Thermal Coefficient Of Refractive Index Research Articles

Refractive index and domain structure of undoped and Nb doped (Na0.41K0.09Bi0.50)TiO3 (NBT-KBT) single crystal grown at MPB composition

Single crystals of undoped and Nb doped NBT-KBT with morphotropic phase boundary composition [(Na0.41K0.09Bi0.50)TiO3] were grown by spontaneous nucleation technique. The lattice parameter was found to be unaffected on Nb doping. Further the temperature dependent refractive indices were measured for four different wavelengths and the Sellmeier coefficients were calculated in the range of 30–160 °C. Refractive index was found to increase linearly with temperature (thermal coefficient of refractive index ∼10−4-10−5/°C). Further, the thermal coefficient was found to increase with the Nb concentration. A set of relations of the thermal coefficient of refractive index as a function of wavelength was established. In addition, the crystal was investigated using polarized light optical microscope. Regions with both ‘a’ and ‘c’ domains, typical of tetragonal structure, were observed in the samples. Further, the conoscopic study revealed that the material is of negative uniaxial type. The presence of domains related to the tetragonal and rhombohedral structures hints the possible coexistence of both the structures as expected for the morphotropic phase boundary composition. The outcome of the investigation would provide valuable inputs about NBT-KBT single crystals for photonic or optoelectronic applications.

Glass formation and optical properties of Sn modified GeS2-Ga2S3-CsCl chalcogenide glasses

Chalcogenide glass is emerging as important IR materials for advanced athermal infrared (IR) optical systems because of its low thermal coefficient of refractive index. New chalcogenide glasses based on 75GeS2-15Ga2S3-10CsCl were developed through the substitution of GeS2 by SnS2. The introduction of heavier tin (Sn) results in the red shift of transmission window, both of visible and long-wavelength IR cut-off edges, the elevation of refractive index dispersion curves, and the decreasing of glass transition temperature. The formation of [SnS4-xClx] structural units, instead of [GeS4-xClx], should be responsible for the variation of these structural properties. In addition, homogeneous Sn modified GeS2-Ga2S3-CsCl chalcogenide glass of Φ30 mm was also prepared successfully, showing it of high potential for commercial applications.

Temperature-Dependent Sellmeier Equations of IR Nonlinear Optical Crystal BaGa4Se7

The thermal dependent principal refractive indices of a new promising IR nonlinear optical crystal BaGa4Se7 at wavelengths of 0.546, 0.5806, 0.644, 0.7065, 1.530, 1.970, and 2.325μm were measured by using the vertical incidence method within the temperature range from 25 to 150 °C. We derived equations of thermal refractive index coefficients as a function of wavelength that could be used to calculate the principal thermal refractive indices at different wavelengths. The temperature-dependent Sellmeier equations were also obtained and used to calculate the phase matching angles for the optical parametric process of BaGa4Se7 crystal at different temperatures.

Optical characterization and all-optical switching of benzenesulfonamide azo dye

A film of benzenesulfonamide azo dye has been prepared by spray pyrolysis method onto BK7 glass substrate with average thickness of 2.7μm. This azo dye was derived from sulfamethoxazole and chromotropic acid by the Fox method. The optical constants (refractive index, n, extinction coefficient, k, dielectric constant, ɛ, optical, σopt, and electrical, σe, conductivities) were calculated for azo dye film by using spectrophotometer measurements of the absorption, transmittance and reflectance at normal incidence in the spectral range 300–900nm. Third order nonlinear properties has been characterized by calculating the effective thermal nonlinear refractive index, n2, and thermo-optic coefficient, dn/dT, of the azo dye solution using thermal lens technique. Furthermore, the thermal lens effect was utilized to demonstrate all optical switching for the sample solution.

Temperature-dependent Sellmeier equations of nonlinear optical crystal Na3La9O3(BO3)8

The principal refractive indices of Na3La9O3(BO3)8 (NLBO) crystal in the wavelength range of 0.363–2.325μm were accurately measured by using the minimum deviation method within the temperature range from 23.5°C to 160°C. We derived the expressions of thermal refractive index coefficient as a function of wavelength that could be used to calculate the principal refractive indices at different wavelengths. The temperature-dependent Sellmeier equations were also derived and used to calculate the phase-matching (PM) angles for a frequency conversion device based on NLBO crystal at different temperatures. We found that the thermal refractive index coefficients of NLBO crystal changed from positive to negative values with the increase of wavelength. In addition, the phase matching conditions for third harmonic generation (THG) at different temperatures were also investigated.

