Crystal growth and spectroscopic analysis of Ho, Pr:Sc₂O₃ crystal for 2.9 μm mid-IR laser

Abstract

Ho3+, Pr3+: Sc2O3 crystal was successfully grown by the TGT method. The spectroscopic properties of the crystal were analyzed. The absorption cross section of Ho, Pr: Sc2O3 at 636 nm was 1.58×10–20 cm2. J-O theory was applied to analyze the fluorescence properties of the grown crystal at 2.9 μm. The intensity parameters Ωt (t=2,4,6), radiative transition rates, branching ratios and radiative lifetime were calculated. Ho, Pr: Sc2O3 exhibited strong emission at 2110 nm and 2864 nm with a stimulated emission cross section of 2.4 × 10–21 cm2 and 4.2 × 10–21 cm2, respectively. The fluorescence lifetime of the Ho3+ 5I6 and 5I7 levels were measured to be 1.64 ms and 5.74 ms. These results show that the Ho, Pr: Sc2O3 crystal would be a potential laser material at the 2.9 μm region.

Optical spectroscopy of Ho3+,Pr3+ co-doped YScO3 crystal

“…We can see that the branching ratio of the 5 I 6 → 5 I 7 transition is about 13.89%. The radiative lifetime of 5 I 6 energy level was calculated to be 1.70 ms, which is lower than that of Ho:LaF 3 (18.99 ms [29]), Ho,Pr:Sc 2 O 3 (6.20 ms [10]) and Ho,Pr:Lu 2 O 3 (7.97 ms [11]). This preprint research paper has not been peer reviewed.…”

“…The peak emission cross sections at 2040 nm and 2890 nm were calculated to be 0.80×10 -20 cm 2 and 1.22×10 -20 cm 2 , with a FWHM of 187.0 nm and 197.4 nm, respectively. The value of emission cross section at 2890 nm is lower than that of Ho,Pr:LiLuF 4 (1.91×10 -20 cm 2 at 2944 nm [8]) and Ho,Pr:CaGdAlO 4 (2.38×10 -20 cm 2 at 2860 nm [12]), but higher than that of Ho,Pr:LiLiF 4 (0.68×10 -20 cm 2 at 2950 nm [9]), Ho,Pr:Sc 2 O 3 (0.54×10 -20 cm 2 at 2864 nm [10]), Ho,Pr:Lu 2 O 3 (0.42×10 -20 cm 2 at 2893 nm [11]) and Ho,Pr:CaF 2 (1.04×10 -20 cm 2 at 2851 nm [18]). The FWHMs are larger than those of Ho,Pr:Sc 2 O 3 (159.0 nm at 2110 nm, 144.6 nm at 2864 nm [10]), which displays the Ho,Pr:YScO 3 crystal may be used as a gain medium for tunable and ultrashort pulse lasers.…”

“…The fluorescence lifetime of the 5 I 6 and 5 I 7 levels was fitted to be 0.31 ms and 5.89 ms, leading to a fluorescence quantum efficiency of 7.6% and 54.2%, respectively. The fluorescence of 5 I 6 multiplet is much higher than that of Ho,Pr:CaGdAlO 4 (0.194 ms [12]), but lower than that of Ho,Pr:LiLuF 4 (1.47 ms [8]), Ho,Pr:Sc 2 O 3 (1.64 ms [10]), Ho,Pr:Lu 2 O 3 (0.55 ms [11]) and Ho,Pr:CaF 2 (2.73 ms [18]). It is noticed that the fluorescence lifetime of the 5 I 6 state is much shorter than that of 5 I 7 state in Ho,Pr:YScO 3 crystal, which can cause the 2.9 μm laser transition to self-terminate.…”

“…Unfortunately, the self-terminating transition ( 5 I 6 → 5 I 7 ) of Ho 3+ ions, namely, the upper energy level 5 I 6 has a shorter lifetime than the lower energy level 5 I 7 [7], extinguished the probability of population inversion for lasing at around the 3 μm wavelength. Co-doping with Pr 3+ ions is an effective way to depopulate the 5 I 7 multiplet of Ho 3+ for population inversion and practical laser operation [8][9][10][11][12][13]. Up to now, laser operations have been demonstrated in Ho,Pr:LiLuF 4 [14,15], Ho,Pr:LiYF 4 [16,17] and Ho,Pr:CaF 2 [18].…”