Structure Absorption Spectra Correlation in a Series of 2,6-Dimethyl-4-arylpyrylium Salts

A combined experimental and theoretical study of the absorption spectra of a group of closely related pyrylium perchlorates 1-11 are presented. Minor changes in the position of the substituents lead to drastic changes in the absorption spectra in this series of compounds. We have attempted to explain the observed changes using the x,y-band notation developed by Balaban and co-workers. Absorption spectra of all compounds are compared with results from time-dependent density functional theory (TDDFT) and Zerner’s intermediate neglect of differential overlap (ZINDO/S) level calculations. Results of the calculations are in good agreement with experimental observations and an interesting correlation between Balaban’s notations and the MO transitions are obtained for simple derivatives. It is suggested that for more complex systems such as R- and â-naphthyl substituted systems, the empirical method is not appropriate.

Optical absorption studies in ion implanted and amorphous semiconductors - Investigations in some tetrahedrally co-ordinated and chalcogenide materials

The thesis provides an overall review and introduction to amorphous semiconductors, followed by a brief discussion on the important structural models proposed for chalcogenide glasses and their electrical, optional and thermal properties. It also gives a brief description of the Physics of thin films, ion implantation and Photothermal Deflection Spectroscopy. A brief description of the experimental setup of a photothermal deflection spectrometer and the details of the preparation and optical characterization of the thin film samples. It deals with the employment of the subgap optional absorption measurement by PDS to characterize the defects, amorphization and annealing behavior in silicon implanted with B+ ions and the profiles of ion range and vacancy distribution obtained by the TRIM simulation. It reports the results of all absorption measurements by PDS in nitrogen implanted thin film samples of Ge-Se and As-Se systems

Tunable diode Laser Absorption Spectroscopy ,Nir Overtone and Life Studies of Some Organic Compound

The present work is mainly concentrated on setting up a NIR tunable diode laser absorption (TDLA) spectrometer for high-resolution molecular spectroscopic studies. For successfully recording the high-resolution tunable diode laser spectrum, various experimental considerations are to be taken into account like the setup should be free from mechanical vibrations, sample should be kept at a low pressure, laser should be in a single mode operation etc. The present experimental set up considers all these factors. It is to be mentioned here that the setting up of a high resolution NIR TDLA spectrometer is a novel experiment requiring much effort and patience. The analysis of near infrared (NIR) vibrational overtone spectra of some substituted benzene compounds using local mode model forms another part of the present work. An attempt is made to record the pulsed laser induced fluorescence/Raman spectra of some organic compounds. A Q-switched Nd:YAG laser is used as the excitation source. A TRIAX monochromator and CCD detector is used for the spectral recording. The observed fluorescence emission for carbon disulphide is centered at 680 nm; this is assigned as due to the n, p* transition. Aniline also shows a broad fluorescence emission centered at 725 nm, which is due to the p,p* transition. The pulsed laser Raman spectra of some organic compounds are also recorded using the same experimental setup. The calibration of the set up is done using the laser Raman spectra of carbon tetrachloride and carbon disulphide. The observed laser Raman spectra for aniline, o-chloroaniline and m-chlorotoluene show peaks characteristics of the aromatic ring in common and the characteristics peaks due to the substitutuent groups. Some new peaks corresponding to low-lying vibrations of these molecules are also assigned

Investigation of nonlinear absorption and aggregation in aqueous solutions of rhodamine B using thermal lens technique

Thermal lensing effect was studied in aqueous solutions of rhodamine B using 532 nm, 9 ns pulses from a Nd:YAG laser. A low intensity He-Ne laser beam was used for probing the thermal lens. Results obtained show that it is appropriate to use this technique for studying nonlinear absorption processes like two photon absorption or excited state absorption and for analyzing dimerization equilibria.

Studies of nonlinear absorption and aggregation in aqueous solutions of rhodamine 6G using a transient thermal lens technique

Dual-beam transient thermal lens studies were carried out in aqueous solutions of rhodamine 6G using 532 nm pulses from a frequency-doubled Nd:YAG laser. The analysis of the observed data showed that the thermal lens method can effectively be utilized to study the nonlinear absorption and aggregation which are taking place in a dye medium.

