S. P. S. Porto

Bio: S. P. S. Porto is an academic researcher from Bell Labs. The author has contributed to research in topics: Light scattering & Raman spectroscopy. The author has an hindex of 18, co-authored 20 publications receiving 3642 citations.

Long‐Transient Effects in Lasers with Inserted Liquid Samples

Abstract: Buildup and decay transients were observed when polar or nonpolar liquid cells were placed within the resonator of a helium—neon laser operating in the red at 6328 A. Similar but smaller effects were also observed with two solids. Time constants were the order of a few seconds for all materials, which suggests a thermal phenomenon, but general heating effects were ruled out by the strong localization of the phenomenon. Transverse motion of the cell by about one beam width caused new transients similar to the initial ones.It is believed that the effects are caused by absorption of the red light in the material, producing a local heating in the vicinity of the beam and a lens effect arising from the transverse gradient of refractive index. Absorptions of 10−3 to 10−4 parts per centimeter are sufficient to produce the effects, and are believed to be reasonable values for the materials studied. One of the most important applications may in fact be for the measurement of small absorbancies.The experiments are ...

Raman Spectra of Ti O 2 , Mg F 2 , Zn F 2 , Fe F 2 , and Mn F 2

Abstract: First-order Raman spectra have been measured at room temperature in five materials of the ${D}_{4h}$ point group: Ti${\mathrm{O}}_{2}$, Mg${\mathrm{F}}_{2}$, Zn${\mathrm{F}}_{2}$, Fe${\mathrm{F}}_{2}$ and Mn${\mathrm{F}}_{2}$. The experiments utilized an argon laser light source and photo-electric detection. The four Raman-active phonon frequencies, predicted by group theory to have symmetries ${A}_{1g}$, ${B}_{1g}$, ${B}_{2g}$, and ${E}_{g}$, were observed and classified in each material. Each spectrum exhibited strong lines of ${A}_{1g}$ and ${E}_{g}$ symmetries, a weak high-frequency line of ${B}_{2g}$ symmetry, and a very sharp ${B}_{1g}$ line at quite low frequency (less than 100 ${\mathrm{cm}}^{\ensuremath{-}1}$ in all the materials except Ti${\mathrm{O}}_{2}$).

Raman Spectrum of Single-Domain BaTi O 3

Abstract: Room-temperature Raman spectra of high-quality single-domain BaTi${\mathrm{O}}_{3}$ crystals are reported. The frequencies of the Raman-active long-wavelength optical phonons are determined and shown to be in reasonable agreement with the Lyddane-Sachs-Teller (LST) relation as well as infrared reflectivity data. The effects of mode damping on the Raman line shape are discussed using a classical lattice-polarization-fluctuation model for the Raman scattering process. Based on this model, it is shown that the soft $E$ mode is overdamped, and at 25\ifmmode^\circ\else\textdegree\fi{}C has an undamped mode frequency ${\ensuremath{\omega}}_{\mathrm{TO}}$ of 36\ifmmode\pm\else\textpm\fi{}3 ${\mathrm{cm}}^{\ensuremath{-}1}$ and a damping constant $\ensuremath{\Gamma}$ of 1.1\ifmmode\pm\else\textpm\fi{}0.1. The temperature dependence of ${\ensuremath{\omega}}_{\mathrm{TO}}$ is given and found to be consistent with the LST relation. The soft ${A}_{1}$ mode is not observed, but is estimated from the LST relation and infrared reflectivity data to be heavily damped ($\ensuremath{\Gamma}\ensuremath{\approx}0.5$) and to have an undamped mode frequency of 180\ifmmode\pm\else\textpm\fi{}10 ${\mathrm{cm}}^{\ensuremath{-}1}$.

Raman Spectra of CaW O 4 , SrW O 4 , CaMo O 4 , and SrMo O 4

Abstract: The first-order Raman spectra of CaW${\mathrm{O}}_{4}$, CaMo${\mathrm{O}}_{4}$, SrW${\mathrm{O}}_{4}$, and SrMo${\mathrm{O}}_{4}$ have been obtained. All theoretically predicted vibrations have been observed, and assignment has been given for the internal vibrations of the tungstate and molybdate ions as well as for the external vibrations involving the rest of the lattice.

