PubMed Health⌕ Search

Biomedical subjects

P Laporta

Publications and source records attributed to P Laporta.

15 recordsLinked to original sources
PubMed2006

Observation of dynamic localization in periodically curved waveguide arrays.

We report on a direct experimental observation of dynamic localization (DL) of light in sinusoidally-curved lithium-niobate waveguide arrays which provides the optical analog of DL for electrons in periodic potentials subjected to ac electric fields as originally proposed by Dunlap and Kenkre [Phys. Rev. B 34, 3625 (1986)10.1103/PhysRevB.34.3625]. The theoretical condition for DL in a sinusoidal field is experimentally demonstrated.

Journal Article↗
PubMed2006

Imaging of Bloch oscillations in erbium-doped curved waveguide arrays.

We report a direct observation of Bloch-like dynamics of light in curved waveguide arrays manufactured in Er:Yb-doped phosphate glass by femtosecond laser writing. The green upconversion fluorescence emitted by excited erbium ions is exploited to image the flow of the guided pump light at approximately 980 nm along the array. Direct and clear evidence of periodic light breathing for single-waveguide excitation, closely related to Bloch oscillations, is reported.

Journal Article↗
PubMed2006

[Cormobidity of sensorineural hearing loss and other autoimmune diseases. Usefulness of laboratory tests].

OBJECTIVES: To value if the sensorineural hearing loss (SHL) in several autoimmune diseases (AD) is also secondary to immunomediation. PATIENTS AND METHODS: In 342 cases with SHL and any AD and 301 normoacoustic controls with AD a non-specific immunologic battery of tests and a Western-blot (WB) for anticochlear autoantibodies were developed, and cases with SHL were treated with deflazacort. RESULTS: Alterations in non-specific battery were similar between cases and controls. But a 12,5% of cases with SHL and a 1,6% of normoacoustic showed a positive WB (p<0,001). Steroid therapy improved hearing in 14,3% of cases. In them, sensitivity and specificity of non-specific battery were 78,4% and 75,5%, respectively, to predict response to therapy. These were 98,9% and 81,6% for WB. CONCLUSIONS: The SHL in cases with AD can be considered immunomediated in a discrete average, but the diagnostic efficiency of WB to predict an improvement after steroid therapy is high.

Adult↗
PubMed2005

Slow light in periodic superstructure Bragg gratings.

A theoretical and experimental analysis of group velocity reduction in periodic superstructure Bragg gratings is presented. Experimental demonstration of group velocity reduction of sub-nanosecond pulses at the wavelength of optical communications is reported using a Moiré fiber grating.

Journal Article↗
PubMed2005

Beam dynamics and wave packet splitting in a periodically curved optical waveguide: multimode effects.

A theoretical and experimental analysis of beam dynamics and wave packet splitting of light in a periodically bent optical waveguide, a phenomenon recently observed [Phys. Rev. Lett. 94, 073002 (2005)] which is the optical equivalent of adiabatic stabilization of atoms in intense and high-frequency laser fields, is presented in the multimode operational regime. Inhibition of wave packet splitting is theoretically predicted and experimentally observed for higher-order mode excitation.

Journal Article↗
PubMed2004

Er:Yb-doped waveguide laser fabricated by femtosecond laser pulses.

Laser action is demonstrated in a 20-mm-long waveguide fabricated on an Er:Yb-doped phosphate glass by femtosecond laser pulses. An output power of 1.7 mW with approximately 300 mW of pump power coupled into the waveguide is obtained at 1533.5 nm. Waveguides are manufactured with the 520-nm radiation from a frequency-doubled, diode-pumped, cavity-dumped Yb:glass laser operating at a 166-KHz repetition rate, with a 300-fs pulse duration.

Journal Article↗
PubMed2004

[Anticochlear antibodies titles measured by Western-blot and hearing recovery level after corticoid therapy in patients with sudden deafness].

OBJECTIVES: Detection of antichoclear antibodies in patients with sudden deafness (SD) ranges from five to forty one percent depending on authors. We tried to correlate the level of antibodies measured by Western-blot (WB) and hearing loss. PATIENTS AND METHODS: Forty nine subjects bearing of SD and a positive WB for bovine cochlear antigen. Hearing loss average was measured at the onset and after treatment with deflazacort 1 mg/kg per day by means of audiometry, and antibody titles were quantified in the diluted sera. RESULTS: Initial loss was 49.4+/-20.6%, and after corticotherapy it was 15.9+/-18.0%. There was no statistically significative correlation titles-hearing loss (y=0.1122x+30.613; R2=0.7552) nor titles-recovery (y=-0.0818x+8.,65; R2=0.3229). CONCLUSIONS: Although predictive capability for treatment response is accepted for WB, quantifying of the antibody titles in patients with SD does not allow to make a prognosis about the average hearing recovery.

Adult↗
PubMed2003

Sub-100-ps amplitude-modulation mode-locked Tm-Ho:BaY2F8 laser at 2.06 microm.

