structure, PILs can disrupt this by rearranging water molecules and forming their own hydrogen bonds.

Simultaneous measurement of temperature and refractive index based on fiber optic Fabry–Pérot cavity in batteries

Abstract A Fabry-Pérot (FP) sensor for simultaneous measurement of refractive index and temperature of an all-fiber synchronous liquid based on the Vernier effect is proposed, special application for internal monitoring of lithium-ion battery electrolytes. The theoretical model of high sensitivity cascade Fabry-Pérot interferometer (PFPI) is established, the sensitivity amplification mechanism of PFPI is analyzed in detail, the perfect matching scheme for measuring the refractive index of the electrolyte inside the battery is designed according to the matching conditions of the optical path, and the corresponding sensors for simultaneous measurement of the temperature and the refractive index are fabricated. The experimental results show that the sensor has a maximum refractive index sensitivity of 15391.5033 nm/RIU, a good linear fit, and can effectively monitor the refractive index change of the electrolyte by 10-4 orders of magnitude during normal charging and discharging of lithium-ion batteries. Compared to traditional epoxy adhesive bonded or laser processed FP sensors, this all-fibre optic structure not only improves temperature and corrosion resistance, but also significantly reduces temperature cross-sensitivity. Its small size and excellent resistance to high temperature and corrosion ensure the sensor's excellent response and broad application prospects in monitoring the refractive index of the electrolyte in 18650 lithium-ion batteries, which provides effective technical support for monitoring the health status of batteries and detecting early safety issues.

Optical property discrepancies found between healthy and unhealthy skin cells using digital holographic microscopy with three wavelengths

Cancer and other health disorders can be differentiated by changes in cell optical properties such as their refractive index, thickness, and topology (height and width). Here, we employ three wavelengths simultaneously in digital holographic microscopy (3λ-DHM) to visualize the whole cell topology as 3D images through a numerical reconstruction algorithm applied to a hologram. By identifying the cell state and the changes in its optical properties, it is possible to discern between healthy and unhealthy cells. The simultaneous use of three wavelengths provides a rapid and straightforward quantitative reconstruction of the whole cell without the need for an unwrapping algorithm. This is a benefit over traditional methods, which often require complicated procedures. The performance of the approach was first validated in a known sample, a silicon dioxide thin film, where we were able to corroborate its refractive index with the values reported in the literature. Then the method was applied to fixed skin cells finding a refractive index of 1.3443 for healthy cells and 1.3246 for cells found in tumor tissue. We discuss and highlight differences based on the refractive index to demonstrate that the employed process can provide reliable information to distinguish characteristics between healthy and unhealthy cells.

A mixing rule for imaginary parts of refractive indices of aerosols or colloids in the Rayleigh regime

A Rayleigh mixing rule that relates the effective imaginary part of the refractive index of a composite medium, such as an aerosol or colloid, to the complex refractive index of the Rayleigh particles is derived using Rayleigh scattering theory. The derivation is simple, straightforward, and only weakly dependent on particle morphology. The Rayleigh mixing rule offers an opportunity to derive the imaginary part of refractive index spectra of Rayleigh particles, suspended in a non-absorbing medium with known refractive index spectrum, from an extinction spectrum of the composite medium. However, for this application, the real refractive index spectrum of the particle must be known reasonably well and the imaginary part must be known well enough to decide between two mathematical solutions for it. The Rayleigh mixing rule is compared with widely used mixing rules (i.e., volume, Maxwell Garnett, and Bruggeman mixing rules) and we show that in the small volume fraction regime both the Maxwell Garnet and Bruggeman mixing rules agree with the Rayleigh mixing rule.

Probability density functions for photon propagation in a binary (isotropic-Poisson) statistical mixture with unmatched positive and negative refractive indexes

The exact homogenized probability density function, for a photon making a step of length s has been analytically derived for a binary (isotropic-Poisson) statistical mixture with unmatched refractive indexes. The companions, exact, homogenized probability density functions for a photon to change direction (“scatter”), with polar ϑ and azimuthal φ angles, and the homogenized albedo, have also been obtained analytically. These functions also apply to negative refractive indexes and can reduce the number of Monte Carlo simulations needed for photon propagation in complex binary (isotropic-Poisson) statistical mixtures from hundreds to just one, for an equivalent homogeneous medium. Note, that this is not an approximate approach, but a mathematically equivalent and exact result. Additionally, some tutorial examples of homogenized Monte Carlo simulations are also given. Published by the American Physical Society 2024

Optimization and multiphysics analysis of high-performance lithium niobate modulators

Thin-film lithium niobate electro-optic modulators (TFLN EOMs) are widely utilized across various fields due to their exceptional performance. In this theoretical study, we optimized a TFLN EOM featuring a multimode interference coupler, cosine-curved waveguides, and a modulating arm straight waveguide structure. By tuning the etching depth, waveguide width, and geometric parameters of the traveling wave electrodes, we achieved a half-wave voltage-length product of 1.6V⋅cm and a 3 dB bandwidth of approximately 140 GHz. Additionally, we performed a multiphysics analysis to investigate the temperature characteristics of the modulator. The results indicate that increased temperature induces thermal-optic effects in the material, leading to changes in the waveguide’s refractive index and the optical beam phase, which results in increased insertion loss. Moreover, the stress generated by thermal expansion is concentrated in the modulator’s waveguide, representing a weak point that is prone to failure.

