NIST is developing a fundamentally new approach for electric (E) field measurements -]9]. The probe is based on the interaction of RF-fields with Rydberg atoms, where alkali atoms placed in atomic vapor cells are excited optically to Rydberg states and an applied RF-field alters the resonant state of the atoms. The Rydberg atoms act like an RF-to-optical transducer, converting an RF E-field to an optical-frequency response. The probe utilizes the concept of Electromagnetically Induced Transparency (EIT), where the RF transition in the four-level atomic system causes a split of the EIT transmission spectrum for the probe laser. This splitting is easily measured and is directly proportional to the applied RF field amplitude. By measuring this splitting we get a direct measurement of the RF E-field strength. The significant dipole response of Rydberg atoms over the GHz regime enables this technique to make direct SI-traceable measurements over a large frequency band including 400 MHz-500 GHz. One of the main contributions to the uncertainties in the approach is due to the perturbation of the measured E-field caused by the size and shape of the vapor cell , , , and . Fundamental to the development of this technique is to have specially designed vapor cells that will have minimal perturbation on the RF field being measured.
Project goals include the development of compact atomic vapor cells (filled with Rb and/or Cs) suitable for atom-based E-field metrology. Ideally, the vapor-cell should be on the order of a few mm and have no stems (that are common found in current technology) in order to have minimal RF perturbation. These new cells should also include hollow-core fiber vapor cells designs.
Phase I expected results:
Design and simulate results for compact vapor cells. The vapor-cell should be on the order of a few mm and have no stems (that are common found in current technology). Successful designs should be compact and have minimal perturbation in the applied RF field. Results of full three-dimensional RF simulations at a range of frequencies are required in order to evaluate impact of the vapor cell on the measured field.
Phase II expected results:
Phase II expected results include using the compact vapor cells designs in Phase I to develop fiber coupled vapor cells. These vapor cell need to have pure atomic vapor (no buffer gasses) and demonstrate a ground-state absorption of 40% or better. Need to demonstrate EIT in the cell. Successful designs should be compact and have minimal perturbation in the applied RF field. Results of full three-dimensional RF simulations are required in order to evaluate impact of the vapor cell on the measured field. Also, in Phase II hollow-core fiber will be designed. Prototypes will be filled with either Cs or Rb and need to demonstrate EIT.
NIST will use our facilities to test the designs.