Temperature Coefficient Of Refractive Index Research Articles

Effect of introducing KNO3 on the preparation of athermal fluorophosphate glass and investigation on its thermo-optical property

The effects of introducing some amount of KNO3 into the raw materials on preparation of fluorophosphate glass are investigated in terms of UV–vis transmittance, absorption coefficient and change of refractive index. As the content of KNO3 reaches 50%, the UV absorption coefficient of the optimized fluorophosphate glass reaches the minimum due to absence of microcrystals in the produced glass. The Schott's Sellmeier dispersion formula and Ghosh's two-polar wavelength-dependent Sellmeier equation were both used to calculate dispersion constants of the optimized fluorophosphate glass. The optimized fluorophosphate glass maintains special characteristics of negative temperature coefficient of refractive index and near-zero thermo-optical coefficient. The lower absorption both in UV and near-infrared (NIR) helps to improve its laser-induced damage resistance. The athermal fluorophosphate glass shows great potential for compensation of thermal-induced distortion in high-power solid-state lasers and high-resolution optical systems.

Temperature Sensing in Space and Transparent Media: Advancements in Off-Axis Digital Holography and the Temperature Coefficient of Refractive Index

An off-axis digital holographic interferometry technique integrated with a Mach–Zehnder interferometer based setup is demonstrated for measuring the temperature and temperature profile of a transparent medium. This technique offers several advantages: it does not require precise optomechanical adjustments or accurate definition of the frequency carrier mask, making it simple and cost-effective. Additionally, high-quality optics are not necessary. The methodology relies on measuring the phase difference between two digitally reconstructed complex wave fields and utilizing the temperature coefficient of the refractive index. In this way, we presented an equation of the temperature as a function of phase changes and the temperature coefficient of refractive index. This approach simplifies the calculation process and avoids the burden of complicated mathematical inversions, such as the inverse Abel transformation. It also eliminates the need for additional work with the Lorentz–Lorentz equation and Gladstone–Dale relation and can be extend for 3D measurements.

Refractive index and temperature coefficient of refractive index of Al2O3- and SiO2-water nanofluids

• Measurements are made of the refractive index and temperature coefficient of refractive index (∂n/∂T) for two nanofluids, Al 2 O 3 -water and SiO 2 -water. • For both nanofluids, the refractive index decreases with increasing temperature and increases with increasing particle concentration. • The variation of refractive index is approximately linear with concentration. • ∂n/∂T for Al 2 O 3 -water nanofluids can be approximated as that of water with an accuracy better than ±5% for a concentration φ < 1%. • For SiO2-water nanofluid, ∂n/∂T can be approximated as that of water with an accuracy of better than ±5% for a concentration φ < 4%. Measurements are made of the refractive index and temperature coefficient of refractive index (∂n/∂T) for two nanofluids, Al 2 O 3 -water and SiO 2 -water, over the temperature range 20–40°C at a wavelength of 632.8 nm. These optical properties are needed for refractive index-based temperature and heat transfer measurements, particularly laser interferometry. A laser beam deflection technique is used to measure the refractive index of the nanofluids. The temperature coefficient of refractive index is determined by measuring the phase change with temperature, using Mach-Zehnder interferometry. Measurements are made for Al 2 O 3 -water nanofluids up to a weight-based concentration of ϕ = 20% and for SiO 2 -water nanofluids up to a weight-based concentration of ϕ = 40%. The refractive index data are used to quantify the errors in interferometric temperature measurements produced by non-homogenous nanofluid suspensions. In the literature, the optical properties of dilute water-based nanofluids are sometimes assumed to be equal to those of water for interferometry experiments. The limits of this approximation are estimated. The current measurements indicate that ∂n/∂T for Al 2 O 3 -water nanofluids can be approximated as that of water with an accuracy better than ±5% for a concentration ϕ < 1%. For SiO 2 -water nanofluid, ∂n/∂T can be approximated as that of water with an accuracy of better than ±5% for a concentration ϕ < 4%.

Temperature Dependence of the Refractive Index of Vitreous Alloys of the Ag-As-S System

The temperature coefficient of refractive index dn/dT is determined for glassy allous of the system along the(Ag2S)x(As2S3)100-x, direction (0 &lt; x &lt;20) in the spectral interval of 1–5 μm at temperature of 77– 400 K theglasses in question are shown to take negative values of dn/dT depending on the composition and wavelength.The dependence of the coefficient on spectrum and temperature is studied using a single oscillator model.

