High-intensity UV Laser Research Articles

Biphotonic Ionization of DNA: From Model Studies to Cell.

Oxidation reactions triggered by low-intensity UV photons represent a minor contribution with respect to the overwhelming pyrimidine base dimerization in both isolated and cellular DNA. The situation is totally different when DNA is exposed to high-intensity UVC radiation under conditions where biphotonic ionization of the four main purine and pyrimidine bases becomes predominant at the expense of singlet excitation processes. The present review article provides a critical survey of the main chemical reactions of the base radical cations thus generated by one-electron oxidation of nucleic acids in model systems and cells. These include oxidation of the bases with the predominant formation of 8-oxo-7,8-dihydroguanine as the result of preferential hole transfer to guanine bases that act as sinks in isolated and cellular DNA. In addition to hydration, other nucleophilic addition reactions involving the guanine radical cation give rise to intra- and interstrand cross-links together with DNA-protein cross-links. Information is provided on the utilization of high-intensity UV laser pulses as molecular biology tools for studying DNA conformational features, nucleic acid-protein interactions and nucleic acid reactivity through DNA-protein cross-links and DNA footprinting experiments.

Control of Charge Transfer in C60–ZnO Composite Under the Influence of UV Laser Radiation by the Methods of Raman Spectroscopy and Photoluminescence

Raman and photoluminescence spectra of nanostructured ZnO films with adsorbed C60 molecules were studied. The possibility of intensive C60–ZnO electronic coupling forming in this composite was investigated. It is shown that such an electron coupling can be significantly enhanced by irradiating the composite with high intensity UV laser radiation (λ = 325 nm).

Enhanced hot-electron production and strong-shock generation in hydrogen-rich ablators for shock ignition

Experiments were performed with CH, Be, C, and SiO2 ablators interacting with high-intensity UV laser radiation (5 × 1015 W/cm2, λ = 351 nm) to determine the optimum material for hot-electron production and strong-shock generation. Significantly more hot electrons are produced in CH (up to ∼13% instantaneous conversion efficiency), while the amount is a factor of ∼2 to 3 lower in the other ablators. A larger hot-electron fraction is correlated with a higher effective ablation pressure. The higher conversion efficiency in CH is attributed to stronger damping of ion-acoustic waves because of the presence of light H ions.

SFRR-E Basic Science Lecture (Elsevier sponsored) - Oxidative degradation pathways of cellular DNA: product formation and mechanistic insights

More than 100 oxidized purine and pyrimidine nucleosides including hydroperoxides and diastereomers have been characterized so far in extensive model studies. However, much less information is currently available on the oxidatively generated base damage to cellular DNA at the exception however of the overwhelming modifications produced by singlet oxygen ((1)O2). This is mostly due to analytical difficulties that are now, at least, partly overcome with the advent of the accurate and sensitive high performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry (HPLC/ESI-MS/MS). Hydroxyl radical ((•)OH) and one-electron oxidants that may be either endogenously formed through oxidative metabolism, phagocytosis, inflammation and other pathological conditions are predominantly at the origin of oxidatively generated damage to cellular DNA. It is worth mentioning that exposure of cells to exogenous physical agents (UVA light, high intensity UV laser, ionizing radiation) and chemicals such as bromate may also induce oxidatively generated damage to DNA. Emphasis is placed in this presentation on the critical survey of the main recently available information concerning the formation of (1)O2, (•)OH and one-electron oxidant-mediated single and more complex DNA damage (tandem lesions, intra- and interstrand cross-links, DNA-protein cross-links) arising from one radical hit. Evidence was provided that (•)OH and one-electron oxidants, through the generation of neutral radicals and radical cations respectively from nucleobases, are able to induce partly common degradation pathways. In addition selective oxidative reactions giving rise to specific degradation products of (•)OH and one-electron oxidation reactions that can be used as representative biomarkers of these oxidants have been identified. Emphasis was recently placed on the detection of oxidatively generated damage to cytosine and 5-methylcytosine in human cells.

