Durham EIT

Graham Purves, Charles Adams, Ifan Hughes

At Durham we are currently looking at three level effects on the Rubidium D2 line . To date we have observed both EIT and Electromagnetically Induced Absorption (EIA) in this system.

Experimental Set-Up

Our pump and probe beams are derived from the same laser, and the frequency difference between them (delta) is controlled using two acousto-optic modulators (AOMs). This allows us a maximum frequency difference between our probe and pump beam of 400 MHz. In practise we operate our AOMs such that delta is less than +-10 MHz. This essentially means that our pump and probe fields are close to single resonance with the same hyperfine transition. It is critical that our beams are as close as possible to being co-propagating. This cancels out the first order Doppler shift, which prevents our signals being limited by the Doppler broadening associated with room temperature rubidium (this would limit our signals to being hundreds of MHz wide). In fact a misalignment of only 0.5 mrad , between the pump and probe beam causes the width of our signals to be limited to 300kHz.

Pump / Probe Polarizations

In order that our radiation fields are close to resonance with three different atomic levels (two ground states and one excited state), then we must use different polarizations for the pump and probe field. This then means that the two ground states are different Zeeman sub-levels of the same hyperfine level. We have carried out measurements using both perpendicularlly linear polarized beams and oppositely circularly polarized pump and probe beams.

Rb vapour cells

All of our measurements to date have been made in room temperature rubidium vapour cells. We are currently developing a new vapour cell which will allow us to vary both the Rb vapour pressure as well as the pressure of a buffer gas.

Varying the Rb vapour pressure will allow us to vary the amount of absorption that we would get on a single photon resonance, and hence vary the size of the EIT signals. The introduction of a buffer gas can dramatically narrow the resonances, by several orders of magnitude. This is of particular interest to us as it will potentially make any interferometer we construct more sensitive to, for example a change in magnetic field.

Content © G. T. Purves, Durham University 2005