Fig. 2: Idealised free-running laser noise PSDs for external cavity diode lasers (ECDL) and optically-pumped solid-state lasers (OPSSL).

a The RIN PSD, demonstrating the low frequency 1/ω (flicker) noise, mid-frequency white noise, the relaxation oscillation peak, and shot noise. b The frequency noise PSD with the same general features as RIN with a fundamental limit of quantum noise. The noise above the β-separation line contributes to the linewidth of the laser, while the noise below the β-separation line contributes to the wings of the laser lineshape.