Temperature dependent optical constants for SiO2 film on Si substrate by ellipsometry

In situ ellipsometry measurements in the spectra range from 246 to 1000 nm were performed on a SiO2/Si system at temperatures varying from 25 to 600 °C. By using Cauchy dispersion model to describe SiO2 layer and B-spline to parameterize Si substrate, the temperature dependent optical constants of SiO2 film and Si substrate were precisely determined and analyzed which is helpful to understand the temperature effect of substrate for ellipsometry measurement. The temperature coefficient of refractive index of SiO2 at elevated temperature was obtained by ellipsometry. The results indicate that the temperature coefficient increases with increasing wavelength and decreasing temperature.

基于1stOpt求解光学玻璃折射率温度系数经验公式常量的方法

基于1stOpt求解光学玻璃折射率温度系数经验公式常量的方法

Frequency analysis of temperature-dependent interferometric signal for the measurement of the temperature coefficient of refractive index.

A method of frequency analysis for the measurement of the temperature coefficient of refractive index (dn/dT) using a Fabry-Perot interferometer was developed and tested against ethanol and water. The temperature-dependent interferometric signal described by Airy's formula was analyzed in both the temperature and frequency domains. By fast Fourier transform, a low-pass filter was designed and employed to eliminate the noise superimposed on the signal. dn/dT was determined accurately from the noise-removed signal by peak analysis. Furthermore, the signal frequency parameters may be utilized for the material thermophysical property characterization. This method lays the foundation for an online dn/dT instrument for monitoring chemical processes.

Thermal refraction defocusing in very-large-core step-index antiguided fiber lasers

Thermal refraction defocusing in very-large-core step-index antiguided fibers is investigated theoretically. Recent analytical methods based on a zero-field approximation for studying the effects of thermal focusing are extended and applied to the defocusing effects that occur in laser media with negative temperature coefficient of refractive index. Intermediate values of thermal defocusing tend to flatten the radial intensity distribution, while strong thermal defocusing is shown to concentrate the intensity near the antiguiding core&#x2013;cladding boundary. The same analysis is also applicable for very-large-core graded-index fibers with a divergent parabolic index profile.

Investigation on thermal properties of a new Nd-doped phosphate glass

Thermal properties of a new Nd-doped phosphate glass were investigated. The thermal expansion coefficient was measured by a dilatometric technique. A Mach–Zehnder interferometer was used to measure the temperature coefficient of refractive index (dn/dT) and the thermo-optic coefficient (ds/dT) in the temperature range of 30–100°C. A low thermal expansion coefficient was observed for the new phosphate glass. The dispersion of the thermo-optic parameters was calculated from an empirical equation. The thermo-optic coefficient (ds/dT) at the working wavelength of 1053nm is lower than those of other high average power glasses. These results indicate that the new Nd-doped phosphate glass is a good candidate for high average power laser applications.

Spectroscopic and photothermal characterization of annatto: Applications in functional foods

Dyes are among the most common additives used primarily to intensify, compensate or add color to manufactured products. The major color detected in annatto seeds comes from carotenoids bixin (C25H30O4) and norbixin (C24H28O4), depending on the extraction method. This article presents absorption and fluorescence spectroscopic characterizations of annatto extracted in aqueous solutions from seeds of the tropical shrub Bixa orellana L. Extractions from seeds were performed using aqueous solution (at 98 °C) with different potential of hydrogen values (pH 6.5–11.2), and the results were compared to those obtained with chemical extraction methods using other solvents. Thermo-optical parameters, such as refractive index temperature coefficient (dn/dT), thermal diffusivity (D), fraction thermal load (φ) and quantum yield (η) were determined for annatto solutions. Finally, the effectiveness of using of different concentrations of annatto dye in bread preparation is investigated as a functional food possibility.

Highly accurate interferometric evaluation of thermal expansion and dn/dT of optical materials

Thermo-mechanical and -optical properties of Y3Al5O12 (YAG), YVO4, and GdVO4 were evaluated with less than 2% of evaluation error. Measured thermal expansion coefficient for YAG, [100]-YVO4, [001]-YVO4, [001]-GdVO4, and [001]-GdVO4 were 6.13, 1.76, 8.24, 1.19, and 7.26 × 10−6/K at room temperature. Temperature coefficients of refractive index for YAG, YVO4 in ordinary and extraordinary polarization, and GdVO4 in ordinary and extraordinary polarization at room temperature for the wavelength of 1.06 μm were 12.1, 15.5, 8.41, 15.2, and 9.92 × 10−6/K, respectively.

