optical characterisation of rare-earth doped fluoride and phosphate ...

5from the UV ( 250 nm) to the mid-IR (8 m) with 0.001 dB/km loss at 2.6 m.The name ZBLAN arises from its constituent elements: ZrF 4 BaF 2 LaF 3 AlF 3 NaF.When dealing with wavelengths in the mid and near IR, applications such as dentistry,remote IR spectroscopy, and industrial quality control can benet from this large,high-transmission window. In contrast, silica bres can only transmit from the UV( 250 nm) to the near IR ( 2 m). Unfortunately, ZBLAN glass has suered fromdiculties in glass bre manufacturing due to crystallisation (see [23] for an overviewof uorozirconate glasses). An alternative material, ZBLALiP, was mooted as possiblyhaving better shaping properties for fabricating bres and microspheres [24]. In thiswork, we build on this argument and show additional benets of ZBLALiP in termsof very ecient upconversion uorescence emissions in the 320-850 nm range. Wehave performed a comprehensive Judd-Ofelt analysis in order to understand the glassbehaviour when doped with erbium.The layout of this thesis is as follows:A general introduction to the optical properties of microspheres is presented inChapter 1. This provides a groundwork for the rest of the thesis. Parameters suchas resonance positions, quality factor limitations, mode volume, and electric eldproles are summarised. The fabrication of the doped microspheres used in this workis also discussed. There is a brief introduction to the topic of optical spectroscopyof laser glasses, which is later used in Chapters 3 and 4. Several topics are covered:the dierence between glasses and crystals, selection rules for radiative transitions,Einstein A and B coecients, excitation mechanisms in ions with multi-phonon decay,and nally thermal issues.The two dierent microsphere-coupling schemes that we considered are discussed