COLLECTED BY

Organization: Archive Team

BERJAYA

Formed in 2009, the Archive Team (not to be confused with the archive.org Archive-It Team) is a rogue archivist collective dedicated to saving copies of rapidly dying or deleted websites for the sake of history and digital heritage. The group is 100% composed of volunteers and interested parties, and has expanded into a large amount of related projects for saving online and digital history.

History is littered with hundreds of conflicts over the future of a community, group, location or business that were "resolved" when one of the parties stepped ahead and destroyed what was there. With the original point of contention destroyed, the debates would fall to the wayside. Archive Team believes that by duplicated condemned data, the conversation and debate can continue, as well as the richness and insight gained by keeping the materials. Our projects have ranged in size from a single volunteer downloading the data to a small-but-critical site, to over 100 volunteers stepping forward to acquire terabytes of user-created data to save for future generations.

The main site for Archive Team is at archiveteam.org and contains up to the date information on various projects, manifestos, plans and walkthroughs.

This collection contains the output of many Archive Team projects, both ongoing and completed. Thanks to the generous providing of disk space by the Internet Archive, multi-terabyte datasets can be made available, as well as in use by the Wayback Machine, providing a path back to lost websites and work.

Our collection has grown to the point of having sub-collections for the type of data we acquire. If you are seeking to browse the contents of these collections, the Wayback Machine is the best first stop. Otherwise, you are free to dig into the stacks to see what you may find.

The Archive Team Panic Downloads are full pulldowns of currently extant websites, meant to serve as emergency backups for needed sites that are in danger of closing, or which will be missed dearly if suddenly lost due to hard drive crashes or server failures.

Collection: Archive Team: URLs

TIMESTAMPS

The Wayback Machine - https://web.archive.org/web/20240719231850/https://lebedev.academia.edu/KseniaKhabarova

Skip to main content

Ksenia Khabarova

LPI, Optical, Faculty Member

Followers

11

Following

19

Co-authors

2

Public Views

Interests

uploads

Papers

Coherent effects contribution to a fast gate fidelity in ion quantum computer

Trapped ions are one of the most promising platforms for quantum computing due to the longest qub... more Trapped ions are one of the most promising platforms for quantum computing due to the longest qubit coherence times and the highest gate fidelities. However, scaling the number of ions (qubits) in a linear Coulomb crystal is the key difficulty on the way to multi-qubit systems. One of the promising pathways to scale the number of qubits is to implement the pulsed non-adiabatic gates based on the sequence of State Dependent Kicks (SDKs). We have analytically and numerically studied the influence of coherent effects in the SDK sequence and, correspondingly, have deduced the influence of the individual SDK error on the net gate’s fidelity. We have shown that the coherence effects significantly impact the fidelity of non-adiabatic gates and must be taken into the account. As practical examples, we have developed a numerical model for full simulation of coherence effects using a linear ion microtrap array and a 2D microtrap array. We have also studied the dependency of the gate fidelity ...

Long 48-cm ULE cavities in vertical and horizontal orientations for Sr optical clock

The development of an optical clock with ultimate accuracy and stability requires lasers with ver... more The development of an optical clock with ultimate accuracy and stability requires lasers with very narrow linewidth. We present two ultrastable laser systems based on 48 cm long Fabry-Perot cavities made of ULE glass in horizontal and vertical configurations operating at 698 nm. Fractional frequency instability of the beat signal between two lasers reaches 1.6e-15 at the averaging time of 1 s. We experimentally characterized the contribution of the different noise sources (power fluctuations, residual amplitude modulation, the Doppler noise, sensitivity to the shock impact) and found that in our case the laser frequency instability to a large extent is determined by an optoelectronic feedback loop. Although the vertical configuration proved to be easier to manufacture and to transport, it turned out that it is much more sensitive to acoustics and horizontal accelerations compared to the horizontal one. Both laser systems were transported over a 60 km distance from the Lebedev Physic...

