Prism Coupling Technique Research Articles

Insights on the effect of process conditions on the optical properties of silver ion exchanged soda-lime silicate glass

The effects of ion exchange time and temperature on the optical properties and plasmonic response of silver ion exchanged soda-lime silicate glass were investigated using scanning electron microscopy (SEM) in energy dispersive spectrometry (EDS) configuration, m-lines spectroscopy, photoluminescence (PL) spectroscopy, and UV–visible absorption spectroscopy. SEM analyses in EDS mode provided profiles of silver oxide molar concentration. These profiles were directly correlated to the silver diffusion coefficient using an adjustment procedure. The effective indices of ion exchanged glasses measured by the standard prism coupling technique (m-lines) allowed access to refractive index distributions in ion exchange regions. These ion-exchanged glasses underwent evaluation to determine their potential suitability for use in multimode planar systems. The PL results acquired after ion exchange demonstrated that the creation of Ag0 atoms from Ag+ ions was responsible for the decline and quenching of PL intensity at ion exchange times and temperatures increase. Silver nanoparticles were generated in the samples subjected to ion exchange at 480 °C without the need for post-exchange treatments. The emergence of the surface plasmon resonance band around 427 nm in the optical absorption spectra confirmed the formation of Ag nanoparticles in annealed glasses. Estimates of the UV–visible absorption spectra indicated an average size of silver nanoparticles ranging from 1.8 to 2.4 nm.

Directional growth of 2-ethylimidazolium d-tartrate crystal along (001) and investigation of optical properties for optical limiting applications

A single crystal of 2-Ethylimidazolium d-Tartrate (2EIMDT) was grown along the preferred direction of (001) by the Sankaranarayanan-Ramasamy method. The growth direction was confirmed by X-ray Diffraction analysis. The optical homogeneity and the defect analysis of the grown crystal were carried out using birefringence interferometry, Williamson-Hall plot, and chemical etching. They revealed that the grown crystal possesses good optical and crystalline quality. Using the optical transmission spectrum, the optical band gap and Urbach energy were estimated to be 5.1 eV and 140 meV, respectively. The temperature dependence of the refractive index and thermo-optic coefficient were measured using the prism coupling technique for different wavelengths. The thermo-optic coefficient was found to be negative with values ∼10−5/°C. The laser damage threshold was estimated to be 6.5 GW/cm2 for a 1064 nm laser. Vickers micro-hardness study revealed that the (001) plane of the crystal is characterized by Meyer's index of 1.93. From the Z-scan measurement, it was found that the grown crystal exhibits two-photon absorption characteristics and the obtained imaginary parts of the third-order nonlinear optical (TONLO) susceptibility is 1.95 × 10−14 esu. Additionally, the onset optical limiting threshold was estimated to be 3.89 × 1012 W/m2 which indicates the potential of 2EIMDT for optical limiting applications.

Laser Induced Damage Study of Dye Doped Polystyrene Films deposited in Glass Substrate by Dip Coating Technique

In the present work, the Laser-induced Damage Morphology of Dye-doped Polystyrene films is investigated. The focus is on the Front and Rear side Damage Morphology at two different Pulse Repetition Frequencies, namely 1 pps and 20 pps. For this experiment, films were deposited on both sides of Borosilicate Glass. It was found that at 1 pps, the front side film is damaged without affecting the glass, while the modified beam propagates through the glass to damage the rear side film. Dendrimer-like microstructures are found on both the front and rear sides of the damaged spots, along with pits and craters. At 20 pps frequency, the front side film is damaged, including damage to the glass, resulting in a large crater on the front surface. The morphological features were studied using Fresnel equations. Polymeric films were fabricated using the Dip Coating Technique, and Film thickness was evaluated using the Prism Coupling technique.

