Marcin Bober

Absolute measurement of the 1S0 − 3P0 clock transition in neutral 88Sr over the 330 km-long stabilized fibre optic link

We report a stability below 7 × 10−17 of two independent optical lattice clocks operating with bosonic 88Sr isotope. The value (429 228 066 418 008.3(1.9)syst (0.9)stat Hz) of the absolute frequency of the 1S0 – 3P0 transition was measured with an optical frequency comb referenced to the local representation of the UTC by the 330 km-long stabilized fibre optical link. The result was verified by series of measurements on two independent optical lattice clocks and agrees with recommendation of Bureau International des Poids et Mesures.

Strontium optical lattice clocks for practical realization of the metre and secondary representation of the second

We present a system of two independent strontium optical lattice standards probed with a single shared ultranarrow laser. The absolute frequency of the clocks can be verified by the use of Er:fiber optical frequency comb with the GPS-disciplined Rb frequency standard. We report hertz-level spectroscopy of the clock line and measurements of frequency stability of the two strontium optical lattice clocks.

Cavity mode-width spectroscopy with widely tunable ultra narrow laser

We explore a cavity-enhanced spectroscopic technique based on determination of the absorbtion coefficient from direct measurement of spectral width of the mode of the optical cavity filled with absorbing medium. This technique called here the cavity mode-width spectroscopy (CMWS) is complementary to the cavity ring-down spectroscopy (CRDS). While both these techniques use information on interaction time of the light with the cavity to determine absorption coefficient, the CMWS does not require to measure very fast signals at high absorption conditions. Instead the CMWS method require a very narrow line width laser with precise frequency control. As an example a spectral line shape of P7 Q6 O₂ line from the B-band was measured with use of an ultra narrow laser system based on two phase-locked external cavity diode lasers (ECDL) having tunability of ± 20 GHz at wavelength range of 687 to 693 nm.

Absolute frequency determination of molecular transition in the Doppler regime at kHz level of accuracy

Abstract We measured absolute frequency of the unperturbed P7 P7 O2 B-band transition ν 0 =  434783.5084857(82) GHz and the collisional self-shift coefficient δ = − 9.381 ( 62 ) × 10 − 21  GHz/(molecule/cm3). With Doppler-limited spectroscopy we achieved the relative standard uncertainty of 2 × 10 − 11 on line position, typical for Doppler-free techniques. Shapes of the spectral line were measured with a Pound-Drever-Hall-locked frequency-stabilized cavity ring-down spectrometer referenced to an 88Sr optical atomic clock via an optical frequency comb.

Accuracy budget of the 88Sr optical atomic clocks at KL FAMO

This paper presents a detailed accuracy budget of two independent strontium optical lattice clocks at the National Laboratory FAMO (KL FAMO) probed with a single shared ultra-narrow laser. The combined instability of the two frequency standards was after 105s of averaging.

Fibre-optic delivery of time and frequency to VLBI station

The quality of Very Long Baseline Interferometry (VLBI) radio observations predominantly relies on precise and ultra-stable time and frequency (T&F) standards, usually hydrogen masers (HM), maintained locally at each VLBI station. Here, we present an operational solution in which the VLBI observations are routinely carried out without use of a local HM, but using remote synchronization via a stabilized, long-distance fibre-optic link. The T&F reference signals, traceable to international atomic timescale (TAI), are delivered to the VLBI station from a dedicated timekeeping laboratory. Moreover, we describe a proof-of-concept experiment where the VLBI station is synchronized to a remote strontium optical lattice clock during the observation.

Two independent strontium optical lattice clocks for practical realization of the meter and secondary representation of the second

We report a system of two independent strontium optical lattice standards probed with a single shared ultra-narrow laser. This allows verification of relative stability of both optical standards. The absolute frequency of the clocks can be roughly verified by the use of an optical frequency comb with the GPS-disciplined Rb frequency standard or, more accurately, by a long distance stabilized fiber optic link with the UTC(AOS) and UTC(PL) via the OPTIME network.

Towards black body radiation shift uncertainty in optical lattice clocks at 10 −18 level at room temperatures

We present current status of work on blackbody radiation impact on ultra-narrow optical resonances. The emissivities of the most popular materials, which are used for construction of vacuum chambers, have been measured in the temperatures close to the room temperature. We have developed a new vacuum system designed exclusively for the emissivity measurements. We have measured the emissivity of samples made from different materials and with different finishing. This data has been also used to perform numerical simulation of temperature distribution of an optical clock vacuum set-up.

Experimental constraint on dark matter-standard model coupling with optical atomic clocks

We have shown that a single optical atomic clock can be used as a detector for the hypothetical dark matter in the form of stable topological defects, for example, monopoles, strings or domain walls. We exploited differences in the susceptibilities to the fine-structure constant of essential parts of an optical atomic clock, i.e. the atoms and the cavity. We perform an experiment which constrained the strength of atomic coupling to hypothetical dark-matter cosmic objects. Under the conditions of our experiments, the degree of constraint was found to exceed the previously reported limits by more than three orders of magnitude [1].

The optical 88Sr lattice clocks and stabilized fibre links: A frequency reference for the VLBI system over a 15.5-km link and an absolute measurement of the clock transition over a 330-km link

We report a system of two independent strontium optical lattice standards with 88Sr probed with a single shared ultra-narrow laser. We achieved frequency stability (frequency between two standards) of 7 × 10-17. The absolute frequency of the clock transition can be measured by the use of an optical frequency comb referenced to the UTC(AOS) and UTC(PL) via the 330-km stabilized fibre optic link of the OPTIME network. The 15.5-km stabilized fibre optic link between National Laboratory for Atomic, Molecular, and Optical Physics (KL FAMO) and Toruń Centre for Astronomy made it possible to use the optical clocks as a frequency reference for the 32-metre precise parabolic antenna of the radio telescope in the Toruń Centre for Astronomy participating in the VLBI networks. We report the worlds first astronomical VLBI measurements referenced to an optical atomic clock.