Two-photon photochemical long-period grating fabrication in pure-fused-silica photonic crystal fiber.

We report what is to our knowledge the first photochemical fabrication of a long-period grating in a pure-fused-silica photonic crystal fiber. The inscription technique is based on a two-photon absorption mechanism and does not require a specially designed photonic crystal fiber with a photosensitive Ge-doped core. The characteristic fluence value for the inscription is an order of magnitude less than that for a standard telecom fiber irradiated under similar conditions with the same grating parameters.

Strong long-period fiber gratings recorded at 352 nm.

We describe long-period grating inscription in hydrogenated telecom fibers by use of high-intensity femtosecond 352 nm laser pulses. We show that this technique allows us to fabricate high-quality 30 dB gratings of 300 microm period and 2 cm length by use of a three-photon absorption mechanism.

Inscription of fiber Bragg gratings by ultraviolet femtosecond radiation.

We report on what is to our knowledge the first fabrication of fiber Bragg gratings by UV femtosecond radiation. The Bragg gratings, with photoinduced refractive-index modulation up to 1.92 x 10(-3) in H2-loaded SMF-28 and up to 1.

Femtosecond measurements of two-photon absorption coefficients at lambda = 264 nm in glasses, crystals, and liquids.

Using ultraviolet femtosecond pulses with high irradiance stability, we measured the two-photon absorption (TPA) coefficients in a number of substances with a total accuracy of approximately 10%. Six commercial fused-silica samples (KU-1, Coming 7940, SQ, Suprasil, Herasil, and Infrasil) possess TPA coefficients (beta values) of approximately 2 x 10(-11) cm/W. For crystalline quartz and sapphire, the following beta values were obtained: (1.

193 nm photolysis of aromatic and aliphatic dipeptides in aqueous solution: dependence of decomposition quantum yield on the amino acid sequence.

The values of molar absorption coefficient and quantum yields of photodecomposition and peptide bond scission were determined for a number of aromatic and aliphatic dipeptides under 193 nm laser irradiation in neutral argon-saturated aqueous solution. Under these conditions we could show that no dependence of the dipeptide decomposition quantum yield on the sequence of amino acid residues exists, neither for aromatic dipeptides nor for aliphatic ones.

Photolysis (193 nm) of aliphatic dipeptides in aqueous solution.

The photodecomposition of four aliphatic dipeptides containing valine and methionine was studied in neutral solution upon excitation at 193nm. The quantum yields of ionization and decomposition in Ar-saturated aqueous solution are phi(e)- = 0.06-0.

Photochemical alterations in DNA revealed by DNA-based liquid crystals.

The preparations of chicken erythrocyte linear double-stranded DNA and superhelical plasmid pBR322 DNA were irradiated by continuous low-intensity UV radiation (I = 25-50 W/m2, lambda = 254 nm) as well as by high-intensity picosecond laser UV radiation (I = 10(11)-10(13) W/m2, lambda = 266 nm). The effect of DNA secondary structure alterations on the formation of liquid-crystalline dispersions from UV-irradiated DNA preparations was studied. It was shown that in the case of linear DNA, watching the disappearance of abnormal optical activity characteristic for cholesteric liquid crystal we managed to detect the presence of photochemical alterations in DNA irradiated by low-intensity UV radiation at an absorbed energy of more than 20 quanta per nucleotide.

212.8 nm laser photolysis of aromatic and aliphatic amino acids and related peptides.

The comparison of the photochemical properties of three aromatic and five aliphatic amino acids and three dipeptides was carried out using 212.8 nm laser irradiation and high performance liquid chromatography. The photochemical sensitivity, photolysis quantum yield and quantum yield of peptide bond scission were determined.

Effects of ultraviolet laser radiation on Venezuelan equine encephalomyelitis virus.

The effects of usual low-intensity continuous (lambda = 254 nm, I = 10 W/m2) UV radiation and high-intensity laser nanosecond (lambda = 266 nm, tau p = 10 ns, I = 10(9) W/m2) or picosecond (lambda = 266 nm, tau p = 23 ps, I = 10(12) W/m2) UV radiation on Venezuelan equine encephalomyelitis virus (a member of the Togaviridae family) were compared. The quantum yields of infectivity inactivation, pyrimidine dimer formation and RNA-protein crosslinking were determined.

Photochemistry of uridine on high intensity laser UV irradiation.

The method of high performance liquid chromatography was applied to investigate the products of single-quantum and two-quantum photo-reactions which occur when an aqueous solution of uridine is irradiated with high intensity nanosecond and picosecond laser UV pulses. A comparison of the experimental results obtained with theoretical models enables a number of photophysical parameters of the highly excited electronic states of the uridine molecule to be determined.

Two-quantum UV photochemistry of nucleic acids: comparison with conventional low-intensity UV photochemistry and radiation chemistry.

The action of high-intensity laser u.v. radiation on nucleic acid molecules and their constituents in vitro and in vivo is compared with the results of low-intensity u.

UV laser induced RNA-protein crosslinks and RNA chain breaks in tobacco mosaic virus RNA in situ.

The efficiency of RNA-protein crosslink and RNA chain break formation under nanosecond or picosecond UV-laser pulse irradiation of tobacco mosaic virus was determined. It was found that on high-intensity UV-laser irradiation the quantum yields of both reactions increase considerably as compared to the usual (low-intensity) UV-irradiation. The RNA-protein crosslink quantum yield was found to be 1.