Abstract

Nowadays there is much interest in compact fiber lasers and amplifiers operating in the visible spectral region because of their numerous applications, including optical data storage, medical diagnostics and laser material processing. Recently, as a candidate for laser and amplifiers at the 0.54 μm band, Tb³⁺-doped fiber has been investigated by the author. The ⁵D₄→⁷F₅ transition of Tb³⁺ acts as a four-level laser system by ⁵D₄ level (20600 cm¹) pumping at a wavelength of 488 mn and a signal gain of 5.5 dB has been confirmed in a Tb³⁺-doped fluoride fiber[l], Furthennore, it is known that co-doping of Yb³⁺ in Tb³⁺-doped materials leads to visible upconversion emission by the Yb³⁺-Tb³⁺ cooperative energy transfer process[2]. In this process two excited Yb³⁺ (sensitizer) ions simultaneously transfer their energy to a Tb³⁺ (activator), so that Tb³⁺ can be excited to the ⁵D₄ level. Because Yb³⁺ ions have the strong absorption cross section in the region of 0.98 μm, we can take advantage of high-performance 0.98 pm laser diode to excite Tb³⁺ ions. The probability of cooperative energy transfer was speculated at most 1% by T. Kushida[3], But the study of the energy transfer efficiency from Yb³⁺ to Tb³⁺ has been superficial, so far. In this study, we investigate the possibilities of Yb³⁺-Tb³⁺ cooperative energy transfer process which enable the 0.98 μm pmnping for Tb³⁺ ions using various host glasses. The energy transfer efficiency as high as 60±11 % was observed for the first time in a borosilicate glass and it was found out that Tb³⁺-Yb³⁺-codoped borosilicate glass was a promising candidate for the 0.54 μm band laser medium pumped at 0.98 μm.

© 2007 IEEE