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 Title: Characterization Of A Thz Electric Field By Molecular Ion Spectroscopy Author(s): Constantin, Florin Lucian Subject(s): Instrument/Technique Demonstration Abstract: The Rydberg atom spectroscopy, exploited for SI-traceable electrometry, allowed to measure weak microwave electric fields at the $\mu$V/cm level. The Doppler-free spectroscopy methods allowed recently significant improvements of the resolution and precision of the measurements with cold trapped HD$^{+}$ molecular ions. The ab-initio molecular ion theory provided accurate predictions of the HD$^{+}$ energy levels and their shifts in external fields. This contribution proposes a new method to characterize a THz electric field that is off-resonantly coupled to the HD$^{+}$ energy levels based on the comparison of the measurements of the lighshifts induced on a two-photon rovibrational transition with the theoretical ab-initio predictions. Precisely, a THz-wave slightly detuned to the Zeeman subcomponents of the (v,L)=(0,0)-(0,1) transition may be characterized by measuring the lightshift of a Zeeman subcomponent of the (v,L)=(0,0)-(2,0) two-photon transition with potential Hz-level uncertainty limited by the molecular ion quantum projection noise. This method allows detecting a THz electric field at the $\mu$V/m level from a THz-wave optimally detuned to a hyperfine transition of HD$^{+}$. An algorithm is proposed to retrieve the amplitudes and the phases of a THz electric field in a Cartesian reference frame from six lightshift measurements using two orientations and three values of the static magnetic field in the ion trap. The Cartesian components of the electric field of a THz-wave, with an intensity of 1 W/m$^{2}$, circularly polarized, and detuned to a hyperfine transition of HD$^{+}$, may be characterized with mV/m-level uncertainties for the amplitudes, and 0.1 rad-level for the phases. Issue Date: 2021-06-22 Publisher: International Symposium on Molecular Spectroscopy Genre: Conference Paper / Presentation Type: Text Language: English URI: http://hdl.handle.net/2142/111561 Date Available in IDEALS: 2021-09-24
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