Thermal lensing and permanent refractive index changes in rare-earth-doped glasses

Abstract

The characteristics of thermal lensing were measured for Eu3+- and Nd3+-doped phosphate glasses under resonant and nonresonant excitation conditions. The relative strengths and response times of the laser-induced lenses were determined and intepreted in terms of the thermal properties of the glass hosts for nonresonant excitation and the coupling of the rare-earth ions to the local vibrations for resonant excitation. Significant enhancement of the strength of thermal lensing was observed for resonant excitation, and this effect was much greater for the Eu-doped glass than for the Nd-doped glass. The response times for thermal lensing were also different for resonant and nonresonant excitation. In addition, a permanent change in the refractive index of Δn = 1.23 × 10−5 was observed for the Eu-doped glass and not for the Nd-doped glass. These results are discussed in terms of the different distributions of vibrational modes generated by the different types of laser excitation of these two rare-earth ions.