Biomedical subjects

L Misoguti

Publications and source records attributed to L Misoguti.

7 recordsLinked to original sources

PubMed2004

In situ UV-vis absorbance measurements for Langmuir films of poly[4'-[[2-(methacryloyloxy)-ethyl]ethylamino]-2-chloro-4-nitroazobenzene] (HPDR13) azopolymer.

In situ UV-vis absorbance measurements are used to investigate aggregation in Langmuir films from the azopolymer poly[4'-[[2-(methacryloyloxy)-ethyl]ethylamino]-2-chloro-4-nitroazobenzene] (HPDR13), a methacrylate derivative of DR13. The level of aggregation in a Langmuir film is intermediate between that of HPDR13 in chloroform solution and in a deposited LB film, as expected. Absorption is negligible at large areas per monomer, and starts to increase at a critical area that is the same as the one obtained in surface potential isotherms, being close to twice the area per monomer for a condensed film. This indicates that the onset for light absorption coincides with a critical packing density where monolayer structuring occurs and there is a sharp change in the effective dielectric constant of the film/water interface. Consistent with a featureless pressure-area isotherm for HPDR13, denoting no significant molecular rearrangement upon film compression, the UV-vis spectra did not vary with the surface pressure. The intensity of absorbed light increased, though, as the film was compressed owing to a higher density of chromophores. At higher subphase temperatures, larger flexibility of HPDR13 chains led to a more compact arrangement, causing the area per monomer to decrease and the absorbed light to increase-with approximately opposite trends.

Journal Article↗

PubMed2003

High-efficiency multipass optical limiter.

We report experimental results on a highly efficient optical limiter that uses a three-mirror, multipass ring configuration. The optical limiter's enhanced performance is based on the accumulative effect that is achieved when the laser beam passes through the sample several consecutive times. Its feasibility was demonstrated for media with different limiting action processes, namely, reverse saturable absorption, nonlinear scattering, and thermal lensing. We employed a frequency-doubled, Q-switched, 10-ns Nd:YAG laser operating at a 5-Hz repetition rate.

Journal Article↗

PubMed2001

Generation of broadband VUV light using third-order cascaded processes.

We report the first demonstration of broadband VUV light generation through cascaded nonlinear wave mixing in a gas. Using a hollow-fiber geometry to achieve broad-bandwidth phase-matching, frequency conversion of ultrashort-pulse Ti:sapphire laser pulses from the visible into the deep UV around 200 and 160 nm is achieved. A new type of quasi-phase-matching is also observed in the VUV for the first time. Conversion using cascaded processes exhibits higher efficiencies, shorter pulse durations, and broader bandwidths than other schemes for generating light in the deep UV, and will enable many applications in science and technology.

Journal Article↗

PubMed2000

Shaped-pulse optimization of coherent emission of high-harmonic soft X-rays

When an intense laser pulse is focused into a gas, the light-atom interaction that occurs as atoms are ionized results in an extremely nonlinear optical process--the generation of high harmonics of the driving laser frequency. Harmonics that extend up to orders of about 300 have been reported, some corresponding to photon energies in excess of 500 eV. Because this technique is simple to implement and generates coherent, laser-like, soft X-ray beams, it is currently being developed for applications in science and technology; these include probing the dynamics in chemical and materials systems and imaging. Here we report that by carefully tailoring the shapes of intense light pulses, we can control the interaction of light with an atom during ionization, improving the efficiency of X-ray generation by an order of magnitude. We demonstrate that it is possible to tune the spectral characteristics of the emitted radiation, and to steer the interaction between different orders of nonlinear processes.

Journal Article↗

PubMed2000

A comparative study of nanosecond and picosecond laser ablation in enamel: morphological aspects.

OBJECTIVE: We have investigated and compared the main morphological features of human enamel tissue under Nd:YAG nanosecond and picosecond laser ablation. BACKGROUND DATA: The use of ultrashort laser pulses on teeth ablation is an alternative to avoid overheating and presents the advantage of minimizing the volume of damaged material during laser ablation. Comparison of the morphology obtained in laser ablation using nanosecond and picosecond laser pulses is a way to investigate the advantages of ultrashort laser pulses for ablation. METHODS: Trains of pulses with picosecond duration from a Q-switched and mode-locked Nd:YAG laser and pulses with nanosecond duration from a Q-switched Nd:YAG laser, both operating at 15 Hz kept at the same average power, were focused in human sound molars for 30 sec. Drilled holes with different morphological characteristics were observed using several laser intensity regimes. Enamel surfaces were examined using a scanning electron microscope (SEM) and their morphological characteristics compared. RESULTS: An interesting contrast between the morphology of the enamel when treated with different level of laser power and pulse duration was observed. Picosecond pulses promote a better-defined material removal with a minimum intermediate region, whereas nanosecond pulses at the equivalent average power level cause a large intermediate modified region between ablated and normal tissue, as well as a complete superficial modification of the existent original structure. CONCLUSION: Our results show an important correlation between the surface morphology and the pulse width of the lasers, suggesting advantages toward the use of ultrashort laser pulses in dentistry.

Dental Caries↗

PubMed1999

Characterization of enamel and dentin response to Nd:YAG picosecond laser ablation.

OBJECTIVE: We investigated the main characteristics of human dental tissue under Nd:YAG picosecond laser ablation. SUMMARY BACKGROUND DATA: The use of ultrashort laser pulses for teeth ablation prevents overheating and is an alternative for mechanical material removal; it also minimizes the volume of damaged material. METHODS: Laser pulses of picosecond at 15 Hz repetition rates from a Q-switched and mode-locked Nd:YAG laser were focused on sound human molars for 30 seconds. Variation of light intensity in the pulse train allowed us to obtain drilled holes with different characteristics. Enamel and dentin surfaces were examined by optical and scanning electron microscope (SEM). The samples consisted of three sound human molars. The ablation rate was determined after taking an average of all samples. RESULTS: Images from the SEM showed an interesting contrast between the morphology of the ablated enamel and dentin regions. In enamel, the ablated region appears to be more superficial than in dentin. The dentin fragility normally causes cracks that originate in the ablated region. The ablation rates in both enamel and dentin demonstrate a saturation behavior as the laser intensity increases. Furthermore, the ablation rate in dentin is about eight times greater than in enamel for the same laser fluence. CONCLUSION: Our results show an important correlation between the surface morphology and the pulsed laser fluence, which is compatible to the ablation mechanisms presented when ultrashort laser pulses are used.

Dental Enamel↗

PubMedDate not supplied

Light-induced storage in layer-by-layer films of chitosan and an azo dye.

The buildup of layer-by-layer (LBL) films from chitosan and the azodye Ponceau-S (PS) was investigated under various experimental conditions, and the resulting films were used in optical storage experiments. The kinetics for the writing process in optical storage was faster for LBL films prepared at low pHs, probably because the films had a larger free volume for isomerization of the chromophores. The nanostructured nature of the LBL films also affected the crystallinity of chitosan, which was considerably decreased in this type of film as chitosan became protonated because of the electrostatic interactions between adjacent layers.

Azo Compounds↗