Refractive index and thickness analysis of planar interfaces by prism coupling technique

Since 2022, various foundries are offering the manufacture of integrated photonic structures for the visible spectrum. As this technology continues to enter the market, there will be an increasing demand for accurate optical and dimensional characterization of these structures. To meet this demand, we have developed a highly precise optical characterization system based on the prism coupling technique, also known as m-lines spectroscopy, to investigate the optical properties of hydrogenated amorphous silicon nitride planar waveguides deposited by plasma-enhanced chemical vapor deposition. In this work, by combining visible spectroscopy with the prism coupling technique to excite modes that propagate resonantly in the waveguide via frustrated total internal reflection, using either parallel or perpendicularly polarized light beams, we were able to analyze the waveguide properties of silicon nitride thin films with an interfacial oxide layer. Furthermore, through numerical simulation of the bilayer structure, we calculate the waveguide’s refractive index and thickness, and determine the characteristics of the interfaces in terms of refractive index and thickness.

Characterization of optical waveguides in Ce3+-doped phosphate glasses formed by He+ion implantation

In this work, the Ce3+-doped phosphate glass is carried out to fabricate the planar waveguides by the 400 keV He+ ion implantation with a dose of 6.0 × 1016 ions cm−2. The dark-mode spectrum of the waveguide at a wavelength of 632.8 nm is obtained by the prism coupling technique. The SRIM 2013 software is used to analyze the energy deposition induced by the ion implantation and the RCM is employed to reconstruct the refractive index profile of the planar waveguide. The end-face coupling technique is applied to the measurement of the propagation mode image of the waveguide at 632.8 nm. The Ce3+-doped phosphate glass waveguide has the potential for an integrated optical device.

Effects of optic axis rotation on the sensing properties of nematic liquid crystal based surface plasmon resonance (SPR) sensor

The effect of different orientations of the optic axis (OA) in the liquid crystal (LC) UCF-1 in two dimensions on the surface plasmon (SP) mode excited along the surface intermediate between a thin silver film and the LC at different temperatures is theoretically studied using the prism coupling technique and a TM-polarized, monochromatic laser with λ = 5890 Å. The shifts in the surface plasmon resonance (SPR) dip angle at different temperatures for varying alignments of the OA in a plane are determined. Changes in the SPR resonance angles with temperature are found to be significant and linear in a major part of the entire anisotropic phase of UCF-1 for the homeotropic orientation. A linear fit is obtained for the variation of SPR angle of resonance with the molecular order parameter over the entire anisotropic range of UCF-1. The effect of deviations of the OA of the LC from the homeotropic orientation in two dimensions on the temperature sensitivity of the SPR angle of resonance in the linear response temperature range is studied, and its influence on the accuracy of measurement by SPR corresponding to a fixed value of the molecular order parameter is investigated.

Application of third-order nonlinear optical materials in complex crystalline chemical reactions of borates

Abstract In order to explore the application of third-order nonlinear optical (NLO) materials in complex borate crystalline chemical reactions, the laser light source with limited wavelength range can be extended to ultraviolet (UV) and deep UV region by using NLO crystal materials and frequency conversion technology, which has become a hot research direction of deep UV light source. The experimental results show that the UV cutoff edge of the grown KLi(HC3N3O3)·2H2O crystal is 237 nm. The refractive index of the crystal was measured by prism coupling technique, and the Sellmeier equation of the refractive index of the crystal was fitted. The chemical bond of the crystal is a fundamental means to understand the relationship between structure and properties. With the emergence of a large number of hybrid functional crystals, the composition and structure of crystals become more complex, and the chemical bond theory has also been greatly developed, and then the chemical bond theory of meta crystals or complex crystals has emerged. Once proposed, the theory has been widely used, such as analyzing the eligibility of luminescent crystals, NLO crystals and high-temperature superconductor crystals. NLO materials are the dominant field of China in the world. Crystals with good nonlinear behavior have more complex crystal structures, due to the theory of amorphous structure, the exploration of this aspect is particularly difficult. For the first time, the influence of the composition of rare earth-doped bismuth borate glass on the crystal precipitation and glass microstructure of NLO materials was systematically studied, which laid a theoretical foundation for further development and understanding of new bismuth borate optical systems.

Scalable optical-to-terahertz converter with a prism-coupled plane-parallel lithium niobate plate.

