Coherent nonlinear effects such as Electromagnetically Induced Transparency\n(EIT), Coherent Population Trapping (CPT), and Slow light are studied in thermal\nRb vapor by both continuous and pulsed laser fields. This work primarily includes\nthree parts: (I) mode-locked rubidium laser and its applications (II) enhanced coupling\nbetween optical and sound waves in the forward direction via ultra-slow light\n(III) optical steering via ultra-slow light in rubidium vapor.\nIn part(I), I describe the construction and study of a mode-locked rubidium laser\noperating at the Rb D1 line using an active mode-locking technique inside the laser\ncavity. The mode-locked laser field is used to observe coherent effects in a dense\nrubidium gas.\nIn part(II), I experimentally demonstrate enhanced acoustic-optic coupling that\noccurs when the velocity of sound is close to the group velocity of light. Dragging of\nthe light by effective motion of the gas in a Rb cell is the origin of enhanced coupling.\nGood agreement between theory and experiment is found.\nIn part(III), I experimentally demonstrate optical beam deflection in coherently\ndriven rubidium vapor due to the steep refraction index profile in the region of EIT.
Coherent nonlinear effects such as Electromagnetically Induced Transparency\n(EIT), Coherent Population Trapping (CPT), and Slow light are studied in thermal\nRb vapor by both continuous and pulsed laser fields. This work primarily includes\nthree parts: (I) mode-locked rubidium laser and its applications (II) enhanced coupling\nbetween optical and sound waves in the forward direction via ultra-slow light\n(III) optical steering via ultra-slow light in rubidium vapor.\nIn part(I), I describe the construction and study of a mode-locked rubidium laser\noperating at the Rb D1 line using an active mode-locking technique inside the laser\ncavity. The mode-locked laser field is used to observe coherent effects in a dense\nrubidium gas.\nIn part(II), I experimentally demonstrate enhanced acoustic-optic coupling that\noccurs when the velocity of sound is close to the group velocity of light. Dragging of\nthe light by effective motion of the gas in a Rb cell is the origin of enhanced coupling.\nGood agreement between theory and experiment is found.\nIn part(III), I experimentally demonstrate optical beam deflection in coherently\ndriven rubidium vapor due to the steep refraction index profile in the region of EIT.
The aim of this book is to present new results in rapidly developing fields of nonlinear optics such as atomic coherence, magneto-optics of atomic media, Doppler-free spectroscopy, time-domain spectroscopy of dense atomic vapors, frequency comb spectroscopy and atom-surface interactions. The discovery of such coherent effects as coherent population trapping (CPT), electromagnetically induced transparency (EIT) and electromagnetically induced absorption (EIA) opened a new avenue for development in many fields of nonlinear optics. Investigations during the last decade have shown many related new results and approaches in nonlinear optics. These include nonlinear magneto-optical processes (NMOP) in the context of high precision magnetometry, quantum information storage and processing, magnetic resonance imaging and magnetic particle detection; the use of ultra-thin (nanometric length) atomic vapor cells in magneto-optical experiments, which show new peculiarities of both coherent effects and NMOP; the use of frequency and amplitude modulated laser beams for NMOP studies in atomic vapors with the aim of extending the range of ultra-precise magnetometers to stronger, particularly geomagnetic fields; application of the counter-propagating beam technique to reveal the Doppler free nonlinear Faraday rotation signals, as a spectroscopic tool and for applications; enhanced nonlinearity due to atomic coherence in multi-state systems; experimental study of EIT in solids; the use of the phase stabilized frequency domain combs of femtosecond laser pulses for velocity selective optical pumping of atomic hyperfine levels, as a direct frequency comb spectroscopy; time-domain nonlinear spectroscopy of dense atomic vapors; atom-surface interactions and laser induced adsorption and desorption of alkali atoms on the surface of solid materials for nanotechnology applications
In this thesis we study light-matter coherence phenomena related to the interaction of a coherent laser field and the so-called Λ-system, a three-level quantum system (e.g., an atom). We observe electromagnetically induced transparency (EIT), slow and stored light in hot rubidium vapor. For example, a 6 μs Gaussian pulse propagate at a velocity of ~1 km/s (to be compared with the normal velocity of 300 000 km/s). Dynamic changes of the control parameter allows us to slow down a pulse to a complete stop, store it for ~100 μs, and then release it. During the storage time, and also during the release process, some properties of the light pulse can be changed, e.g., frequency chirping of the pulse is obtained by means of Zeeman shifting the energy levels of the Λ-system. If, bichromatic continuous light fields are applied we observe overtone generation in the beating signal, and a narrow `dip' in overtone generation efficiency on two-photon resonance, narrower than the `coherent population trapping' transparency. The observed light-matter coherence phenomena are explained theoretically from first principles, using the Lindblad master equation, in conjunction with the Maxwell's equations. Furthermore, we analyze an optical delay-line based on EIT and show that there is in principle (besides decoherence) no fundamental limitation, but the usefulness today is scant. The combination of EIT and a photonic crystal cavity is inquired into, and we show that the quality value of a small resonator (area of 2.5λ×2.5λ with a missing central rod) can be enhanced by a factor of 500 due to the increased modal density close to two-photon resonance. Open system effects (decoherence effects) are thoroughly investigated using a coherence vector formalism, furthermore, a vector form of the Lindblad equation is derived. Specifically we find an open system channel that lead to slow light and gain.
