Intrinsic Spectrum Analysis of Laser Dynamics Based on Fractional Fourier Transform

The intrinsic spectrum that results from the coupling of spontaneous emission in a laser cavity can determine the energy concentration and coherence of lasers, which is crucial for optical high-precision measurements. To date, it has been difficult to analyze the intrinsic spectrum in high-speed laser dynamics processes, especially under the condition of fast wavelength sweeping. In this work, a new method to analyze the laser intrinsic spectrum is proposed with laser energy decomposition into a series of chirp-frequency signals, which is realized by fractional Fourier transform (FRFT) of the coherently reconstructed laser waveform. The new understanding of the energy distribution of lasers contributes to accurate characterization of laser dynamic parameters in the time-frequency domain. In a proof-of-concept experiment, the time-frequency dynamic process of a commercial wavelength-swept laser is tested for different wavelength-scanning speeds, and the most suitable measurement time window width required for the narrowest FRFT-based spectrum is also explored. The proposed analysis method of laser dynamic parameters will promote the understanding of laser dynamics and benefit optical precision measurement applications.