Monday, 07 October 2013, 10:30 a.m.
Sala Grande Palazzina B via alla Cascata 56/C
Photodarkening in Yb-doped optical fibres
Multidisciplinary Nanotechnology Centre
College of Engineering, Swansea University, UK
The seminar reviews the work done on photodarkening and we present the outcomes of our project consortium with latest results on photodarkening investigation, measurement and mitigation in fiber lasers. We first discuss the impact of photodarkening phenomenon in fibre laser, we review possible origins of the phenomenon and we discuss proposed mitigation methods (thermal bleaching, codoping with Al, P or Ce, mitigation by using peculiar fiber design, different active ion inversions, O2 or H2 loading). In the second part of the seminar we focus on the main recent outcomes. We demonstrate the need for a standard set-up to avoid underestimation of photodarkening equilibrium losses and we suggest photodarkening losses scale with the square of Yb doping level. Investigation on visible light emission suggest an interplay of visible light with the Yb excited level and we evaluate the impact of color-center generation of Yb lifetimes. Finally we present an extensive investigation of photobleaching, both as post-irradiation and as simultaneous bleaching. We show evidence photobleaching can effectively mitigate the impact of photodarkening on laser performance when highly-doped Al-silicate fibers are used.
Keywords: fiber lasers, photodarkening, RED glasses.