This dissertation reports experimental studies of nonlinear optical effects manifested by electromagnetically induced transparency (EIT) in cold Rb atoms. The cold Rb atoms are confined in a magneto-optic trap (MOT) obtained with the standard laser cooling and trapping technique. Because of the near zero Doppler shift and a high phase density, the cold Rb sample is well suited for studies of atomic coherence and interference and related applications, and the experiments can be compared quantitatively with theoretical calculations. It is shown that with EIT induced in the multi-level Rb system by laser fields, the linear absorption is suppressed and the nonlinear susceptibility is enhanced, which enables studies of nonlinear optics in the cold atoms with slow photons and at low light intensities. Three independent experiments are described and the experimental results are presented. First, an experimental method that can produce simultaneously co-propagating slow and fast light pulses is discussed and the experimental demonstration is reported. Second, it is shown that in a three-level Rb system coupled by multi-color laser fields, the multi-channel two-photon Raman transitions can be manipulated by the relative phase and frequency of a control laser field. Third, a scheme for all-optical switching near single photon levels is developed. The scheme is based on the phase-dependent multi-photon interference in a coherently coupled four-level system. The phase dependent multi-photon interference is observed and switching of a single light pulse by a control pulse containing ∼20 photons is demonstrated. These experimental studies reveal new phenomena manifested by quantum coherence and interference in cold atoms, contribute to the advancement of fundamental quantum optics and nonlinear optics at ultra-low light intensities, and may lead to the development of new techniques to control quantum states of atoms and photons, which will be useful for applications in quantum measurements and quantum photonic devices.
Summary form only given. Electromagnetically induced transparency (EIT) has been the subject of many experimental and theoretical studies over recent years. Most recently, substantial experimental and theoretical work in this area has been focused on the use of EIT to give ultraslow group velocities for light in both ultracold atomic gas and hot atomic vapors. Much of this interest is based on the fact that slowing the group velocity of a laser pulse down to the speed of sound in the same material can produce strong coupling between acoustic waves and the electromagnetic field. It has been suggested that a giant nonlinearity obtained by this method might be utilized for efficient multi-wave mixing and quantum nondemolition measurements. Slow light might also allow a very efficient nonlinear interaction between laser pulses of extremely low (down to a single photon) energies. Here, we report the first direct observation of an ultraslow group velocity of light down to 45 m/s in a solid, well below the speed of sound in the medium. This group velocity is fundamentally limited only by the inhomogeneous broadening of the ground state transition. At low coupling beam intensities, the fraction of centers that are pumped into the "dark state" increases with coupling laser power, so that the observed group delay is increasing with coupling beam intensity. At higher intensities, power broadening reduces the sharpness of the dispersive feature and the observed group delay decreases.
Short pulses of narrow-line low-intensity dye-laser light nearly resonant with the Zeeman-split 2P21 resonance line (7948 \AA{}) of rubidium were observed to propagate through dilute rubidium vapor as slowly as (141)c. These slow pulse velocities showed that most of the energy in the propagating wave was contained by the vapor as coherent atomic excitation. The observed pulse velocities vp are in good agreement with the equation ${v}_{p}=\frac{d\ensuremath{\omega}}{\mathrm{dk}}$ for the group velocity obtained from linear-dispersion theory. Also, the experimental results are quantitatively explained by adiabatic following, in which the pseudomoments of the atoms remain aligned along the effective field of the laser light. The adiabatic-following model allows for a direct comparison of our results with the work on self-induced transparency. For high-intensity light, adiabatic following predicts a nonlinear pulse velocity and the possibility of observing self-steepening.