Size dependence of refractive index of goldnanoparticles

The extinction spectra of spherical gold nanoparticles suspended in a homogeneous media were measured and the results were adjusted with Mie's theory together with an appropriate modification of the optical properties of bulk material considering the limitation that introduces the size of nanoparticles on the dielectric function. Usually, the contribution of free electrons to the dielectric function is modified for particle size, while the contribution of bound electrons is assumed to be independent of size. This work discusses the separated contribution of free and bound electrons on the optical properties of particles and their variation with size for gold nanoparticles. The effects of dielectric function and its changes with size on extinction spectra near plasmon resonance are considered. The damping constant for free electrons was changed with size as usual and a scattering constant of C = 0.8 was used. For the bound electron contribution, two different models were analysed to fit the extinction spectra: on the one hand, the damping constant for interband transitions and the gap energy were used as fitting parameters and on the other, the electronic density of states in the conduction band was made size-dependent. For the first model, extinction spectra corresponding to particles with radius R = 0.7 nm were fitted using two sets of values of the energy gap and damping constant: $latex Eg = 2.3 eV \ and \ \gamma_{\mathrm {b}}=158~\mathrm {meV}/\hbar \ or \ Eg = 2.1 eV \ and \ \gamma_{\mathrm {b}}=200~\mathrm {meV}/ \hbar$. For the second model, a simple assumption for the electronic density of states and its contribution to the dielectric function in terms of size allowed to adjust extinction spectra for all samples explored (from 0.3 to 1.6 nm radius). This last model uses only one parameter, a scale factor R0 = 0.35 nm, that controls the contribution of the bound electrons in nanoparticles. Contrast between the maximum and the minimum in the extinction spectra near the resonance at 520 nm or alternatively the broadening of the plasmon band can be used to determine the size of gold nanoparticles with radius smaller than 2 nm

Sobre el uso del sistema KCl:Eu⁺² para estudiar el contenido de ozono atmosférico

Las zonas de absorción del sistema luminiscente KCl:Eu⁺² se ajustan muy bien para detectar variaciones en la transmisión de la radiación solar provocadas por el cambio en el contenido se ozono atmosférico. Se describe un dispositivo pequeño y liviano basado en este proceso adecuado para realizar perfilajes desde globos zonda.Centro de Investigaciones Óptica

Fundamentos de láser : I - Aplicaciones en terapia médica

Este libro refleja mi actividad docente de más de 40 años en la UNLP, especialmente en las facultades de Ciencias Exactas e Ingeniería. Esta labor incluye el contacto con prácticamente todas las licenciaturas en ciencias y con todas las ramas de la ingeniería. Agradezco a todos los estudiantes que han compartido este camino con distinto grado de entusiasmo, rescatando especialmente a aquellos que por su lejanía con la temática específica de mis cursos, presentaron los mayores desafíos. Este camino incluye también la actividad docente de posgrado que incluye tanto a los estudiantes de doctorado como a los de distintas maestrías. Les agradezco entonces a aquellos que me han permitido estar en la frontera del conocimiento. Por último no puedo dejar de agradecerles a mis compañeros del Centro de Investigaciones Ópticas el compartir tantas horas de trabajo en las cuales las discusiones sobre la docencia ocuparon una buena parte.Facultad de Ciencias Exacta