THE CHOICE OF COMPONENTS AND THE IMPACT OF SURFACTANTS AND CO-SURFACTANTS ON EPLERENONE NANOEMULSION SYNTHESIS FOR GEL-BASED TRANSDERMAL APPLICATION

Objective: This research aims to establish an efficient methodology for selecting nanoemulsion components to synthesize eplerenone nanoemulsion for gel-based transdermal applications. Methods: The chemical compatibility study of eplerenone was investigated by FTIR, DSC, and solubility in oils, surfactants, and co-surfactants as the criteria for choice. We used visual appraisal and grading to assess the effectiveness of emulsification. Various excipients were tested depending on solubility. The final appearance, dispersibility, and ease of emulsification were used to visually assess the degree of self-emulsification of oil and emulsifier in a 1:3 mass ratio. Co-surfactants were assessed by mixing particular emulsifiers in a 2:1 (w/w) ratio with co-surfactants, and the oily component was added at a 1:3 (w/w) ratio to evaluate Smix's emulsification potential. A central composite design synthesized, evaluated, and optimized eplerenone nanoemulsions. Optimized nanoemulsions were characterized after a thermodynamic stability study for droplet size, ζ potential, viscosity, refractive index, pH measurements, and TEM. All the selected formulations were found to be stable, and the droplet size was found to be<110 nm. Results: Eplerenone was chemically compatible, and its maximum solubility was 171.3±0.92 and 169.3±2.22 in Kollicream®OA and Paceol, respectively. The evidence impressively found that Tween 20 and Kolliphor®EL were discovered as active emulsifiers, and Transcutol®P was revealed to be a co-surfactant. Outcomes showed that the emulsification efficacy of Kolliphor®EL (3% w/w) was able to emulsify Kollicream®OA (1% w/w), and Paceol failed. As well, Smix [Kolliphor®EL (2% w/w) and Transcutol®P (1% w/w)] were able to emulsify Kollicream®OA (1% w/w). Conclusion: The main conclusion from this work is the application of a visual appraisal and grading system to assess the final appearance, dispersibility, and ease of emulsification to eradicate the toxicity and irritation that nanoemulsions can cause. Optimised nanoemulsions can further formulate eplerenone's nanoemulsion gel for transdermal application.

PEG600 induced krill oil-based nanoemulsion system: ternary phase behaviour and cytotoxicity assessment

BackgroundEndogenous substances of krill oil (KO) are lipophilic in nature and have clinical significance viz. DHA/EPA, phospholipids and astaxanthin. To improve the nanodispersibility of endogenous substances of KO, a self-nanoemulsifying system (SNE) was developed.ResultsTernary phase behaviour of KO was explored in ethanol (ET); propylene glycol, (PG); and PEG600 using Tween80 and Tween20 as surfactants. PEG600 induced the self-nanoemulsification of KO and yielded one phase region (OPR); dilution lines (KO/Smix fraction containing PEG600) traversed across OPR, produced a fully dilutable nanoemulsion system. PEG600-based nanoformulations (NFs) of KO underwent phase transformation via percolation behaviour in nanostructure domains (86–207 nm). PEG600 induced ternary phase behaviour of KO as revealed from rheological data (higher eta values), refractive index (nonlinear) and conductivity (bimodal) patterns. Induced phase transformation could be an interaction between aqueous phase and KO/Tween20 in PEG600 environment; generating highly viscous domains of low electrical conductivity. NFs offered antioxidant activity over corresponding coarse systems (p < 0.01) as measured using DPPH method. Optimized NFs (F4 and F6) inhibited the growth of skin cancer cell line (A431) in the range of 100–500 × dilutions.ConclusionPhase behaviour of KO was induced by PEG600, transforming the dilution pattern via generation of one phase region; however, ethanol and propylene glycol as co-solvents did not. PEG600-based NFs of KO possessed antioxidant as well as cytotoxic to skin cancer cell lines (A431).

