In present paper we report a study and demonstration of rare earth doped photo-thermo-refractive glasses for monolithic integration of laser sources/amplifiers and volume Bragg gratings. Namely, we demonstrated laser action of neodymium and ytterbium-erbium doped photo-thermo-refractive glasses. In addition, we studied the influence of the rare earth dopants on the photosensitivity of photo-thermo-refractive glass. It was shown that introduction of rare earth dopants not only increase the viscosity of the glass that leading to the longer heat treatment time, but also decrease the ability of fluorine to form sodium fluorine nanocrystals in the glass host. In accordance with this data we developed and demonstrated a new glass composition which overcomes these drawbacks and can act as both holographic and laser active medium. Thus new rare earth doped photo-thermo-refractive glass can be very attractive and promising medium for monolithic integration of lasers/amplifiers and volume Bragg gratings on the united laser-holographic substrate.
We report the results of a thorough investigation into the initial stages of the photo-thermo-induced crystallization process in photo-thermo-refractive glass. The spectral location of the absorption peak characteristic of the surface plasmon resonance in the silver nanoparticles is known to be highly sensitive to the dielectric parameters of the nanoparticle surrounding. We have studied the evolution of the peak location in the course of PTI crystallization process and shown that the red shift of the peak in glass is caused by the occurrence, around the silver nanoparticles, of highly-refractive shell of a mixed nature. The blue shift of the peak that can be observed under the reduced speed of the process was shown to be inflicted by the precipitation of sodium fluoride crystals. During further analysis was proven that shell is of 5.7 angstrom thickness. A couple of models examining shell possible evolution was proposed, namely sodium bromide and silver bromide crystal solid solution and silver bromide inclusions into the surrounding glass layer. Both approaches were modeled to obtain surface plasmon resonance shifts equal to experimentally observed ones. It was shown also that the observed blue shift of the plasmon resonance peak at the later stage of PTI crystallization is due to the NaF precipitation.
In present paper, we represent a study on the effect of RE dopants (lanthanum, erbium, ytterbium, and neodymium) on the process of the photo-thermo-induced (PTI) crystallization. During this work, we investigated each step of the PTI crystallization process including silver particle formation, growth of shell and nanocrystal. To perform these observations, we reduced the temperature of thermal treatment below the glass transition temperature to slow down all processes inside the glass. We found out that the silver nanoparticles formation process does not depend from the concentration of RE ions and is the same as in case of the parent PTR glass. In other hand the growth kinetics of AgBr-NaBr shell and NaF nanocrystals differ from the parent glass and depend on RE concentration. Our observations show no difference in final position of plasmon resonance, which means that the PTI crystallization process itself stays the same and is not affected by the RE dopants. Further study shows that utmost achievable refractive index change falls off with rare earth dopant concentration increase mainly due to the bond formed between dopant and fluorine. This bond prevents fluorine from participation in crystallization process thus overall volume fraction of the crystalline phase decreases. This effect can be corrected by addition of fluorine in the chemical composition of the glass at the synthesis. In conclusion, we show that refractive index change in doped glass with appropriate concentration of additional fluorine is same as in the parent glass (1500 ppm).
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