# Impact of Intracavity Power Variations toward Ultrashort Pulse Generation
## 5 Pulse Laser Performance
As illustrated in Figure 11a, the pulse duration of the 30% output coupling ratio at 99 mW pump power is evaluated. First, the pulse duration is determined by measuring the value of its full width of half maximum (FHWM) pulse duration. In this experiment, the FWHM value is 1250 fs. The pulse is fitted with the sech\({}^{2}\) fitting curve, which has a 0.648 decorrelation factor. Based on this fitting, the actual pulse duration is 810 fs after multiplying with this decorrelation factor. The same analysis is applied to other output coupling ratios, and their pulse duration values are presented in Figure 11b. The slowest pulse occurs using a 10% output coupling ratio; however, this condition is already near to its transform-limited pulse by referring to the value of its time-bandwidth product (TBP) of 0.319. Although a 30% output coupling ratio produces the shortest pulse, its TBP value is recorded at 0.378. This indicates that the generated pulse is slightly chirped. Figure 12a,b depict the evolution of average output power and pulse energy with respect to pump power at different output coupling ratios. In general, the average output power increases in tandem with pump power after the threshold power. The repetition rate of the pulse is almost constant; therefore, the pulse energy is also directly proportional to the pulse power. Figure 12c summarizes the value of the average output power and pulse energy at the maximum pump power of 99 mW. According to experimental results, the average output power rises as the output coupling ratio increases. This is owing to the increment of the OC loss as a result of the photon count reduction at the entrance of the EDF (after the WDM, refer to Figure 6). Since the pump power is maintained at 99 mW, the population inversion level in the EDF is also increased due to the reduction in the photon count. This is also translated to the reduction in gain saturation in the EDF, as explained previously. At the highest output coupling ratio of 50%, the amplificat  
Figure 10: (**a**) RF spectrum using the 30% output coupling ratio and (**b**) the PER value at the fundamental frequency for different output coupling ratio values using 99 mW pump power. Figure 9: Pulse repetition rate of EDFL with GNP-SA; (**a**) oscilloscope trace of the output pulse for 30% and (**b**) different output coupling ratio values. section transversely; the pump depletion is the lowest compared with the other OCs. In this case, the pump depletion is inversely proportional to the increment of the output coupling ratio (refer to Figure 8b). For the situation of pump depletion, the amplified signal is reabsorbed in the region where the photon count number at signal wavelength is greater than that of pump wavelength. Therefore, the localized signal power along the EDF depends on the photon count number at the entrance of the EDF. The dynamic of this phenomenon leads to the quality of the pulse generated from this laser cavity. Figure 11: Pulse duration of EDFL with GNP-SA; **(a)** autocorrelator trace of the output pulse using a 30% output coupling ratio and **(b)** the pulse duration value of different output coupling ratio values. Figure 12: **(a)** Power and **(b)** energy development of EDFL with GNP-SA for different output coupling ratio values. **(c)** The value of output power and energy at the maximum pump power for different output coupling ratios.