Investigation of gain characteristics in mixed crystals LiMeF4 (Me = Y, Lu, Yb) doped by Ce3+ ions

Differential gain spectra in the range 295-335 nm were measured in crystals of scheelite structure LiY1 - x Lu x F4 (x = 0-1), doped by Ce3+ ions. It is shown that variation of Lu 3+ and Y3+ ions relative content in LiY1 - x Lu x F4 crystals allows to manipulate the spectral width of the amplification band. Cross-sections of excited-state absorption at the wavelengths of Ce3+ luminescence, probability ratios of formation and thermal destruction of color centers depending on the Y3+ ions content in LiY1 - x Lu x F4 crystals were estimated. Even better gain characteristics have been demonstrated by LiLuF 4:Ce3+, doped by Yb3+ ions. The highest optical gain coefficient with a wide amplification band among studied samples was observed in LiLuF4:Ce3+ crystal, codoped by Yb 3+ ions. © 2014 Pleiades Publishing, Ltd

Pump-probe experiments with Ce3++Yb3+:KY 3F10 and Ce3++Yb3+:CaF2 crystals

Here we report on pump-probe studies of KY3F10 and CaF2 doped with Ce3+ and Yb3+ ions. The crystals Ce3+:KY3F10 and Ce3+: CaF2 show attractive spectral characteristics for tunable UV lasers application but have poor photochemical stability. Their properties under intense UV pumping are affected by excited state absorption and color centers formation. This work was aimed at dynamic processes investigation induced by laser radiation of UV spectral range in KY3F10 and CaF2 doped with Ce3+ and Yb3+ ions. Optical gain was observed on CaF2:Ce3++Yb3+ in the range 325-335 nm for the first time. It proves Yb3+ ions coactivation antisolarant effect elaborated by us earlier3. It is shown that in investigated crystals under a pump radiation, resonant to 4f-5d Ce3+ ions transitions several types of color centers (CC) are formed. Set of these CC types are determine the absorption at expected stimulated emission spectral range and magnitude of the induced loses is dependent on many factors. As a result of competition between CC formation, free charges recombination and CC photodestruction this balance can be shifted towards either rising or dropping losses at 5d-4f Ce3+ ions luminescence spectral range. © 2011 SPIE

The concept of fruit in the Gramineae and its use in the taxonomy of the family

O uso do termo "fruto" em Gramíneas é impreciso e inconsistente. Por ser seco, monospérmico, indeiscente e apresentar-se com o pericarpo aderido ao tegumento da semente e frequentemente confundido com esta. Algumas vezes, a unidade de dispersão, a espigueta e o antécio são confundidos com o fruto. O fruto das gramíneas é uma cariopse. Sua morfologia interna e externa encerram grande número de características passíveis de uso taxonômico. As classificações da cariopse atualmente existentes não são inteiramente satisfatórias.The use of the term "fruit" in relation to the Gramineae often lacks precision and consistency. Because it is a dry, monospermic, indehiscent type of fruit and because its pericarp is adherent to the seed coat, it is often mistaken for the seed. The unit of dispersal, the spikelet and the anthoecium are sometimes misinterpreted as the fruit. The basic grass fruit is the caryopsis and its internal and external morphological features represent a great source of evidence for taxonomic use. The existing classification of the caryopsis and research needs in the field are discussed

Color centers transient absorption and ultra-short pulse lasing from LiLu0.7Y0.3F4:Ce3+ active medium

© OSA 2015. We have obtained the single pulse laser oscillation with 400±10 ps pulse duration at 311 nm from LiLu0.7Y0.3F4:Ce3+ crystal due to passive Q-switch by means of pump induced color centers absorption. In this work we discuss the role of intrinsic transient color centers on losses dynamics

Ultra-short pulses UV lasing in multifunctional Ce:LiY<inf>0.3</inf>Lu<inf>0.7</inf>F<inf>4</inf> active medium