Size dependence of refractive index of gold nanoparticles

The extinction spectra of spherical gold nanoparticles suspended in a homogeneous media were measured and the results were adjusted with Mie’s theory together with an appropriate modification of the optical properties of bulk material considering the limitation that introduces the size of nanoparticles on the dielectric function. Usually, the contribution of free electrons to the dielectric function is modified for particle size, while the contribution of bound electrons is assumed to be independent of size. This work discusses the separated contribution of free and bound electrons on the optical properties of particles and their variation with size for gold nanoparticles. The effects of dielectric function and its changes with size on extinction spectra near plasmon resonance are considered. The damping constant for free electrons was changed with size as usual and a scattering constant of C = 0.8 was used. For the bound electron contribution, two different models were analysed to fit the extinction spectra: on the one hand, the damping constant for interband transitions and the gap energy were used as fitting parameters and on the other, the electronic density of states in the conduction band was made size dependent. For the first model, extinction spectra corresponding to particles with radius R = 0.7 nm were fitted using two sets of values of the energy gap and damping constant: Eg = 2.3 eV and γb = 158 meV/h or Eg =2 .1 eV and γb = 200 meV/ h . For the second model, a simple assumption for the electronic density of states and its contribution to the dielectric function in terms of size allowed to adjust extinction spectra for all samples explored (from 0.3 to 1.6 nm radius). This last model uses only one parameter, a scale factor R0 0.35 nm, that controls the contribution of the bound electrons in nanoparticles. Contrast between the maximum and the minimum in the extinction spectra near the resonance at 520 nm or alternatively the broadening of the plasmon band can be used to determine the size of gold nanoparticles with radius smaller than 2 nm.Facultad de IngenieríaCentro de Investigaciones Óptica

Centro de Investigaciones Ópticas (CIOp)

Exposición realizada en el marco del  Encuentro del Ministerio de la Producción, Ciencia y Tecnología de la Provincia de Buenos Aires con autoridades y centros de la Comisión de Investigaciones Científicas de la Provincia de Buenos Aires. Exposiciones de los directores de los Centros de Investigación propios, asociados y vinculados

Thermal effects in phase-conjugation in saturable absorbers with picosecond pulses

Phase conjugation reflcction with efficiencies of 400% for microsecond pulses and ~50% Tur picosecond pulses has been obtained in saturable absorber dye Solutions. The effect of difTcrcnt solvcnls on thc gencration of the thermal pitase grating involved was investigated

Picosecond phase-conjugate reflection from organic dye saturable absorbers

Phase conjugation with conversion efficiences of up to 50% has been obtained in DODCI and other saturable absorbers with picosecond pulses from a mode-locked dye laser. Reflectivity shows a quadratic dependence on pump intensity up to $latex \sim 500 \ MW cm-2

Relajación de moléculas de colorantes orientadas por campo eléctrico en películas acrílicas

Se determinó la evolución temporal de la absorbancia de películas acrílicas dopadas con el colorante Disperse Red 1 y orientadas bajo un campo eléctrico intenso con el fin de analizar el proceso de relajación espacial. Los resultados se ajustaron con el modelo de Kohlrausch-Williams-Watts y con una función biexponencial. Se presentan además resultados de generación de segunda armónica como prueba de la orientación y ruptura de la centrosimetría del medio.Measurements of optical absorbance was used to study the relaxation of acrylic films doped with a dye and poled by electric field. Results were adjusted by the model of Kohlrausch-Williams-Watts and a biexponencial funtion. Second harmonic generation was presented as a test of orientation and the lack of symmetry of the poled film.Centro de Investigaciones Óptica

Population mechanisms in visible carbon monoxide pulsed lasers

The population mechanism in the Ångstrom system of a CO pulsed laser are studied through analysis of the rotational intensities distribution of the emitted bands. The observed spectra were simulated by using a simple excitation model. The results suggest that, apart from electron impact, there is a strong radiative contribution of the VUV 4+system to the gain of the visible emission through a selective depletion of the lower laser level

Alternative method for concentration retrieval in differential optical absorption spectroscopy atmospheric gas pollutant measurements

Differential optical absorption spectroscopy is a widely used technique for open-column atmospheric-gas pollution monitoring. The concentration retrieval is based on the fitting of the measured differential absorbance through the Lambert-Beer law. We present an alternative method for calculating the gas concentration on the basis of the proportionality between differential absorbance and differential absorption cross section of the gas under study. The method can be used on its own for single-component analysis or as a complement to the standard technique in multicomponent cases. The performance of the method for the case of cross interference between two gases is analyzed. The procedure can be used with differential absorption cross sections measured in the laboratory or taken from the literature. In addition, the method provides a criterion to discriminate against different species having absorption features in the same wavelength range