Piotr Ablewski

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.

Absolute frequency measurement of rubidium 5S–7S two-photon transitions

We report the absolute frequency measurements of rubidium 5S-7S two-photon transitions with an optical frequency comb. The digital lock to the transition, the procedures of evaluating the accuracy budget and measurements of the frequency with the optical frequency comb are tested with a simple setup for the sake of comparison of two optical lattice strontium clocks. The narrow, two-photon transition, 5S-7S (760 nm) is insensitive to a magnetic field and promising candidate for frequency standard. The preformed tests yield the transition frequency with accuracy better than reported previously.

Self-referenced, accurate and sensitive optical frequency comb spectroscopy with a virtually imaged phased array spectrometer

We present a cavity-enhanced direct optical frequency comb spectroscopy system with a virtually imaged phased array (VIPA) spectrometer and either a dither or a Pound-Drever-Hall (PDH) locking scheme used for stable transmission of the comb through the cavity. A self-referenced scheme for frequency axis calibration is shown along with an analysis of its accuracy. A careful comparison between both locking schemes is performed based on near-IR measurements of the carbon monoxide ν=3←0 band P branch transitions in a gas sample with known composition. The noise-equivalent absorptions (NEA) for the PDH and dither schemes are 9.9×10(-10) cm(-1) and 5.3×10(-9) cm(-1), respectively.

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.

VIPA spectrometer calibration and comb-cavity locking schemes comparison for sensitive and accurate frequency comb spectroscopy

In direct frequency comb spectroscopy with a VIPA spectrometer, the resolution of the spectrometer is usually insufficient to resolve the comb modes. Thus, one can either filter the modes, reducing the density of spectral elements or cope with the inability to uniquely identify spectral elements with individual comb modes by calibrating the spectrometer itself. Here, we present a way to make use of the inherent frequency accuracy of a stabilized frequency comb to calibrate the spectrometer. We also present a comparison between two commonly used schemes to stabilize the coupling between a frequency comb and cavity resonances: the Pound-Drever-Hall locking scheme and the swept coupling scheme.

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.