Sakr, Hesham
(2016)
Towards mid-infrared fibre lasers: rare earth ion doped chalcogenide glasses and fibres.
PhD thesis, University of Nottingham, UK.
Abstract
This Project is aimed at developing rare earth ion doped chalcogenide glasses targeting mid-infrared (MIR) fibre lasers, emitting in the wavelength region 4 – 5 μm. The work reported in this thesis has two objectives: (i) a study of the Ge-As-In-Se glass system when doped with a single species of rare earth (RE) ions, i.e. praseodymium (Pr3+) or cerium (Ce3+), or when co-doped with two rare earth ion species: Pr3+ and Ce3+, and (ii) a study of the effect of replacing a gallium (Ga) additive with an indium (In) additive on the physical and optical properties of the undoped and Pr3+ doped Ge-As-(Ga/In)-Se glasses and fibres.
The MIR, i.e. 3 – 25 μm wavelength, offers to advance many photonics areas including bio-medical imaging spectroscopy for human tissue sensing in vivo for early cancer diagnosis. Low loss RE-ion doped MIR fibre lasers are potential pumps for MIR supercontinuum generation (SCG) sources for a compact MIR broadband device. Also, MIR fibre narrowband lasers offer potential new wavelengths for laser medical surgery. To date, there are no MIR rare earth ion doped glass fibre lasers emitting at wavelengths ≥ 4 μm. Selenide (Se)-based glasses, a member of the chalcogenide glass family, are known for their wide transparency up to 12 μm and good rare earth ion solubility.
In the Project, an additive to the Ge-As-Se glass system of indium or gallium is considered to help decluster the rare earth ions and increase their solubility in the as-prepared Pr3+ doped Ge-As-(Ga/In)-Se glasses. However, an indium additive is concluded here to achieve a lower rare earth ion solubility limit than that obtained using the equivalent gallium additive in the Ge-As-(Ga/In)-Se glass systems.
On the other hand, the photoluminescent intensity is concluded here to be approximately doubled when using an indium additive in Pr3+ doped Ge-As-In- Se, compared to the analogous gallium glasses. Furthermore, the decay lifetime, at the same emission wavelength of 4.7 μm, is found to be longer in the Pr3+ doped Ge-As-In-Se glasses when compared to the Pr3+ doped Ge-As- Ga-Se glasses.
Overall, for a singly-doped Ge-As-In-Se glass system, Pr3+ offer wide photoluminescence spectral emission in the range 3 – 6 μm, which promotes this type of glass fibre as an active source for MIR laser emission in the target range of 4 – 5 μm. However, the photoluminescent decay lifetime, at 4.7 μm, of Pr3+ doped Ge-As-In-Se is concluded to decrease substantially with the number of thermal processes invoked to fabricate the glass-based fibres; a lifetime of 7 – 9 ms measured on the as-prepared fibres is compared to the decay lifetime of 9 – 10.1 ms that were found in the bulk glasses.
Alternatively, the addition of Ce3+ in the Ge-As-In-Se glass system is concluded to offer a larger absorption cross-section than that of the Pr3+ in the wavelength range 3.5 – 5 μm. Co-doping the Pr3+ / Ce3+ in Ge-As-In-Se in order to enhance the MIR photoluminescence emission in the range 3 – 6 μm is also investigated.
It is concluded that rare earth ions, in particular Ce3+ and / or Pr3+, doped chalcogenide glass fibres based on the Ge-As-In-Se glass system, developed through this Project, are strong candidates towards achieving MIR fibre lasers.
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