Temperature dependence of the small-signal gain of a Cr³⁺ and Nd³⁺ co-doped Y₃Al₅O₁₂ ceramic

Abstract

There is a demand for higher-efficiency neodymium and chromium co-doped yttrium aluminum garnet (Nd/Cr:YAG) ceramics that can be excited by broadband light sources, such as flash lamps. We experimentally investigated the temperature dependence of the gain coefficient of a Nd/Cr:YAG ceramic (Nd: 1.0 at%, Cr: 2.0 at%). The gain coefficient at 1064 nm decreased with increasing temperature when Nd3+ was directly excited at 808 nm. However, when Nd3+ was excited via energy transfer from Cr3+ excited at 610 nm, the gain coefficient increased with increasing temperature. This temperature dependence was theoretically explained by solving the rate equations for Nd/Cr:YAG. Nd/Cr:YAG ceramics pumped with flash lamps may provide good laser performance without loss of gain even at high temperatures.

Analyses of energy transfer of Cr3+ and Nd3+ co-doped Y3Al5O12 ceramic powders at the 4 T 1 level of Cr3+ ion excitation

“…As the Cr 3+ concentration increased, the decay time of the Cr 3+ fluorescence of Cr:YAG was substantially shortened, showing the apparent deviation from the single exponential decay, likely because of the concentration quenching effect. 23) As shown in Fig. 2(b), the Cr 3+ fluorescence for the Nd/Cr:YAG ceramic powder samples decayed faster than those for the Cr:YAG ceramics powder samples at the same Cr 3+ concentrations because the excitation energy transferred from Cr 3+ to Nd 3+ .…”

“…This is due to the increases in energy transfer and quenching parameters with increasing Cr 3+ concentration. 23)…”

“…The coupled 2 E and 4 T 2 levels are referred to as the thermally coupled 2 E-4 T 2 level because some of the population stored in the metastable level of 2 E is thermally excited to the 4 T 2 level. 21) We previously investigated the temperature dependence [20][21][22] and concentration dependence 23) of the energy transfer process of Nd/Cr:YAG ceramics with 4 T 2 level excitation. In Nd/Cr:YAG ceramics, the energy transfer from Cr 3+ to Nd 3+ can be explained by dipole-dipole interactions, even if the concentration quenching of Cr 3+ is included.…”

“…In Nd/Cr:YAG ceramics, the energy transfer from Cr 3+ to Nd 3+ can be explained by dipole-dipole interactions, even if the concentration quenching of Cr 3+ is included. 23) In the case of 4 T 2 level excitation, the excitation energy relaxes to the metastable 2 E-4 T 2 level, and then some of the stored energy in the 2 E-4 T 2 level transfers to the excited levels of Nd 3+ with rapid relaxation to the 4 F 3/2 level. The conclusions were explained by theory and experimental data.…”

“…The conclusions were explained by theory and experimental data. [21][22][23] Fujioka et al reported that the fluorescence intensity of Nd 3+ in Nd/Cr:YAG ceramic powders excited at 440 nm ( 4 T 1 level) increased with increasing Cr 3+ concentration up to 6.0 mol% and then decreased because of concentration quenching. 15) However, they could not discuss the energy transfer process in detail because the fluorescence lifetime was considered effective.…”