New ceramic materials based on yttrium oxide Y
2
O
3
with isovalent (Yb
2
O
3
, Nd
2
O
3
, and Lu
2
O
3
) and heterovalent (ZrO
2
and HfO
2
) components are synthesized, and their spectroscopic ...properties are investigated. Possible channels of losses in the gain of stimulated radiation in the radiative transitions of Nd
3+
and Yb
3+
ions in ceramics with heterovalent additives are studied. The results of measurements of Y
2
O
3
ceramics doped with zirconium and hafnium ions, the emission bandwidth and the lifetimes of the
4
F
3/2
and
2
F
5/2
levels of Nd
3+
and Yb
3+
ions, respectively, are presented. It is shown that the nonradiative population of the
4
F
3/2
levels of neodymium ions is due to their dipole-dipole interaction with Zr
3+
and Hf
3+
ions. Laser generation in (Yb
0.01
Lu
0.24
Y
0.75
)
2
O
3
0.88
(ZrO
2
)
0.12
ceramics with disordered crystalline structure was achieved at a wavelength of 1034 nm with a differential efficiency of 29%.
The basic design principles of high-intensity laser systems based on coherent combining of radiation of multichannel laser facilities are considered. The influence of the instability of parameters of ...individual beams on coherent combining efficiency is analyzed, and requirements on their values for realization of high-efficiency coherent combining are determined. The fundamental possibility of coherent combining of parametrically amplified femtosecond pulses is experimentally demonstrated for the first time. Combining pulses with an energy of ∼1 mJ (pulse duration of 25–30 fs) with an efficiency exceeding 83% is realized by using a spherical mirror and a specially developed high-precision electro-optical relative time jitter stabilization scheme, which ensures its stability at ∼170 as level. The analysis conducted and the experimental data confirm that there are no fundamental limitations on intensity scaling of the high-intensity laser system based on coherent combining being developed at the Institute of Laser Physics of the Siberian Branch of the Russian Academy of Sciences.
We have developed a technique for investigating the evolution of spatial inhomogeneities in high-power laser systems based on multi-stage parametric amplification. A linearised model of the ...inhomogeneity development is first devised for parametric amplification with the small-scale self-focusing taken into account. It is shown that the application of this model gives the results consistent (with high accuracy and in a wide range of inhomogeneity parameters) with the calculation without approximations. Using the linearised model, we have analysed the development of spatial inhomogeneities in a petawatt laser system based on multi-stage parametric amplification, developed at the Institute of Laser Physics, Siberian Branch of the Russian Academy of Sciences (ILP SB RAS).
Bulk crystals of new huntite type borates were grown by TSSG method using eutectic LiBO
2
–LiF as a flux. Chemical composition, X‐ray diffraction, optical absorption and fluorescence spectra of the ...grown samples were studied.
Display omitted
•Cationic Ag+ and Agnδ+ species are active sites in low temperature CO oxidation.•An appropriate Si/Al ratio is essential for CO oxidation over supported Ag catalyst.•Broensted ...acidity of zeolite correlates with the catalyst activity.•Consecutive oxidizing and reducing pretreatments promote catalytic activity.•Ag/ZSM-5 (80) catalyst displayed the highest activity in CO oxidation.
Silver catalysts supported on ZSM-5 (Si/Al=30, 50 and 80) were investigated for low-temperature CO oxidation to study the nature of the silver active sites and their formation under the influence of the support chemical composition and redox pretreatments. The catalysts were characterized by HRTEM, FTIR, XPS, diffuse reflectance UV–Vis spectroscopy, NH3 thermodesorption (NH3 TPD) and temperature-programmed reduction (H2 TPR). The chemical composition (Si/Al ratio) of the ZSM-5 zeolite support significantly affects catalytic properties of Ag/ZSM-5 samples: the lower the Broensted acidity of the zeolite support, the higher the activity of the catalysts. Interestingly, while oxidizing pretreatment of catalysts led to a significantly better performance than reducing pretreatments, the consecutive reducing treatment of the preoxidized samples significantly promoted the catalytic activity for low-temperature CO oxidation. Thus, Ag/ZMS-5 catalyst with Si/Al=80, pretreated consecutively in oxidizing and reducing conditions, showed the highest activity, reaching 90% CO conversion at just 40°C. Comparison of activity and characterization results showed that silver particles with size below 2nm are the most active; larger particles are just “spectators”. The most probable silver active centers in the low-temperature CO oxidation are ionic species, mostly charged clusters Agnδ+, strongly interacting with the support. The obtained results in low-temperature CO oxidation might be of particular interest for neutralization of exhaust gases of car engines during “cold start”.