Atomic clouds stabilized to measure dilation of time

Nature, 2022

48 -cm-long room-temperature cavities in vertical and horizontal orientations for Sr optical clock

Applied Optics, 2021

The development of an optical clock with ultimate accuracy and stability requires lasers with ver... more The development of an optical clock with ultimate accuracy and stability requires lasers with very narrow linewidths. We present two ultrastable laser systems based on 48-cm-long Fabry-Perot cavities made of ultralow expansion glass in horizontal and vertical configurations operating at 698 nm. Fractional frequency instability of the beat signal between the two lasers reaches 1.6×10-15 at the averaging time of 1 s. We experimentally characterized the contribution of the different noise sources (power fluctuations, residual amplitude modulation, the Doppler noise, and sensitivity to the shock impact) and found that in our case the laser frequency instability to a large extent is determined by an optoelectronic feedback loop. Although the vertical configuration was easier to manufacture and transport, it is much more sensitive to acoustics and horizontal accelerations compared to the horizontal one. Both laser systems were transported over a 60 km distance from the Lebedev Physical Institute to the All-Russian Scientific Research Institute for Physical-Engineering and Radiotechnical Metrology (VNIIFTRI), where they serve as local oscillators for spectroscopy of the clock transition in the recently developed strontium optical clock.

Laser systems stabilized to cryogenic silicon cavities for precision measurements

EPJ Web of Conferences, 2019

We consider laser systems stabilized to external Fabry-Perot silicon cavities operated at cryogen... more We consider laser systems stabilized to external Fabry-Perot silicon cavities operated at cryogenic temperatures. In order to characterize frequency stability two identical systems were created. Fractional frequency instability of individual system reached 6×10-15 at 1 s. Different sources of noises were studied, and the dominant one now is the fluctuations of residual amplitude modulation.

Improved Wavelength Measurement of 2S1/2→2P1/2 and 2D3/2→3[3/2]1/2 Transitions in Yb+

Journal of Russian Laser Research, 2019

Motional states of laser cooled Yb ions in an optimized radiofrequency trap

Laser Physics, 2019

$Research paper thumbnail of {"__content__"=>"Mass selective laser cooling ofThin a multisectional linear Paul trap loaded with a mixture of thorium isotopes.", "sup"=>[{"__content__"=>"229"}, {"__content__"=>"3+"}]}$

{"__content__"=>"Mass selective laser cooling ofThin a multisectional linear Paul trap loaded with a mixture of thorium isotopes.", "sup"=>[{"__content__"=>"229"}, {"__content__"=>"3+"}]}

European journal of mass spectrometry (Chichester, England), Aug 1, 2017

We consider an experiment on trapping and laser cooling ofThions in a linear Paul trap in the pre... more We consider an experiment on trapping and laser cooling ofThions in a linear Paul trap in the presence of undesirable impurities such as ions of the radioactive isotopeTh. We suggest a method of separating these impurities by means of selective laser cooling utilizing the isotope shift of cooling transitions inThandThions. According to our estimation, the isotope shift is equal to 3.4 GHZ and makes laser separation of these isotopes possible.

Loading of mass spectrometry ion trap with Th ions by laser ablation for nuclear frequency standard application

European journal of mass spectrometry (Chichester, England), Aug 1, 2017

We describe an original multisectional quadrupole ion trap aimed to realize nuclear frequency sta... more We describe an original multisectional quadrupole ion trap aimed to realize nuclear frequency standard based on the unique isomer transition in thorium nucleus. It is shown that the system effectively operates on Th, Thand Thions produced by laser ablation of metallic thorium-232 target. Laser intensity used for ablation is about 6 GW/cm. Via applying a bias potential to every control voltage including the RF one, we are able not only to manipulate ions within the energy range as wide as 1-500 eV but to specially adjust trap potentials in order to work mainly with ions that belong to energy distribution maximum and therefore to effectively enhance the number of trapped ions. Measurement of energy distributions ofTh,Th,Thions obtained by laser ablation allows us to define optimal potential values for trapping process. Observed number of ions inside trap in dependence on trapping time is found to obey an unusually slow - logarithmic decay law that needs more careful study.

The GBAR antimatter gravity experiment

Hyperfine Interactions, 2015

The GBAR project (Gravitational Behaviour of Anti hydrogen at Rest) at CERN, aims to measure the ... more The GBAR project (Gravitational Behaviour of Anti hydrogen at Rest) at CERN, aims to measure the free fall acceleration of ultracold neutral anti hydrogen atoms in the terrestrial gravitational field. The experiment consists preparing anti hydrogen ions (one antiproton and two positrons) and sympathetically cooling them with Be+ ions to less than 10 μK. The ultracold ions will then be photo-ionized just above threshold, and the free fall time over a known distance measured. We will describe the project, the accuracy that can be reached by standard techniques, and discuss a possible improvement to reduce the vertical velocity spread.