Simulation of Thermal-Optical Effects on a PMMA Fresnel Lens Used in Solar Concentrators

This study presents an integrated opto-mechanical analysis of a PMMA Fresnel lens used in solar concentrators for concentrated photovoltaic systems. The temperature dependence of refractive index of the PMMA lens was analyzed based on its temperature coefficient of refractive index dn/dT. In addition, the thermal distortion of the Fresnel lens under various temperature rises was computed by finite element analysis (FEA). Then, the temperature induced effects, variation of refractive index and the deformed lens geometry, were imported into ray tracing simulation simultaneously. Finally, the thermal-optical effects on the optical performance of a flat Fresnel lens were successfully investigated and discussed, including the maximum irradiances on the receiver and the optical efficiencies under different temperature rises.

An incoherent light source excited thermal lens microscope

We report a thermal lens microscope (TLM) based on an incoherent light source (ILS) excitation. By introducing a three-layer system into an optimized ILS-excited TLM, the sensitivity can be amplified up to 10 times for a 100-μm aqueous sample. The sensitivity enhancement originates from two additional thermal lenses formed by the heat transferred from the sample to the top and bottom layers with high temperature coefficient of refractive index. It is predicted that with a power of about 10 mW used for exciting a 100-μm sample, the limit of detection of the ILS-excited TLM can go down to 5.5 × 10−6 AU.

Self-Induced Phase Modulation for Thermo-Optical Characterization of Annatto Extracted Using Different Solvents

Thermo-optical parameters, including the refractive index temperature coefficient (d n/d T) and the absolute non-radiative quantum efficiency (φ), were determined in solutions of a natural dye using a method based on thermally driven self-phase modulation (SPM) effects. The ring-pattern response to SPM effects was determined for annatto extracts obtained from the seeds of the tropical shrub Bixa orellana L. This approach determined the linear behavior of the ring numbers ( N) observed in the far-field region as a function of excitation laser power ( Pe). Thermooptical characterizations of bixin (C25H30O4) solutions extracted using three solvents (toluene, chloroform, and acetone) were performed. The φ results are in good experimental agreement with those obtained using the thermal lens (TL) technique. Values obtained for thermal diffusivity parameters were typical for pure solvents.

Temperature dependence of refractive characteristics of optical plastics

In this study we investigate the variation of refractive characteristics of optical plastics with temperature in the range of 10 to 50 oC. We have measured the indices of several optical polymers as Optorez 1330, Zeonex E48R, Polymethyl methacrylate, S-low styrene and Bayer by means of the deviation angle method. The obtained refractive index data is presented at five standard spectral lines in the visible region. A decrease of refractive index values with increasing temperature is observed. Dependence on measuring wavelength is also noticed. We have calculated the temperature coefficients of refractive indices of the studied optical plastics. Charts of refractive index of some of the materials versus temperature are presented. Temperature dependence of dispersion curves based on Cauchy-Schott's approximation and Abbe numbers is also considered.

High-Temperature Sensing Using Miniaturized Fiber In-Line Mach–Zehnder Interferometer

A miniaturized single fiber in-line Mach-Zehnder interferometer is proposed for high-temperature sensing. The interferometer has a microcavity in one of its arms, formed by removing part of the fiber core and cladding, while the other arm remains in the fiber core. Because the fiber core exhibits a temperature coefficient of refractive index which is different from that of air, the interferometer is sensitive to temperature variation. The microcavity structured interferometer also has excellent sustainability to high temperatures up to 1100°C . The system is compact, reliable and can detect the temperature at precise location.