An optimal stretcher-compressor scheme is designed for laser facilities based onbased on optical parametric chirped-pulse amplification under picosecond (∼100 ps) pumping, which enables one to attain ...petawatt peak power of pulses less than 10 fs with high contrast and low aberrations. The stretcher design is based on an Öfner telescope with spherical mirrors and two diffraction gratings, one being placed at the center of the spherical mirrors. It is shown to be the only possible aberration-free stretcher design. The simulation performed has shown that a compressor consisting of four transmission diffraction gratings with an aperture 112 × 125 mm, a thickness of 3 mm, and chirped mirrors with 100-mm aperture that introduce −4500 fs
2
dispersion allows amplified pulse compression down to <10 fs length and 1 PW peak power with the total
B
-integral lower than 1. The designed stretcher-compressor system is planned to be implemented in the high power femtosecond laser system being developed at ILP SB RAS.
Bulk crystals of new huntite type borates were grown by TSSG method using eutectic LiBO2–LiF as a flux. Chemical composition, X‐ray diffraction, optical absorption and fluorescence spectra of the ...grown samples were studied.
Bulk crystals of nonlinear optical materials NdYSB and PrYSB without striation defects were grown using novel LiBO2–LiF flux. It was confirmed that introduction of Y atoms to the Nd(Pr)Sc3(BO3)4 stabilizes the R32 huntite‐type structure, like it was shown for YLSB crystals. Taken together with the presence of active Nd3+ and Pr3+ rates, the studied crystals are suggested as promising self frequency doubling materials.
Display omitted
•In Au/TiO2 and Au/La2O3/TiO2 samples gold is present in three electronic states: Au0, Au+ and Au3+.•Cationic Au+ species are active sites in liquid phase n-octanol oxidation.•Au0 and ...Au3+are not active sites in the studied process.
We investigated the influence of metal loading in gold catalysts supported on titania, either unmodified or La-modified, on their catalytic performance and the formation of active sites for selective oxidation of n-octanol under mild conditions. Catalysts were characterized by BET, EDX, ICP, HRTEM, FTIR CO and XPS. Gold content had a significant effect on the catalytic properties of unmodified catalysts: activity of Au/TiO2 increased by increasing the metal load. However, in the case of a lanthanum-modified support samples, an increase of gold content from 0.5 to 4 wt.% had no effect on its activity (ca. 40% conversion after 6 h for all catalysts). This catalytic behavior is due to a change in the surface concentration of Au+ ions. For the unmodified catalysts, the surface concentration of Au+ ions increased with increasing gold loading, and, as a consequence, a significant increase in activity was observed. For La-modified catalysts, the surface concentration of Au+ ions is almost the same for all gold concentrations; as a result, no increase in activity was observed with the increase in gold content. It points to Au+ ions as the most probable active sites for the studied reaction.
We studied mechanical, optical, and lasing parameters of neodymium-doped yttrium oxide ceramics synthesised by using a new technology involving the laser synthesis of nanopowders and their magnetic ...pulsed compaction. The fracture toughness of ceramics to cracks and its microhardness were measured to be K{sub IC} = 0.9-1.4 MPa m{sup 1/2} and H{sub {nu}} = 11.8 GPa, respectively. Ceramic samples sintered in the temperature range from 1550 to 2050{sup 0}C have the porosity (1-150)x10{sup -4}% and the optical loss coefficient {alpha}{sub 1.07} = 0.03-2.1 cm{sup -1} at a wavelength of 1.07 {mu}m. It is shown that such porosity does not affect the optical loss coefficient of light. Lasing at {approx}1.079 {mu}m with a slope efficiency of 15% was obtained in a 1.1-mm-thick sample pumped by laser diodes. (active media. lasers)
PDF