The Rydberg constant and proton size from atomic hydrogen

Science (New York, N.Y.), Oct 6, 2017

At the core of the "proton radius puzzle" is a four-standard deviation discrepancy betw... more At the core of the "proton radius puzzle" is a four-standard deviation discrepancy between the proton root-mean-square charge radii () determined from the regular hydrogen (H) and the muonic hydrogen (µp) atoms. Using a cryogenic beam of H atoms, we measured the 2S-4P transition frequency in H, yielding the values of the Rydberg constant= 10973731.568076(96) per meterand= 0.8335(95) femtometer. Ourvalue is 3.3 combined standard deviations smaller than the previous H world data, but in good agreement with the µp value. We motivate an asymmetric fit function, which eliminates line shifts from quantum interference of neighboring atomic resonances.

Towards compact transportable optical clock based on 171Yb+

2018 European Frequency and Time Forum (EFTF), 2018

We report on a new project aimed for development of a transportable compact optical clock based o... more

Long 48-cm ULE cavities in vertical and horizontal orientations for Sr optical clock

The development of an optical clock with ultimate accuracy and stability requires lasers with ver... more The development of an optical clock with ultimate accuracy and stability requires lasers with very narrow linewidth. We present two ultrastable laser systems based on 48 cm long FabryPerot cavities made of ULE glass in horizontal and vertical configurations operating at 698 nm. Fractional frequency instability of the beat signal between two lasers reaches 1.6∙10 at the averaging time of 1 s. We experimentally characterized the contribution of the different noise sources (power fluctuations, residual amplitude modulation, the Doppler noise, sensitivity to the shock impact) and found that in our case the laser frequency instability to a large extent is determined by an optoelectronic feedback loop. Although the vertical configuration proved to be easier to manufacture and to transport, it turned out that it is much more sensitive to acoustics and horizontal accelerations compared to the horizontal one. Both laser systems were transported over a 60 km distance from the Lebedev Physical...

Photoionization dynamics of Mg atoms during Paul trap loading using a two-color UV laser system

Trapped ions have proven to be a powerful instrument in quantum logic, precision metrology and te... more Trapped ions have proven to be a powerful instrument in quantum logic, precision metrology and tests of fundamental theories. Many applications require isotopically pure ion crystals to be trapped; however, selective loading methods require either isotopically pure atom sources or dedicated ultraviolet laser systems. Here we investigate the loading dynamics of the isotopically pure magnesium ion crystals photoionized and Doppler-cooled with a two-color UV laser system at 285 nm and 280 nm. The system shares the same tapered amplifier and the first stage of a second-harmonic generation for both wavelengths, which significantly reduces the complexity and cost of the experiment. A selective loading rate of 0.05 ions s−1 was achieved, supporting theoretical evaluations.

Challenging QED with Atomic Hydrogen

Testing theories means to compare precise measurements with theoretical predictions. I will descr... more

Simultaneous bicolor interrogation in thulium optical clock providing very low systematic frequency shifts

Nature Communications

Optical atomic clocks have already overcome the eighteenth decimal digit of instability and uncer... more Optical atomic clocks have already overcome the eighteenth decimal digit of instability and uncertainty, demonstrating incredible control over external perturbations of the clock transition frequency. At the same time, there is an increasing demand for atomic (ionic) transitions and new interrogation and readout protocols providing minimal sensitivity to external fields and possessing practical operational wavelengths. One of the goals is to simplify the clock operation while maintaining the relative uncertainty at a low 10−18 level achieved at the shortest averaging time. This is especially important for transportable and envisioned space-based optical clocks. Here, we demonstrate implementation of a synthetic frequency approach for a thulium optical clock with simultaneous optical interrogation of two clock transitions. Our experiment shows suppression of the quadratic Zeeman shift by at least three orders of magnitude. The effect of the tensor lattice Stark shift in thulium can a...

