Billy Richards

Infrared emission and energy transfer in Tm 3+ , Tm 3+ -Ho 3+ and Tm 3+ -Yb 3+ -doped tellurite fibre

The infrared emission spectra and decay lifetimes of Tm(3+)-doped and Tm(3+)-Ho(3+), Tm(3+)-Yb(3+) co-doped tellurite fibres were measured using 808 nm and 978 nm diode laser pump sources in the range 1.35 mum to 2.2 mum. The spectra were compared with varying fibre lengths and core diameters. Tm(3+)-doped fibre shows strong emission at ~1.8 mum and when co-doped with Ho(3+), energy transfer results in strong Ho(3+) fluorescence at ~2.0 mum. These fibres show promise for compact mid-IR fibre laser sources.

Enhancement in pump inversion efficiency at 980 nm in Er 3+ , Er 3+ /Eu 3+ and Er 3+ /Ce 3+ doped tellurite glass fibers

Amplification properties have been compared in Er(3+), Er(3+)/Eu(3+) and Er(3+)/Ce(3+) doped tellurite glass fibers using a 980 nm pumping scheme. The pump efficiency has been compared in the 3 types of fibers. Er(3+) ion upconversion in bulk glasses and fibers in visible range has been measured and the Er(3+) ion IR fluorescence intensity and lifetimes have been recorded to understand the amplification characteristics. Codoping with Ce3+ is more efficient in Er(3+) doped tellurite fibre.

A Yb3+/Tm3+/Ho3+ triply-doped tellurite fibre laser

Continuous wave laser emission at 2.1 microm from a Yb(3+)/Tm(3+)/Ho(3+) triply-doped tellurite fibre laser is reported. The fibre was pumped at 1.1 microm by a Yb(3+)-doped double-clad silica fibre laser. For a 17 cm fibre length and 99%???60% reflectance cavity, the threshold was 15 mW and the slope efficiency was 25%. A maximum output of 60 mW was observed for a launched pump power of 270 mW, corresponding to 22% optical-to-optical efficiency.

Tm3+/Ho3+ codoped tellurite fiber laser

Continuous-wave and Q-switched lasing from a Tm(3+)/Ho(3+) codoped tellurite fiber is reported. An Yb(3+)/Er(3+)-doped silica fiber laser operating at 1.6 microm was used as an in-band pump source, exciting the Tm(3+) ions into the (3)F(4) level. Energy is then nonradiatively transferred to the upper laser level, the (5)I(7) state of Ho(3+). The laser transition is from the (5)I(7) level to the (5)I(8) level, and the resulting emission is at 2.1 microm. For continuous wave operation, the slope efficiency was 62% and the threshold 0.1 W; the maximum output demonstrated was 0.16 W. Mechanical Q switching resulted in a pulse of 0.65 microJ energy and 160 ns duration at a repetition rate of 19.4 kHz.

Review on structural, thermal, optical and spectroscopic properties of tellurium oxide based glasses for fibre optic and waveguide applications

Abstract This review focuses on the engineering of the structural, thermal, optical and spectroscopic properties of tellurium oxide (TeO2) glasses for their applications in fibre optic and waveguide devices. Unlike silica optical fibres, tellurium oxide glass fibres and light waveguides support propagation of light beyond ∼2 μm, where silica fibres become opaque. Silica fibres also have limited solubility for rare earth oxides due to silica’s structure, which is where tellurium oxide fibres and light waveguides can offer significant opportunities to engineer novel lasers and amplifiers for integrated optics. In this review, we compare the structural properties of TeO2 based glasses, modified by incorporating alkali, alkaline earth, and other oxide compounds. Based on Raman, UV, visible and infrared spectroscopic data, the structural aspects of tellurite glasses are discussed. The effects of compositional modification on the thermal and viscous flow properties are also compared and related with the resistance against devitrification. The significance of glass to crystal phase transformation during cooling and heating is explained in the context of preform and fibre fabrication. The review also reports on the characterisation of OH− impurities in tellurite glasses. Recent developments in tellurite fibre lasers and femtosecond laser inscribed waveguide fabrication are discussed.

Spectroscopic and lasing performance of Tm3+- doped bulk TZN and TZNG tellurite glasses operating around 1.9 µm

We report spectroscopic and bulk laser performance characteristics for Tm(3+)-doped tellurite glasses when used as gain media operating around 1.9 microm. Two glass hosts studied are TZN and TZNG and their performances have been compared. In each case, well-characterized cw laser performance was obtained and this has been related to detailed spectroscopic measurements of the important lasing parameters of the laser transitions around 1900 nm when pumped at 793 nm. The maximum output power achieved was 124 mW from the TZNG sample with an associated slope efficiency of 28 % with a tuning range of 135 nm. Efficiency and loss analyses yielded a calculated maximum attainable efficiency of 48 % in Tm(3+):TZN compared to 28 % for the TZNG host.

Numerical Rate Equation Modeling of a

Judd-Ofelt analysis is performed on measurements of bulk samples of Tm³⁺- and Ho³⁺-doped tellurite glass from which the host-dependent Judd-Ofelt intensity parameters are extracted. These have then been used to calculate the radiative rates and branching ratios in this particular material system. A rate-equation approach is then used to model an experimentally realized ~2.1 μm Tm³⁺/Ho³⁺ codoped tellurite fiber laser and extract values of the energy transfer and upconversion rate parameters in TeO₂-ZnO-Na₂O (TZN) glass. Excellent agreement is found between simulated and experimental data, which indicates the validity of the approach.

{\sim {\hbox {2.1}}-}\mu{\hbox {m}}-{\rm Tm}^{3+}/{\rm Ho}^{3+}

We present an overview of rare-earth doped heavy metal oxide and oxy-fluoride glasses which show promise as host materials for lasers operating in the 2-5 μm spectral region for medical, military and sensing applications. By engineering glass composition and purity, tellurite and germanate glasses can support transmission up to and beyond 5 μm and can have favourable thermal, mechanical and environmental stability compared to fluoride glasses. We discuss techniques for glass purification and water removal for enhanced infrared transmission. By comparing the material properties of the glass, and spectroscopic performance of selected rare-earth dopant ions we can identify promising compositions for fibre and bulk lasers in the mid-infrared. Tellurite glass has recently been demonstrated to be a suitable host material for efficient and compact lasers in the ~2 μm spectral region in fibre and bulk form and the next challenge is to extend the operating range further into the infrared region where silica fibre is not sufficiently transparent, and provide an alternative to fluoride glass and fibre.

Co-Doped Tellurite Fiber Laser

A rate equation approach is used to model an experimentally realized ~ 2 mum Tm3+-doped tellurite fiber laser utilizing an in-band pumping scheme (3H6 rarr 3F4) . Excellent agreement between the theoretically predicted and experimentally measured slope efficiency is obtained. It is shown that in order to achieve agreement between the predicted and measured thresholds it is important to include cross-relaxation mechanisms with the 3H4 level, even with the in-band pumping scheme. By fitting the results of the model with level lifetime measurements and the threshold pump powers we have extracted the cross-relaxation parameters of Tm-doped tellurite glass.

Oxide glasses for mid-infrared lasers

Optimisation of femtosecond pulsed laser deposition parameters for the fabrication of silicon thin films is discussed. Substrate temperature, gas pressure and gas type are used to better understand the deposition process and optimise it for the fabrication of high-quality thin films designed for optical and optoelectronic applications.