Measurement of thermal refractive index coefficients of nonlinear optical crystal RbBe2BO3F2

The principal refractive indices of RbBe2BO3F2 (RBBF) crystal at wavelengths of 0.194, 0.254, 0.363, 0.405, 0.435, 0.546, 0.644, 0.706, and 1.014μm are accurately measured by using the vertical incidence method within the temperature range from 24 to 160°C. Equations of thermal refractive index coefficients as a function of wavelength that could be used to calculate the principal thermal refractive indices at different wavelengths are derived. Moreover, experimental phase-matching angles for second harmonic generation of RBBF at 266nm wavelength at different temperatures as well as the theoretical values built on our experiment results are also given.

Temperature-dependent Sellmeier equations of nonlinear optical crystal La_2CaB_10O_19

The thermal dependence principal refractive indices ofLa(2)CaB(10)O(19) (LCB) crystal at wavelengths of 0.254, 0.365, 0.405, 0.480, 0.546, 0.644, 0.852, 1.014, and 2.325 μm were accurately measured by using the vertical incidence method within the temperature range from 25 to 170 °C. We derived equations of thermal refractive index coefficients as a function of wavelength that could be used to calculate the principal thermal refractive indices at different wavelengths. The temperature-dependent Sellmeier equations were also derived and used to calculate the phase-matching angles for the third-harmonic generation of LCB crystal at different temperatures. Theoretical and experimental phase-matching angles for the type I third-harmonic generation of LCB crystal at different temperatures were in good agreement.

Thermal refractive index coefficients of nonlinear optical crystal CsB_3O_5

The principal refractive indices of crystal CsB3O5 (CBO) at the wavelengths of 0.266, 0.355, 0.532, 0.473, 0.633, 1.064, and 1.338 μm are accurately measured by using the autocollimation method within the temperature range from 40°C to 190°C. We derive and report equations of thermal refractive index coefficients as a function of wavelength that could be used to calculate the principal thermal refractive indices at different wavelengths. Sellmeier equations at different temperatures were derived and used to calculate the phase-matching angles for the third-harmonic generation and the fourth-harmonic generation of CBO crystal at different temperatures.

THRESHOLD-TUNABLE OPTICAL LIMITERS OF Au NANOPARTICLES IN CASTOR OIL

Optical limiting performance of gold nanoparticles (AuNPs) in castor oil is studied using a low power laser irradiation at 532 nm. Our results suggest that it is possible to tune the optical limiting threshold of the AuNPs by modifying the parameters of the set-up and gold nanoparticle concentration of the colloids. The closed Z-scan measurements reveal that non-local thermal nonlinear refraction process is responsible for the limiting action of the colloids. We have investigated the Z-scan behavior of the samples based on the non-local thermal nonlinear refraction process without using photo-thermal thin lens approximation. It is shown that this model is in good agreement with the experimental results and large enhancement factors are measured for values of nonlinear thermal refractive index and thermo-optical coefficients of the colloids at higher gold nanoparticle concentration compared to the measurement of castor oil.

Temperature-dependent index of refraction of monoclinic Ga_2O_3 single crystal

We present temperature-dependent refractive index along crystallographic b[010] and a direction perpendicular to (100)-plane for monoclinic phase (β) Ga(2)O(3) single crystal grown by the optical floating zone technique. The experimental results are consistent with the theoretical result of Litimein et al.1. Also, the Sellmeier equation for wavelengths in the range of 0.4-1.55 μm is formulated at different temperatures in the range of 30-175 °C. The thermal coefficient of refractive index in the above specified range is ~10(-5)/°C.

Thermo-Optical Properties of Colloids Enhanced by Gold Nanoparticles

This work presents a study on the thermo-optical properties of colloidal gold nanoparticles (AuNPs) under a low power laser irradiation at 532 nm. Samples of various gold volume fractions, ranging from 2.5×10-4 to 19.5×10-4%, are synthesized by nanosecond pulsed laser ablation of a pure gold plate in the distilled water. The formation of the AuNPs has been evidenced by optical absorption spectra and transmission electron microscopy. We investigate the effect of the gold nanoparticle concentration on thermo-optical properties of the colloids using the Z-scan technique. The nonlinear optical measurements exhibit a very large nonlinear refraction close to the surface plasmon resonance frequency of the nanoparticles. Our results reveal that the heat diffusion in the colloids is due to nonlocal thermal process. As the gold concentration increases, the temperature change within and around gold nanoparticles greatly enlarges the thermo-optic and thermal nonlinear refractive index coefficients of the samples. This work suggests that thermal nonlinear refraction will play an important role in development of photonic applications involving metal nanoparticles colloids.