Estimation of uncertainty budget for a thulium optical clock

FIFTH INTERNATIONAL CONFERENCE ON QUANTUM TECHNOLOGIES (ICQT-2019)

Laser Cooling of Lanthanides: from Optical Clocks to Quantum Simulators

EPJ Web of Conferences, 2015

Precision spectroscopy of 2S– n P transitions in atomic hydrogen for a new determination of the Rydberg constant and the proton charge radius

by Ksenia Khabarova and R. Pohl

Physica Scripta, 2015

Spectroscopy of intercombination transition 1 S 0 – 3 P 1 for secondary cooling of strontium atoms

Quantum Electronics, 2015

ABSTRACT In the framework of the project aimed at creating an optical standard on cold Sr atoms w... more ABSTRACT In the framework of the project aimed at creating an optical standard on cold Sr atoms we have realised sub-Doppler spectroscopy of the intercombination transition 1S0 - 3P1 (689 nm) in a cell with Sr vapour and in a cloud of atoms loaded in a magneto- optical trap (MOT). By measuring Zeeman splitting of the 3P1 level in the magnetic field of the MOT we have succeeded in fine adjustment of the MOT relative to a minimum of the magnetic field, which is necessary for successful secondary-stage cooling on the intercombination transition. In turn, absorption saturation spectroscopy in the vapour cell provides the long-term frequency stability of the second-stage cooling laser at λ = 689 nm.

Coherent effects contribution to a fast gate fidelity in ion quantum computer

Trapped ions are one of the most promising platforms for quantum computing due to the longest qub... more Trapped ions are one of the most promising platforms for quantum computing due to the longest qubit coherence times and the highest gate fidelities. However, scaling the number of ions (qubits) in a linear Coulomb crystal is the key difficulty on the way to multi-qubit systems. One of the promising pathways to scale the number of qubits is to implement the pulsed non-adiabatic gates based on the sequence of State Dependent Kicks (SDKs). We have analytically and numerically studied the influence of coherent effects in the SDK sequence and, correspondingly, have deduced the influence of the individual SDK error on the net gate’s fidelity. We have shown that the coherence effects significantly impact the fidelity of non-adiabatic gates and must be taken into the account. As practical examples, we have developed a numerical model for full simulation of coherence effects using a linear ion microtrap array and a 2D microtrap array. We have also studied the dependency of the gate fidelity ...

Long 48-cm ULE cavities in vertical and horizontal orientations for Sr optical clock

The development of an optical clock with ultimate accuracy and stability requires lasers with ver... more The development of an optical clock with ultimate accuracy and stability requires lasers with very narrow linewidth. We present two ultrastable laser systems based on 48 cm long Fabry-Perot cavities made of ULE glass in horizontal and vertical configurations operating at 698 nm. Fractional frequency instability of the beat signal between two lasers reaches 1.6e-15 at the averaging time of 1 s. We experimentally characterized the contribution of the different noise sources (power fluctuations, residual amplitude modulation, the Doppler noise, sensitivity to the shock impact) and found that in our case the laser frequency instability to a large extent is determined by an optoelectronic feedback loop. Although the vertical configuration proved to be easier to manufacture and to transport, it turned out that it is much more sensitive to acoustics and horizontal accelerations compared to the horizontal one. Both laser systems were transported over a 60 km distance from the Lebedev Physic...

Atomic clouds stabilized to measure dilation of time

Nature, 2022

48 -cm-long room-temperature cavities in vertical and horizontal orientations for Sr optical clock

Applied Optics, 2021

The development of an optical clock with ultimate accuracy and stability requires lasers with ver... more The development of an optical clock with ultimate accuracy and stability requires lasers with very narrow linewidths. We present two ultrastable laser systems based on 48-cm-long Fabry-Perot cavities made of ultralow expansion glass in horizontal and vertical configurations operating at 698 nm. Fractional frequency instability of the beat signal between the two lasers reaches 1.6×10-15 at the averaging time of 1 s. We experimentally characterized the contribution of the different noise sources (power fluctuations, residual amplitude modulation, the Doppler noise, and sensitivity to the shock impact) and found that in our case the laser frequency instability to a large extent is determined by an optoelectronic feedback loop. Although the vertical configuration was easier to manufacture and transport, it is much more sensitive to acoustics and horizontal accelerations compared to the horizontal one. Both laser systems were transported over a 60 km distance from the Lebedev Physical Institute to the All-Russian Scientific Research Institute for Physical-Engineering and Radiotechnical Metrology (VNIIFTRI), where they serve as local oscillators for spectroscopy of the clock transition in the recently developed strontium optical clock.

