ULISS project: First comparison of two cryocooled sapphire oscillators at the 10&lt;sup&gt;&amp;#x2212;15&lt;/sup&gt; level

S Grop,V Giordano,Y Kersale,B Dubois,G Haye,J.-L Masson,E Rubiola,P.-Y Bourgeois

doi:10.1109/fcs.2012.6243705

Abstract

We already demonstrated a state-of-the-art Cryogenic Sapphire Oscillator (CSO), which incorporates a pulse-tube cooler instead of a bath cryostat - thus eliminating the need for regular supplies and manual transferring of liquid helium. The advent of reliable and cryocooled (CSO) open the possibility to implement such an ultra-stable reference not only in metrological laboratories with liquid helium facilities but also in remote sites like base stations for space navigation, VBLI antenna sites, ... The first prototype, i.e. ELISA, has been implemented in the ESA ground station in Malargüe (Ar) in April 2012. A second CSO was recently achieved using the same technology but specially designed to be transportable. After its complete assembly the CSO was coold down for the first time, and a preliminary frequency stability evaluation was done by direct comparison between the two CSOs. The Allan deviation was derived from data collected during more than 3 days. A short term frequency stability better than 2×10 -15 at 1s was obtained. In spite of bad environemental conditions (infrastructure works in the building: implementation of an air conditioning in our laboratory which is not still effective) the frequency stability stays better than 4×10 -15 for τ <; 1,000s and 1×10 -14 over one day.

Highlights

We recently developped a Cryogenic Sapphire Oscillator (CSO) named Elisa presenting a short term frequency stability better than 3×10−15 for 1 s ≤ τ ≤ 1000 s and achieving 4.5×10−15 for one day integration [1], [2]
In this paper we present the frequency stability characterization of the newly built CSO demonstrating the reproductibility of our technology and we summarize the main results obtained at the LTF and CNES
This assembly is thermally connected to the second stage of a pulse tube cryocooler specillay designed to ensure a high thermal stability (±1 mK) and a low level of mechanical vibration: axial displacement less than 2 μm at the PT cycle frequency (≈ 1 Hz)

Summary

INTRODUCTION

We recently developped a Cryogenic Sapphire Oscillator (CSO) named Elisa presenting a short term frequency stability better than 3×10−15 for 1 s ≤ τ ≤ 1000 s and achieving 4.5×10−15 for one day integration [1], [2]. It incorporates a pulse-tube cryocooler instead of a bath cryostat, eliminating the need for regular supplies and manual refilling of liquid helium.

SCHEMATIC ARCHITECTURE OF THE CRYOCOOLED SAPPHIRE OSCILLATOR INSTRUMENTS

ULISS FREQUENCY STABILITY CHARACTERIZATION

INSTALLATION OF ELISA IN DSA3

Test of an all-optical microwave signal generation

10 MHz ULISS

Test of an ultra-low noise microwave frequency synthesis

CONCLUSION