Based on zero-padding and frequency-domain self-filtering, a robust and effective spectrum centroid carrier-removal method for carrier interferogram analysis is proposed. The interferogram is first spatial zero padded to increase the frequency resolution, and then the frequency domain self-filtering is carried out to suppress the noise and enhance the carrier component. Finally, the carrier frequencies are estimated by calculating the spectral centroid of the upside lobe. The simulations and experiments are carried out to testify the feasibility of this method. In addition, some factors, such as the carrier frequency values, the level of random noise, and the window size of the spectral filter, are analyzed and discussed. Compared with existing carrier-removal methods, the proposed method is effective and accurate for suppressing the carrier-removal error.
A midinfrared (mid-IR) saturable absorber mirror (SAM) was fabricated by coating aluminum film on Fe2+:ZnSe crystal, based on the vacuum evaporation method. By employing the prepared SAM, we demonstrated a high-power passively Q-switched Er3+-doped ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAN) fiber laser at 2.8 μm. The highest output power in excess of 1.01 W was obtained with a pulse energy of 11.37 μJ and pulse duration of 0.73 μs, corresponding to a repetition rate of 88.84 kHz. To the best of our knowledge, these values represent the highest output power/pulse energy from a passively Q-switched ZBLAN fiber laser around 2.8 μm. Our results demonstrate that Fe2+:ZnSe SAM is a promising device for high-power/high-energy pulse generation in compact mid-IR fiber lasers.