Papers by Keyword: Thermo-Optic Coefficient

Abstract: The growing interest for the use of 4H-SiC in photonics is triggering the interest for more accurate characterizations of this semiconductor from the optical and opto-electronic point of view. In this work we report about new measurements run on an undoped 4H-SiC substrate, finalized at determining the precise dependence of its refractive index on temperature in the visible spectrum, and precisely at the wavelength of λ=632.8 nm, in a temperature range from room temperature (RT) to 400K. Measurements are performed by exploiting the properties of a Fabry-Perot cavity interrogated with a laser beam. It is known that the transmitted radiation intensity shows fringes that shift with temperature and the refractive index. By precisely monitoring the transmitted signal, the thermo-optic coefficient dn/dT can be determined with a resolution that approaches 10^-6 K^-1.

Abstract: A novel azobenzene optically polymer (P-DA) was synthesized based on the azo chromophore molecule, chiral reagent L(-)-tartaric acid, acryloyl chloride and methacrylate. The P-DA was characterized by FT-IR, UV-Vis spectroscopy, 1H NMR, DSC and TGA. The P-DA had high thermal stability up to its glass-transition temperature (Tg) of 110 oC and 5 % heat weight loss temperature of 199 oC. The UV-induced trans/cis photoisomerization and reflex-isomerization behaviors were investigated. The results indicated that the P-DA solution could undergo photochromism after irradiated by 365 nm UV light. The optical parameters: refractive index (n), the dielectric constant (ε) and thermal volume expansion coefficient (β) of P-DA were obtained. The thermo-optic coefficients are one order of magnitude larger than those of the inorganic materials, such as SiO2 (1.1×10−5 oC -1 and LiNbO3 (4×10−5 oC -1) and was larger than the organic material such as polystyrene (-1.23×10-4 oC -1) and PMMA (-1.20×10-4 oC -1). The conclusion had a little significance to develop optical communication.

Abstract: A novel azobenzene polyelectrolyte (ABAPE) was synthesized based on chromophore 4-(4’-nitrophenylazo) naphthol (NPAN), epoxychloropropane and α-methacrylic acid. The ABAPE was characterized by FT-IR and UV-vis spectroscopy. The aggregation behaviors of ABAPE were investigated based on different pH values by the UV-vis spectroscopy. The isomerization behavior of the ABAPE in DMAC solution was studied by 256 nm UV irradiation light. Attenuated total reflection (ATR) method was adopted and carried out the measurement of refractive index of the thin film. The thermo-optic coefficient (dn/dT) was -2.9228×10-4°C-1 and was bigger than inorganic materials such as silica glass, zinc silicate glass, borosilicate glass and the organic materials of polystyrene and PMMA. These results showed that the polyelectrolyte could be used to carry out optical storage and thermo-optic switch.

Abstract: We applied a picosecond dynamic grating technique for investigation of thermal diffusivity, sound velocity, thermo-optic and photoelastic coefficients in heavily doped 4H-SiC substrates. Spatial modulation of thermal properties was achieved by intraband carrier absorption at excitation by an IR picosecond laser pulse (1064 nm) and subsequent carrier thermalisation. Decay of dynamic grating at its various periods and sample temperatures was monitored at 532 nm wavelength. The thermal diffusivity DT = 0.94 cm2/s, thermo-optic coefficient dn/dT = 3.610–5 K-1 and effective photoelastic constant = – 0.10 were determined at 300 K. DT value increased at lower temperatures and saturated below 100 K. Temperature dependences of thermo-optic coefficient and thermal expansion were found in good correlation with heat capacity peculiarities.