A nonlinear optical converter of femtosecond laser pulses to terahertz radiation, which combines the tilted-pulse-front pumping and prism coupling techniques, is proposed and experimentally tested. In contrast to the conventional tilted-pulse-front scheme with a prism-shaped LiNbO3 crystal, the converter consists of a plane-parallel LiNbO3 plate sandwiched between two dielectric prisms. One prism is used to couple the pump beam into the LiNbO3 plate, another prism couples the generated terahertz radiation out of the plate. The proposed scheme enables scaling to large-diameter LiNbO3 wafers and large-aperture high-energy pump laser beams resulting in generation of strong terahertz fields. In a proof-of-principle experiment with a 1-mm thick, small size (1 × 2 cm2) LiNbO3 plate pumped by a mJ-class laser, the conversion efficiency comparable to that of the conventional scheme (∼0.1%) was demonstrated.

Optical and thermo-optical properties of polyvinyl alcohol/carbon nanotubes composites investigated by prism coupling technique

In this paper, optically tunable polyvinyl alcohol (PVA) nanocomposite films containing carboxyl functionalized multi-walled carbon nanotubes (COOH-MWCNT) were developed using the solution casting method. The compositional dependence on morphological, structural, optical, and thermo-optical properties of these nanocomposites was studied using scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and prism coupling measurements. It was be found that a small loading with MWCNT affects the molecular mobility of PVA/MWCNT nanocomposites and results in prominent modifications of their optical and thermo-optical properties. The incorporation of 0.1 wt% harms improving PVA's refractive characteristics, whereas with nanotubes content in the range of 0.1–1 wt%, the refractive index increases. The refractive indices were measured at different wavelengths (from 404 to 1548 nm) and the dispersion coefficients were calculated. The temperature dependence of the refractive index of PVA nanocomposites in the temperature range from 30 °C to 110 °C was also explored and the thermo-optic coefficients were determined. The measured thermo-optic coefficients (dn/dT) were found to be negative below the glass transition temperature and on the order of 10−4/°C. Furthermore, dn/dT decreases with the thermal expansion coefficient and increases with the MWCNT weight fraction. The promising results suggest an enormous potential of PVA/MWCNT composites for use in tunable optical devices.

Electronic energy loss and ion velocity correlation effects in track production in swift-ion-irradiated LiNbO3: A quantitative assessment between structural damage morphology and energy deposition

• Essential factors including electronic energy loss and ion velocity co-affect latent track damage. • Damage morphologies from spherical defects to discontinuous and continuous tracks are confirmed. • Atomic energy deposition and temperature evolution are determined by inelastic thermal spike model. • A quantitative relationship between ion irradiation condition and track damage response is proposed. • The work provides a deeper insight for understanding ion-solid interactions and damage behaviors. The primary motivation for studying how irradiation modifies the structures and properties of solid materials involves the understanding of undesirable phenomena, including irradiation-induced degradation of components in nuclear reactors and space exploration, and beneficial applications, including material performance tailoring through ion beam modification and defect engineering. In this work, the formation mechanism of latent tracks with different damage morphologies in LiNbO 3 crystals under 0.09–6.17 MeV/u ion irradiation with an electronic energy loss from 2.6–13.2 keV/nm is analyzed by experimental characterizations and numerical calculations. Irradiation-induced damage is preliminarily evaluated via the prism coupling technique to analyze the correlation between the dark-mode spectra and energy loss profiles of irradiated regions. Under the irradiation conditions of different ion velocities and electronic energy losses, different damage morphologies, from individual spherical defects to discontinuous and continuous tracks, are experimentally characterized. During ion penetration process, the ion velocity determines the spatiotemporal distribution of deposited irradiation energy induced by electronic energy loss, meaning that the two essential factors including electronic energy loss and ion velocity co-affect the track damage. The inelastic thermal spike model is used to numerically calculate the spatiotemporal evolutions of energy deposition and the corresponding atomic temperature under different irradiation conditions, and a quantitative relationship is proposed by comparison with corresponding experimentally observed track damage morphologies. The obtained quantitative relationship between irradiation conditions and track damage provides deep insight and guidance for understanding the damage behavior of crystal materials in extreme radiation environments and selecting irradiation parameters, including ion species and energies, for ion beam technique application in atomic-level defect manipulation, material modification, and micro/nanofabrication.

