Storage of Airy wavepackets based on electromagnetically induced transparency.

The research of Airy beams has attained much attention due to their unique characteristics. Coherent control of Airy beams is important for further light beam manipulation and information processing. In this paper, we experimentally investigate the storage and retrieval of 2D Airy wavepackets in a solid-state medium driven by electromagnetically induced transparency (EIT). The transverse profile of the weak probe pulse is modulated by Airy wavepackets. Under EIT condition, the probe Airy wavepackets are stored into the experimental medium by manipulating the intensity of the control field, and later retrieved by the opposite process. The retrieved Airy wavepackets keep a high similarity compared with those before the storage. Furthermore, the self-healing property of the retrieved Airy wavepackets is investigated. This storage of Airy wavepackets develops the control method of Airy beams, which will be useful in further applications.

Observation of the fluorescence spectrum for a driven cascade model system in atomic beam.

We experimentally study the resonance fluorescence from an excited two-level atom when the atomic upper level is coupled by a nonresonant field to a higher-lying state in a rubidium atomic beam. The heights, widths and positions of the fluorescence peaks can be controlled by modifying the detuning of the auxiliary field. We explain the observed spectrum with the transition properties of the dressed states generated by the coupling of the two laser fields. We also attribute the line narrowing to the effects of Spontaneously Generated Coherence between the close-lying levels in the dressed state picture generated by the auxiliary field. And the corresponding spectrum can be viewed as the evidence of Spontaneously Generated Coherence. The experimental results agree well with calculations based on the density-matrix equations.

Intensity-dependent effects on four-wave mixing based on electromagnetically induced transparency.

We extend the study on a four-wave mixing (FWM) scheme of contiuous-wave lasers in a hot rubidium vapor when the probe and coupling fields work in the electromagnetically induced transparency (EIT) regime while the pump and signal fields work in the two-photon Raman regime. Our experimental results show that the generated signal field is well contained in an EIT dip of the incident probe field as a result of efficient FWM. We find, in particular, that an optimal FWM process can only be attained when the coupling and pump fields are well matched in intensity. If the probe intensity is far beyond the EIT condition, however, the nonlinear efficiency of energy transfer from the probe field to the signal field will be greatly reduced.

Coherence generation and population transfer by stimulated Raman adiabatic passage and π pulse in a four-level ladder system.

We propose a new scheme for achieving the complete population transfer and the optimal coherence generation between the ground state and the Rydberg state in a four-level ladder system by combining the STIRAP or fractional STIRAP technique and the π pulse technique. We consider, in particular, two different situations where spontaneous emission from the two highest states are neglected or not. Our numerical calculations show that the time width and the delay time of the π pulse are two critical parameters for attaining the maximal population transfer and coherence generation in this scheme.

Controlled light-pulse propagation via dynamically induced double photonic band gaps.

We analyze the optical response of a standing-wave driven four-level atomic system with double dark resonances. Fully developed double photonic band gaps arise as a result of periodically modulated refractive index within the two electromagnetically induced transparency widows. We anticipate that the dynamically induced band gaps can be used to coherently control the propagation of light-pulses with different center frequencies and may have applications in all-optical switching and routing for quantum information networks.

Efficient frequency conversion induced by quantum constructive interference.

We demonstrate in experiment an efficient cw four-wave mixing scheme with maximal intensity conversion efficiency up to 73% in a double-Λ system of hot rubidium atoms. Relevant theoretical analysis shows that this high conversion efficiency benefits greatly from the constructive interference between two four-wave mixing channels, characterized by two different space-dependent phases.

Dual-channel all-optical wavelength conversion switching by four-wave mixing.

We report an experimental demonstration of dual-channel all-optical wavelength conversion switching in hot Rb vapor. In a four-level atomic system, a coupling field and a pump field interact with both (87)Rb and (85)Rb isotopes simultaneously and facilitate the generation of two nonlinear signals when the probe field is applied to the corresponding transition. Each nonlinear signal is switched on and off separately by the pump field at different frequencies based on four-wave mixing and isotope shifts.