Optimization of chalcogenide glass in the As–Se–S system for automotive applications

Infrared transmitting glasses in the As–Se–S system have been optimized by taking in account specifications for automotive application. The As 2Se 3 glass has been chosen as the starting composition and sulfur is introduced in order to improve some optical and mechanical properties. As expected, the Sulfur introduction decreases the refractive index as well as its change as function of temperature. The relationship between the refractive index and the glass composition has been established. The thermal coefficient of refractive index for sulfur containing glasses can be lower than 4 × 10 −5 K −1, which is considerably lower than that of germanium, the most used infrared transmitting materials. Influence of sulfur on other properties has also been studied.

Measurement of thermo-optic properties of Y3Al5O12, Lu3Al5O12, YAIO3, LiYF4, LiLuF4, BaY2F8, KGd(WO4)2, and KY(WO4)2 laser crystals in the 80–300K temperature range

Thermo-optic materials properties of laser host materials have been measured to enable solid-state laser performance modeling. The thermo-optic properties include thermal diffusivity (β), specific heat at constant pressure (Cp), thermal conductivity (κ), coefficient of thermal expansion (α), thermal coefficient of the optical path length (γ) equal to (dO∕dT)∕L, and thermal coefficient of refractive index (dn∕dT) at 1064nm; O denotes the optical path length, which is equal to the product of the refractive index (n) and sample length (L). Thermal diffusivity and specific heat were measured using laser-flash method. Thermal conductivity was deduced using measured values of β, Cp, and the density (ρ). Thermal expansion was measured using a Michelson laser interferometer. Thermal coefficient of the optical path length was measured at 1064nm, using interference between light reflected from the front and rear facets of the sample. Thermal coefficient of the refractive index was determined, using the measured values of γ, α, and n. β and κ of Y3Al5O12, YAIO3, and LiYF4 were found to decrease, as expected, upon doping with Yb.

Nanosecond surface interferometry measurements on designed and commercial polymers

The effect of the ablation mechanism on surface morphology changes during an ablation process was studied by comparing three different polymers: a triazene polymer, a polyimide and poly(methylmethacrylate) (PMMA) with nanosecond surface interferometry. The triazene polymer, for which only indications for a photochemical ablation mechanism had been detected in previous studies, revealed no surface swelling, which could be attributed to a thermal ablation mechanism. For polyimide, a photothermal ablation mechanism is usually used to describe the ablation process at irradiation wavelengths ≥248 nm. However, the interferometric measurements do not show any surface swelling, which would be a clear indication for a thermal ablation mechanism. A surface swelling was only detected for PMMA with irradiation at 248 nm and fluences below the threshold of permanent surface modification. The detected phase shift, which is proportional to the change of the film thickness and the refractive index, can be explained by the opposite signs of the thermal expansion coefficient and the thermal refractive-index coefficient.

Sellmeier’s equation and the expression of the thermal refractive-index coefficient for a Nd_0007Gd_0993VO_4 crystal

The principal refractive indices of a Nd0.007Gd0.993VO4 crystal for wavelengths of 0.488, 0.6328, 1.064, 1.0795, and 1.3414 microm under the temperature range of 20-170 degrees C are measured by the autocollimation method, and the Sellmeier's equation and the expression of the thermal refractive-index coefficient are then obtained. The reliability of these results is checked by comparing the calculated values with the measured values for the measured wavelengths and the temperature region, as well as with the published values by Studenikin et al. [Quantum Electron. 25, 1162-1165 (1995)] for wavelengths of 0.491, 0.546, 0.578, 0.632, 0.808, and 1.062 microm at 20 degrees C. In addition, the birefringence and the thermal coefficient of the birefringence were obtained by measured results. The results show that the birefringence is larger than that of a YVO4 crystal and that the thermal coefficient of birefringence is less than that of a YVO4 crystal. Therefore it can be expected that the GdVO4 crystal is not only an excellent laser crystal but also an excellent birefringent crystal used in a modern optical transmission system as a passive fiber-optic component.

