Frequency noise measurements of 1.5 μm erbium lasers against molecular and Fabry-Perot reference lines

Frequency stability measurements, by using a molecular absorption as a frequency discriminator, have been performed on a diode-pumped Er-Yb:glass microlaser locked to different acetylene absorption lines between 1.53 μm and 1.54 μm wavelengths. From the measured residual frequency fluctuations, a long-term (24-hour) rms frequency stability of 160 kHz under locking conditions for the 195 THz optical oscillator have been obtained. The Allan standard deviation of the beat frequency between two independently stabilized lasers was also measured showing a fractional frequency stability below 10^-9 for integration times between 100 μs and 100 s. To investigate the spectral density of the frequency noise of this laser source, we are now using a very sensitive optical frequency discriminator based on a Fabry-Perot interferometer used as the reference in a Pound-Drever servo loop. The calculated sensitivity of this frequency noise detector is at the 0.3 Hz/Hz^1/2 level with the measured electronic noise floor of 300 nV/Hz^1/2. Results of the laser frequency noise under both free-running and frequency-stabilized conditions will be reported at the conference and particular emphasis will be given to the precise measurement of the flicker noise components at low and very-low Fourier frequencies