Oxidatively generated base damage to cellular DNA by hydroxyl radical and one-electron oxidants: Similarities and differences

Hydroxyl radical (OH) and one-electron oxidants that may be endogenously formed through oxidative metabolism, phagocytosis, inflammation and pathological conditions constitute the main sources of oxidatively generated damage to cellular DNA. It is worth mentioning that exposure of cells to exogenous physical agents (UV light, high intensity UV laser, ionizing radiation) and chemicals may also induce oxidatively generated damage to DNA. Emphasis is placed in this short review article on the mechanistic aspects of OH and one-electron oxidant-mediated formation of single and more complex damage (tandem lesions, intra- and interstrand cross-links, DNA–protein cross-links) in cellular DNA arising from one radical hit. This concerns DNA modifications that have been accurately measured using suitable analytical methods such as high performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry. Evidence is provided that OH and one-electron oxidants after generating neutral radicals and base radical cations respectively may partly induce common degradation pathways. In addition, selective oxidative reactions giving rise to specific degradation products of OH and one-electron oxidation reactions that can be used as representative biomarkers of these oxidants have been identified.

Thermal sensitivity studies of fibre Bragg gratings inscribed by high-intensity femtosecond UV laser pulses

We studied the thermal sensitivity of fibre Bragg gratings (FBGs), fabricated in single-mode standard telecom (SMF-28) and photosensitive Ge/B codoped (Fibercore PS 1250/1500) fibres with high-intensity (140–210 GW/cm 2) 264 nm 220 fs laser pulses. The accurate measurement of Bragg wavelength thermal shift in the mentioned fibres brought about the values of 9.62 ± 0.04 and 8.03 ± 0.12 pm/°C, respectively. The comparison of the thermal sensitivity values for FBGs made in the same fibres by low-intensity UV irradiation or by another inscription technique (scanning phase mask instead of static one) did not reveal any significant differences. This confirms that the thermal sensitivity of Bragg gratings is determined only by the material parameters of the fibres and does not depend on the inscription mechanism and/or fabrication technique.

Proton Acceleration by High-Intensity UV Laser Irradiation with Thin Foils

Proton acceleration experiments using an intense ultraviolet laser were conducted for the first time. The laser system produced pulses having energies of up to 750 mJ at a wavelength of 248 nm with a temporal duration of 400 fs. Thin copper foils of 4 μm were used as targets, and the maximum intensity on the target was 1.3 × 1018 W/cm2. The highest energy of protons was 700 keV, which was observed when the laser beam was ppolarized and was incident on the target at an angle of 30°C . Fast electrons were generated by vacuum heating or resonance absorption because of the polarization dependence. These protons were accelerated in the target normal direction, which is suggestive of the target normal sheath acceleration mechanism (TNSA).

Long-period gratings in a standard telecom fibre fabricated by high-intensity femtosecond UV and near-UV laser pulses

We inscribed long-period gratings in a hydrogenated SMF-28 Corning fibre using a point-by-point technique and as a light source high-intensity (100–1000 GW cm−2) femtosecond (220–250 fs) pulses at the fourth, fifth and third harmonics (264, 211 and 352 nm, respectively) of Nd:glass laser radiation. The strength of the transmission loss peak reaches 30 dB in gratings recorded with a period of 300 µm and a length of 2 cm, which is significantly higher than the strength of long-period gratings inscribed with the same parameters by any other photochemical method. The analysis of the absorbed energy distribution revealed that such long-period gratings are induced via a two-photon absorption mechanism (or three-photon in the case of 352 nm excitation) and characterized by preferential energy deposition in the cladding, which leads to a high asymmetry of refractive index change (relative to the fibre core) and results in high birefringence properties of gratings formed by high-intensity UV and near-UV radiation.

Fiber Bragg grating inscription by high-intensity femtosecond UV laser light: comparison with other existing methods of fabrication: erratum

Get PDF Email Share Share with Facebook Tweet This Post on reddit Share with LinkedIn Add to CiteULike Add to Mendeley Add to BibSonomy Get Citation Copy Citation Text Stephen A. Slattery, David N. Nikogosyan, and Gilberto Brambilla, "Fiber Bragg grating inscription by high-intensity femtosecond UV laser light: comparison with other existing methods of fabrication: erratum," J. Opt. Soc. Am. B 22, 1143-1143 (2005) Export Citation BibTex Endnote (RIS) HTML Plain Text Citation alert Save article

Fiber Bragg grating inscription by high-intensity femtosecond UV laser light: comparison with other existing methods of fabrication

By use of high-intensity (approximately 200 GW/cm2) femtosecond 264-nm laser light and a phase mask technique, Bragg grating inscription in a range of different photosensitive and standard telecom fibers (both H2-free and H2-loaded) was studied. The dependences of the induced refractive index modulation versus the incident fluence as well as the thermal decay curves were compared with similar dependences for gratings fabricated by other existing methods. It was shown that with high-intensity UV laser irradiation, two-quantum photoreactions occur in the irradiated fiber core, that result in a significant photosensitivity enhancement of the investigated fibers in comparison with conventional low-intensity 248-nm exposure (by 6-128 times, depending on fiber type and irradiation intensity).

