This paper examines the steady state and time resolved emission spectroscopy of Tm3+ doped and Tm3+-Ho3+, Tm3+-Yb3+ co-doped tellurite fibers for mid-IR fiber laser design which find applications for lidar. These doped fibers show promising properties for compact and tunable laser sources in the visible and mid-IR when pumped at 800 nm, 980 nm and 1480 nm which can be used for remote chemical sensing and atmospheric monitoring. Tellurite glass has a lower cut-off phonon energy than silica glass and is more environmentally stable than fluoride glass, and coupling these properties with its high rare-earth ion solubility and high refractive index make this glass a very interesting material in which to study the fluorescence properties of these rare earth ions. We have measured the mid-IR fluorescence properties in varying lengths of multi-mode and single-mode fiber for the 3H4-3H6 (~1.85 μm), 3H4-3F4 (~1.46 μm) transitions in Tm3+ and the 5I7-5I8 (~2.05 μm) transition in Ho3+. We have also measured the visible emission from these fibers due to excited state absorption (ESA) as there is blue and green emission in Tm3+ and Tm3+-Ho3+ doped fibers respectively when pumped at 800 nm, and strong red and blue emission in the Tm3+-Yb3+ when pumped at 980 nm. These results in fiber are compared to bulk glass results and are used to describe the pumping schemes and energy transfer mechanisms of these rare earth ions in tellurite fiber.
Er-doped silicate thin films were deposited by the pulsed laser deposition technique, starting from an Er-doped silicate glass of composition: 65%SiO2 - 3%Al2O3 - 11%Na2O - 10%PbF3 - 10%LaF3 - 1%ErF3. The irradiations were performed with an ArF excimer laser (pulse length ~ 30 ns) in a dynamic flow of oxygen at a pressure of 5 Pa. The laser fluence at the target surface was about 2 J/cm2. The films were deposited on pure silica substrates, either at room temperature or heated to 200°C. The morphology of the films was studied by using optical microscopy, scanning electron microscopy and atomic force microscopy. The optical transmission of the films in the NIR-visible-UV regions (200-2500 nm) was recorded by using a double beam spectrophotometer. The optical spectra were analyzed by a computer code to evaluate the refraction index n and the extinction coefficient k along with the film thickness. The optical transmission was performed soon after the deposition and after one month to evaluate the aging effects. The films deposited at room temperature presented cracks over all the area of the film when submitted to SEM inspection or ion etching. Films deposited at 200°C remained undamaged. Optical waveguides were fabricated in the films deposited at 200°C by ion etching. Very low losses (down to 0.74 dB/cm) were measured by the prism coupling technique.
We report the results of emission and amplification in Tm3+- and Er3+-fibres for signal gain in the 1420 nm to 1600 nm wavelength range, which covers S-, C- and L-bands of silica fibre optical communication networks. The paper explains the mechanism for alleviating the pump excited state absorption (ESA) in Er-doped tellurite fibres for maximizing the pump inversion efficiency at 980 nm using the Ce-ions as a co-dopant and via the structural modification of TeO2 glass using B2O3. The spectroscopic data and gain bandwidth of Er-doped fibres are reported in the C- and L-bands. Methods for enhancing gain in the S-band using the co-dopants (Tb3+, Yb3+) with 800 nm and 980 nm pumping schemes are also explained. The measured maximum relative gain in short fibres of 5 to 10 cm in length in C- and L-bands are: 30 dB and 15 dB, respectively. By comparison the internal gain in a 20 cm long Tm/Yb ion co-doped fibre pumped with a 980 nm source was
7 dB.
The radiative transition in Tm3+-doped fibre at 1.47 μm (3H4 → 3F4) remains a potential route for designing efficient fibre
and waveguide amplifiers for the S-band (1420-1520 nm). The transition however suffers from a long metastable
lifetime (5 times longer) than the 3H4 level, which means that the 3F4 level must be depopulated rapidly for efficient
inversion for laser and amplifiers applications. One of the known means so far for depopulation of the lower 3F4 level is
via co-doping with other rare-earth ions, essential for modest gain. For the Tm3+ - Ho3+ and Tm3+ - Tb3+ doped tellurite
glasses, the IR static and time-resolve fluorescence spectra and the lifetimes of the upper 3H4 and lower 3F4 lasing levels
for 1.47 μm of Tm3+ were measured. The energy transfer rate and non-radiative transfer efficiency between donors and
acceptors are compared. The quenching mechanism has been explained. Both the Ho3+and Tb3+ ions reduce the lifetimes
of the upper and lower lasing levels, with Tb3+ ions proving more effective than the effects observed for Ho3+ ions.