We report the generation of sub-100-ps pulse trains near the 2.06-microm wavelength in an actively mode-locked diode-pumped Tm-Ho:BaYF laser operating at room temperature. Transform-limited, 97-ps Gaussian pulses at a 100-MHz repetition rate with an average power in excess of 20 mW and with a carrier wavelength tunable by approximately 50 nm near 2.066 microm are demonstrated.

Journal Article↗
PubMed2003

Quantum-mechanical analogy of beam propagation in waveguides with a bent axis: dynamic-mode stabilization and radiation-loss suppression.

Wave propagation in an optical waveguide with a bent axis is studied under the scalar and paraxial wave approximations, and the quantum mechanical analogy with the electron dynamics in an atomic potential interacting with an intense electromagnetic field is highlighted. In particular we show that for a truncated parabolic waveguide with a periodically curved axis, a dynamic mode splitting with reduced radiation losses can be observed, which is fully analogous to the phenomenon of wave packet dichotomy and ionization quenching found in strong-field atomic physics.

Journal Article↗
PubMed2002

Measurement of superluminal optical tunneling times in double-barrier photonic band gaps.

Tunneling of optical pulses at 1.5 microm wavelength through double-barrier periodic fiber Bragg gratings is experimentally investigated in this paper. Tunneling time measurements as a function of the barrier distance show that, far from resonances of the structure, the transit time is paradoxically short--implying superluminal propagation--and almost independent of the barrier distance. This result is in agreement with theoretical predictions based on phase-time analysis and provides, in the optical context, an experimental evidence of the analogous phenomenon in quantum mechanics of nonresonant superluminal tunneling of particles across two successive potential barriers.

Journal Article↗
PubMed2002

Experimental observation of superluminal pulse reflection in a double-Lorentzian photonic band gap.

We report on the experimental observation of superluminal reflection of picosecond optical pulses at 1.5 microm using a specially designed 30-cm-long fiber Bragg grating (FBG) that realizes a spectral reflectivity profile given by the superposition of two closely spaced Lorentzian lines. Probing pulses of 380 ps duration tuned midway between the two Lorentzian lines are reflected without appreciable distortion with a measured peak pulse advancement of approximately 60 ps. The achievement of the negative group delay is due to the interference of the two resonance modes of the FBG structure and has a close connection to the phenomenon of negative group velocity for pulse propagation in an inverted medium possessing a doublet line.

Journal Article↗
PubMed2001

Superluminal optical pulse propagation at 1.5 microm in periodic fiber Bragg gratings.

We report on the experimental observation of superluminal tunneling of picosecond optical pulses in a periodic fiber Bragg grating. Optical pulses of 380-ps duration, generated by an externally-modulated single-frequency erbium-ytterbium laser operating near 1.5-microm wavelength, were propagated at a group velocity greater than approximately 1.97 times the speed of light in vacuum across a 2-cm long fiber grating. Owing to the very large ratio between the thickness of the barrier (2 cm) and the wavelength of probing optical pulses ( approximately 1.5 microm), our experiment allows for the observation of superluminal tunneling in the optical region by direct optoelectronic time-domain measurements.

Journal Article↗
PubMed2000

Excess noise in intracavity laser frequency modulation

The response to perturbations and to stochastic noise of a laser below threshold subjected to an intracavity periodic frequency modulation is theoretically studied. It is shown that, when the modulation frequency is close to the cavity axial mode separation but yet detuned from exact resonance, the laser exhibits a strongly enhanced sensitivity to external noise, which includes large transient energy amplification of perturbations in the deterministic case and enhancement of field fluctuations in presence of a continuous stochastic noise. This large excess noise is due to the nonorthogonality of Floquet laser modes which makes it possible continuous energy transfer from the forcing noise to transient growing perturbations.

Journal Article↗
PubMed1983

Effects of laser irradiation on hematoporphyrin-treated normal and transformed thyroid cells in culture.

Laser irradiation of tissues treated in vivo with the hematoporphyrin derivative (HPD) is known to result in a cytocidal effect, reportedly more pronounced in the tumor than in the surrounding normal tissues. In order to ascertain if this phenomenon had a clear cellular basis, it has been now reproduced in vitro in a model system consisting of normal and transformed cell lines. Epithelial rat thyroid cells were infected and transformed with a RNA oncogenic virus. Both the original (normal) and the viral-transformed (tumorigenic) cells were incubated with HPD and exposed to two types of laser irradiation: 631 nm, continuous wave; and 337.1 nm, pulsed. Under the conditions tested, the percentage survival of the transformed cells was found to be lower (up to approximately 3 times) than that of the normal cells. The cytocidal effect was greater using the pulsed than using the continuous-wave irradiation. The difference between normal and tumor cells was more evident at 30 micrograms than at 50 micrograms of HPD per ml. The HPD not followed by laser irradiation had no effect on the cell growth rate. The findings of a significant difference in the sensitivity to photoactivated HPD between normal and tumor cells under strictly controlled and highly comparable conditions opens new possibilities to the study of the cellular and molecular mechanisms involved in the phototherapy of tumors. Furthermore, studies in vitro on the active components of the photosensitizer and on their selectivity towards the tumor cells, explained at a cellular level, will lead to better approaches to photochemotherapy in vivo.

Animals↗