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At least 19 recordsLinked to original sources
PubMed2026

Comparison of a 755-nm picosecond laser and a 1565-nm nonablative fractional laser for the treatment of atrophic acne scars: a 20-week prospective, randomized, split-face clinical study.

To compare the efficacy and safety of a 755-nm picosecond laser with a diffractive lens array (P-DLA) and a 1565-nm nonablative fractional laser (NAFL) for the treatment of atrophic acne scars. Twenty-seven patients with atrophic acne scars underwent three sessions of randomized split-face treatment with P-DLA and NAFL at 4-week intervals. Patients were followed up at 1, 2, and 3 months after the final treatment. Efficacy was assessed using the &#xc9;chelle d'&#xc9;valuation Clinique des Cicatrices d'Acn&#xe9; (ECCA) grading scale, the Investigator's Global Assessment (IGA) score, patients' self-rated improvement, and overall satisfaction. Treatment-related adverse reactions were recorded daily by patients until resolution. Both modalities demonstrated significant improvements in scar appearance based on ECCA score, IGA score, and patients' self-rated improvement (P&#x2009;<&#x2009;0.001). No statistically significant differences in efficacy were observed between the two treatments. However, the P-DLA group showed higher patient satisfaction (P&#x2009;=&#x2009;0.035) and a more favorable safety profile, including shorter durations of erythema and edema and the absence of crusting. Both P-DLA and NAFL were effective and safe for the treatment of atrophic acne scars, with similar efficacy. P-DLA offered better tolerability.

Humans↗
PubMed1979

Analysis of picosecond laser induced fluorescence phenomena in photosynthetic membranes utilizing a master equation approach.

A Pauli master equation is formulated and solved to describe the fluorescence quantum yield, phi, and the fluorescence temporal decay curves. F(t), obtained in picosecond laser excitation experiments of photosynthetic systems. It is assumed that the lowering of phi with increasing pulse intensity is due to bimolecular singlet exciton annihilation processes which compete with the monomolecular exciton decay processes; Poisson statistics are taken into account. Calculated curves of phi as a function of the number of photon hits per domain are compared with experimental data, and it is concluded that these domains contain at least two to four connected photosynthetic units (depending on the temperature), where each photosynthetic unit is assumed to contain approximately 300 pigment molecules. It is shown that under conditions of high excitation intensities, the fluorescence decays approximately according to the (time)1/2 law.

Kinetics↗
PubMed1977

Picosecond laser study of fluorescence lifetimes in spinach chloroplast photosytem I and photosystem II preparations.

Fractions enriched in either Photosystem I or Photosystem II have been prepared from chloroplasts with digitonin. A more detailed analysis of the decay kinetics of fluorescence excited by a picosecond laser pulse has been possible compared to experiments with unfractionated systems. The Photosystem I fractions show a very short component (less than or equal to 100 ps) at room temperature which is apparently independent of pulse intensity over the range of photon densities used (5 - 10(13)--1 - 10(16) photons cm-2). The Photosystem II fraction has a short initial lifetime at room temperature which is strongly intensity-dependent approaching 500 ps at low photon densities, but decreasing to close to 150 ps at the highest photon densities. All of these room temperature decays appear to be non-exponential, and may possibly be fitted by at t1/2 expression, expected from a random diffusion of excitations via Förster energy transfer. On cooling to 77K, lifetimes of both Photosystem I and Photosytem II increase, the lengthening with Photosystem I being more striking. The Photosystem I decays become intensity dependent like the Photosystem II, and at the lowest photon densities decays which are more nearly exponential within the experimental error give initial lifetimes of about 2 ns. The non-exponential decays seen at high photon densities appear to fit a t1/2 expression.

Chloroplasts↗
PubMed1976

Picosecond kinetics of chlorophyll and chlorophyll/quinone solutions in ethanol.