Effect of hydroxyl impurity on temperature coefficient of refractive index of synthetic silica glasses

We have studied the temperature coefficient of the refractive index of synthetic silica glasses with various hydroxyl impurities. The refractive index was measured at 15 °C and 35 °C at 1.707–0.238 μm wavelengths. The temperature coefficient of a low-OH group (110 wt. ppm) containing glass increased from 8.0 ± 0.2 × 10 −6/°C (at 1.707 μm) to 14.0 ± 0.2 × 10 −6/°C (at 0.238 μm), although it increased respectively from 7.0 ± 0.2/°C to 12.0 ± 0.2 × 10 −6/°C for a high-OH group (1300 wt. ppm) containing glass. The three-term Sellmeier equation, having two terms with resonance photon energies in the vacuum ultraviolet region and one term in the infrared region, was used to analyze the wavelength dispersion of the refractive index. Increasing temperatures shifted the resonance energy in the second term by −4.14 ± 0.4 × 10 −4 eV/°C for low-OH (110 wt. ppm) glass and −2.64 ± 0.4 × 10 −4 eV/°C for high-OH (1300 wt. ppm) glass. The fundamental absorption edge in the vacuum ultraviolet region shifted by −8.8 ± 0.7 × 10 −4 eV/°C for the low-OH glass and −6.3 ± 0.7 × 10 −4 eV/°C for the high-OH glass in a region of 25–100 °C. Both high-OH glass shift rates were lower than low-OH glass shift rates. The lower temperature coefficient for the Si–OH-related band probably explains the smaller temperature coefficient for high-OH glass: the absorption band of Si–O–H structure is located at lower energy side close to the fundamental absorption band associated with the Si–O–Si structure.

A high-power 975 nm tilted cavity laser with a 0.13 nm K−1 thermal shift of the lasing wavelength

We address design and performance issues of a 975 nm range tilted cavity laser (TCL) based on GaAs/GaAlAs waveguide and GaInAs quantum wells as an active medium. The all-epitaxial design of a TCL includes a cavity and a multilayer interference reflector (MIR). The cavity and the MIR are constructed as follows. The cavity confines one tilted optical mode, and the wavelength of this mode as a function of the tilt angle follows a first dispersion curve. The reflectivity spectrum of the MIR for tilted incidence of light has a well-pronounced stopband, and the stopband reflectivity maximum follows a second dispersion curve. The two dispersion curves intersect at one optimum tilt angle and one optimum wavelength λ0. At the wavelength λ0 the leakage loss of the optical mode through the MIR to the substrate has a minimum, which favors lasing at this optimum wavelength. The thermal shift of λ0 is governed by the shift of the intersection point. As the photon energy corresponding to the operation wavelength of the laser 975 nm is close to the resonance with the electronic energy gap in GaAs, the refractive index temperature coefficient dn/dT of GaAlAs strongly increases at the GaAs side. This gives a tool to control the thermal shift of λ0 by replacing some layers of the cavity by a superlattice containing narrow insertions of GaAs. Such a superlattice may have the same averaged refractive index at room temperature, but significantly different values of dn/dT, thus affecting the thermal shift of λ0. Within this approach broad-area (100 µm) devices have been fabricated showing a high temperature stability of the lasing wavelength (0.13 nm K−1), low threshold current density (300 A cm−2), a high power operation (>7 W in pulsed mode and >1.5 W in continuous wave mode), a high spectral stability at high output power, and a narrow vertical far-field beam divergence (FWHM ∼ 20°).

Reduced Temperature Dependence of Lasing Wavelength in Membrane Buried Heterostructure DFB Lasers With Polymer Cladding Layers

An athermal operation of the lasing wavelength in a membrane buried heterostructure distributed feedback (BH-DFB) laser was demonstrated by adopting a polymer (benzocyclobutene) cladding layer which has a negative temperature coefficient of refractive index. Membrane BH-DFB lasers of core thickness 65 nm were operated under room-temperature continuous-wave conditions. The temperature dependence of the lasing wavelength was measured to be 2.45times10-2 nm/degC, which is about 20%-30% of that for conventional semiconductor lasers

Thermo-optical characterization of tellurite glasses by thermal lens, thermal relaxation calorimetry and interferometric methods

In this work the thermal lens, thermal relaxation calorimetry and interferometric methods are applied to investigate the thermo-optical properties of tellurite glasses (in mol%: 80TeO2–20 Li2O(TeLi), 80TeO2–15Li2O–5TiO2 (TeLiTi-5) and 80TeO2–10Li2O–10TiO2 (TeLiTi-10)). Thermal diffusivity, thermal conductivity, specific heat and the temperature coefficients of refractive index, optical path length, thermal expansion and electronic polarizability were determined. The use of three independent methods was useful for a complete characterization of the studied tellurite glasses. In addition, our results showed that the thermal expansion coefficient and the temperature coefficient of the optical path length (dS/dT) were significantly modified with the introduction of titanium, which may be relevant for the application of these glasses in the photonic area.