M. Kailasnath

Laser emission from the whispering gallery modes of a graded index fiber

Whispering gallery mode (WGM) laser emission has been observed from rhodamine B doped polymer optical graded index (GI) fiber by transverse pumping with a frequency doubled Q-switched Nd:YAG laser. The propagation and confinement of these modes were also observed. A variation in the free spectral range from 0.29 to 1.24 nm is obtained along the length due to the confinement of WGMs in the GI fiber.

Tuning whispering gallery lasing modes from polymer fibers under tensile strain

Wavelength tuning of whispering gallery lasing modes has been observed from Rhodamine-B-doped polymer fibers under tensile strain. Good quality whispering gallery lasing modes are produced from both solid and hollow fibers by transverse optical pumping. The lasing modes are shifted linearly toward the shorter wavelength side when the fiber is elongated in the axial direction. Compared with solid fiber, the lasing modes of hollow fiber can be tuned over the entire gain spectrum with a tuning range of ∼5  nm. It is found that the tuning of the lasing modes of hollow fiber is reversible.

Enhanced random lasing from a colloidal CdSe quantum dot-Rh6G system

In this letter, we report random laser action in a system where optical amplification is provided by colloidal CdSe quantum dots (CQDs) triggered by the emission from Rhodamine 6G. The laser emission from CdSe QDs is optically excited by Rh-6G which in turn is photo-pumped by a frequency-doubled Q-switched Nd : YAG laser system at an excitation wavelength of 532 nm. At intensities greater than the threshold value, laser emission is characterized by narrowing peaks.

Random lasing with enhanced photostability of silver nanoparticle doped?polymer optical fiber laser

We report on the realization of a silver (Ag) nanoparticle doped polymer optical fiber random laser. Lasing characteristics and photostability of the system with varying concentration of Ag nanoparticles have been investigated. It was found that there is an enhanced spectral narrowing and emission intensity in rhodamine 6G–Ag nanoparticle doped polymer optical fiber compared to that of bare rhodamine 6G doped polymer optical fiber. In contrast with the latter, low-threshold coherent feedback random lasing with improved photostability was observed for an optimum concentration of Ag nanoparticles in the gain medium.

Microring lasing from a dye-doped polymer-coated silica fiber

We demonstrate pulsed, photopumped multimode laser emission in the visible spectral range from cylindrical microcavities of dye-doped thin polymer film deposited on silica core optical fiber. The laser emission is characterized by narrow emission lines (~0.05 nm), a well-defined excitation threshold and high Q ~ 1.2 × 104. We observed two different sets of resonant laser modes: namely, waveguided ring modes in the polymer film and whispering gallery modes close to the optical fiber surface.

Fabrication and Photostability of Rhodamine-6G Gold Nanoparticle Doped Polymer Optical Fiber

We report on fabrication of a rhodamine-6G-gold-nanoparticle doped polymer optical fiber. The gold nanoparticle is synthesized directly into the monomer solution of the polymer using laser ablation synthesis in liquid. The size of the particle is found from the transmission electron microscopy. Rhodamine-6G is then mixed with the nanoparticle-monomer solution and optical characterization of the solution is investigated. It is found that there is a pronounced quenching of fluorescence of rhodamine 6G due to fluorescence resonance energy transfer. The monomer solution containing rhodamine 6G and gold nanoparticles is now made into a cylindrical rod and drawn into a polymer optical fiber. Further, the photostability is calculated with respect to the pure dye doped polymer optical fiber.

Microring embedded hollow polymer fiber laser

Strongly modulated laser emission has been observed from rhodamine B doped microring resonator embedded in a hollow polymer optical fiber by transverse optical pumping. The microring resonator is fabricated on the inner wall of a hollow polymer fiber. Highly sharp lasing lines, strong mode selection, and a collimated laser beam are observed from the fiber. Nearly single mode lasing with a side mode suppression ratio of up to 11.8 dB is obtained from the strongly modulated lasing spectrum. The microring embedded hollow polymer fiber laser has shown efficient lasing characteristics even at a propagation length of 1.5 m.

Size Dependent Optical Nonlinearity and Optical Limiting Properties of Water Soluble CdSe Quantum Dots

We present third-order optical nonlinear absorption in CdSe quantum dots (QDs) with particle sizes in the range of 4.16–5.25 nm which has been evaluated by the -scan technique. At an excitation irradiance of 0.54 GW/cm2 the CdSe QDs exhibit reverse saturation indicating a clear nonlinear behavior. Nonlinearity increases with particle size in CdSe QDs within the range of our investigations which in turn depends on the optical band gap. The optical limiting threshold of the QDs varies from 0.35 GW/cm2 to 0.57 GW/cm2 which makes CdSe QDs a promising candidate for reverse-saturable absorption based devices at high laser intensities such as optical limiters.

Influence of pH on the thermo-optic properties of CdSe QDs prepared by a microwave irradiation method

In this letter the optical behavior as well as the thermal properties of CdSe quantum dots (QDs) capped with mercapto succinic acid (MSA) are studied and analyzed. CdSe QDs with an average particle size of 7.0 nm are prepared by a microwave irradiation method. The unique structure of MSA plays an important role in determining the PL intensity and better stability by controlling the pH of the medium. A significant increase in thermal diffusivity with pH values is observed with a mode matched thermal lens method. At the optimum value of pH, the surface charge of nanoparticles increases, which increases the repulsive forces. The resulting reduced agglomeration of QDs enhances mobility and improves heat transport. There is a clear correlation between luminous intensity and thermal diffusivity in these nano fluids containing CdSe QDs.

Influence of Solvent on Size and Properties of ZnO Nanoparticles

The nanosized zinc oxide powder was synthesized in ethylene glycol, methanol and toluene solvents using zinc oxalate and oxalic acid as precursors without using any surfactant. A variety of techniques like UV‐VIS absorption spectroscopy, X‐ray diffraction (XRD), photoluminescence (PL), Fourier transform infrared spectroscopy (FT‐IR) and Scanning electron microscopy (SEM) were used to carry out structural and spectroscopic characterizations of the nanoparticles. The size and optical properties were investigated against used initial solvent and it was found that the solvent plays a key role in determining the size and property of zinc oxide nanoparticles.