© 2016 Optical Society of America.The single pulse laser oscillation with 400 ± 10 ps pulse duration at 311 nm from LiY0.3Lu0.7F4:Ce3+ crystal was obtained from intracavity loss modulation via pump-induced color centers bleaching. Modulation of average losses is regulated via color centers concentration that determines the multifuncionality of solarizable LiY0.3Lu0.7F4:Ce3+ active medium

Reconstruction of Transcription Control Networks in Mollicutes by High-Throughput Identification of Promoters

Bacteria of the class Mollicutes have significantly reduced genomes and gene expression control systems. They are also efficient pathogens that can colonize a broad range of hosts including plants and animals. Despite their simplicity, Mollicutes demonstrate complex transcriptional responses to various conditions, which contradicts their reduction in gene expression regulation mechanisms. We analyzed the conservation and distribution of transcription regulators across the 50 Mollicutes species. The majority of the transcription factors regulate transport and metabolism, and there are four transcription factors that demonstrate significant conservation across the analyzed bacteria. These factors include repressors of chaperone HrcA, cell cycle regulator MraZ and two regulators with unclear function from the WhiA and YebC/PmpR families. We then used three representative species of the major clades of Mollicutes (Acholeplasma laidlawii, Spiroplasma melliferum and Mycoplasma gallisepticum) to perform promoters mapping and activity quantitation. We revealed that Mollicutes evolved towards a promoter architecture simplification that correlates with a diminishing role of transcription regulation and an increase in transcriptional noise. Using the identified operons structure and a comparative genomics approach, we reconstructed the transcription control networks for these three species. The organization of the networks reflects the adaptation of bacteria to specific conditions and hosts

Intracavity losses investigation of LiCaAlF6:Ce3+ laser

We have discovered that total intracavity losses, being dependent on color centers amount, go down for higher pump energies for LiCaAlF6: Ce3+. This dependence is explained by the formation by the pump radiation and destruction of color centers due to laser radiation. The more energy remains in the lasing cavity, the lower the color centers absorption. Such dependencies were investigated for active medium crystals grown by different methods. Influence of growth conditions on active media characteristics is discussed. As a result we have shown for the first time that the crystal LiCaAlF6:Ce3+ internal losses depend on the pump energy. Method has been worked out to determine the intracavity losses of the laser, which allows evaluation of prospects of its practical use in the most correct way. © 2011 SPIE

Distribution coefficient of Pr3+ ions in crystals of solid solutions LiF-LuF3-YF3-PrF3

© Published under licence by IOP Publishing Ltd. Aim of this work was to investigate the possibility of increasing the distribution coefficient of Pr3+ ions in fluoride crystals with scheelite structure. As a result of investigations by XRF and optical absorption spectroscopy the absorption cross section for 3H0 3P0 transitions Pr3+ ions was clarified and segregation coefficient of Pr3+ ions in LiY0,3Lu0,7F4 mixed crystals was estimated

Thermal profiling of solid-state active media

© 2018 IEEE. The fluorescence intensity ratio technique to the thermal profiling of solid-state laser materials is developed. The temperature distribution inside the excited area of LiY0.8Yb0.2F4: Tm3+(0.2 at.%) crystals during z-scanning was studied

Laser tests as a tool for studying photodynamic processes in UV active media

Opportunities of laser tests as a powerful and unique research tool of active medium fundamental properties directly in real laser operation conditions for variable intracavity losses are discussed. New technique of laser experimental data interpretation was developed and applied to the analysis of laser tests results for the series of Ce3+:LiYbxLu 1-xF4 single crystals. Contribution coefficient into total pump-induced intracavity losses of ESA from upper laser level of Ce 3+ ions and CC absorption at the laser wavelength was estimated. Basic parameters relevant to laser action performance were defined: Ce 3+ ions ionization cross-section by pumping radiation and Ce 3+ ion ESA at the laser wavelength, CC absorption (ionization) cross-section at the both pumping and laser radiation wavelength, life-times of transient and long-living color centers, stimulated emission cross-section and relative values of pump-induced free-charges trapping rate by host lattice defects and their corresponding recombination rate