The stability performance of laser-pumped Rbcell atomic clocks is affected by the laser spectral characteristics. It is then important to investigate the laser spectrum, especially since laser noise measurements are rarely found in the literature. We present a frequency-noise power spectrum characterization of laser diode currently employed in a high-performing Rb clock. The measurement is performed by using a narrowlinewidth reference laser. The beatnote between the two sources is processed with a custom frequency-to-voltage (f/V) converter whose output is finally digitized with an FFT spectrum analyzer.

The knowledge of the frequency noise spectrum of a diode laser is of interest in several high resolution experiments. Specifically, in laser-pumped vapor cell clocks, it is well established that the laser frequency noise plays a role in affecting the clock performances. It is then important to characterize the frequency noise of a diode laser, especially since such measurements are rarely found in the literature and hardly ever provided by vendors. In this paper, we describe a technique based on a frequency-to-voltage converter that transforms the laser frequency fluctuations into voltage fluctuations. In this way, it is possible to characterize the laser frequency noise power spectral density in a wide range of Fourier frequencies, as required in cell clock applications.

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