Direct comparison of 3 optical femtosecond comb generators

Project Description

This project should investigate means to valid comb generators. The BEV is currently operating two comb generators of quite different design: a Ti:Saphire laser working around 800 nm and a system based on a fiber-laser around 1500 nm. The fiber based comb is transportable and can serve as a link between different, stationary combs.

Proposed setup for the direct comparison: The light of a (monomode) test laser is split in two beams, one for each comb. The data acquisition (that is the frequency readings) should be performed in the way the lab uses for standard calibration. Both combs use the same locally available time reference. The laser frequency measured by the two combs (operating under different parameters) is compared and evaluated. Since data readings are not synchronized in this way, scatter corresponding to relative frequency stability of test laser and reference frequency is expected and  long measurement times are required to get meaningful results. In the comb used it is also possible to synchronize all frequency counters which should lead to a sub Hz scatter for 1 s integration time and thus to a better characterization. It should be noted that the stability of the laser used is not too important. Simple two mode stabilized types are even preferable over MeP lasers since the absence  of frequency modulation reduces the scatter in  the 1 s samples. It is planned  to perform  the experiments with a 633 nm HeNe laser and a 532 nm / 1064 nm Nd:YAG laser. The anticipated test procedure involves three comparisons:

  • BEV-comb1 with BEV-comb2 at the BEV
  • CMI-comb with BEV-comb2 at the CMI
  • BEV-comb1 with BEV-comb2 at the BEV

Final Report 2011-09-22

A direct comparison of three optical femtosecond comb generators from the two institutes involved was performed. These combs are operated as laser frequency calibration facilities in their home labs.
A simple experimental technique for the evaluation of the measurement uncertainty for comb based laser calibrations was developed during this project. The main idea in the applied scheme is the comparison of two combs while they actually calibrate a laser frequency.
We found an upper bound of the uncertainty contribution originating from the comb system (including evaluation procedure, excluding frequency reference) which was in the order of a few parts in 10–15. The experiments presented here led to significant improvement of CMCs for both NMIs involved. These CMCs are already published in the KCDB. Moreover contributions regarding tracking capability of repetition rate servos and counting capability were discovered which would be very difficult to detect without the use of the proposed scheme.
The main challenge was the transport of one comb from Vienna to Prague (and back) without changing the metrological characteristics of this instruments.
A detailed report will be published in the proceedings of the MacroScale 2011 conference.

Length (L)
Coordinating Institute
BEV (Austria)
Participating Partners
CMI (Czech Republic)