Continuous generation of delayed light

Abstract

We use a Raman four-wave mixing process to read-out light from atomic coherence which is continuously written. The light is continuously generated after an effective delay, allowing the atomic coherence to evolve during the process. Contrary to slow-light delay, which depends on the medium optical depth, here the generation delay is determined solely by the intensive properties of the system, approaching the atomic coherence lifetime at the weak driving limit. The generated light is background free. We experimentally probe these properties utilizing spatial diffusion as an 'internal clock' for the atomic evolution time. Continuous generation of light with a long intrinsic delay can replace discrete write-read procedures when the atomic evolution is the subject of interest.

Structured beams invariant to coherent diffusion

“…In the excited level 5P 1/2 , both hyperfine levels, namely the four state |e 1 = |5P 1/2 ; F = 1, 2; m = 1 and |e 2 = |5P 1/2 , F = 1, 2; m = −1 , participate in the process. The diffusion constant in the cell D = 9.7 ± 0.5 cm 2 /s is measured independently utilizing standard light storage experiments [29,7,25] and agrees with the calculated values [19,16] (for further details refer to Supplementary Material of Ref. [3]).…”

“…For the experimental study of diffusion of structured complex fields, we exploit electromagnetically induced transparency (EIT) within a unique four-wave mixing scheme studied in Ref. [25]. The spatially-shaped 'probe' beam is imprinted onto warm atoms, and a 'signal' beam is continuously retrieved from them and measured.…”

“…The atoms diffuse during this process, and the retrieved signal conveys their diffusion evolution. The effective diffusion time is equal to the group delay τ due to EIT in the medium [25,3].…”

“…More details are given in Ref. [25]. For a uniform incoming probe field E in , the generated signal E s in the limit of weak EIT |Sf | 1 is given by…”

“…Using the Fourier transformation Ẽ(q) = d 2 r 2π E(r)e −iq•r for the transverse coordinates r = (x, y) and under the assumptions of weak EIT and confined spatial frequencies q 2 = |q| 2 |γ 2p + Γ|/D, it can be shown that [25] Ẽs (q) ∝ Ẽin (q)e −Dτ q 2 , (…”