194 369 569.4(5) MHz optical frequency standard based on 13C2H2 p(16) saturated line

A novel, compact, and reliable Er-Yb:glass laser operating at around 1.54 μm wavelength was developed, with single-frequency and linearly-polarized output power in excess of 10 mW over a continuous tunability range of 17 nm. An external Fabry-Perot resonator containing a low-pressure acetylene cell was used to perform saturation spectroscopy of different absorptions in the (v₁+v₃) rotovibrational band. By using two nested control loops, the laser was frequency locked to the 1 MHz Doppler-free P(16) line of ¹³C₂H₂ at 1. 543 μm wavelength. This particular transition of the acetylene molecule was very recently recommended by the CCL (Comite Consultatif de la Longueur) of the CIPM for the mise en pratique du metre. The frequency stability achieved, as evaluated from the loop error signal, way in the range of ±40 kHz peak-to-peak (Δv/v≅2×10^-10) and the correspondingly calculated Allan deviation is σ_y(τ)<10^-11for integration times τ≥1 s and remains significantly low, 10^-11<σ_y(τ)<3×10^-10 for 10^-2 s≤τ≤50s and σ_y(τ)<10^-12 for τ>70 s. This is the first Italian optical frequency standard in the 1.5 μm band, namely at a frequency of 194 369 569.4(5) MHz and it is now ready for international intercomparisons.