Excitation of Metastable Helium Atoms to Rydberg States by STIRAP

I.A. Kudriavtsev, V. V. Petrunin

Oleg Kritsun, Benjamin Dietzek, H. Metcalf

E. H. S. Burhop

Petr M. Anisimov, Yuan Sun, Harold J. Metcalf

X. L. Lu, Yuan Sun, H. Metcalf

We have set up a STIRAP excitation mechanism for helium from the metastable 23S state into Rydberg states, via the intermediate level 33P . A uv laser at 389 nm and an ir laser at 780-815nm are used as the pump and Stokes beams respectively. Our purposes is to examine how well STIRAP works to efficiently produce the Rydberg atoms, and also to apply STIRAP for further coherent manipulations of helium. To examine the efficiency of the STIRAP process, we use the state selectivity of the light force on atoms to physically separate atoms with different internal states. We use the bichromatic force on a transition different from those used for Rydberg excitation. We do not measure an excitation efficiency close to the ~100% theoretical optimum but instead only about 50%. To gain more insight into this coherent process, an excitation path interferometer is envisioned that showes the expected interference, via the final population of the Rydberg level.

Deqian Yuan

Research in optically induced transitions between dierent atomic levels has a long history. For transitions between states driven by a coherent optical eld, the theoretical eciency could be ideally high as 100% but there could be many factors preventing this. In the three state helium atom excitation process, i.e. 23S! 33P! nL , the stimulated emission from intermediate state makes it hard to achieve ecient population transfer to the nal state through an intuitive excitation order. One technique to achieve a higher eciency is Stimulated Raman Adiabatic Passage (STIRAP) which is being studied and under research in our lab. Unlike traditional three level excitation processes, STIRAP actually uses a counter intuitive pulsed laser beams timing arrangement. The excitation objects are metastable helium atoms traveling in a vacuum system with a longitudinal velocity of 1070 m/s. We are using a 389 nm UV laser to connect the 23S and the 33P state and a frequency tunable 790 nm iii IR laser to connect the 33P state and the dierent Rydberg states. A third 1083 nm wavelength laser beam drives the 23S ! 23P transition to transversely separate the residual metastable atoms and the Rydberg atoms for eciency measurements. The data is taken by a stainless steel detector in the vacuum system. As the Rydberg atoms will get ionized by blackbody radiation under room temperature, we can utilize this for their detection. An ion detector sitting on the eld plate is capable to collect the ion signals of the Rydberg atoms for detection. So far the whole system has not been ready for data collection and measurement, so here we are using data and results from previous theses for discussions. The highest transition frequency that has ever been achieved in our lab is around 70% after corrections. | 144 pages