Three-channel all-optical routing in a Pr3+:Y2SiO5 crystal.

We experimentally demonstrate a three-channel all-optical routing based on light storage in a Pr(3+):Y(2)SiO(5) crystal. By switching off the control field under the condition of electromagnetically induced transparency, the optical information of the probe light pulse can be stored in the crystal. When three retrieve control fields are switched on in the release process, the stored optical information from one light channel can be transferred (or distributed) into three different light channels. Also we show that this all-optical routing can be time-delayed. Such a multichannel all-optical routing in solids may have practical applications in quantum information and all-optical network.

Slowing and storage of double light pulses in a Pr3+:Y2SiO5 crystal.

We experimentally demonstrate the slowing and storage of double light pulses in a Pr(3+):Y(2)SiO(5) crystal using a multilevel-tripod scheme. Owing to double dark-state polaritons of the tripod-type system, two signal pulses can be simultaneously slowed. Also, we realize the simultaneous storage (and retrieval) of double light pulses by switching off (and back on) the control field. Slowing and storage of double light pulses in solids may have practical applications in quantum information and quantum networks.

Transmission and reflection of electromagnetically induced absorption grating in homogeneous atomic media.

We theoretically study the transmission and reflection of the probe travelling wave in an electromagnetically induced absorption grating (EIG), which is created in a three-level Lambda-type atomic system when the coupling field is a standing wave. Using the system, we show that a photonic stop band can exist on one side away from the resonance point in ultracold atomic gas, while there is an enhanced absorption at resonance and small reflection around it in the thermal atomic gas. Because our method can deal with such two cases, it is helpful to further understand the effects of the Doppler effect on atomic coherence and interference.

Slow light based on coherent hole-burning in a Doppler broadened three-level Lambda-type atomic system.

We show theoretically that the propagation of light can be slowed down considerably using the method of coherent hole-burning in a Doppler broadened three-level lambda-type atomic medium without the Doppler-free configurations. The reduction of group velocity of light pulse is achieved by the application of a saturating beam and a strong coupling beam which produce a narrow spectral hole-burning at resonance. We can obtain a larger group index than that using the method of saturation absorption spectroscopy in Doppler-broadened two-level atomic systems.

SHG in doped GaSe:In crystals.

Optical transmission range and phase matching (PM) conditions for second harmonic generation (SHG) of Er3+:YSGG and CO2 laser in indium doped GaSe:In(0.1, 1.23, 2.32 mass%) are studied in comparison with these in pure and sulfur doped GaSe:S(0.09, 0.5, 2.2, 3 mass%) crystals. No changes in transparency curve are found in GaSe crystals up to 2.32 mass% indium content, but as small change as 0.18 degrees in PM angle for 2.79 microm Er3+:YSGG laser SHG and approximately 0.06 degrees for 9.58 microm CO2 laser emission line SHG are detected. PM properties of the crystals are evaluated as a function of temperature over the range from -165 to 230 degrees C. The value of dtheta/dT, the change in PM angle with variation of temperature, is found to be very small for GaSe:In crystals. While for SHG of Er3+:YSGG laser, dtheta/dT =22"/1 degrees C only, it is as small as -4.9"/1 degrees C for that of CO2 laser radiation. Linear variation of PM angle with temperature increasing is an indicator of absence of crystals structure transformation within temperature range from -165 to 230 degrees C. Thus, application of GaSe:In solid solutions in high average power nonlinear optical systems seems to be prospective.

SHG phase matching in GaSe and mixed GaSe1(1-x)S(x), x < or =0.412, crystals at room temperature.

