Laboratory of Time and Frequency, in cooperation with Bureau International des Poids et Mesures (BIPM), is involved in the realization of the international atomic timescales TAI and UTC and the Polish Atomic Timescale TA (PL). It also participates as the only center in Poland in co-creating the European Galileo location system. Equipped with two primary frequency standards (Cs fountains), four atomic clocks and the latest time scales linking systems, it is possible to maintain high accuracy of timing, with a timing error of less than 100 picoseconds. It is one of the best results among time laboratories in the world. Local implementation of UTC, UTC (AOS) generated in the laboratory,  allows for linking to the UTC scale with an accuracy better than 5 ns.

The Time and Frequency Laboratory, together with other laboratories affiliated to the national TA (PL), creates the Polish Time Scale and participates in the creation of the world universal time UTC. The Observatory in Borówiec is the only Polish facility that co-creates and will actively participate in the European GALILEO system.

The Time and Frequency Laboratory is equiped the following measuring equipment:

• Two primary frequency standards based on the cesium atomic fountain design, AOS-CsF1 and AOS-CsF2
• two commercial high performance cesium standards: HP5071A of American production;
• Russian KVARZ CH1-75A hydrogen maser,
• SYMMETRICOM ρ (τ) MHM2010 hydrogen maser, American production;
• SATRE TWSTFT and TWSTFT SDR Two Way Time Transfer System;
• TTS-2 time transfer receiver (8 channels, single frequency, only GPS satellites);
• TTS-3 time transfer receiver (20 channels, double frequency, GPS and GLONASS satellites);
• TTS-4 time transfer receiver (116 channels, 2 observation frequencies, GPS, GLONASS and GALILEO satellites);
• TTS-5 time transfer receiver (216 channels, 9 observation frequencies, GPS, GLONASS, GALILEO and Beidou satellites);
• fiber optic links:
• Borówiec – Poznań – Warsaw
• Borówiec-Poznań-Toruń).

Atomic time and frequency standards

“Polish atomic clock – cesium fountain” (decision No. 6436 / IA / SP / 2015). Two AOS-CsF1 and AOS-CsF2 atomic fountain systems have been operating since 2017. The device is based on atomic spectroscopy, using a cloud of cold atoms to measure the atomic transition of the hyperfine structure of the cesium 133 isotope. It is one of the most accurate physical realizations of the SI unit of time – atomic second.

The complete set of apparatus consists of

• a physical package of a vacuum system with resonance cavity,  a magneto-optical trap chamber,
• a system of lasers and optics responsible for generating laser pulses of the appropriate wavelength to obtain a cloud of cold atoms,
• a commercial source of microwave frequency corresponding to the value (9192631770 Hz) of the definition of the SI second,
• the electronics controlling the set of the experiment.

Hydrogen masers:

Two hydrogen masers SYMMETRICOM ρ (τ) MHM2010 and KVARZ CH1-75A are atomic clocks using the quantum transition in the H2 hydrogen molecule corresponding to radiation with a frequency of 1420405752Hz. Long-term stability of hydrogen masers (~ 2×10-16) exceeds the stability of cesium clocks (1×10-15 ). Hydrogen masers are the basis for the generation of the most accurate time scales in the world.

Time and frequency transfer systems

TTS receivers

The main methods of high-accuracy time transfer between laboratories use navigation satellite systems (GPS, Galileo, GLONAS and Beidou), For this purpose, the line of TTS-X receivers constructed at the Observatory is used.

The popular “CommonView” method, is based on simultaneous observations of the same navigation satellite by two stations. Both stations measure the time difference between their clock and that of the GNSS system. The lab time comparison is made by subtracting these differences. The most important factors influencing the accuracy of the distribution and time comparison with GNSS (GPS, GLONASS, GALILEO and Beidou satellites) are:

• uncertainty of ephemeris broadcasts by satellite;
• satellite clock errors;
• ionospheric refraction;
• tropospheric refraction;
• errors related to internal delays of receivers;
• effects related to the reflections of GNSS signals;
• inaccuracy of the coordinates of the receiver antenna;
• lack of technical and software unification of the receivers.

The second  method using navigation satellites is based on the  measurement of the phase of the carrier sfrequency transmitted by the satellites –  this method is called „Precise Point Positioning”. The results obtained with it reach the accuracy of 20 ps.

Fiber optic links

• 420 km long Borówiec (AOS) – Warsaw (GUM) fiber optic link was launched in March 2012. The 8 optical amplifiers (EDFA) of the AGH Kraków University of Science and Technology are installed on the link, characterized by the automatic temperature calibration. This is new method of time transfer (comparing of atomic clocks) using fiber optic techniques. It shows accuracy better than that of satellite techniques, at the level of 1-2 ps (10^-12 s).
• The same technology – ELSTAB technique, provides UTC (AOS) 10 MHz and 1 PPS signals to the National Laboratory of Atomic, Molecular and Optical Physics (KL FAMO) and to the UMK radio telescope in Piwnice near Toruń.

The real time chart of UTC(AOS) – UTC(PL) comparisons is available here