Longitudinal and Transverse Optical Lattice Vibrations in Quartz

Abstract: The vibrational Raman spectrum of quartz has been obtained by means of argon laser excitation. Vibrations ascribed by earlier investigators to multiphonon processes are shown to be longitudinal components of the doubly degenerate species-$E$ vibrations. The frequency splittings observed between the longitudinal and transverse components of each species-$E$ mode are shown to agree very well with the values calculated using classical oscillator theory. The frequency and symmetry of each of the vibrations in $\ensuremath{\alpha}$-quartz are correlated with those of $\ensuremath{\beta}$-quartz. A discussion of the complications introduced by birefringence and anisotropy is also presented. It is shown that frequency splittings between longitudinal and transverse vibrations due to electrostatic forces are in some cases much greater for quartz than the frequency shifts due to the anisotropy of the short-range interatomic forces, contrary to what has been concluded previously in the literature.

Raman spectrum of anatase, TiO2

Abstract: Raman spectra of anatase have been observed in natural and synthetic crystals. Both crystals show the same spectral features. The Raman band occurring at 516 cm−1 at room temperature is split into two peaks centred at 519 cm−1 and 513 cm−1 at low temperature (73 K). The six Raman active fundamentals predicted by group theory are all observed and assigned. The spectra are analyzed by a simple model considering only short-range forces and the calculated vibrational frequencies are in good agreement with the observed Raman frequencies.

Electrical and optical properties of TiO2 anatase thin films

Abstract: Electrical and optical spectroscopic studies of TiO2 anatase thin filmsdeposited by sputtering show that the metastable phase anatase differs in electronic properties from the well‐known, stable phase rutile. Resistivity and Hall‐effect measurements reveal an insulator–metal transition in a donor band in anatase thin films with high donor concentrations. Such a transition is not observed in rutile thin films with similar donor concentrations. This indicates a larger effective Bohr radius of donor electrons in anatase than in rutile, which in turn suggests a smaller electron effective mass in anatase. The smaller effective mass in anatase is consistent with the high mobility, bandlike conduction observed in anatase crystals. It is also responsible for the very shallow donor energies in anatase. Luminescence of self‐trapped excitons is observed in anatase thin films, which implies a strong lattice relaxation and a small exciton bandwidth in anatase. Optical absorption and photoconductivity spectra show that anatase thin films have a wider optical absorption gap than rutile thin films.

Normal mode determination in crystals

Abstract: The group theoretical methods by which the symmetries of normal modes in crystals may be determined are outlined, and a series of tables are presented to facilitate rapid determination of the selection rules for vibrational transitions. Emphasis is placed on the method of nuclear site group analysis in which the number of infrared and Raman active modes of each symmetry may be obtained without detailed analysis of the symmetry elements in the crystallographic unit cell or the construction of tables. By using the tables presented here for most cases identification of the crystallographic space group is sufficient information to allow determination of the vibrational mode selection rules by inspection. Several examples are included in which crystals are analyzed by each of the methods.

Synthesis and Characterization of Nitrogen-Doped TiO2 Nanophotocatalyst with High Visible Light Activity

Abstract: Nitrogen-doped TiO2 nanocatalysts with a homogeneous anatase structure were successfully synthesized through a microemulsion−hydrothermal method by using some organic compounds such as triethylamine, urea, thiourea, and hydrazine hydrate. Analysis by Raman and X-ray photoemission spectroscopy indicated that nitrogen was doped effectively and most nitrogen dopants might be present in the chemical environment of Ti−O−N and O−Ti−N. A shift of the absorption edge to a lower energy and a stronger absorption in the visible light region were observed. The results of photodegradation or the organic pollutant rhodamine B in the visible light irradiation (λ > 420 nm) suggested that the TiO2 photocatalysts after nitrogen doping were greatly improved compared with the undoped TiO2 photocatalysts and Degussa P-25; especially the nitrogen-doped TiO2 using triathylamine as the nitrogen source showed the highest photocatalytic activity, which also showed a higher efficiency for photodecomposition of 2,4-dichlorophenol. T...