Laser systems stabilized to cryogenic silicon cavities for precision measurements

EPJ Web of Conferences, 2019

We consider laser systems stabilized to external Fabry-Perot silicon cavities operated at cryogen... more We consider laser systems stabilized to external Fabry-Perot silicon cavities operated at cryogenic temperatures. In order to characterize frequency stability two identical systems were created. Fractional frequency instability of individual system reached 6×10-15 at 1 s. Different sources of noises were studied, and the dominant one now is the fluctuations of residual amplitude modulation.

Improved Wavelength Measurement of 2S1/2→2P1/2 and 2D3/2→3[3/2]1/2 Transitions in Yb+

Journal of Russian Laser Research, 2019

Motional states of laser cooled Yb ions in an optimized radiofrequency trap

Laser Physics, 2019

$Research paper thumbnail of {"__content__"=>"Mass selective laser cooling ofThin a multisectional linear Paul trap loaded with a mixture of thorium isotopes.", "sup"=>[{"__content__"=>"229"}, {"__content__"=>"3+"}]}$

{"__content__"=>"Mass selective laser cooling ofThin a multisectional linear Paul trap loaded with a mixture of thorium isotopes.", "sup"=>[{"__content__"=>"229"}, {"__content__"=>"3+"}]}

European journal of mass spectrometry (Chichester, England), Aug 1, 2017

We consider an experiment on trapping and laser cooling ofThions in a linear Paul trap in the pre... more We consider an experiment on trapping and laser cooling ofThions in a linear Paul trap in the presence of undesirable impurities such as ions of the radioactive isotopeTh. We suggest a method of separating these impurities by means of selective laser cooling utilizing the isotope shift of cooling transitions inThandThions. According to our estimation, the isotope shift is equal to 3.4 GHZ and makes laser separation of these isotopes possible.

Loading of mass spectrometry ion trap with Th ions by laser ablation for nuclear frequency standard application

European journal of mass spectrometry (Chichester, England), Aug 1, 2017

We describe an original multisectional quadrupole ion trap aimed to realize nuclear frequency sta... more We describe an original multisectional quadrupole ion trap aimed to realize nuclear frequency standard based on the unique isomer transition in thorium nucleus. It is shown that the system effectively operates on Th, Thand Thions produced by laser ablation of metallic thorium-232 target. Laser intensity used for ablation is about 6 GW/cm. Via applying a bias potential to every control voltage including the RF one, we are able not only to manipulate ions within the energy range as wide as 1-500 eV but to specially adjust trap potentials in order to work mainly with ions that belong to energy distribution maximum and therefore to effectively enhance the number of trapped ions. Measurement of energy distributions ofTh,Th,Thions obtained by laser ablation allows us to define optimal potential values for trapping process. Observed number of ions inside trap in dependence on trapping time is found to obey an unusually slow - logarithmic decay law that needs more careful study.

The GBAR antimatter gravity experiment

Hyperfine Interactions, 2015

The GBAR project (Gravitational Behaviour of Anti hydrogen at Rest) at CERN, aims to measure the ... more The GBAR project (Gravitational Behaviour of Anti hydrogen at Rest) at CERN, aims to measure the free fall acceleration of ultracold neutral anti hydrogen atoms in the terrestrial gravitational field. The experiment consists preparing anti hydrogen ions (one antiproton and two positrons) and sympathetically cooling them with Be+ ions to less than 10 μK. The ultracold ions will then be photo-ionized just above threshold, and the free fall time over a known distance measured. We will describe the project, the accuracy that can be reached by standard techniques, and discuss a possible improvement to reduce the vertical velocity spread.

The Rydberg constant and proton size from atomic hydrogen

Science (New York, N.Y.), Oct 6, 2017

At the core of the "proton radius puzzle" is a four-standard deviation discrepancy betw... more At the core of the "proton radius puzzle" is a four-standard deviation discrepancy between the proton root-mean-square charge radii () determined from the regular hydrogen (H) and the muonic hydrogen (µp) atoms. Using a cryogenic beam of H atoms, we measured the 2S-4P transition frequency in H, yielding the values of the Rydberg constant= 10973731.568076(96) per meterand= 0.8335(95) femtometer. Ourvalue is 3.3 combined standard deviations smaller than the previous H world data, but in good agreement with the µp value. We motivate an asymmetric fit function, which eliminates line shifts from quantum interference of neighboring atomic resonances.

