Intense 28  μm emission of Ho^3+ doped PbF_2 single crystal

Abstract

A Ho³⁺-doped PbF₂ mid-IR laser crystal was successfully grown using the vertical Bridgman method. An intense 2.8 μm emission in Ho:PbF₂ crystal was observed for the first time. By analyzing the absorption and emission measurements of the Ho:PbF₂ crystal with the Judd-Ofelt theory, the intensity parameters Ω(2,4,6), exited state lifetimes, branching ratios, and emission cross-sections were calculated. It is found that the Ho:PbF₂ crystal has high fluorescence branching ratio (20.99%), large emission cross section (1.44×10⁻²⁰ cm²), long fluorescence lifetime (5.4 ms), and high quantum efficiency (88.4%) corresponding to the stimulated emission of Ho³⁺: ⁵I₆→⁵I₇ transition. The structure of Ho:PbF₂ crystal was also analyzed by the Raman spectrum, and it was found that the Ho:PbF₂ crystal possesses low phonon energy of 257 cm⁻¹. We propose that the Ho:PbF₂ crystal may be a promising material for 2.8 μm laser applications.

Spectroscopic properties of Ho3+-doped PbF2 single crystal for 2μm lasers

“…At last, the as grown crystal was cooled to room temperature at the rate of 30°C/cm-40°C/h. The concentration and segregation coefficient of Ho 3+ ion in the PbF 2 crystal has been provided in our previous work [17] with a value of 2.2 Â 10 20 ions/cm 3 , and 1.15, respectively.…”

“…Compared with oxide crystals, fluorides are more attractive to achieve high-energy Q-switched operation, as they possess several advantages: (i) lower phonon energy suppressing nonradiative relaxation between adjacent energy levels; (ii) longer fluorescence lifetime improving energy storage [15,16]. In our previous work [17], we have focused our scientific program on a new potential gain medium Ho:PbF 2 crystal for efficient laser operation, which has been proved with low phonon energy of 257 cm À1 , good 2.8 lm MIR emission performances, and low absorption coefficient in typical H 2 O absorption band at 3 lm, and potential interest for laser applications. However, to our knowledge, there is no work has been carried out on the spectroscopic properties of this crystal in sufficient detail, especially in the wavelength of $2 lm.…”

Growth, structure, and spectroscopic properties of a Cr3+, Tm3+, Ho3+, and Pr3+co-doped LuYAG single crystal for 2.9 μm laser

“…Therefore, it is very significant to investigate and find 2.911 μm laser crystals in order to obtain this special wavelength laser. It is well known that the Ho 3+ ions, which possess abundant energy levels [11][12][13], are natural candidates for realizing 2.8-3.1 μm lasers corresponding to the transition from the 5 I 6 to 5 I 7 level [14,15]. Nevertheless, two bottleneck effects restrict the conversion efficiency of the 2.8-3.1 μm Ho 3+ lasers.…”

Enhanced emission of 286 μm from diode-pumped Ho^3+/Yb^3+-codoped PbF_2 crystal

“…It is well know that Ho 3+ is a natural candidate for ∼3 µm lasers owing to the 5 I 6 → 5 I 7 transition [6,7]. However, the ∼3 µm laser operation cannot be obtained efficiently due to (i) the lack of commercialized laser diodes (LD) corresponding to the intrinsic absorption of Ho 3+ ions, and (ii) the population bottleneck effect that occurs with the 5 I 6 → 5 I 7 transition which is a self-terminated transition.…”

“…Among many alternatives, fluoride crystals are more favorable in several respects: (i) lower phonon energy suppressing nonradiative relaxation between adjacent energy levels, (ii) longer fluorescence lifetime improving energy storage, and (iii) lower refractive index limiting nonlinear effects under intense laser pump [14][15][16]. In our previous work [7], we have reported a new MIR laser crystal Ho 3+ :PbF 2 , which has low phonon energy of 257 cm −1 , good 2.8 µm MIR emission performances, and low absorption coefficient in typical H 2 O absorption band at 3 µm. PbF 2 crystallizes in the cubic space group (Fm3m) with fluorite structure, which makes it possible to grow into the form of large-size transparent single crystals [17].…”