Use of spectral transmittance model to improve the detection accuracy of chromium in soil

As a new quantitative analysis method for heavy-metal elements in soil, the main function of the polarization resolution model is to filter out the disturbance of other elements on the spectral signal of target plasma. In order to quantify the mechanism of improving detection performance, the spectral transmittance of plasma intensity in the polarization-resolved optical path has been derived, and the relationship between the intensity of polarization-resolved laser-induced breakdown spectroscopy (PRLIBS) and the characteristic peak wavelength has been defined. Using the spectral data in the wavelength range of 424.50–429.24 nm as the characteristic signal, a quantitative analysis method for detection of the Cr element in soil has been developed. The improvement of spectral intensity stability at the characteristic peak of Cr I 425.7 was analyzed, and the mechanism of enhancing the detection accuracy was elucidated. Research has shown that, based on the polarization characteristics of Cr element plasma, PRLIBS is not affected by the matrix effects of soil and characterizes the amplitude conversion from the reference concentration of Cr element to the plasma spectral intensity. The spectral transmittance of plasma spectra depends not only on the characteristic peak wavelength and complex refractive index of heavy-metal elements but also on the measurement conditions such as spatial geometric angles and reflectivity of the transmission medium.

Formation of optical resonances at the initial stage of radiation destruction of disperse medium made of a transparent dielectric by means of a powerful laser

By means of numerical simulation, we study optical resonances that arise when radiation from an ytterbium fiber laser (λ = 1065 ± 3.25 nm), a blue diode laser (λ = 450±8 nm) or a CO2 laser (10.6 μm) is scattered on a single particle of a transparent dielectric (an oxide, a fluoride, ZnSe), as well as in an ensemble of randomly packed particles of various sizes. If the particle diameter is comparable to the radiation wavelength (but is no less than 3λ/4) then, at a certain ratio between the particle diameter, the refractive index of its material and the radiation wavelength, the particle becomes a microresonator. The maximum intensity of scattered radiation inside or outside such particle depends on the combination of the above-said parameters and can exceed the intensity of the incident radiation dozens of times. In case of a powder, the interference pattern is formed by all particles at once and, occurrence of an optical resonance is more likely. Even with a slight change in the radiation wavelength of an ytterbium laser or a blue diode laser (within the lasing line width), some particles in the powder become microresonators, while others cease to be microcavities. Therefore, concentration of scattered radiation of the ytterbium laser in individual particles plays a key role at the initial stage of optical destruction of the powder. As the experiment shows, this allows to overcome the threshold of optical destruction of porous targets made of various transparent substances (CaF2, SiO2, BaF2, YbF3, Fe:MgAl2O4, Al2O3, 1mol.%Nd:Y2O3, YSZ, TiO2, ZnSe) by means of a radiation pulse from an ytterbium laser having low intensity (0.46 MW/cm2). With the refractive index of the material increasing from 1.429 (CaF2) to 2.479 (TiO2), the average delay in the formation of a laser plume decreases from 46 ms to 25 μs, i.e. by three orders of magnitude. This correlates with the fact that in the calculations, the maximum intensity of this laser's radiation scattered in the powder increases with n increasing. In compliance with this are the results of obtaining nanopowders from transparent oxides and ZnSe by means of pulse-periodic radiation of an ytterbium laser. Output of the nanopowder Yb0.05:Y1.95O3:(ZrO2)0.05 with n = 1.901 (for Y2O3) is 15 g/h, and the maximum output (100 g/h) is realized in case of ZnSe (n = 2.482). At the same time, it is not possible to obtain nanopowder from CaF2 (n = 1.429), because the moving target does not evaporate.

Fabrication of silicon microparticle dispersion as terahertz wave refractive index control material

Optical systems utilizing terahertz waves hold significant potential across various fields; however, the materials for the optical elements that constitute such systems are currently scarce and the range of refractive indices that can be handled is limited. In the visible light region, there are refractive index control materials made of nanocomposites with dispersed dielectric nanoparticles. However, few technologies for refractive index control materials exist in the terahertz wave region. In this study, we developed an Si microparticle dispersion in which Si microparticles are dispersed in a cycloolefin polymer (COP) matrix as a high refractive index material for terahertz waves. Results showed that a material with a refractive index between that of Si and COP can be designed by changing the volume fraction of the Si cube, a subwavelength structural particle, in the dispersion. A method in which Si cubes werefabricated by dicing with COP and using a mold was implemented to produce four types of Si microparticle dispersions with Si concentrations of 1 vol%, 5 vol%, 15 vol%, and 25 vol%. The effective refractive index was evaluated, and results demonstrated that in the 0.1–0.2 THz range, including the D band of the Beyond 5G/6G communication band, the effective refractive index values were according to the concentration, achieving control in the range of 1.53–1.96. Additionally, the Si cubes were uniformly dispersed in the dispersion with random orientations in three dimensions, making them an optical material with minimal polarization dependence. The proposed Si microparticle dispersion can be used as a new refractive index control material in the terahertz band.