Towards compact transportable optical clock based on 171Yb+

2018 European Frequency and Time Forum (EFTF), 2018

We report on a new project aimed for development of a transportable compact optical clock based o... more

Long 48-cm ULE cavities in vertical and horizontal orientations for Sr optical clock

The development of an optical clock with ultimate accuracy and stability requires lasers with ver... more The development of an optical clock with ultimate accuracy and stability requires lasers with very narrow linewidth. We present two ultrastable laser systems based on 48 cm long FabryPerot cavities made of ULE glass in horizontal and vertical configurations operating at 698 nm. Fractional frequency instability of the beat signal between two lasers reaches 1.6∙10 at the averaging time of 1 s. We experimentally characterized the contribution of the different noise sources (power fluctuations, residual amplitude modulation, the Doppler noise, sensitivity to the shock impact) and found that in our case the laser frequency instability to a large extent is determined by an optoelectronic feedback loop. Although the vertical configuration proved to be easier to manufacture and to transport, it turned out that it is much more sensitive to acoustics and horizontal accelerations compared to the horizontal one. Both laser systems were transported over a 60 km distance from the Lebedev Physical...

Photoionization dynamics of Mg atoms during Paul trap loading using a two-color UV laser system

Trapped ions have proven to be a powerful instrument in quantum logic, precision metrology and te... more Trapped ions have proven to be a powerful instrument in quantum logic, precision metrology and tests of fundamental theories. Many applications require isotopically pure ion crystals to be trapped; however, selective loading methods require either isotopically pure atom sources or dedicated ultraviolet laser systems. Here we investigate the loading dynamics of the isotopically pure magnesium ion crystals photoionized and Doppler-cooled with a two-color UV laser system at 285 nm and 280 nm. The system shares the same tapered amplifier and the first stage of a second-harmonic generation for both wavelengths, which significantly reduces the complexity and cost of the experiment. A selective loading rate of 0.05 ions s−1 was achieved, supporting theoretical evaluations.

Challenging QED with Atomic Hydrogen

Testing theories means to compare precise measurements with theoretical predictions. I will descr... more

Simultaneous bicolor interrogation in thulium optical clock providing very low systematic frequency shifts

Nature Communications

Optical atomic clocks have already overcome the eighteenth decimal digit of instability and uncer... more Optical atomic clocks have already overcome the eighteenth decimal digit of instability and uncertainty, demonstrating incredible control over external perturbations of the clock transition frequency. At the same time, there is an increasing demand for atomic (ionic) transitions and new interrogation and readout protocols providing minimal sensitivity to external fields and possessing practical operational wavelengths. One of the goals is to simplify the clock operation while maintaining the relative uncertainty at a low 10−18 level achieved at the shortest averaging time. This is especially important for transportable and envisioned space-based optical clocks. Here, we demonstrate implementation of a synthetic frequency approach for a thulium optical clock with simultaneous optical interrogation of two clock transitions. Our experiment shows suppression of the quadratic Zeeman shift by at least three orders of magnitude. The effect of the tensor lattice Stark shift in thulium can a...

Estimation of uncertainty budget for a thulium optical clock

FIFTH INTERNATIONAL CONFERENCE ON QUANTUM TECHNOLOGIES (ICQT-2019)

Laser Cooling of Lanthanides: from Optical Clocks to Quantum Simulators

EPJ Web of Conferences, 2015

Precision spectroscopy of 2S– n P transitions in atomic hydrogen for a new determination of the Rydberg constant and the proton charge radius

by Ksenia Khabarova and R. Pohl

Physica Scripta, 2015

Spectroscopy of intercombination transition 1 S 0 – 3 P 1 for secondary cooling of strontium atoms

Quantum Electronics, 2015

ABSTRACT In the framework of the project aimed at creating an optical standard on cold Sr atoms w... more ABSTRACT In the framework of the project aimed at creating an optical standard on cold Sr atoms we have realised sub-Doppler spectroscopy of the intercombination transition 1S0 - 3P1 (689 nm) in a cell with Sr vapour and in a cloud of atoms loaded in a magneto- optical trap (MOT). By measuring Zeeman splitting of the 3P1 level in the magnetic field of the MOT we have succeeded in fine adjustment of the MOT relative to a minimum of the magnetic field, which is necessary for successful secondary-stage cooling on the intercombination transition. In turn, absorption saturation spectroscopy in the vapour cell provides the long-term frequency stability of the second-stage cooling laser at λ = 689 nm.