The mechanism of quenching by quinones of the lowest excited singlet state of chlorophyll has been investigated using picosecond laser spectroscopy. With chlorophyll alone, laser excitation resulted in immediate (less than 10 ps) bleaching of the 665 nm band and production of new absorption bands in the regions 460-550 and 800-830 nm. The lifetimes of these changes were greater than 500 ps. Addition of 2,6-dimethylbenzoquinone caused quenching of these absorbance changes. No indication of chlorophyll cation radical formation was obtained. Thus, the interaction between quinone and the chlorophyll excited singlet state results in energy dissipation without measurable formation of radical species having lifetimes longer than 10 ps. This is in marked contrast to the quenching of the chlorophyll lowest triplet state by quinones, during which easily detectable stable radical formation has been observed.

Chlorophyll↗
PubMed1978

Spectroscopic studies of oxy- and carbonmonoxyhemoglobin after pulsed optical excitation.

The photolysis of HbO2 and HbCO has been investigated with picosecond laser techniques. Transient absorption spectra were measured in the Soret and visible regions after excitation with 353- or 530-nm pulses. The photoproducts appeared within 8 psec and exhibited considerably broadened deoxyhemoglobin-like spectra, which persisted to 680 psec. The altered spectra are attributed to the production of deoxyheme conformational and spin states that might result from the intense excitation.

Carboxyhemoglobin↗
PubMed1977

Picosecond and microsecond pulse laser studies of exciton quenching and exciton distribution in spinach chloroplasts at low temperatures.

Studies of the fluorescence quantum yield and decay times, determined at the emission maxima of 685 and 735 nm, using picosecond laser pulses for excitation, indicate that the pigments which are responsible for the 735 nm emission derive their energy by transfer of singlet excitons from the light-harvesting pigments and not by direct absorption of photons. Microsecond pulse laser studies of the fluorescence quantum yields at these two fluorescence wavelengths indicate that long lived quenchers (most probably triplet states), which quench singlet excitions, accumulate preferentially within the long wavelength pigment system which gives rise to the 735 nm emission band.

Chloroplasts↗
PubMed1979

Suprathreshold retinal damage due to single 6 picosecond 1060 nm laser light pulses.

The retinas of rhesus monkeys were exposed to 6 ps laser light pulses at 1060 nm at 62 and 95 muJ. Lesions were examined by light and transmission and scanning electron microscopy. Evidence of damage was seen in all retinal layers, being most severe in the photoreceptor inner and outer segments. In addition to damage mechanisms previously proposed, it is suggested that the peak power flux density achieved with extremely short pulses may lead to some absorbance by inner retinal layers.

Animals↗
PubMed1979

Quenching of fluorescence by triplet excited states in chloroplasts.

The fluorescence quantum yield in spinach chloroplasts at room temperature has been studied utilizing a 0.5-4.0 mus duration dye laser flash of varying intensities as an excitation source. The yield (phi) and carotenoid triplet concentration were monitored both during and following the laser flash. The triplet concentration was monitored by transient absorption spectoscopy at 515 nm, while the yield phi following the laser was probed with a low intensity xenon flash. The fluorescence is quenched by factors of up to 10-12, depending on the intensity of the flash and the time interval following the onset of the flash. This quenching is attributed to a quencher Q whose concentration is denoted by Q. The relative instantaneous concentration of Q was calculated from phi utilizing the Stern-Volmer equation, and its buildup and decay kinetics were compared to those of carotenoid triplets. At high flash intensities (greater than 10(16) photon . cm-2) the decay kinetics of Q are slower than those of the carotenoid triplets, while at lower flash intensities they are similar. Q is sensitive to oxygen and it is proposed that Q, at the higher intensities, is a trapped chlorophyll triplet. This hypothesis accounts well for the continuing rise of the carotenoid triplet concentration for 1-2 mus after the cessation of the laser pulse by a slow detrapping mechanism, and the subsequent capture of the triplet energy by carotenoid molecules. At the maximum laser intensities, the carotenoid triplet concentration is about one per 100 chlorophyll molecules. The maximum chlorophyll ion concentration generated by the laser pulses was estimated to be below 0.8 ions/100 chlorophyll molecules. None of the observations described here were altered when a picosecond pulse laser train was substituted for the microsecond pulse. A simple kinetic model describing the generation of singlets and triplets (by intersystem crossing), and their subsequent interaction leading to fluorescence quenching, accounts well for the observations. The two coupled differential equations describing the time dependent evolution of singlet and triplet excited states are solved numerically. Using a single-triplet bimolecular rate constant of gammast = 10(-8) cm3 . s-1, the following observations can be accounted for: (1) the rapid initial drop in phi and its subsequent levelling off with increasing time during the laser pulse, (2) the buildup of the triplets during the pulse, and (3) the integrated yield of triplets per pulse as a function of the energy of the flash.

