New Focus Tunable Laser Linewidth
The Root-Allan variance, like the heterodyne linewidth, is a measure of the frequency stability of an oscillator. It can be interpreted as the laser spectral content over a given time interval and gives you a very accurate description of long-term laser frequency variations.* The measured Root-Allan variance for two of our tunable lasers shows that the linewidth is narrowest (~50 kHz) at short integration times and increases with integration time. The short-time fluctuations are mainly due to electrical fluctuations. The long-time fluctuations are mainly due to slow temperature changes, and the middle-time spikes are the result of acoustically excited mechanical resonances in the laser cavity. The curve fit is based on a model that includes flicker and random-walk frequency noise. The linewidth at longer time intervals can be estimated by extrapolating the line.