13 research outputs found
Multi-photon ionisation spectroscopy for rotational state preparation of N+2
In this paper we investigate the 2 + 1′ resonance enhanced multi-photon ionisation (REMPI) of molecular nitrogen via the a1Πg(v = 6) intermediate state and analyse its feasibility to generate molecular nitrogen ions in a well defined ro-vibrational state. This is an important tool for high precision experiments based on trapped molecular ions, and is crucial for studying the time variation of the fundamental constant mp/me using N+2. The transition is not reported in the literature and detailed spectral analysis has been conducted to extract the molecular constants of the intermediate state. By carefully choosing the intermediate ro-vibrational state, the ionisation laser wavelength and controlling the excitation laser pulse energy, unwanted formation of rotationally excited molecular ions can be suppressed and ro-vibrational ground state ions can be generated with high purity
Quantum cascade laser frequency stabilisation at the sub-Hz level
Quantum Cascade Lasers (QCL) are increasingly being used to probe the
mid-infrared "molecular fingerprint" region. This prompted efforts towards
improving their spectral performance, in order to reach ever-higher resolution
and precision. Here, we report the stabilisation of a QCL onto an optical
frequency comb. We demonstrate a relative stability and accuracy of 2x10-15 and
10-14, respectively. The comb is stabilised to a remote near-infrared
ultra-stable laser referenced to frequency primary standards, whose signal is
transferred via an optical fibre link. The stability and frequency traceability
of our QCL exceed those demonstrated so far by two orders of magnitude. As a
demonstration of its capability, we then use it to perform high-resolution
molecular spectroscopy. We measure absorption frequencies with an 8x10-13
relative uncertainty. This confirms the potential of this setup for ultra-high
precision measurements with molecules, such as our ongoing effort towards
testing the parity symmetry by probing chiral species
A simple 2 W continuous-wave laser system for trapping ultracold metastable helium atoms at the 319.8 nm magic wavelength
High-precision spectroscopy of the HD+ molecule at the 1-p.p.b. level
Recently we reported a high-precision optical frequency measurement of the (v, L): (0, 2)→ (8, 3) vibrational overtone transition in trapped deuterated molecular hydrogen (HD+) ions at 10 mK temperature. Achieving a resolution of 0.85 parts-per-billion (p.p.b.), we found the experimental value [ν0 = 383, 407, 177.38 (41) MHz] to be in agreement with the value from molecular theory [νth 383, 407, 177.150 (15) MHz] within 0.6 (1.1) p.p.b. (Biesheuvel et al. in Nat Commun 7:10385, 2016). This enabled an improved test of molecular theory (including QED), new constraints on the size of possible effects due to ‘new physics,’ and the first determination of the proton–electron mass ratio from a molecule. Here, we provide the details of the experimental procedure, spectral analysis, and the assessment of systematic frequency shifts. Our analysis focuses in particular on deviations of the HD+ velocity distribution from thermal (Gaussian) distributions under the influence of collisions with fast ions produced during (laser-induced) chemical reactions, as such deviations turn out to significantly shift the hyperfine-less vibrational frequency as inferred from the saturated and Doppler-broadened spectrum, which contains partly unresolved hyperfine structure
Two-photon laser spectroscopy of antiprotonic helium and the antiproton-to-electron mass ratio
Physical laws are believed to be invariant under the combined transformations of charge, parity and time reversal (CPT symmetry).
This implies that an antimatter particle has exactly the same mass and absolute value of charge as its particle counterpart. Metastable antiprotonic helium is a three-body atom consisting of a normal helium nucleus, an electron in its ground state and an antiproton occupying a Rydberg state with high principal and angular momentum quantum numbers, respectively n and l, such that
n~l+1 ~ 38. These atoms are amenable to precision laser spectroscopy, the results of which can in principle be used to determine the antiproton-to-electron mass ratio and to constrain the equality between the antiproton and proton charges and masses. Here we report two-photon spectroscopy of antiprotonic helium, in which two antiprotonic helium isotopes are irradiated by two counter-propagating laser beams. This excites nonlinear, two-photon transitions of the antiproton of the type (n,l) -> (n-2, l-2) at deep-ultraviolet wave-lengths (139.8, 193.0 and 197.0 nm), which partly cancel the Doppler broadening of the laser resonance caused by the thermal motion of the atoms. The resulting narrow spectral lines allowed us to measure three transition frequencies with fractional precisions of 2.3–5 parts in 10^9. By comparing the results with three-body quantum electrodynamics calculations, we derived an antiproton-to-electron mass ratio of 1,836.1526736(23), where the parenthetical
error represents one standard deviation. This agrees with the
proton-to-electron value known to a similar precision