Observation of large contrast electromagnetically induced absorption resonance due to population transfer in a three-level Λ-system interacting with three separate electromagnetic fields.

We describe a new scheme to induce large contrast (nearly 50%) absorption resonances using three co-propagating fields which interact with a three-level Λ-system (obtained by the D(2) transition of (87)Rb atoms) in an N-configuration scheme. A single mode laser which couples the upper ground state to the excited state of (87)Rb is phase modulated at half the hyperfine splitting frequency. The resultant three line spectrum interacts with the atomic vapor yielding a population transfer which increases the absorption by an amount which depends on the carrier to modulation side band intensity ratio.

Multi-field frequency modulation spectroscopy.

We Study a modification of classical FM spectroscopy in the cases where several electromagnetic fields are FM modulated, each in a different manner. This complex spectrum scans a multi-photon resonant atomic medium with the output detected by a phase-sensitive scheme. The demodulated output signal reveals the spectroscopic features of the probed medium. The case in which two different carriers are FM modulated at the same frequency and index but with an opposite phase with respect to each other is analyzed theoretically. This configuration is essential for probing Coherent Population Trapping (CPT) resonances induced by a directly modulated diode laser. Employing a macroscopic model to describe the physical properties of CPT leads to a superb fit between predicted and measured CPT characteristics.

Dependence of small-scale atomic clock performance on frequency modulation parameters used in the frequency control loop.

We demonstrate a direct correspondence between FM parameters used in a frequency-locked loop that is based on multifield FM spectroscopy and the stability of a small-scale coherent population trapping atomic clock. Optimized FM parameters lead to an Allan deviation of 2.8 x 10(-11)/square root tau, while the clock stability deteriorates in a predictable manner for the other FM parameters.