Direct Measurement of Laser Noise Spectrum with a Frequency-to-Voltage Converter

The stability performance of laser-pumped Rb-cell 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 a laser diode currently employed in a high-performing Rb clock. The measurement is performed by using a narrow-linewidth 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.