We demonstrate the stabilization of an all-in-fiber polarization maintaining semi-conductor saturable absorber mirror (SESAM) mode locked frequency comb oscillator with an intra-cavity waveguide electro-optic phase modulator (EOM) to a narrow linewidth HeNe laser over 46 hours. The high feedback bandwidth of the EOM allows a coherent optical lock with an in-loop integrated phase noise of 1.12 rad (integrated from 10 Hz to 3 MHz) from the carrier signal. No piezo fiber stretcher was required to guarantee long-term stabilization, preventing mechanical degradation of the optical fibers and enabling a long lifetime of the oscillator. As an application a hybrid stabilization scheme is presented, where a comb tooth is phase locked to a longitudinal mode of the large ring laser "G" located at the Geodatic Observatory Wettzell. The hybrid stabilization scheme describes the optical lock of the frequency comb to the G laser and the simultaneous compensation of the ring laser frequency drift by comparing the comb repetition rate against an active H-maser reference. In this context the ring laser reached a fractional Allan deviation of 5 · 10 at an integration time of 16384 s.
Deuterium (D2) lamps are commonly used for relative spectral-and/or absolute calibration of spectroradiometers in the UV wavelength range, especially below 250nm. A significant contribution to the measurement uncertainties of those calibrations is the long term instability (ageing) of the spectral output of deuterium lamps which is significantly higher than for halogen lamps typically used for spectroradiometer calibrations in the visible wavelength range or in photometric applications.We present an analysis of the ageing behaviour of an ensemble of D2-lamps, identify typical characteristics of the ageing process and suggest simple strategies for monitoring of, and potentially correcting for, the temporal changes in the spectra of deuterium lamps.
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