Coherent Control of Laser Field and Spectroscopy in Dense Atomic Vapor

Coherent effects are studied in a dense atomic vapor driven by laser fields. With optical properties dramatically modified by these effects, the medium can be used to manipulate some of the properties of laser field. Our experiments demonstrate the coherent control over transmission, spatial distribution and noise feature of the laser field interacting with coherent media. The results have potential applications in the field such as precision metrology, precision spectroscopy, optical imaging and lithography. We develop an experiment to investigate the atomic excitation by few-cycle radio frequency (RF) pulses interacting with Zeeman sublevels. The system provides the flexibility to fully control all parameters of RF pulses. Such a flexibility can not be achieved in optical domain. Based on this system, experiments can be conducted to simulate processes in ultra-short laser physics. In particular, we study the carrier-envelope effect of few-cycle pulses and the strong off-resonant excitation by short pulses. We also discuss the selective reflection spectrum on a highly dense atomic vapor in which the dipole-dipole interaction can not be neglected. The spectrum broadening due to dipole-dipole interaction is much broader than the Doppler broadening. Our experiments show that the excitation by a pump laser can reduce the dipole-dipole interaction, thus reduce the broadening and improve the spectral resolution. The excitation dependence is studied at various atomic densities

Experimental observation of carrier-envelope phase effects by multicycle pulses

We present an experimental and theoretical study of carrier-envelope phase (CEP) effects on the population transfer between two bound atomic states interacting with pulses consisting of many cycles. Using intense radio-frequency pulse with Rabi frequency of the order of the atomic transition frequency, we investigated the influence of CEP on the control of phase dependent multi-photon transitions between the Zeeman sub-levels of the ground state of $^{87}$Rb. Our scheme has no limitation on the duration of the pulses. Extending the CEP control to longer pulses creates interesting possibilities to generate pulses with accuracy that is better then the period of optical oscillations.Comment: 8 Pages, 6 Figure

Broadband Optical Two-Dimensional Coherent Spectroscopy of a Rubidium Atomic Vapor

Optical two-dimensional coherent spectroscopy (2DCS) has become a powerful tool for studying energy level structure, dynamics, and coupling in many systems including atomic ensembles. Various types of two-dimensional (2D) spectra, including the so-called single-quantum, zero-quantum, and double-quantum 2D spectra, of both D lines (D$_1$ and D$_2$ transitions) of potassium (K) atoms have been reported previously. For rubidium (Rb), a major difference is that the D-lines are about 15 nm apart as opposed to only about 3 nm for K. Simultaneously exciting both D-lines of Rb atoms requires a broader laser bandwidth for the experiment. Here, we report a broadband optical 2DCS experiment in an Rb atomic vapor. A complete set of single-quantum, zero-quantum, and double-quantum 2D spectra including both D-lines of Rb atoms were obtained. The experimental spectra were reproduced by simulated 2D spectra based on the perturbation solutions to the optical Bloch equations. This work in Rb atoms complements previous 2DCS studies of K and Rb with a narrower bandwidth that covers two D-lines of K or only a single D-line of Rb. The broadband excitation enables the capability to perform double-quantum and multi-quantum 2DCS of both D-lines of Rb to study many-body interactions and correlations in comparison with K atoms.Comment: 10 pages, 7 figure

Coherent Excitonic Coupling in an Asymmetric Double InGaAs Quantum Well Arises from Many-Body Effects

We study an asymmetric double InGaAs quantum well using optical two-dimensional coherent spectroscopy. The collection of zero-quantum, one-quantum, and two-quantum two-dimensional spectra provides a unique and comprehensive picture of the double well coherent optical response. Coherent and incoherent contributions to the coupling between the two quantum well excitons are clearly separated. An excellent agreement with density matrix calculations reveals that coherent interwell coupling originates from many-body interactions

Long range dipole-dipole interaction in low-density atomic vapors probed by double-quantum two-dimensional coherent spectroscopy

Optical double-quantum two-dimensional coherent spectroscopy (2DCS) was implemented to probe interatomic dipole-dipole interactions in both potassium and rubidium atomic vapors. The dipole-dipole interaction was detected at densities of $4.81 \times 10^8$ cm$^{-3}$ and $8.40 \times 10^9$ cm$^{-3}$ for potassium and rubidium, respectively, corresponding to a mean interatomic separation of 15.8 $\mu$m or $3.0\times 10^5a_0$ for potassium and 6.1 $\mu$m or $1.2\times 10^5a_0$ for rubidium, where $a_0$ is the Bohr radius. We report the lowest atomic density at which dipole-dipole interactions are detected. The experimental results confirm the long range nature of the dipole-dipole interaction which is critical for understanding many-body physics in atoms/molecules. The long range interaction also has implications in atom-based applications involving many-body interactions. Additionally, we demonstrated that double-quantum 2DCS is sufficiently sensitive to probe dipole-dipole interaction at densities that can be achieved with cold atom in a magneto-optical trap, paving the way for double-quantum 2DCS studies of cold atoms and molecules. The method can also open a new avenue to study long-range interactions in solid states systems such as quantum dots and color centers in diamonds.Comment: 5 pages, 4 figure