Carotenoids↗
PubMedDate not supplied

Chlorophyll orientation and exciton migration in the photosynthetic membrane.

Measurements of the linear dichroism and of the polarization of the fluorescence with oriented chloroplasts have revealed a definite orientation of the pigment molecules with respect to the membrane plane. The Qy transition moments of the chlorophyll a molecules are more closely inclined with respect to this plane for the forms absorbing at longer wavelengths than for those absorbing at shorter wavelengths. The fluorescence depolarization by energy transfer, determined with magnetically-oriented chloroplasts, indicates that the degree of local order increases with wavelength for the different (absorption wavelength) forms of chlorophyll a in vivo. Laser pulses of either picosecond or microsecond duration have been used to probe the emission spectrum, lifetime and quantum yield of fluorescence of chloroplasts at various temperatures. With single picosecond pulses, singlet-singlet annihilations occur within the light-harvesting chlorophyll molecules. In the case of microsecond pulses, triplet excitions act as efficient quenchers of the singlets. By monitoring both the yield of carotenoid triplets and of the fluorescence during and after a laser flash, one can show that the carotenoid triplets account for part of but not all the fluorescence quenching.

Chlorophyll↗
PubMed1977

Exciton annihilation in the two photosystems in chloroplasts at 100 degrees K.

The fluorescence yield (F) of spinach chloroplasts at 100 degrees K measured at 735 nm (photosystem I fluorescence-F 735) and at 685 nm (photosystem II fluorescence-F 685) has been determined with different modes of laser excitation. The modes of excitation included a single picosecond pulse, sequences of picosecond pulses (4, 22, and 300 pulses spaced 5 ns apart) and a single nonmode-locked 2-mus pulse (MP mode). The F 735/F 685 intensity ratios decrease from 1.62 to 0.61 when a single picosecond pulse (or low-power continuous helium-neon laser) is replaced by excitation with the 300-ps pulse train (PPT mode) or MP mode. In the PPT mode of excitation, the 735-nm fluorescence band is quenched by a factor of 45 as the intensity is increased from 10(15) to 10(18) photons/cm(2) per pulse train and the 685-nm fluorescence is quenched by a factor of 10. In the MP mode, the quenching factors are 25 and 7, respectively, in the same intensity range. Fluorescence quantum yield measurements with different picosecond pulse sequences indicate that relatively long-lived quenching species are operative, which survive from one picosecond pulse to another within the pulse train. The excitonic processes possible in the photosynthetic units are discussed in detail. The differences in the quenching factors between the MP and PPT modes of excitation are attributed to singlet-singlet annihilation, possible when picosecond pulses are utilized, but minimized in the MP mode of excitation. The long-lived quenchers are identified as triplets and/or bulk chlorophyll ions formed by singlet-singlet annihilation. The preferential quenching in photosystem I is attributed to triplet excitons. The influence of heating effects, photochemistry, bleaching, and two-photon processes is also considered and is shown to be negligible.

Chloroplasts↗
PubMed1978

Modulation of the primary electron transfer rate in photosynthetic reaction centers by reduction of a secondary acceptor.

