We discuss theoretical and experimental investigations of gain phenomena and refractive index control in atomic systems due to coherences induced by a pump laser. Experimental results in potassium vapor are compared with 3-level and 4-level models.
We report a proof-of-principle experiment where the refractive index of an atomic vapor is enhanced while maintaining vanishing absorption of the beam. The key idea is to drive alkali atoms in a vapor with appropriate control lasers and induce a gain resonance and an absorption resonance for a probe beam in a two-photon Raman configuration. The strength and the position of these two resonances can be manipulated by changing the parameters of the control lasers. By using the interference between these two resonances, we obtain an enhanced refractive index without an increase in the absorption.
Theoretical and experimental work of the past few years has demonstrated that the \noptical response of multi-state atomic systems can be controlled efficiently using \nquantum coherence and interference effects. These effects include: lasers operating \nwithout population inversion, novel techniques for resonantly enhanced nonlinear \noptics, enhancement and manipulation of the refractive index, and modification of \nspontaneous emission. In the present paper, we discuss manifestations of these \neffects of quantum interference in one of the simplest multilevel atomic system, in \nwhich two upper levels are coupled a static field. In this way we probe the extent \nto which optical of such systems can be "engineered" using atomic \ncoherence. The present treatment provides useful insights into the physics of this \nphenomenon.
Summary form only given. Quantum coherence phenomena offer a powerful method of controlling the optical properties of an atomic vapor, such as the absorption and refractive index. We demonstrate the use of quantum coherence to induce controllable birefringence in an atomic vapor and to thereby provide complete and efficient control over the polarization state of a probe laser beam propagating through the vapor. Quantum coherence has been previously observed to produce small polarization rotations, but these experiments suffered from significant absorption loss and produced rotations of at most a few degrees. Our experiments demonstrate the ability to induce linear or circular birefringence in an initially isotropic system that can be used to change the polarization state of a probe beam from linear to any desired polarization state with a total energy throughput greater than 97%.
Summary form only given. Intensive theoretical work, carried out in the past decade, has indicated that optical properties of matter can be dramatically affected by atomic coherence and interference effects. In particular, atomic coherence and interference was shown to lead to such intriguing phenomena as electromagnetically induced transparency, lasing without population inversion (LWI), and resonant enhancement of refractive index accompanied by vanishing absorption. In the present paper we report the first experimental observation of LWI oscillation and the first demonstration of index enhancement.
The potential to precisely control both the linear and nonlinear index of refraction through optical manipulation of the atomic states has recently pushed warm alkali vapors to the forefront of research in the field of quantum sensors, quantum memories, and quantum fluids of light. Rubidium (Rb) vapor in centimeter-scale glass cells or millimeter-scale MEMS cells has proven to be a very promising platform for these applications, yet only a handful of research works have been dedicated to the investigation of the (non)linear refractive index of Rb vapor. We present results of theoretical calculations of the (non)linear refractive index of warm Rb vapor, based on the optical Bloch equations for 6-level Rb atoms interacting with a probe laser. They are compared to the experimental results obtained using an interferometric technique, showing excellent quantitative agreement. A Kerr nonlinear refractive index n2 of up to 10−4 cm2/W is obtained. Python scripts for all theoretical calculations presented in this work are provided, including the refractive index calculation, that can readily be used in practical implementations for simulating the (non)linear refractive index of Rb vapor including the effects of Doppler broadening, transit time broadening, pressure broadening, saturation, optical pumping, and spin-exchange collisions.