Optical absorption studies of free (H2Pc) and rare earth (RePc) phthalocyanine doped borate glasses

Optical absorption studies of free base and rare earth incorporated phthalocyanine doped borate glass matrix are reported for the first lime. The absorption spectra recorded in the UV- VIS region show two well defined absorption bands of phthalocyanine (Pc) molecule, namely the Soret band (B) and the Q band. The Q band always shows its characteristic splitting in all the doped glass matrices and the intensities of these components are found to vary from one Pc to another. Some of the important optical parameters, namely optical absorption coefficient (a), molar extinction coefficient (ε), absorption cross section (σa), oscillator strength (f), electric dipole strength (q2), absorption half bandwidth (Δλ) of the principal optical transitions have also been evaluated. Moreover, the spectral dependence of refractive index (n) and thereby the optical dielectric constant (ε) on wavelength yielded values of carrier concentration to effective mass ratio (N/m*) of the phthalocyanine molecule in the present glassy systems. Optical band gap (Eg) and width of the band tail (Et) are computed and their variations among the prepared samples are also discussed.

Characteristics of two-photon absorption in methanol solutions of Rhodamine 6G using laser induced pulsed photoacoustics

Two-photon absorption in methanol solutions of Rhodamine 6G is investigated by photoacoustics using the second harmonic of a pulsed Nd:YAG laser. Competition between one-photon and two-photon processes is observed, depending critically on the sample concentration and input light flux.

Photoacoustic observation of excited singlet state absorption in the laser dye rhodamine 6G

S1 to S3 excited singlet state absorption and two-photon absorption in Rhodamine 6G at the pump wavelengths of 532 and 1064 nm respectively are investigated. The advantages of employing the pulsed photoacoustic technique for conveniently observing excited singlet state absorption are discussed. It is shown that, since photoacoustics and fluorescence are complementary phenomena, analysis using both techniques will yield a better understanding of optical processes in molecules like Rhodamine 6G.

Studies on Two-Photon Absorption of Aniline Using Thermal Lens Effect

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 I Al -. I B2 transition of aniline.

Photoacoustic detection of two photon absorption in formaldehyde using pulsed dye laser

Absorption spectra of formaldehyde molecule in the gas phase have been recorded using photoacoustic (PA) technique with pulsed dye laser at various power levels. The spectral profiles at higher power levels are found to be different from that obtained at lower laser powers. Two photon absorption (TPA) is found to be responsible for the photoacoustic signal at higher laser power while the absorption at lower laser power level is attributed to one photon absorption (OPA) process. Probable assignments for the different transitions are given in this paper.

Observation of two-photon absorption in rhodamine 6G using photoacoustic technique

Two-photon absorption in Rhodamine 6G using the second harmonic of a pulsed Q-switched Nd:YAG laser has been studied by photoacoustic technique. It is observed that there is a competition between one-photon and two-photon absorption processes. At lower concentration the two-photon process is predominant over the one-photon process.

NIR to UV absorption spectra and the optical constants of phthalocyanines in glassy medium

Optical absorption studies of phthalocyanines (Pc-s) in borate glass matrix have been reported for the first time. Measurements have been done corresponding to photon energies between 1.1 and 6.2 eV for free base, manganese, iron, nickel, molybdenum, cobalt and copper phthalocyanines. Several new discrete transitions are observed in the UV–vis region of the spectra in addition to a strong continuum component of absorption in the IR region. Values of some of the important optical constants viz. absorption coefficient (α), molar extinction coefficient (ε), absorption cross-section (σa), band width (Δλ), electric dipole strength (q2) and oscillator strength (f) for the relevant electronic transitions are also presented. All the data reported for Pc-s in the new matrix have been compared with those corresponding to solution, vapor and thin film media.

Nonlinear optical absorption in silver nanosol

Nonlinear optical absorption in silver nanosol was investigated at selected wavelengths (456 nm, 477 nm and 532 nm) using open aperture Z-scan technique. It was observed that nature of nonlinear absorption is sensitively dependent on input fluence as well as on excitation wavelength. Besides, the present sample was found to exhibit reverse saturable absorption (RSA) and saturable absorption (SA) at these wavelengths depending on excitation fluence. RSA is attributed to enhanced absorption resulting from photochemical changes. SA observed for fluence values lower and higher than those corresponding to RSA are, respectively, attributed to plasmon bleach and saturation of RSA.

Two and Three Photon Absorption in Rhodamine 6G Methanol Solutions Using Pulsed Thermal Lens Technique

Dual beam transient thermal lens studies were carried out in rhodamine 6G methanol solutions using 532 nm pulses from a frequency doubled Nd:YAG laser. Analysis of thermal lens signal shows the existence of different nonlinear processes like two photon absorption and three photon absorption phenomena along with one photon absorption. Concentration of the dye in the solution has been found to influence the occurrence of the different processes in a significant way.