Tm and Tm–Tb-doped germanate glasses for S-band amplifiers

Population inversion between the 3H4 and the 3F4 excited states of Tm3+ investigated by means of numerical solutions of the rate equations system in Tm3+-doped and Tm3+, Ho3+-codoped fluoride glasses

“…A population inversion density of 1.6 Â 10 18 Tm 3+ ions cm À3 was obtained for a pump intensity of 2.7 kW cm À2 , which is $5.3 times bigger that one verified in Tm(0.1%):Ho(0.15%):Ge-Ga-As-S-CsBr [7] ($3 Â 10 17 cm À3 ). This population inversion density is also higher than that one estimated for Tm(0.1%):Tb(0.2%):GLKZ [4] ($2 Â 10 17 cm À3 ) and for Tm(0.1%):Tb(0.15%):Ge-Ga-As-S-CsBr [7] ($2.5 Â 10 17 cm À3 ) glasses for similar pumping conditions. This result points that Tm:Ho:ZBLAN doped with 0.5 mol% of Tm 3+ and codoped with 1 mol% of Ho 3+ maximizes its amplification potential gain based on the Tm 3+ -stimulated emission near 1.5 mm, so making this material very promising system for light signal amplification in S-band of telecommunication.…”

“…In addition, this reminiscence luminescence of 3 F 4 state exhibits an exponential decay with a lifetime similar to that one observed for single Tm-doped ZBLAN ($7 ms). On the other hand, residual 3 F 4 luminescence was not observed in the case of Tm:Ho in tellurite [10], chalcogenide [7] and Tm:Tb in germanate (GLKZ) [4] glasses. This luminescence effect (residual) evidences that the fast energy migration through 3 F 4 excited states leads to two distinct types of Tm 3+ excited ions in ZBLAN glass (or classes): (i) class 1-excited Tm 3+ ions close by Ho 3+ that has a K 1 transfer rate resultant from Tm( 3 F 4 )-Ho( 5 I 7 ) transfer minus Ho( 5 I 7 )-Tm( 3 F 4 ) back-transfer rates and (ii) class 2-excited Tm 3+ ions ( 3 F 4 ) far from Ho 3+ ions (or isolated) having an intrinsic lifetime of $7 ms.…”

“…Nevertheless, the lifetime of the lower 3 F 4 level involved in the 1.47 mm emission is considerably longer than that of the upper 3 H 4 level ($6 times is observed in Tm:ZBLAN and Tm:Ge-Ga-As-S-CsBr, and $8.3 times in germanate glasses). To realize population inversion in Tm 3+ ions, Ho 3+ (0.15%) or Tb 3+ (0.15%) ions have been used to codope the Tm-doped material to depopulate the 3 F 4 level of Tm 3+ in fluoroindate [2], fluorozirconate (ZBLAN) [3,4], fluorogermanate [5], tellurite [6] and chalcogenide [7] glasses. Because the energies of 5 I 7 and 7 F 0,1,2 levels of Ho 3+ and Tb 3+ , respectively, coincide with the energy of the 3 F 4 level, holmium and terbium ions may actuate as deactivator of the 3 F 4 lowest excited state of Tm 3+ to improve the population inversion of Tm 3+ ions in many luminescent solid materials.…”

“…This population inversion was calculated using the numerical solutions obtained using the Runge-Kutta method applied to the rate equations system. This method has been recently used to investigate the population inversion of 3 H 4 -3 F 4 transition of Tm 3+ in Tm:Tb [4] and Tm:Eu:germanate [8] glasses giving an important contribution for understanding the potential and limitations of Tm 3+ and Tm-doped materials for light signal amplification.…”

Excited state dynamics of the Ho3+ ions in holmium singly doped and holmium, praseodymium-codoped fluoride glasses

“…The luminescent 3 F 4 level of Tm 3+ , for example, can be efficiently depopulated by Ho 3+ and Tb 3+ ions in fluorozirconate ͑ZBLAN͒, tellurite, Ge-Ga-As-S-CsBr and GeO 2 -Li 2 O-K 2 O -ZnO codoped glasses, making these materials suitable for use as optical amplifiers operating in 1.4-1.5 m region of the spectrum. [1][2][3][4][5] For applications requiring laser operation at 2.9 m, Ho 3+ -doped LiYF 4 ͑YLF͒ crystal 6 operating on the 5 I 6 → 5 I 7 transition has the potential for pulsed laser operation despite the longer ϳ16 ms lifetime of the lower laser ͑ 5 I 7 ͒ level when compared to the lifetime of the upper laser ͑ 5 I 6 ͒ level which is ϳ3 ms. 7 Many applications, however, require continuous wave ͑cw͒ operation in this spectral range. To achieve this end, a deactivator ion must be introduced in order to quench the excited state population in the 5 I 7 level.…”