The Pure Photonics laser displays wander behavior over 1s+ time-periods (30-40MHz over 10secs). Locking it to a more stable reference (gascell, etalon, or different) allows for a stabilized solution along with the inherent narrow linewidth and low Gaussian noise.
Users can use the FM input to control the frequency of the device (100kHz bandwidth, 100MHz optical amplitude) or the AM input (1MHz bandwidth, optical amplitude up to 1GHz, but dependent on power setting). Use of the AM setting has the disadvantage of also introducing amplitude modulation. Oftentimes, longer term drift (moving the signals on these inputs away from their center point and reducing the available range) will occur and the FTF, modified through the RS-232 interface or the Clean Measurement input, can be adjusted to recenter the input. Both AM and FM input are DC-coupled.
For PPCL700 devices with a Frequency Modulation input and Clean Measurement (ADC) input, Pure Photonics provides a firmware based on our PPCL590 (gas cell locked laser), that automatically controls the laser to lock to the error signal provided onto the ADC input. That firmware is available for download and an application note is available.