Highly sensitive plasmonic nanorod hyperbolic metamaterial biosensor

Plasmonic sensing based on nanostructures is a powerful analytical tool for ultrasensitive label-free biomolecule detection that holds great potential in the field of clinical diagnostics and biomedical research. Here, we report the fabrication, the characterization, and the principle of operation of gold nanorod hyperbolic metamaterials (NHMMs) along with ultrasensitive bulk refractive index and label-free biomolecular detection. By combining electron-beam lithography and nanoscale electroplating, we demonstrate the fabrication of a highly ordered, height-controllable, and vertical array of nanorods. By exciting the bulk plasmon–polariton mode in the NHMM using a prism-coupling technique and integrating the sensor in microfluidics, we demonstrate that the bulk sensitivity and figure of merit of our device could reach 41,600 nm/RIU and 416 RIU-1, respectively. The physical mechanism of this high bulk sensitivity is revealed through theoretical and experimental studies. Moreover, by bio-functionalizing the surface of the NHMM sensor, monitoring the binding of streptavidin at dilute concentrations is performed in real time. We test different concentrations of streptavidin ranging from 200 to 5 µg/mL, and the NHMM biosensor exhibits a 1 nm wavelength shift for a 5 µg/mL streptavidin detection. By fitting the Hill equation of the NHMM biosensor and taking into account the level of noise (0.05 nm) as the minimum wavelength shift of the detectable limit, the limit of detection of the NHMM biosensor to streptavidin can be estimated to be 0.14 µg/mL (2.4 nm). As a direct comparison, a 0.5 nm wavelength shift for 20 µg/mL of streptavidin is reported when using a conventional gold film sensor under identical experimental conditions. The developed plasmonic NHMM sensor shows tremendous potential for highly sensitive bulk solutions and biomolecule detection and provides a promising avenue for free-label biosensing applications in the future.

Using High-k VPP Modes in Grating-Coupled Graphene-Based Hyperbolic Metamaterial for Tunable Sensor Design

Volume plasmon polariton (VPP), a high- k mode that arises due to the coupling between two even modes of adjacent layers of an hyperbolic metamaterial (HMM) configuration, is very difficult to be excited by using prism coupling technique due to huge wave-vector mismatch. In this work, we present a graphene-based HMM structure integrated with metal grating to facilitate excitation of VPP modes. A graphene HMM is composed of multilayer graphene super-lattice similar to metal-dielectric super-lattice structure. We report the analytical formulation of the dispersion relation and numerical analysis of the characteristics of the excited VPP modes for the proposed structure in Terahertz frequency region. The best achieved imaging resolution (spatial) of our proposed structure is 15 nm when used as an infra-red imaging platform. As a sensing platform, a maximum sensitivity of 11,050 nm/RIU is achieved for this configuration. The tunability of the resonance wavelength with respect to the structural parameters of the device is also studied and confirmed. Such promising findings are expected to make the proposed structure with integrated excitation coupler a potential candidate for tunable sensor design for different nanophotonic applications, including imaging, and, biomedical and chemical sensing applications.

Bulk crystal growth, crystalline perfection and optical homogeneities of 2AP4N single crystals for second and third order frequency conversion and terahertz (THz) device applications

Bulk size organic 2AP4N single crystals were grown by a point seed rotation technique using methanol solvent. The lattice dimensions of the grown crystal and their various crystalline planes have been analyzed by XRD measurement and also the lattice strain was calculated. The lattice perfection was examined by HRXRD and found to be extremely good. The optical transparency and cut-off value of the grown crystal were analyzed by the UV–Vis NIR measurement. The crystalline homogeneity has been confirmed by the birefringence and Mach-Zehnder interferometry techniques. The SHG measurement has been carried out with different particles. The refractive indices of grown crystal have been measured in different wavelengths by prism coupling technique and the Sellmeier's co-efficient has been calculated. The Type-I and Type-II phase-matching angles were determined and the crystal was cut along the phase-matching angles. The third order nonlinear optical parameters were analyzed by Z-scan technique. In addition, the crystal shows potential to generate pulsed Terahertz (THz) radiation by optical rectification using 800 nm wavelength at 140 fs, obtained from Ti: Sapphire Laser. The generated THz spectrum is extended up to 3.0 THz. The maximum conversion efficiency of the generated signal is of the order of 0.64 × 10 −5 %. •Optically high quality with bulk size single crystal was grown by seed rotation technique •The grown crystal has high optical homogeneities and crystalline perfection •SHG efficiency is 4.5 times that of KDP material •Type-I and Type-II phase matching elements have been made •Third-order nonlinear susceptibility ‘ χ (3) ’ is 8.68 × 10 −8 esu. •The maximum conversion efficiency of the generated THz signal is 0.64 × 10 −5 %.

