  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.
