Impacts of Laboratory Vibrations and Laser Flicker Noise on Digital Holography

In this paper, we experimentally demonstrate the impacts of laboratory vibrations and laser flicker noise on digital holography (DH). Specifically, we measure both the vibration efficiency and the coherence efficiency of our DH system at various focal-plane array integration times and path-length differences between the signal and reference. These efficiencies, in practice, contribute to the overall mixing efficiency, which is a measure for how well the detected signal and reference interfere. The results show that when the integration time is ≤1 ms, the laboratory vibrations are negligible with a vibration efficiency of 100%; however, when the integration time equals 100 ms, the laboratory vibrations lead to a 94% vibration efficiency. In addition, the results show that the effective coherence length of the master-oscillator (MO) laser increases by 280% when the integration time decreases from 100 ms to 100 μs. To account for this outcome, we present a model of the coherence efficiency based on the frequency noise of the MO laser. The model fit to the DH data then shows that the frequency of the MO laser is flicker-noise dominated. As a result, decreasing the integration time improves the overall mixing efficiency because of high-pass filtering in both the vibration efficiency and the coherence efficiency. Based on previous published efforts, these results have direct ties to the achievable signal-to-noise ratio of a DH system.