Abstract Low frequency noise (LFN) of highly coherent laser (linewidth below 10 kHz) is analyzed using an unbalanced Mach- Zehnder interferometer (UMZI) with adjustable long arm span. Furthermore, the Laser Relative Excess Noise (LREN) is introduced here to set a comparison of the laser coherence in relation to its emission power. The LREN is obtained using the addition of laser high and low frequency noises that appear in excess to the ideal power spectral density (PSD) Lorentzian distribution. Using this approach, it is possible to compare the tested laser in relation to an ideal laser with the same linewidth. LFN (LFN linewidth 1 kHz Mach UMZI (UMZI span Furthermore (LREN PSD (PSD distribution approach

Abstract The longitudinal, flexural, and torsional modes of acoustical resonances are presented for a long and small thickness cylindrical fiber spool. The fiber spool is built using a monomode optical fiber tightly wound in a helix form around a cylindrical Styropor. The acoustical resonance values are obtained using a Mach Zehnder interferometer with the fiber spool in the long (2 km) arm and a small linewidth laser. To reduce spurious signals, the interferometer was placed inside a vacuum chamber. The measured and theoretical results reasonably agree up to the first fifteen resonant longitudinal modes and for the first five flexural and torsional resonant modes, with a span from 10 Hz up to 200 Hz.