TY  - GEN
Y1  - 2020///
UR  - https://archiv.ub.uni-heidelberg.de/volltextserver/28798/
KW  - atomic physics
KW  -  intra-cavity high harmonic generation
KW  -  HHG
KW  -  frequency comb
KW  -  extreme ultraviolet
KW  -  XUV
KW  -  femtosecond enhancement cavity
KW  -  fsEC
KW  -  frequency metrology
KW  -  XUV spectroscopy
KW  -  highly charged ions
KW  -  HCI
KW  -  ultra-high vacuum
KW  -  UHV
KW  -  laser technology
KW  -  multi-photon ionization
KW  -  velocity-map imaging
KW  -  VMI
KW  -  optical atomic clock
KW  -  xenon
AV  - public
ID  - heidok28798
TI  - An extreme-ultraviolet frequency comb enabling frequency metrology with highly charged ions
A1  - Nauta, Janko
CY  - Heidelberg
N2  - Highly charged ions (HCI) have been proposed as extremely sensitive probes for physics beyond the Standard Model, such as a possible ?-variation, and as novel frequency standards,
due to their insensitivity to external fields. We aim at performing ultra-high precision spectroscopy of HCI in the extreme ultraviolet (XUV) region, where many transitions
are located. Therefore, we have developed an XUV frequency comb. Femtosecond pulses from a 100 MHz phase-stabilized near-infrared comb are amplified and fed into an enhancement
cavity inside an ultra-high vacuum chamber. In the tight focus (w0 = 15 ?m) of the astigmatism-compensated cavity, intensities ~10^14 W/cm^2 are reached. As a first
application, we perform multi-photon ionization of xenon using the velocity-map imaging technique. The high repetition rate facilitates fast data acquisition even at low intensities, enabling future precision tests in nonlinear physics. Finally, we have observed outcoupled
XUV radiation, produced in the cavity focus, up to the 35th harmonic order (42 eV; 30 nm). No signs of mirror degradation were observed during five hours of continuous
operation. Using He:Xe gas mixtures, improved phase-matching conditions led to 49 ?W output power at 16 eV. This is sufifcient to drive HCI transitions with kHz excitation rates and is an important step towards XUV frequency metrology with HCI.
ER  -