The optical properties of p-type GaSe and mixed GaSe(1-x)S(x), x=0.04, 0.023, 0.090, 0.133, 0.175, 0.216, 0.256, 0.362, 0.369, and 0.412, crystals were studied to reveal the potentials for phase matching and frequency conversion. Comparative experiment on Er3+:YSGG and CO2 laser SHG at identical experimental conditions is carried out at room temperature. Any change in polytype structure of GaSe1(1-x)S(x) was not found.

Construction of refractive-index profile of Ag+-Na+ ion-exchange channel waveguide by two-dimensional inverse matrix method.

The refractive-index profile of ion-exchange channel waveguide is reconstructed by near-field measurement combined with two-dimensional inverse matrix method, which can avoid the problems brought by multimeasurements and iteration smoothing in the process. The method used here has the advantages of convenient operation and accurate results for the characteristics of the asymmetric channel waveguide. It can be also applied to the refractive-index profile measurements of graded index fibers, polarization maintaining fibers, and single-mode planar waveguides.

Observation of CARS signal via maximal atomic coherence prepared by F-STIRAP in a three-level atomic system.

We control the atomic coherence and the population transfer among Rb hyperfine atomic levels by the fractional stimulated Raman adiabatic passage (F-STIRAP) in a L-type configuration, and verify the theoretical predictions. Applying this technique, we are able to prepare the atoms with maximal coherence to enhance coherent anti-Stokes Raman scattering (CARS) signal. In our experiment by scanning the frequency of one laser from 794.9839 nm to 794.9844 nm with the 794.9698 nm laser frequency fixed to generate a maximum of the CARS signal we are able to obtain the energy level diagram of the sample.

Optical information transfer between two light channels in a Pr(3+):Y(2)SiO(5)crystal.

We experimentally demonstrate light storage and release in a four-level double-lambda atomic system of a Pr (3+):Y(2)SiO(5) crystal. Based on the technique of light storage, we realize optical information transfer between two light channels. The coherent optical information of a probe pulse stored in the crystal can be selectively released into two different light channels by varying the frequency and propagation direction of the switch-on control field.

Wide-tunable, high-energy AgGaS(2) optical parametric oscillator.

Nanosecond AgGaS(2) type-I singly resonant optical parametric oscillator pumped by a Q-switched 1.064 mum Nd:YAG laser is demonstrated experimentally. Continuously tunable 2.6-5.3 mum radiation and output pulse energy up to 0.6 mJ at 4 mum are achieved in a single-stage conversion process. The analysis of pump threshold is investigated both theoretically and experimentally.

Image routing via atomic spin coherence.

Coherent storage of optical image in a coherently-driven medium is a promising method with possible applications in many fields. In this work, we experimentally report a controllable spatial-frequency routing of image via atomic spin coherence in a solid-state medium driven by electromagnetically induced transparency (EIT). Under the EIT-based light-storage regime, a transverse spatial image carried by the probe field is stored into atomic spin coherence. By manipulating the frequency and spatial propagation direction of the read control field, the stored image is transferred into a new spatial-frequency channel. When two read control fields are used to retrieve the stored information, the image information is converted into a superposition of two spatial-frequency modes. Through this technique, the image is manipulated coherently and all-optically in a controlled fashion.

Investigation of spontaneously generated coherence in dressed states of (85)Rb atoms.

We investigate the effects of spontaneously generated coherence (SGC) on the electromagnetically induced transparency features in a four-level Lambda-type system. We show that double-transparency windows and a controllable narrow absorption peak can be obtained with the presence of SGC. We present an equivalent system without the rigorous requirement of close-lying levels to observe the phenomena. We also experimentally demonstrate the corresponding features in a rubidium atomic beam.

Coherence transfer between atomic ground states by the technique of stimulated Raman adiabatic passage.

We experimentally and theoretically demonstrate that the atomic coherence can be completely transferred or arbitrarily contributed among the different levels in a four-level atomic (tripod) scheme by a group of coupled pulse sequences. This technique can be applied to the information conversion in slow-light storage, quantum logical gates, and so on, which is based on the atomic coherence effect.