Investigation of long-period fiber gratings induced by high-intensity femtosecond UV laser pulses

Using high-intensity (up to 500 GW/cm2) 264 nm laser radiation, we fabricated long-period fiber gratings (LPFGs) in standard telecom and photosensitive fibers and compared the inscription efficiency with that for other existing methods of recording. We studied the temperature sensing properties of the fabricated gratings. We demonstrated the effect of thermal recovery of a LPFG resonance peak, which could be used for a fine adjustment of its transmission loss value and wavelength position.

Subnuclear trafficking and gene targeting by steroid receptors.

Through the use of novel imaging techniques, we have observed direct steroid receptor binding to a tandem array of a hormone-responsive promoter in living cells. We found that the glucocorticoid receptor (GR) exchanges rapidly with regulatory elements in the continued presence of ligand. We have also reconstituted a GR-dependent nucleoprotein transition with chromatin assembled on promoter DNA, and we discovered that GR is actively displaced from the chromatin template during the chromatin remodeling process. Using high-intensity UV laser crosslinking, we have observed highly periodic interactions of GR with promoter chromatin. These periodic binding events are dependent on GR-directed hSWI/SNF remodeling of the template and require the presence of ATP. Both the in vitro and in vivo results are consistent with a dynamic model ("hit-and-run") in which GR first binds to chromatin after ligand activation, recruits a remodeling activity, and is simultaneously lost from the template. We also find that receptor mobility in the nucleoplasm is strongly enhanced by molecular chaperones. These observations indicate that multiple mechanisms are involved in transient receptor interactions with nucleoplasmic targets.

Droplet-size distribution gradient induced by laser curing in polymer dispersed liquid crystals

We have studied the morphology and electro-optical properties of polymer dispersed liquid crystals prepared by polymerization-induced phase separation (PIPS) under high intensity UV laser curing. The results have shown that localized high intensity curing generates a gradient of the droplet size distribution outside the directly irradiated area as a consequence of the non-uniform spatial distribution of the scattered intensity. Such a distribution of the droplet size reflects in a peculiar electro-optical behaviour that could find potential application in optical devices. Both shape and spatial extent of the droplet size gradient are affected by the spatial velocity of polymerization which in turn strongly depends on the intensity of the curing laser beam. This dependence has also been experimentally investigated.

Morphological and Electro-Optical Properties of Polymer Dispersed Liquid Crystals Cured by High Intensity Laser Radiation

We have studied the morphology and the electrooptical properties of Polymer Dispersed Liquid Crystals prepared by the Polymer Induced Phase Separation technique under high-intensity UV laser curing. Photoinduced thermal convective motions have been observed in the directly illuminated area, which originates unusual morphological patterns consisting of ordered and/or disordered structures, depending on the curing intensity. We show that transition between ordered (columnar) and disordered (turbulent) motion is possible by increasing the laser beam intensity and the flow patterns associated to both these regimes can be frozen in by the photo-polymerization process. We show also that localized high-intensity curing generates a gradient of the droplet-size distribution outside the directly irradiated area essentially due to the non-uniform spatial-distribution of scattered intensity. This complex morphology reflects into a peculiar electrooptical behavior that could find potential application in new optical devices.

High Intensity UV Laser Curing of Polymer Dispersed Liquid Crystals

As it is well known, the final morphology of PDLCs samples depends on a number of parameters among which light intensity, curing time and temperature are probably the most important once one has choose a particular mixture to cure. In this work, we show the influence of these different external curing parameters on the film morphology of PDLCs obtained by strong UV laser irradiation of the homogeneous prepolymer-liquid crystal mixture. In particular, we show that some of these parameters can affect the morphological uniformity of the samples and can give rise to a highly interconnected‘channel’ pattern, while the classic‘droplets’ morphology is almost completely lost.

Theoretical modelling of phenomena in the pulsed-laser deposition process: Application to Ti targets ablation in low-pressure N2

We present an analysis describing the phenomena that are involved in the interaction process between high intensity UV laser radiation and a solid target in a low-pressure gas environment. The laser action upon the solid surface is described by solving the one-dimensional (1D) heat-conduction equation. The 1D hydrodynamic model is further applied to describe the interaction between laser radiation and the plasma expanding in front of the target. The laser radiation absorption in the vapor plasma is considered using a multicomponent fluid model. The transit of ablated material from target to collector is treated by a Monte Carlo method. The time and space distributions of the main plasma parameters (e.g., atom density and plasma electron temperature and density) are calculated. Finally, the thickness profile of a film deposited on a collector parallel to the target is predicted. For comparison with available experimental data, the calculations were carried out for the case of a Ti target submitted to a multipulse UV laser irradiation in low-pressure nitrogen, when depending on gas pressure, stoichiometric TiN was deposited or mixtures of amorphous and crystalline Ti, TiN, Ti2N, and even Ti oxides were obtained.

