## 3 Self-Referenced DPSSLs with Bulk Gain Material
### Chromium-Doped Lasers  
The first CEO detection from a DPSSL was demonstrated in 2001 by [PERSON] _et al._, in a Kerr-lens modelocked Cr:LiSAF laser [55]. This laser was pumped by two 670 nm diodes with a total power of 700 mW to produce 115 mW average output power at 894 nm in modelocked operation with \(\sim\)60 fs pulse duration and 93 MHz repetition rate. A CEO beat signal with an SNR exceeding 40 dB in a 100 kHz resolution bandwidth (RBW) was obtained after spectral broadening in a PCF and an \(f\)-to-\(2f\) interferometer, but the CEO was not stabilized due to the limited access to the sealed box of the LiSAF laser as explained by the authors. The pump diodes were driven by a battery for low-noise operation.  
A femtosecond laser based on a bulk Cr-doped material, namely Cr:forsterite, has been fully-stabilized and referenced to an H-maser [43]. However, this oscillator was not directly pumped by a laser diode, but by an Yb:fiber laser. Therefore, it is not exhaustively discussed here, but only briefly mentioned to highlight one of the key benefits of DPSSLs that is the direct pump current modulation capability for self-referencing. Instead, an acousto-optic modulator was needed in this laser system for pump power control, as direct pump modulation was not feasible.  
\begin{table}
\begin{tabular}{|c|c|c|c|c|c|c|c|c|c|c|c|c|} \hline
**Type** & **Gain** & \(\lambda\) & \(P_{m}\) & \(f_{m}\) & \(f_{m}\) & **At** & **ML** & **Pump** & **CEO** & **CEO Lock** & **CEO Inter. Noise (mrad)** & **Other** & **Refs.** \\ \hline  & CrLiSAF & 894 & 0.115 & 0.093 & \(-\)60 & KLM & STM & & not stabilized & - & [55] \\ \cline{2-13}  & Yb-KYW & 1033 & 0.250 & 0.16 & \(-\)300 & SESSAM & FBG-STM & \(f_{m}\) & 100 & 300 [0.1 Hz\(-\)1 MHz] & \
\begin{tabular}{c} External amplification + \\ compression \\ \end{tabular} & [25, 26] \\ \cline{2-13}  & Yb-KGW & 1042 & 2.2 & 1.0 & \(-\)290 & SESSAM & STM & & not stabilized &
\begin{tabular}{c} External compression \\ \end{tabular} & [19] \\ \cline{2-13}  & Yb-KGW & 1047 & 3.4 & 1.06 & 125 & SESSAM & MTM & & not stabilized & - & [20] \\ \cline{2-13}  & Yb-KGW & 1040 & 0.6 & 0.133 & 100 & SESSAM & MTM & \(f_{m}\) & \(-\)300 & 407 [1 Hz\(-\)5 MHz] & - & [56] \\ \cline{2-13}
**Bulk** & \
\begin{tabular}{c} CrLiSAF \\ \end{tabular} & 1062 & 1.7 & 1.0 & \(-\)60 & SESSAM & MTM & \(f_{m}\) & \(-\)300 & 744 [1 Hz\(-\)5 MHz] & - & [21] \\ \cline{2-13}  & Yb-CALGO & 1055 & 1.7 & 1.0 & 63 & SESSAM & VHG-MTM & \(f_{m}\) & \(-\)200 & 339 [1 Hz\(-\)5 MHz] & - & [57] \\ \cline{2-13}  & Yb & 1047 & 0.205 & 0.1 & 111 & SESSAM & FBG-STM & \(f_{m}\) & \(-\)130 & 83 [1 Hz\(-\)1 MHz] & - & [29] \\ \cline{2-13}  & Yb-KGW & 1031 & 0.215 & 0.1 & 155 & SESSAM & \(f_{m}\) & \(-\)100 & 1100 [1 Hz\(-\)1 MHz] &
\begin{tabular}{c} External compression \\ \end{tabular} & [58] \\ \cline{2-13}  & Er-Yb-glass & 1558 & 0.11 & 0.075 & 170 & SESSAM & FBG-STM & \(f_{m}\) & 5.5 & 720 [1 Hz\(-\)100 kHz] & - & [27, 28] \\ \cline{2-13}  & Er-Yb-glass & 1558 & 0.11 & 0.075 & 170 & SESSAM & FBG-STM & OOM & 40-50 & 65 (00 *) [1 Hz\(-\)100 kHz] & - & [44] \\ \cline{2-13}  & Er-Yb-glass & 1560 & 0.115 & 0.1 & 190 & SESSAM & FBG-STM & AOFS-FB & not reported & 118 & - & [59] \\ \hline  & Yb-LuO & 1035 & 7 & 0.064 & 142 & SESSAM & VHG-MTM & & not stabilized & - & [60] \\ \cline{2-13}  & Yb-YAG & 1030 & 17 & 0.038 & 250 & KLM & MTM & \(f_{m}\) & not reported & 250 [100/200 (00 **) & \multirow{2}{*}{[61]} \\  
* ML: modelocking STM: single-transverse-mode; MTM: multi-transverse-mode; FBG-STM: fiber Bragg-graining-stabilized single-transverse-mode; VHG-MTM: volume holographic grating-stabilized multi-transverse-mode; OOM: opto-optical modulation; AOFS-FB: accurate-optic frequency shifter feedback; IC-AOM: intra-cavity acoustic-optic modulator. Integrated phase noise without the contribution of technical noise at 50 Hz and harmonics; ** out-of-loop measurement.  
\end{table}
Table 1: List and main parameters of CEO-stabilized or self-referenceable DPSSLs reported in the literature (bulk DPSSLs and TDLs).