Optical fiber sensors developed for measuring pH values usually employ an unclad and unstrained section of the fiber. In this paper, we describe the design and fabrication of a microbent fiber optic sensor that can be used for pH sensing. In order to obtain the desired performance, a permanently microbent portion of a plastic optic fiber is coated with a thin film of dye impregnated sol-gel material. The measurements are simultaneously carried out in two independent detection schemes viz., the bright field detection configuration for detecting the core modes and dark field detection configuration, for detecting the cladding modes. The results of measurements of core mode-power and cladding mode-power variation with change in pH of a solution surrounding the coated portion of the fiber is presented. This paper thus demonstrates how a bare plastic fiber can be modified for pH sensing in a simple and cost effective manner.

Photoacoustic spectrum of samarium phthalocyanine powder is recorded and compared with previously reported UV-vis absorption spectra of the same dissolved in different liquid and solid host media. The Davidov splitting of Q band is observed in the PA spectrum but the two bands are overlapped considerably and the shorter wavelength band is more intense and dominating one in the powder spectrum.

Microbent optical fibers are potential candidates for evanescent wave sensing. We investigate the behavior of a permanently microbent fiber optic sensor when it is immersed in an absorbing medium. Two distinct detection schemes, namely, bright-field and dark-field detection configuration, are employed for the measurements. The optical power propagating through the sensor is found to vary in a logarithmic fashion with the concentration of the absorbing species in the surrounding medium. We observe that the sensitivity of the setup is dependent on the bending amplitude and length of the microbend region for the brightfield detection scheme, while it is relatively independent of both for the dark-field detection configuration. This feature can be exploited in compact sensor designs where reduction of the sensing region length is possible without sacrificing sensitivity. © 2002 Society of Photo-Optical Instrumentation Engineers.

Two-photon absorption spectrum of aniline is recorded using thermal lens effect with optical parametric oscillator as the pump source. Studies show that the two-photon absorption spectrum observed corresponds to 1A1 → 1B2 transition of aniline.

Hydrochloric acid (HCl) doped Polyaniline (PANI) and Polyaniline-Multiwalled Carbon Nano Tube (MWNT) composite samples were synthesized using chemical oxidative polymerization technique. Transmission Electron Microscopy (TEM) and Raman spectroscopy studies clearly establish the formation of PANI (HCl) and PANI (HCl)-MWNT composites. Thermal diffusivity measurements were carried out using Open Photo Acoustic Cell (OPC) technique in transmission configuration and the thermal diffusivity values were calculated. The thermal diffusivity of the composite samples is found to be greater than that of pure PANI. It increases with increase in MWNT loading upto aniline to MWNT feed ratio 1:0.3 and later decreases for the 1:0.5 sample. Still the thermal diffusivity of PANI (HCl)-MWNT composite sample is higher than that of PANI (HCl).The enhancement in thermal diffusivity is due to the high thermal conductivity of MWNT. The decrease in thermal diffusivity of the 1:0.5 sample is explained using dopant induced phonon scattering and thermal interfacial contact resistance. The present study offers ample scope for tailoring the thermal diffusivity parameters of polyaniline composites according to device requirements.