The paper discusses the application of Tm3+ and Tm3+/Ho3+-co-doped tellurium oxide fibres for LIDAR applications. Suitably co-doped tellurium oxide glass offers an excellent opportunity for developing high-power tunable laser compact devices, using both the 800 nm, 980 nm, and 1480 nm pumping schemes. Rare-earth ions have large solubility in tellurite glass, which we aim to exploit for designing Tm3+ and Tm3+/Ho3+ lasers operating in the 1.8μm and 2.9μm ranges. The importance of this wavelength band in characterising atmospheric CO2 and OH measurements will be explained, using the following transitions in Tm3+:3F4 - 3H6 (1.8 μm), 3H4 - 3H5 (2.3 μm) and in Ho3+: 5I7 - 5I8 (2.1 μm) and 5I6 - 5I7 (2.9 μm), all of which can be achieved via the pumping schemes at above wavelengths. The paper discusses the spectroscopic characterisations of bulk glass and their applications in the design of single-mode fibres for laser experiments. For 980 nm pumping scheme, the efficient energy transfer via Yb3+-ion co-doping to the respective lasing levels in Tm3+ and Ho3+ is explained. The results from the steady state fluorescence spectroscopy measurements for the energy transfer analysis are explained for laser design. The paper also explains the fibre pumping scheme and laser experiments in the 1.8 μm and 2.05 μm region.
The main aim of this paper is to demonstrate potential materials and fibres for 589 nm and 569 nm high-power laser sources, which can be developed by using rare-earth ions (Eu3+, Sm3+) as dopants in glass fibres. In this paper, we also discuss the advantages of using high-power excitation sources: for example the NIR semiconductors at 980 nm and 800 nm and high-power Yb-fibre laser based systems for high-power upconverted lasers. In this context the spectroscopic properties of Eu3+-Er3+ and Sm3+- based glass and fibre systems are also discussed in bulk oxide glasses and in fibre geometries for designing lasers at 589 nm and 569 nm for adaptive optics.
The main objective of the paper is to demonstrate rare-earth (Tm3+, Er3+, Ho3+) and transition-metal ion (Cr-ion) doped glass fibres as potential broadly tunable laser devices. The paper will discuss the spectroscopy of metal ions and suitability of glass hosts for designing efficient devices, which can be pumped using commercially available semiconductor or fibre-based IR laser sources, e.g. at 800, 980, 1020, 1040, and 1480 nm wavelengths. The spectroscopic properties of transition metal ion-host systems are compared briefly with those of crystal based devices. Results of the measured spectroscopic properties for Cr-ion and rare-earth ion doped fibre systems particularly pumped using NIR wavelength from Ti-sapphire sources are also reported.
The paper compares the spectroscopic properties of RE-doped and transition-ion doped modified silicate glasses for their applications in broadband amplifiers and tunable lasers. The effect of structural modification with fluorine in Er-doped modified silicate is discussed by the reference of reduced Er-Er ion cross relaxation in the host. The measured lifetimes for the 4I13/2→4I15/2 transition at 1 mole percent in modified silicate glass samples having fluoride to oxide ratio (F/O) of 0.25 vary between 11 and 12 ms. The measured lifetime at room temperature is for 3T2→3A2 in Cr4+-doped silicate was 250 μs derived from a double exponential. The mechanisms for the prolonged lifetime of upper levels in both Er- and Cr-doped glasses are discussed.
Tellurite glasses doped with Er3+ and Tm3+ are investigated for broadband amplifiers in the third telecommunications window. Fluorescence spectra and lifetimes of Er3+ and Tm3+ in tellurite glass were measured. Stimulated emission cross-sections were calculated using the McCumber method for Er3+ and the Judd-Ofelt analysis for Tm3+. The obtained emission parameters are compared with those in other glass hosts. The potential advantages of tellurite glass as amplifier host are discussed.
Tellurite glasses doped with Er3+, Tm3+ and Nd3+ are investigated for broadband amplifiers in the third telecommunications window. Fluorescence spectra and lifetimes of Er3+, Tm3+ and Nd3+ in tellurite glass were measured. Stimulated emission cross- sections were calculated using the McCumber method for Er3+ and the Judd-Ofelt analysis for Tm3+ and Nd3+. The obtained emission parameters are compared with those in other glass hosts. The potential advantages of tellurite glass as amplifier host are discussed.
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