Index of content:
Volume 92, Issue 7, 01 October 2002
- LASERS, OPTICS, AND OPTOELECTRONICS (PACS 42)
92(2002); http://dx.doi.org/10.1063/1.1489710View Description Hide Description
Rate equations describing the dynamic processes in erbium-doped pentaphosphate crystals were developed to obtain the population processes of all levels of ions in pentaphosphate crystals under 650 nm laser excitation. The effects of pump power on the population (ρ) dynamic process were analyzed. The spontaneous radiative processes, multiphonon nonradiative processes, absorption of the pump photons, corresponding stimulated radiation processes, and all other possible energy transfer processes between ions were included in the rate equations. The pump power was assumed to be constant with time (t). Considering that the equation would be held if was small enough and using the initial condition the time-dependent populations of all states could be obtained from the rate equations, from which the steady-state solution of the rate equation was deduced. The comprehensive study of the population dynamic process of all energy-level ions in crystal when excited by has resulted in the conclusion that the strong upconversion luminescence would behave excellently when 650 nm pump laser power reaches the level of The representative population dynamic process when excited by laser power indicates and levels have a kind of great takeover co-contribution in up-converting population to higher states. The steady-state population probability of is as small as 0.0617. The population of the state increases rapidly to about a 0.362 high level and sequentially decreases smoothly to a stable value of about a 0.0374 low level, which implies a population already having been upconverted to higher level. Excellent results clearly exhibit that the main up-conversion luminescent level has a great population probability of about 0.212, which results in a strong up-conversion luminescence of 543 nm, and it is so exciting that a very strong 379 nm blue up-conversion luminescence could be achieved when 650 nm pump laser power is enhanced to the level of The results of this article are significant both to science and applications.
92(2002); http://dx.doi.org/10.1063/1.1504178View Description Hide Description
A diode-end-pumped intracavity frequency doubled green laser is demonstrated. The infrared laser output and pump-to-green conversion efficiency have been investigated as a function of crystal length and concentration. Results show that optimum ion concentration is around 2–3 at. %, in excellent agreement with theoretical predictions. Due to the broad absorption bands of this crystal, output power does not depend on diode temperature within a range. The influence of concentration on the quantum efficiency has been also analyzed. We have found that for optimum ion concentration quantum efficiency is as high as 0.7. Finally, the spectral distribution of green light is explained in terms of a combination of both second harmonic and frequency mixing processes between the two infrared oscillating lines.
Photochemical reaction of divalent-germanium center in germanosilicate glasses under intense near-ultraviolet laser excitation: Origin of 5.7 eV band and site selective excitation of divalent-germanium center92(2002); http://dx.doi.org/10.1063/1.1505979View Description Hide Description
The photochemical reaction of in optical fiber preform and the origin of the 5.7 eV optical absorption band induced by intense ultraviolet laser excitation have been investigated using a near-ultraviolet XeF excimer laser (3.7 eV) as the main excitation source. Based on the previous and present experimental results, it is concluded that the 5.7 eV optical absorption band does not originate from the Ge(2) electron trapped center. In place of this model, we have proposed an alternative structural model for the origin of the 5.7 eV band taking into account the experimental fact that the corresponding center is diamagnetic. In addition, it is found that the site selective excitation of the center can be achieved by using laser sources with different photon energies.
92(2002); http://dx.doi.org/10.1063/1.1501748View Description Hide Description
Fabrication of polymer light-emitting diodes based on emission from the phosphorescent molecule fac tris(2-phenylpyridine) iridiumdoped into a poly(vinyl carbazole) host are reported. Several spin-coatingsolvents were evaluated for deposition of the polymer layer; toluene and chlorobenzene were found to consistently produce device-quality films with sufficient incorporation of the dopant. For single-layered devices with cathodes, the luminance efficiency at 20 mA/cm2 was measured to be 8.7 Cd/A for devices processed from chlorobenzene. This efficiency could be increased by over a factor of two with a trilayered device geometry consisting of the dopedpolymer layer, a hole-blocking layer, and electron transport layer. Further increases in efficiency, up to 30 Cd/A and 8.5% external quantum efficiency, were observed when a second dopant of 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole was added to the polymer emitter layer.