## 3 Experimental Results and Discussion
Compared to the earlier reported PSQ Er:Lu\({}_{2}\)O\({}_{3}\) ceramic laser at 2.7 u\(\parallel\), the average output power and slope efficiency in the present work have increased by nearly an order of magnitude [29]. This can be attributed to the modified cavity structure with increased utilization efficiency for the pump power, together with the optimized SA parameters with a decreased intracavity insertion loss. It is worth noting, that the pulse duration of 70 ns is close to the limit set by the cavity length and by the SA's modulation depth [24; 33]. Further shortening in pulse duration should be possible by reducing the  
Figure 3: Measured pulse duration and repetition rate as function of the absorbed pump power. Figure 2: Output power as a function of the absorbed pump power of the Er:Lu\({}_{2}\)O\({}_{3}\) ceramic laser under CW and passively Q-switched mode of operation. Inset: laser output spectrum at 2716 nm. cavity length and hence the cavity roundtrip time, for example microchip laser, or/and using a SA with a higher modulation depth. As a proof-of-principle experiment, the lasing characteristics of the PSQ Er:Lu\({}_{2}\)O\({}_{3}\) ceramic were further evaluated with a simple, low-loss, two-mirror cavity. In this configuration we placed the SESAM slightly closer to the Er:Lu\({}_{2}\)O\({}_{3}\) ceramic so that the physical length of the cavity was reduced to 19 mm. When the absorbed pump increased to greater than 2.1 W, Q-switched pulses of \(\sim\)40-ns were produced. With the increase in the pump power, pulses of 32-ns duration were obtained. Note that the pulse duration of 32 ns is close to the limit set by the cavity length as well [24]. This implies that constructing an efficient microchip-type Q-switched Er:Lu\({}_{2}\)O\({}_{3}\) ceramic laser and generating sub-nanosecond pulses with MHz repetition rates should be possible [24; 25]. Due to the influence of \begin{table}
\begin{tabular}{l c c c c c c c} \hline \hline
**Gain Medium** & **SA** & \begin{tabular}{c} **Wavelength,** \\ \(\upmu\)m \\ \end{tabular} & \begin{tabular}{c} **Pulse** \\ **Width, ns** \\ \end{tabular} & \begin{tabular}{c} **Output** \\ **Power, mW** \\ \end{tabular} & \
\begin{tabular}{c} **Pulse** \\ **Energy, W** \\ \end{tabular} &
\begin{tabular}{c} **Peak** \\ **Power, W** \\ \end{tabular} & **Ref.** \\ \hline Er:Lu\({}_{2}\)O\({}_{3}\) crystal & BP & 2.84 & 359 & 755 & 7.1 & 19.2 & [21] \\  & MoS2 & 2.84 & 335 & 1030 & 8.5 & 23.8 & [22] \\  & g-CsN4 & 2.84 & 351 & 1090 & 11.1 & 31.6 & [23] \\ \hline Er:Lu\({}_{2}\)O\({}_{3}\) ceramic & SESAM & 2.716 & 660 & 60 & 1.8 & 2.7 & [29] \\  & SESAM & 2.716 & 70 & 692 & 9.8 & 139.2 & This work \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Comparison of output characteristics of the Er:Lu\({}_{2}\)O\({}_{3}\) lasers operating around 3 \(\upmu\)m passively Q-switched by various SAs reported so far. Figure 4: Pulse energy and the corresponding peak power of the Q-switched laser versus the absorbed pump power. Figure 5: Temporal profiles of the Q-switched pulse trains at different time scales. the unabsorbed pump on the SA, the PSQ laser operation was not as stable as the first configuration [34]. Further optimization should be provided by eliminating the residual pump via placing a dichroic filter after the laser element or applying dichroic coatings on the output face of the laser gain medium.