Optical amplification by upconversion in Tm–Yb fluoroindate glass

Abstract Evidence of a positive optical gain at 650 nm is observed in Tm 3+ –Yb 3+ codoped fluoroindate glass in an upconversion pump and probe experiment. The 1 G 4 level of the Tm 3+ ions is populated by an upconversion mechanism under excitation of the Yb 3+ ions at 975 nm with high power pulsed laser and give rise to an intense emission from the 1 G 4 to the 3 F 4 levels. The 1 G 4 → 3 F 4 electronic transition is stimulated with a low signal at 650 nm as a probe. Under this condition, we reach the population inversion necessary between the Tm 3+ levels of the transition 1 G 4 → 3 F 4 and we observed an increase of the emission intensity at the signal wavelength due to the stimulated emission. Transient positive optical gain around 3 cm −1 (∼12 dB/cm) has been measured in Tm–Yb codoped fluoroindate glass during the first 400 μs.