We apply the Fabry–Pérot (FP) scanning interferometer, which is normally used for continuous wave (CW) laser linewidth measurement, for the measurement of pulsed laser linewidths. We analyze the response of the FP interferometer to continuous and pulsed lasers, also different detectors and suitable oscilloscope test parameters being selected for the measurement. For low-speed detectors, we set our oscilloscope to 1-MΩ impedance matching in the sampling mode. For high-speed detectors, we use the same oscilloscope test parameters or 50-Ω impedance matching with the peak-detection mode. With our setup, we achieve on-line linewidth measurement of a nanosecond pulsed laser for single-longitudinal and multi-longitudinal modes. Meanwhile, the linewidth measurement at different pulse repetition rates as low as 1 Hz is also demonstrated. The possibility of detecting the linewidth for pulse widths larger than 100 ps in the 1-μm band is discussed. The application range of the FP scanning interferometer is thus extended to the measurement of pulsed laser linewidths. Keywords: Pulsed laser, Linewidth, Fabry–Pérot interferometer
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