Fig. 3 | Nature Communications

Fig. 3

From: Chasing the thermodynamical noise limit in whispering-gallery-mode resonators for ultrastable laser frequency stabilization

Fig. 3

Frequency noise of the thermal-compensation resonator. a The frequency noise power spectral density (FNPSD) measured by the beat frequency between the laser and the table top Fabry-Pérot (FP) cavity reference laser. The FNPSD of free-running laser used in our experiment (black curve) and of the laser stabilized to the compensated resonator (olive). The thermodynamical FNPSD predictions from thermorefractive (blue) and thermal expansion noise (red) are also illustrated for comparison. The thermorefractive noise shows f −1.5 frequency dependence (magenta dashed line) predicted by our theoretical model. b The measured linewidth (fullwidth at half maximum) on a spectrum analyzer with 47 Hz resolution bandwidth (RBW) and 40 ms sweep time over the 5 kHz span, giving a ≈ 100 Hz Lorentzian linewidth fit. The effective linewidth evaluated from the olive curve is 119 ± 2 Hz and the linewidth without the 60 and 120 Hz power-line noise is determined to be 25 ± 0.3 Hz

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