Temperature dependent refractive index, thermo-optic coefficient and birefringence of negative biaxial imidazolium l-tartrate non-linear optical crystal

Imidazolium L-tartrate (IMLT) single crystal has been grown by slow cooling seed rotation technique. The temperature dependent refractive index (RI) has been measured along the principal axes in the temperature range 30–125 °C. The prism coupling technique has been used to determine the refractive index with accuracy ~ 5 × 10−4. The transmission spectra depict good transparency in the range 340–1350 nm. The principal axes directions have been identified using polarized light microscopy. Principal directions have been found rotated by 44° in the orthogonal xz-plane with respect to the crystallographic x-axis. The generalized temperature dependent equations for the Sellmeier’s and thermo-optic (dn/dT) coefficients have been determined. The thermo-optic coefficients (TOC) in the above-specified range have been found to be negative and are ~10−5/°C. An important set of empirical relations between TOC and wavelength (407–1551 nm) has also been established which is useful for estimating TOC in the temperature range of 30–125 °C. Based on the birefringent measurement it has been confirmed that the IMLT crystal is a negative biaxial crystal.

Prism coupling technique investigation of optical and thermo-optical properties of polyvinyl alcohol and polyvinyl alcohol/silica nanocomposite films

In this paper, the optical and thermo-optical properties of polyvinyl alcohol (PVA) and polyvinyl alcohol/silica (PVA/SiO 2) nanocomposite films were characterized by using the prism coupler technique. The polymer films were deposited by solution casting method at room temperature. The refractive indices of TE polarization mode, nTE, of all samples were measured at 444 nm, 633 nm, 829 nm, and 1308 nm, respectively. The wavelength dependence of the refractive index is well described by Cauchy’s equation. The effect of polymer molecular weights and the concentration of silica nanoparticles on the optical properties of PVA films was also investigated and discussed. The refractive index of the PVA films was found to increase with molecular weight, whereas it decreases with the concentration of SiO 2 in PVA matrix. The variation of the refractive index of neat PVA and PVA/SiO 2 nanocomposite films with temperature in the range of 30 to 70 °C was determined. Both PVA and PVA/SiO 2 nanocomposites show negative thermo-optic coefficients (dn∕dT) of the order of 10−4 °C−1. Moreover, it was found that the addition of silica in the PVA affect thermo-optic coefficients of the films. The obtained results suggest that PVA is a material with tunable refractive indices and it is suitable for use in optical devices such as optical temperature sensors.

The effect of gamma-ray irradiation on bulk optical plastic materials

We present our study of the effect of gamma-ray irradiation on bulk optical plastic materials as follows: three types of sheets commonly used for eyeglass lenses (CR-39, MR-8 and Trivex), cyclo olefin polymer ZEONEX E48R, styrene methyl methacrylate NAS21, polymethyl methacrylate PLEXIGLAS®7N, polyphenylsulfone EUROPLEX® PPSU, and poly(n-methyl methacrylimide PLEXIMID®8813. We used the panoramic gamma-radiation facility with 60Co source with applied doses 14.6 kGy and 54.2 kGy. For the thought properties, we measured the transmission spectra from 200 to 1800 nm and refractive indices using the prism coupling technique at six wavelengths 532.0, 654.2, 846.4, 1308.2, 1549.1, and 1652.1 nm. We also studied the possibility of using several approximation methods for evaluating the refractive indices including Cauchy, Cauchy–Schott, Herzberger, Sellmeier, Sellmeier-2, and Sellmeier with an infrared correction. The measurements showed that the most precise determination model of the refractive indices was obtained by the Sellmeier approximation with an infrared correction. The transmission spectra measurement showed that the CR-39 and EUROPLEX® PPSU polymers did not change significantly after the irradiation and the refractive indices measurement showed that ZEONEX E48R and EUROPLEX® PPSU did not change the refractive indices values.

