→ GSTP ANNUAL REPORT 2011 - ESA

→ Core TeChnoloGiCAl elemenTS for
oPTiCAl ATomiC CloCkS
ESA is enhancing its support to scientific and technological developments
in key aspects of Optical Frequency Metrology and Optical
Atomic Frequency Standards. This is with a view to applying these
developments to meet future requirements of Space Missions, where
the required levels of stability and accuracy exceed the theoretical
limits of the highest performance microwave atomic clocks. Atomic
Clocks in the optical domain have today already experimentally surpassed
microwave clock performance both in fractional frequency
instability and inaccuracy.
The overall goal of the activity is the developmental support for the
preparation of sub-system elements of an Optical Atomic Frequency
Standard (OAFS), flight demonstrator, meeting a predefined specification
and flight envelope in Space in the coming decade.
The activity was formulated to be conducted in 3 phases. Phase 1
was initiated in 2011 with two parallel contracts with the participation
of DE, UK, IE, FR, AT and CH.
Each contractor proposed a different implementation approach leading
to a different frequency standard. The possibilities that are being
considered are broadly divided into:
(a) A laser cooled neutral atom (“Lattice Clocks”)
(b) A single laser cooled trapped ion (“Ion Clocks”)
Lattice Clocks offer the prospect of high frequency stability, as a
consequence of their superior Signal to Noise Ratio (SNR), over Ion
Clocks at short timescales (1 second) whilst the single trapped ion,
being essentially isolated from the surrounding environment represents,
in principle and in practice, the most accurate optical frequency
standard. The architecture and operation of a single ion
lattice Clocks Approach
> Neutral Strontium Lattice development
> Compact Sr + Trap
standard is the least complex of (a) and (b) above and, consequently,
offers the prospect of the development of a more compact optical
atomic frequency standard for space operation.
It also offers the possibility to be even further simplified, and even
scaled down from its current system dimensions, with the implementation
of micro integration technology which has been developed
in the micro-electronics industry.
There are several sub-system elements that, in total, comprise a
complete OAFS or clock technology and the exact description of
these elements depends entirely on the clock (system) chosen. The
key sub-systems of an Optical Atomic Clock include three principal
elements:
1. A Physics Package (PP) which will provide the trapped Ion/
Atom source (and isotope) and will thus define the interrogation
wavelength
After
and
the
spectral
successful
conditions.
flight qualification
2. Cooling
of
&
PLs
auxiliary
and manufacturing
lasers, which will
of the
be developed with clear
goals for the
vehicle
achievement
subsystems,
of an
2010
appropriate
was
spectral performance
with optimization
mainly
for
devoted
the space
to the
environment.
vehicle
3. Ultra narrow
integration
linewidth,
and equipment
frequency stabilized Local Oscillator.
In terms
testing.
of the probe laser development/Optical Local Oscillator
(OLO), the principal challenges to be addressed are the achievement
of ultra-narrow laser linewidth