Photosynthetic application of picosecond spectroscopic techniques to bacterial reaction centers has led to a much greater understanding of the chemical nature of the initial steps of photosynthesis. Within 10 ps after excitation, a charge transfer complex is formed between the primary donor, a "special pair" of bacteriochlorophyll molecules, and a transient acceptor involving bacteriopheophytin. This complex subsequently decays in about 120 ps by donating the electron to a metastable acceptor, a tightly bound quinone.Recent experiments with conventional optical and ESR techniques have shown that when reaction centers are illuminated by a series of single turnover flashes in the presence of excess electron donors and acceptors, a stable, anionic ubisemiquinone is formed on odd flashes and destroyed on even flashes, suggesting that the acceptor region contains a second quinone that acts as a two-electron gate between the reaction center and subsequent electron transport events involving the quinone pool.Utilizing standard picosecond techniques, we have examined the decay of the charge transfer complex in reaction centers in the presence of the stable semiquinone, formed by flash illumination with a dye laser 10 s before excitation by a picosecond pulse. In this state the decay rate for the charge transfer complex is considerably slower than when no electron is present in the quinone acceptor region. This indicates fairly strong coupling between constituents of the reaction center-quinone acceptor complex and may provide a probe into the relative positions of the various components.

Bacteriochlorophylls↗
PubMed1978

Picosecond chemical and biological events.

Picosecond spectroscopy is a relatively new field of science that utilizes ultrashort laser pulses to monitor events taking place in the 10(-12) second regime. The continuing development of picosecond spectroscopy has made possible the detection and measurement of the primary events in many physical and tiological processes. This article describes a currently used picosecond spectroscopy system that is capable of reliably recording picosecond events. Two areas of picosecond research are discussed; one concerns the interaction of electrons in fluids, and the second the primary events in vision.

Chemical Phenomena↗
PubMed1975

Primary charge separation in bacterial photosynthesis: oxidized chlorophylls and reduced pheophytin.

Bacteriopheophytin, the magnesium-free base of bacteriochlorophyll, undergoes reversible one-electron reduction in organic solvents to yield an anionic free radical with characteristic optical and electron spin resonance spectra. The reduction potential of bacteriopheophytin, E1/2 approximately --0.55 V against a normal hydrogen electrode, compared to E1/2 approximately --0.85 V for bacteriochlorophyll, renders it a likely electron acceptor in the primary charge separation of photosynthesis. Comparison of these data with picosecond optical changes recently observed upon pulsed laser excitation of bacterial reaction centers leads us to propose that bacteriopheophytin is indeed a transient electron acceptor and that the primary charge separation of bacterial photosynthesis occurs between the bacteriochlorophyll complex P870 and bacteriopheophytin to yield the radicals of the oxidized chlorophyll dimer cation and reduced pheophytin anion.

Bacteriochlorophylls↗
PubMed1979

Nanosecond X-ray diffraction from biological samples with a laser-produced plasma source.

By using 4.45-angstrom radiation generated by Cl+15 ions in a laser plasma and nanosecond exposures, low-angle x-ray diffraction patterns were obtained from dried rat spinal nerves and a powder of cholesterol. Three to four 400-picosecond, 45-joule pulses were required for the exposure. This new technique should have wide application in structural kinetic studies.

Animals↗
PubMed1979

Photochemistry of rhodopsin and isorhodopsin investigated on a picosecond time scale.

Bovine rhodopsin and isorhodopsin were excited with a single 530-nm, 7-ps light pulse emitted by a mode-locked Nd 3+ glass laser at room temperature. Within 3 ps of excitation, absorbance changes due to formation of bathorhodopsin were observed. The difference spectra generated during and 100 ps after pulse excitation are presented. The data show that bathorhodopsin formation is completed within 3 ps for both the primary pigments and suggest that a single common bathorhodopsin is photochemically formed from both primary pigments. Our findings provide additional support for the cis-trans isomerization model of the primary event in vision. Additional absorption transients that were observed near 670 and 460 nm are discussed.

Animals↗