High-Intensity UV Laser Photolysis of DNA and Purine 2‘-Deoxyribonucleosides: Formation of 8-Oxopurine Damage and Oligonucleotide Strand Cleavage as Revealed by HPLC and Gel Electrophoresis Studies

Emphasis was placed in this work on the measurement of purine oxidation products generated upon nano- and picosecond UV laser biphotonic photolysis of 2‘-deoxyadenosine, 2‘-deoxyguanosine, calf thy...

Influence of the local helical conformation on the guanine modifications generated from one-electron DNA oxidation.

Two major products, 2,2-diamino-4-[(2-deoxy-beta-D-erythro-pentafuranosyl)amino]-5-(2H )-oxazolone and its imidazole derivative have been generated from one-electron oxidation of the free 2'-deoxyguanosine. The formation of 7,8-dihydro-8-oxoguanine (8-oxodG), not detected in this case, has been observed from DNA exposed to oxidizing agents. Since these compounds are thought to reflect, respectively, either deprotonation or hydration of the transient guanyl radical cation, these findings suggested that the helical structure could influence the chemical decomposition pathway of the guanine moiety. In the present study, we have photoionized DNA sequences by exposure to high-intensity UV (266 nm) laser pulses. Homo- or heteroduplexes, including guanines in various environments as well as Gn runs, were used as templates. Lesions were analyzed, at the nucleotide level, by taking advantage of the specific removal of 8-oxodG from DNA by the formamidopyrimidine DNA glycosylase (Fpg protein) and of the differential sensitivity of 8-oxodG and oxazolone to piperidine. Variations were observed in the relative yield of each type of lesion at individual guanines of the DNA sequences. We found that the Fpg lesions predominate in regions of stable double helix but are decreased in favor of the piperidine ones in regions of destabilization of the helix. Results are discussed in terms of a relationship between intramolecular rearrangements of the guanyl radical cation and the DNA helical conformation and dynamics.

Asymmetric photolysis of biomolecules under high-intensity UV laser irradiation

The excitation of optical isomers to the electronic vibrational state S 1 by high-intensity circularly polarized laser UV light results in a significant growth (by more than two orders of magnitude) of the anisotropy factor in asymmetric photolysis. It has been demonstrated for two types of biomolecules, namely, DL-tyrosine amino acid in aqueous solution and provitamin D 3 (7-dehydrocholesterol) in ethanol solution, that the anisotropy factor increased from 8.8×10 −5 and 1.5 × 10 −4 to 2.4 × 10 −2 and 4.4 × 10 −2, respectively.

Photochemical crosslinking in oligonucleotide-protein complexes between a bromine-substituted 2-5A analog and 2-5A-dependent RNase by ultraviolet lamp or laser

2′,5′-oligoadenylates known as 2-5A [p x (A2′p) n A; x = 2 or 3, n ≥ 2] are produced in interferon-treated cells in response to double-stranded RNA. 2-5A binds with high affinity to a 2-5A-dependent RNase resulting in the cleavage of single-stranded RNA. An efficient, rapid, and extremely sensitive photoaffinity labeling method was developed to facilitate detection of 2-5A-dependent RNase. A bromine-substituted and radioactive derivative of 2-5A, the 5′-monophosphate, p(A2′p) 2(br 8A2′p) 2A3′-[ 32P]Cp, was synthesized as probe for 2-5A-dependent RNase. Even though this bromine-substituted analog of 2-5A bore no 5′-terminal triphosphate or diphosphate, it bound to 2-5A-dependent RNase with the same high affinity as did 2-5A per se but it was a less effective activator of the RNase under the present assay conditions. The presence of bromine atoms in the 2-5A analog enhanced by more than 200-fold crosslinking to 2-5A-dependent RNase under a uv lamp; many additional polypeptides were also labeled but at much lower levels. Furthermore, using high-intensity uv laser irradiation (308 nm) covalent attachment of the bromine-substituted 2-5A analog to 2-5A-dependent RNase was readily achieved within 10 −6s.