Düsseldorf 2007 – wissenschaftliches Programm

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MO: Fachverband Molekülphysik

MO 63: Spectroscopy in He-droplets / Ultracold Molecules I (gemeinsam mit Q)

MO 63.5: Vortrag

Freitag, 23. März 2007, 11:45–12:00, 6B

Sub-megaherz infrared spectroscopy of trapped HD⁺ ions at millikelvin temperatures — •Jeroen Koelemeij, Bernhard Roth, Andreas Wicht, Ingo Ernsting, and Stephan Schiller — Institut für Experimentalphysik, Universität Düsseldorf

We have performed an absolute frequency measurement of the (v′=4,J′=3) ← (v=0,J=2) overtone transition at 1395 nm in the molecular HD⁺ ion with sub-megaherz accuracy. Trapped HD⁺ ions are sympathetically cooled to millekelvin temperatures by storing them together with Be⁺ ions, which are laser cooled to ∼ 10 mK using near-resonant 313 nm light. Vibrational overtone spectroscopy at 1395 nm is done using (1+1′) resonance-enhanced multiphoton dissociation (REMPD), where a second photon at 266 nm selectively dissociates the HD⁺ ions in v′=4. The loss of HD⁺ ions due to the REMPD process manifests itself as a change in the 313 nm Be⁺ fluorescence when the motion of the HD⁺ ions is resonantly driven by an ac electric field. The 1395 nm probe laser is a narrowband grating-enhanced diode laser with resonant optical feedback, which is locked to a femtosecond frequency comb. The comb is stabilized to a hydrogen maser which is referenced to GPS for long term stability. This allows tuning and measurement of the 1395 nm laser frequency with an accuracy better than 10 kHz. The 0.5 MHz uncertainty in our final result is due to measurement noise, Doppler broadening and, to a lesser extent, systematic uncertainties associated with external fields in the ion trap, and uncertainties in the ab initio data used for the spectral fit model.