Fast-response halogenated 4-alkyl-4′′-cyano-p-terphenyls as dual frequency addressing nematics

Twenty-two compounds belonging to halogenated 4-alkyl-4′′-cyano-p-terphenyls have been synthesized and mesomorphic properties using polarizing optical microscope and differential scanning calorimetry have been determined. The birefringence of the compounds using prism coupling technique was determinated. The multicomponent eutectic mixture consisted of synthesised compounds was prepared and investigated. The prepared mixture exhibits very broad nematic phase range, over 140 °C, with the melting point below 0 °C. Dielectric studies revealed that prepared mixture is very useful for dual frequency adressing system, because it posses large positive dielectric anisotropy (above 22) and becomes negative above the relatively low cross-over frequency (14 kHz). The total response time of the prepared mixture measured at room temperature at low operating voltage (24 V) is short (6.5 ms) which is suitable for fast switching optical applications.

Experimental evidence for preservation of electro-optic property in titanium-diffused lithium niobate waveguide

Abstract Electro-optic (EO) property of titanium-diffused LiNbO3 optical waveguide was studied using prism coupling technique. The EO-effect-induced increment ΔN of effective refractive index (at the wavelength 1311 nm) was measured as a function of externally applied electric field E for TM0 and TM1 modes guided in the titanium-diffused LiNbO3 planar waveguide. By using the linearity between ΔN and E, the EO coefficient r33 is determined. For reference, the measurement was also performed on a bulk material of congruent LiNbO3, yielding r33 = 24.9 ± 0.8 p.m./V, which is in qualitative agreement with that obtained by extrapolating previously reported result to the 1311 nm wavelength, ~24 p.m./V, confirming the feasibility of the measurement method. Measurements on the titanium-diffused planar waveguide give r33 = 25.7 ± 0.6 p.m./V for the TM0 mode and 25.7 ± 0.4 p.m./V for the TM1 mode. Both values can be considered as identical within the error, and are the same as that of the bulk material, indicating that the EO property is well preserved in the titanium-diffused LiNbO3 waveguide. The main reason is that the LiNbO3 crystalline phase is well preserved in the titanium-diffused waveguide layer.

Modal Characterization of Planar Waveguide Formed by Ag+/Na+ Ion Exchange in Soda Lime Glass

Modal characterization carried out reported in this paper was aimed determining the refractive index and thickness profile of Ag+/Na+ Ion Exchanged planar waveguides formed in Soda Lime Glass. Modal characterization was carried out using prism coupling technique and applied to all waveguides fabricated at temperature of 240 °C, 260 °C and 280 °C and processed for different duration. It was shown that the number of modes tends to increase with the increase of both temperature and duration of ion exchange process.

Fluorophosphate Glasses with High Terbium Content for Magneto-optical Applications

Fluorophosphate glasses are investigated following the composition law (1 – x)(70NaPO3 – 30BaF2) – xTbF3 with x = 35, 40, 45, and 50 mol %. Bubble-free vitreous rods of 5 cm length and 4 mm in diameter are obtained without crystallization from 35 to 50 mol % of TbF3 by using the conventional melt-quenching process. The maximum content of Tb3+ ions successfully dissolved in these glasses corresponds to an ionic density of 8.88 × 1021 ions cm–3, which is the highest value ever reported in a fluorophosphate glass matrix, to our knowledge. Thermal, structural, and optical properties were characterized respectively by DSC, Raman spectroscopy, prism coupling technique, UV–visible-NIR, and Verdet constant measurement. The increase of the terbium content from 35 to 50 mol % in the glass results in an increase of its glass transition temperature (Tg) from 352 to 390 °C, a decrease of its thermal stability against crystallization (ΔT) from 153 to 73 °C, and an increase of both its refractive index and Verdet consta...