## 1 Introduction  
Laser radiation at \(\sim\)2.7-\(\upmu\)m is important for practical applications and scientific research. Being regions of water absorption and molecular fingerprints, laser sources at \(\sim\)2.7-\(\upmu\)m are useful for biomedical therapy [1, 2] and atmospheric sensing [3]. In addition, these lasers are utilized for generating 3-5-\(\upmu\)m laser emission [4, 5], which corresponds to an atmosphere transparent window. Lasers at \(\sim\)2.7-\(\upmu\)m also facilitate studies of laser materials that is suitable to generate deep-infrared lasing [6, 7]. Both the applications and research require versatile \(\sim\)2.7-\(\upmu\)m laser sources with short pulse duration and high repetition rate. A simple approach to generate \(\sim\)2.7-\(\upmu\)m pulses is Q-switching ion-based (as Er\({}^{3+}\), Ho\({}^{3+}\), Dy\({}^{3+}\) and Cr\({}^{2+}\)) lasers. Er-based lasers operating on the transition between \({}^{4}\)I\({}_{11/2}\) and \({}^{4}\)I\({}_{13/2}\) energy levels are most often utilized because of the mature pump sources of flashlamps and -976-nm laser diodes (LDs). With 50 atom % Er:YAG (Y\({}_{3}\)Al\({}_{5}\)O\({}_{12}\)), 30 atom % Er:YSGG (Y\({}_{3}\)Sc\({}_{2}\)Ga\({}_{3}\)O\({}_{12}\)), and 15 atom % Er:YLF (LiYF\({}_{4}\)) laser materials, \(\sim\)2.7-\(\upmu\)m pulses at durations of tens of nanoseconds have been obtained. However, the repetition rates of these lasers are generally limited to several Hertz due to the severely thermal effects generated during laser operations [8, 9, 10, 11]. Laser pulses at \(\sim\)2.7-\(\upmu\)m with repetition rates at the kilohertz scale have been generated from Er:ZBLAN (ZrF\({}_{4}\)-BaF\({}_{2}\)-LaF\({}_{3}\)-AlF\({}_{3}\)-NaF) fiber lasers, which are more thermally advanced [12, 13]. However, the pulse durations are hundreds of nanoseconds because fibers have limited energy storage capability. So far, short pulses at \(\sim\)2.7-\(\upmu\)m with high repetition rates are rare. The use of Er-based sesquioxides is promising in terms of obtaining \(\sim\)2.7-\(\upmu\)m laser pulses with short pulse durations and high repetition rates. As \(\sim\)2.7-\(\upmu\)m laser oscillation can be realized from Er-based sesquioxides with low doping concentrations (lower than \(\sim\)7 atom %) [14, 15], the thermal effects generated during laser operation are greatly alleviated. In addition, sesquioxides have high thermal conductivity, which decreases slightly with increasing doping concentration [16]. Furthermore, Er-based sesquioxides have long \(\sim\)2.7-\(\upmu\)m fluorescence lifetimes (e.g., an order of magnitude longer than that of Er:YAG), making them beneficial for energy storage [17]. Unfortunately, sesquioxides have extremely high melting points (\(>\)2400 \({}^{\circ}\)C), imposing serious challenges for traditional single-crystal-growthapproach. In this aspect, polycrystalline ceramics are superior to single crystals since they can be sintered at much lower temperatures. Moreover, transparent ceramics have advantages over crystals in terms of their rapid fabrication in large scale and composite structures, flexible doping concentrations, and good thermo-mechanical properties [18]. Recently, sesquioxide ceramics have been successfully fabricated and mainly explored to realize continuous-wave (CW) laser operation at \(\sim\)2.7-\(\upmu\)m. A passively Q-switched \(\sim\)2.7-\(\upmu\)m Er:Y\({}_{2}\)O\({}_{3}\) ceramic laser with a pulse duration of 4.47 \(\upmu\)s and a pulse repetition rate of 12.6 kHz was realized, aiming to demonstrate the broadband availability of black-phosphorus [19]. For actively Q-switched operation, an acousto-optically Q-switched Er:Y\({}_{2}\)O\({}_{3}\) ceramic laser was demonstrated, generating pulses with durations of 41-190 ns in the range of 0.3-10 kHz [20].