Light-induced absorption in pure B12TiO20 crystal and crystals doped with Nd, Mo, W, and V was investigated using the pump-probe method. Q-switched frequency-doubled (532 nm) YAG:Nd laser with pulse duration approximately 20 ns was applied for sample irradiation. Investigation of pump-induced transmission was carried out by means of a tunable dye laser radiation at (lambda) 1 equals 568 nm and (lambda) 2 equals 698 nm. The dependence of the light-induced absorption coefficient on the pump beam intensity and probe wavelengths was determined. The two-center model was used to explain the observed results.
A comparative experimental study of two versions of an injection-seeding laser system containing a slave laser (SL) with a ring-linear dual-channel competitive cavity and with a simple ring one is presented. The spectral purity of the SL output radiation and efficiency of the SL reverse wave suppression in dependence on the seeding conditions are investigated. It is shown that in the case of a dual-cavity competitive SL with a ring main channel both the spectral background and reverse radiation are fully suppressed. This is realized in a compact scheme without optical isolators and at any ratios between the SL energy and the seeding source one.
A laser cavity containing highly selective reflector based on a multipass grazing-incidence diffraction grating is described. The operation of the multipass selective reflector (MPSR) is demonstrated and studied experimentally in the case of pulsed dye laser pumped by frequency-doubled Nd:YAG laser. Numerical calculations concerning gain- switched Ti:Sapphire laser with MPSR are also done. An increasing of the spectrally pure output energy more than 5 times is achieved. Decrease of the threshold energy and broadening of the tuning range of several times are also observed depending on the pumping conditions. The calculations show that, in the case of gain-switched Ti:Sapphire laser pumped by Nd:YAG laser, the temporal characteristics of the radiation, the build-up time and the pulse duration are considerably shortened by using MPSR. The improved energy, spectral, and temporal parameters of tunable lasers with MPSR make them suitable for different applications (spectroscopy, biology, DIAL, etc.) as a separate sources or as a part of injection-seeding tunable laser systems.
An injection seeding of narrowband and broadband radiation into a highly selective tunable laser is described. An increase of the laser output energy by a factor of 1,5 is achieved. Laser oscillations are induced by injection seeding when the active medium is pumped below the laser threshold. Optical signal as small as 0.2 nJ is detected and amplified by a factor of 150.
Photochemistry can be used as a tool to investigate biological
processes. Various natural compounds and phototherapeutic agents
including llavin , psoralen , hematopor phyrin and phtalocyanine
derivatives have been shown to oxydize purine components upon exposure
to near - UV and visible light. It is usually assumed that it is the
sensitizer in its triplet state which is the reactive species in
photooxidation reactions either via an electron or hydragen atom
transfer Ctype ID or via singlet oxygen and superoxide anion
generation (type II) . It is currently accepted that superoxide
radicals can generate hydroxyl COH ) radicals which are known to be
the mai n DNA - damagirig speci es . Recenti y the use of photoserisi ti zed
reactions as a tool of probing biomolecular structures and processess
has been reviewed Cl - 3).
KEYWORDS: Photolysis, Chemistry, High power lasers, Ultraviolet radiation, Electroluminescence, Temperature metrology, Mass spectrometry, Chromatography, Picosecond phenomena, Photochemistry
Biophotonic excitation of purine and pyrimidine nucleobases becomes of increasingly importance as the laster intensity increases. Under these conditions the overall energy absorbed is much higher than the threshold energy required to generate pyrimidine and purine cathion radicals estimated to lies iin the 5-5.5 eV range (1). It is now communly accepted that the cathion radical is the primary damaging species generated upon two-quantum laser photolysis of nucleic acids derivatives. The chemistry of pyrimidine and purine cathion radicals in aqueous solutions has not been well udnerstood until recently. Two major exception delt with the initial chemical reaction of photo and ratioation - induced radical cation in low temperature thymine and thymidine - 5 - phosphate (2, 3) and at room temperature where the pyrimidine radical cathions were generated through an electron transfer reaction to photoexcited mendione in a triplet state.
KEYWORDS: Particles, Proteins, Picosecond phenomena, Laser applications, Ultraviolet radiation, Photons, Information operations, In vivo imaging, Life sciences, Chlorine
A picosecond UV laser radiation was used to cross-link proteins to DNA in nuclei, whole cells and different chromating preparations. All histones as well as high-mobility group 1 proten were identified immunochemically in the covalently linked protein-DNA complexes. Irradiation of the nuclieohistone resulted in cross-linking 20% of bound histones to DNA as a result of two-quantum photoreaction with a maximum quantum yield 3.10 -4 for double stranded DNA. When nuclei, total bromatin Hi-depleted chromatin and core particles were irradiated and then trypsinized or treated with clostripain to cleave respectively the N-, C- and N- terminal histone tails, no histones have been found covalently linked to DNA. However whilst the yield of cross-links was similar in total and H1-depleted chromatin in core particples the efficiencey was 3-4 times lower for H2A, H2B and H4 10-12 times lower for H3. This finding we consider as a direct evidence for interaction of non structured N- tails of core histones with linker DNA. Cross-linking in core particles depends on the ionic strength. All histones were identified in the complex formed up to 0.4 N NaCl, no cross-linking was observed when irradiation was carried out at salt concentration higher than 0.4 M. The cross-linking ability was preserved both upon physiological acetylation of histones knows to be restriced to the N-terminal tails and with chemically acetylated chromatin. This finding is direct evidence that postsynthetic histone acetylation does not release the N-terminal tails from interaction with DNA.
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