Precision spectroscopy for fundamental tests
|Determination of the ground state energy of helium with an XUV frequency comb
have demonstrated high-precision spectroscopy from 85-51 nm using a
Ramsey-XUV frequency comb. This "Ramsey comb" is based on
harmonic upconversion of two amplified frequency comb pulses. With this
system we determined the energy position of the ground state of
helium with an accuracy of 6 MHz (an 8-fold improvement over the
previous determination with conventional single nanosecond pulse
One issue with the previous system (used for the helium measurement)
was the need to calibrate the phase shift induced between the two
pulses due to the parametric amplifier and in the harmonic generation
process. Also the time delay between the pulses was limited to 10 ns.
We have now developed a new system
where a phase measurement is no longer necessary. Moreover, the pulses
can be selected under computer control over more than a microsecond. We
performed measurements with this system on two-photon transitions in
Rb, Kr and H2 (Spring 2017, paper in preparation). With this we have
shown that kHz-level
accuracy is possible (see here) and the prospects are very good to go down to wavelengths as short as 30 nm with the Ramsey-comb technique.
Currently the measurements of the helium ground state is 6 times more
accurate (6 MHz) than current theory (36 MHz). Once the theory becomes
better, we pick this up again, and will measure the 1s^2 - 1s2s 1S0
transition at 2x120 nm. We expect to be able to improve it by 100x to reach 50 kHz.
D.Z. Kandula, C. Gohle, T.J. Pinkert, W. Ubachs, K.S.E. Eikema,
"XUV frequency-comb metrology on he ground state of helium"
Phys. Rev. A 84, 062512 (2011)
T.J. Pinkert, D.Z. Kandula, C. Gohle, I. Barmes, J. Morgenweg, K.S.E. Eikema, "Widely tunable XUV frequency comb generation"
Opt. Lett. 36, 2026-2028 (2011)
D.Z. Kandula, C. Gohle, T.J. Pinkert, W. Ubachs, K.S.E. Eikema, "Extreme Ultraviolet Frequency Comb Metrology",
Phys. Rev. Lett. 105, 063001 (2010)
see also Physics Synopsys, and Nature Research Highlights
|Direct frequency comb spectroscopy on Ca ions to test for a possible variation of the fine-structure constant alpha.
the incredible accuracy of frequency comb lasers, one can now test
whether the fundamental constants such as the fine-structure constant
is actually constant. We do this by comparing transitions in ions with
observations done with telescopes. With a telescope you can effectively
look back into the past over many billions of years. If you take care
of the red-shift (due to the expanding universe), one can check whether
alpha has changed on a cosmological timescale. Our part of the
comparison is in providing accurate laboratory values for the principle
transitions that are interesting for such a comparison. To this end we
have performed direct frequency comb spectroscopy in Ca+ ions in the UV
by frequency doubling a full-reprate frequency comb. The calcium ions
are trapped in a RF Paul-trap. Laser cooling on the 397 nm transition
reduced the temperature to 13 mK for precision spectroscopy. Also a
'forbidden' clock transition could be excited directly with the
frequency comb at 729 nm.
Recently (Spring 2017) we took the Ca+ trap apart to recycle it partly for the new He+ 1S-2S spectroscopy experiment currently under construction.
A.L. Wolf et al., "Direct frequency-comb spectroscopy of a dipole-forbidden clock transition in trapped 40Ca+ ions"
Opt. Lett., 36, 49-51 (2011)
A.L. Wolf, S.A. van den Berg, W. Ubachs, K.S.E. Eikema, "Direct Frequency Comb Spectroscopy of Trapped Ions"
Phys. Rev. Lett. 102, 223901 (2009)
|Projects in collaboration with other groups: He*, H2, Ca, CO
a collaboration with the group of dr. Wim Vassen (PI) we determined the
transition frequency of the highly forbidden 2 3S1 - 2 1S0 transition
in meta-stable helium at the 1 kHz level. From this measurement a
nuclear charge radius difference could be derived. We intend to improve
this measurement by an order of magnitude in the near future.
Other projects involve molecular hydrogen and simple atomic systems via
a collaboration with prof. W. Ubachs and dr. Edcel Salumbides, and the CO molecule in
collaboration with dr. H. Bethlem.
W. Ubachs, J.C.J. Koelemeij, K.S.E. Eikema, E.J. Salumbides, "Physics beyond the Standard Model from hydrogen spectroscopy",
J. Mol. Spectr. 320, 1-12 (2016)
J. Biesheuvel, J. Ph. Karr, L. Hilico, K.S.E. eikema, W. Ubachs, J.C.J.
Koelemeij, "Probing QED and the fundamental constants through laser
spectroscopy of vibrational transitions in HD",
Nature Communications 7, 10385 (2016)
R. van Rooij, J.S. Borbely, J. Simonet, M.D. Hogerland, K.S.E. Eikema,
R.A. Rozendaal, W. Vassen, "Frequency metrology in quantum
degenerate helium: direct measurement of the 2 3S1 - 2 1S0 transition",
Science 333, 196-198 (2011)
A.J. de Nijs, E.J. Salumbides, K.S.E. Eikema, W. Ubachs, H.L. Bethlem,
"UV-frequency metrology on CO a 3Π: isotope effects and sensitivity to a variation of the proton-to-electron mass ratio",
Phys. Rev. A 84, 052509 (2011)
Salumbides, E.J., Maslinskas, V., Dildar, I.M., Wolf, A.L., Duijn, E.J.
van, Eikema, K.S.E. & Ubachs, W. "High precision frequency
measurement of the 423 nm Ca I line",
Phys. Rev. A 83, 012502 (2011).
J.J. Liu, E.J. Salumbides, U. Hollenstein, J.C.J. Koelemaij, K.S.E.
Eikema, W. Ubachs, F. Merkt, "Determination of the ionization and
dissociation energies of the hydrogen molecule",
J. Chem. Phys. 130, 174306 (2009)
E.J. Salumbides, D. Bailly, A. Khramov, A.L. Wolf, K.S.E. Eikema, M. Vervloet, W. Ubachs
Improved Laboratory Values of the H-2 Lyman and Werner Lines for
Constraining Time Variation of the Proton-to-Electron Mass Ratio
Phys. Rev. Lett. 101, 223001 (2008)
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