III. Electron Spin Resonance Results

ODMR scheme

The ODMR scheme uses  circularly polarized pump laser light (σ⁺ and σ^–) to  selectively address the electron spin states. The four ESR transitions take place between the eight hyperfine ground levels when a π-pulse in the fixed frequency cavity is applied.

⁸⁷Rubidium energy levels. In a magnetic field the fine structure splits into several hyperfine levels.

In the indermediate magnetic field neither m_F nor {m_I, m_J} is a good quantum number. The diagonalization of  the Hamiltonianleads to linear combinations (mixing) of the basis set. The eigenenergies are given by the Breit-Rabi formula, which uses the hyperfine constant a_HFS, and the Landé g_J factor as parameters.

Electronic Paramagnetc Resonance

The influence of the droplet is immediately apparent as shift of the ESR lines of ⁸⁷Rb monomers on He_N to the respective free atom peak by up to 129 μT in the spectrum.

ESR spectrum of ⁸⁷Rb: Embedded monomers on helium droplets are shifted with respect to the free atom peak

This effect is droplet size dependent. By changing the nozzle source conditions we were able to record a different shift for different mean droplet sizes. By using the Breit-Rabi formula we report the change of the Fermi contact term  dependence on the mean droplet size. The results are in excellent agreement with previous measurements on ⁸⁵Rb.[1]

The shift in the EPR spectrum is droplet size dependent.

The change of a_HFS can by interpreted as a compression of the radial part of the Rb valence electron wave function due to the helium droplet:
δa_HFS / a_HFS = δ|ψ(0)|² / |ψ(0)|²

The Fermi contact term for Rubidium on helium nano-droplets is a measure for the modification of the wave function.

No evidence within  experimental uncertainty was found for a change of the Landé factor g_J.

← II. Optical Pumping of Rubidium IV. Simple Pump model →