Ultra-high resolution XUV spectroscopy

The narrowband extreme ultraviolet (XUV) laser at LCVU is used in a number of studies that all focus on precision inquiries of highly excited states in gas-phase molecules. The bandwidth of the system is better than can be achieved at any synchrotron in the world.
In molecular nitrogen and in carbon monoxide, the most strongly bound molecules in nature, the absorption spectrum lies at short wavelengths, primarily in the XUV-domain. In both molecules Rydberg states and valence states of singlet and triplet symmetry strongly interact and give rise to a wealth of (pre)- dissociation phenomena that bear a great impact: N2 in the Earth atmosphere
absorbing the light from the sun, and CO in the interstellar medium absorbing the light from nearby stars. The pre-dissociation processes are investigated in detail with our setup.
Molecular hydrogen, the most abundant molecule in the universe, exhibits strong XUV absorption as well, via the so-called Lyman and Werner systems. Ultra-precise transition frequencies, measured with the XUV-laser are compared with the red-shifted spectral observations from quasars. This study has led to the most stringent limit on a possible variation of the proton-to-electron mass ratio (μ) on a cosmological time scale: Δμ/μ = -0.5 +/- 3.6 x 10-5 (2σ) [Ubachs and Reinhold, Phys. Rev. Lett. 92 (2004) 101302].

Contact: Wim Ubachs, e-mail: wmg.ubachs@few.vu.nl
Atomic, Molecular and Laser Physics

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Experimental setup of the pulsed dye amplifier laser system used for producing Fouriertransform
limited laser pulses in the visible range, and for further upconversion into the extreme ultraviolet range.