Measurement of refractive indices and thermal refractive index coefficients of Cr3+?Be3Al2Si6O18 by auto-collimation method

The principal refractive indices and the thermal refractive index coefficients for Be3Al2Si6O18 crystal doped with 1.01wt% Cr2O3 have been accurately measured by the auto-collimation method at wavelengths of 0.488, 0.53975, 1.064, 1.0795 and 1.3414 μm, and temperatures of 308.2, 328.6, 359.1 and 395.4 K respectively. Based on the measured results of principal indices of 0.488, 0.6328, 1.0795 and 1.3414μm, the Sellmeier’s equations and the thermal refractive index coefficients have been obtained, and the result has been proven to be accurate by error analysis.

Study of the refractive properties of laser dye solvents: toluene, carbon disulphide, chloroform, and benzene

This paper is devoted to the calculations of the optical and dielectric dispersion of four non and less polar laser dye solvents (toluene, carbon disulphide, chloroform and benzene). The calculations are based on measured values of refractive indices n and its temperature gradient dn/dT at two different laser wavelengths (514.5 and 632.8 nm). The thermal coefficient of refractive index dn/dT and that of permittivity de/dT as a function of the wavelength are also calculated. Additionally, other important constants as a function of temperature are graphically represented.

Studies on the phase-matching condition and the cut-off wavelength of Nb:KTiOPO 4 crystal

The measured results of the cut-off wavelengths of KTiOPO 4 (KTP) crystal grown from the raw material containing 7.5 and 13 mol% Nb 2O 5 (referred as 7.5 and 13 mol% Nb:KTP crystals in this paper) by top-seed flux method are presented as well as those of the optimal phase-matching (PM) angles at 1064 and 1079.5 nm lines for KTP crystals grown from raw material containing different concentrations of Nb 2O 5. The Sellmeier’s equation and thermal refractive index coefficients for 7.5 mol% Nb:KTP crystal have been obtained and then the optimum PM angles at 1064 and 1079.5 nm and the cut-off wavelength as well as the nonlinear optical properties are calculated. It is shown that the calculated results of optimum PM angles at 1064 and 1079.5 nm and cut-off wavelength for 7.5 mol% Nb:KTP crystal agree fairly well with the measured results. It is concluded that the noncritical PM condition at 1064 nm line can be satisfied in KTP crystal grown from the raw material containing about 3 mol% Nb 2O 5. The cut-off wavelength of 13 mol% Nb:KTP crystal has blue-shifted to 937 nm, achieving 468.5 nm blue coherent radiation.

Temperature dependence of refractive index of glassy SiO2 in the infrared wavelength range

An interferometric method was used for the determination of refractive index of glassy SiO2 in the infrared (IR) wavelength region (1.44<λ<4.77μm) at temperatures ranging from 23.5 to 481°C by IR spectroscopy. The refractive index was found to increase with temperature at a given wavelength. Irregularities of the thermal coefficient of the refractive index (dn/dT) with temperature were observed and explained by the existence of crystal-like microstructures in silica glass. Optical dispersion (dn/dλ) exhibits a maximum at a given temperature. The wavelength at the maximum depends on temperature, showing irregularities with temperature like the thermal coefficient of refractive index.

The thermal refractive index coefficients of 7.5 mol % Nb:KTiOPO4 crystals

The principal refractive indices and thermal refractive index coefficients for Nb:KTiOPO4 (KTP) crystal grown by the top-seed flux method from a starting material containing 7.5 mol % Nb have been measured using the autocollimation method. Using measurements made at wavelengths of 0.53975, 0.6328, 1.0795, and 1.3414 μm, in the temperature range from ambient to 188 °C, it is possible to determine the constants of the Sellmeier equations and the thermal refractive index coefficients as a function of wavelength. Also, the temperature acceptance bandwidth at 90° second harmonic generation noncritical phase matching direction was calculated. Comparison of these results with those for undoped KTiOPO4 [K. Rato, IEEE J. Quantum Electron QE-28, 1974 (1992)] and KNbO3 [B. Zysset, I. Biaggo, and P. Gunter, J. Opt. Soc. Am. B 9, 380 (1992)] implies that Nb-doped KTP crystals are suitable for blue coherent light devices.