Prospects of Holmium-doped fluorides as gain media for visible solid state lasers

Abstract

Abstract:In this paper we report on the suitability of Ho 3+ :LiLuF 4 and Ho 3+ :LaF 3 as active media for solid state lasers emitting in the green spectral region. The ground state absorption spectra were measured and employed to calculate the emission cross section spectra via the reciprocity method. These allowed to derive the gain characteristics for various inversion ratios. The decay dynamics of the 5 F 4 , 5 S 2 multiplet, which would act as upper laser level, were investigated to estimate the quantum efficiency. Measurements of the excited state absorption were conducted which showed that stimulated emission is the dominating effect around 550 nm. Laser operation was demonstrated in the green spectral region by employing Ho 3+ :LaF 3 as gain medium. Laser oscillation occurred in a self-pulsed regime with a maximum average output power of 7.7 mW, a repetition rate of 5.3 kHz, and a pulse duration of 1.6 µs. To the best of our knowledge this constitutes the first green laser emission of a Ho 3+ -doped crystal at room temperature.

Out of the blue: semiconductor laser pumped visible rare‐earth doped lasers

“…Detailed investigations revealed, that already at room temperature and in case of the low-phononenergy host LiLuF 4 , this lifetime is strongly quenched by non-radiative phonon-assisted transitions via the 5 F 5 -multiplet and further multiplets back into the ground state [46]. Therefore, only very low phonon energy host materials such as heavier halides [47,48] are regarded to be suitable host materials for visible cw lasers based on Ho 3+ .…”

“…18) and 574 nm operated in a self-pulsed regime [61] due to the long lifetime of the terminal laser level 6 H 13/2 . Co-doping with Tb 3+ -or Eu 3+ -ions significantly decreased Figure 19 Laser characteristics of Ho 3+ :LaF 3 under 2ω-OPSLpumping at 479 nm [46]. It should be noted that the laser operated in a self-pulsed regime with a few μs pulse duration and several kHz repetition rate.…”

“…Despite these comparably low cross sections, the fluorescence lifetime of the upper laser level is significantly shorter than 1 ms and amounts to only about 100 μs, e.g., for Ho 3+ :LiLuF 4 . Detailed investigations revealed, that already at room temperature and in case of the low‐phonon‐energy host LiLuF 4 , this lifetime is strongly quenched by non‐radiative phonon‐assisted transitions via the 5 F 5 ‐multiplet and further multiplets back into the ground state . Therefore, only very low phonon energy host materials such as heavier halides are regarded to be suitable host materials for visible cw lasers based on Ho 3+ .…”

“…At the 5 F 4, 5 S 2 → 5 I 7 transition around 750 nm, flash‐lamp pumped pulsed laser operation was also demonstrated at room temperature in Ho 3+ :LiYF 4 . Only recently the first report on blue‐pumped laser operation of Ho 3+ in the visible was published . Laser experiments under 2ω‐OPSL‐pumping were conducted with Ho 3+ :LaF 3 and Ho 3+ :LiLuF 4 .…”

Research Progress of Rare-earth Doped Laser Crystals in Visible Region

“…在室温下实现 5 F 4 , 5 S 2 → 5 I 7 跃迁脉冲 激光输出[96] 。最近, 首次使用蓝光 2ω-OPSL 泵浦 Ho : LaF 3 和 Ho : LiLuF 4 实现可见波段激光输出[97] 。 Ho : LaF 3 晶体在 549 nm 波长处输出功率不到 10 mW,…”