Negative refractive index in a Doppler broadened three-level Λ-type atomic medium

We have achieved a negative refractive index with significantly reduced absorption in a three-level Λ-type atomic gas medium under Doppler broadening. It shows that the conditions for obtaining negative refractive index in the presence of Doppler broadening are very different from those of Doppler broadening absent. In particular, in order to obtain negative refractive index in the case of Doppler broadening the coupling laser intensity must be approximately ten times greater than that when the Doppler broadening is ignored. Meanwhile, the frequency band of negative refractive index with Doppler broadening is significantly expanded (about a hundred times) compared to that without Doppler broadening, however, the amplitude of negative refractive index decreases with increasing temperature (or Doppler width). Even in some cases as temperature (Doppler width) increases, the left-handedness of the material can disappear. In addition, we also show that the amplitude and the frequency band of negative refractive index can be changed by adjusting the intensity and the frequency of coupling laser. Our theoretical investigation can be useful for selection of laser parameters under different temperature conditions to achieve negative refractive index in experimental implementation.

Characteristics of Collimators Based on the Large-Mode-Area CMCF for Coupling Laser Beam

A new collimator based on a homemade concentric multilayer-core fiber (CMCF) is proposed and experimentally demonstrated. This collimator was fabricated using a tail fiber with large mode area and single-mode operation. By exploiting the optical transmission matrix, the propagation characteristic and coupling mechanism of this CMCF-based collimator was introduced meticulously. The coupling losses of the laser beam using this collimator in the off-axis, angular, and axial deviations were analyzed separately. In order to determine the relationship between the geometric redundancy of this collimator and the effective mode field area of the tail fiber, the corresponding mathematical model was established. Through model calculation and experiment measurement, the coupling properties of the collimator were improved effectively. Compared with the common SMF-based collimator, the declination redundancy of the CMCF-based one improved by 20%, which could make the coupling of the optical fiber collimator easier. Therefore, this collimator has potential application value in the laser diode coupling unit and high-speed optical communication system.

Optical lattice with spin-dependent sub-wavelength barriers

We analyze a tripod atom light coupling scheme characterized by two dark states playing the role of quasi-spin states. It is demonstrated that by properly configuring the coupling laser fields, one can create a lattice with spin-dependent sub-wavelength barriers. This allows to flexibly alter the atomic motion ranging from atomic dynamics in the effective brick-wall type lattice to free motion of atoms in one dark state and a tight binding lattice with a twice smaller periodicity for atoms in the other dark state. Between the two regimes, the spectrum undergoes significant changes controlled by the laser fields. The tripod lattice can be produced using current experimental techniques. The use of the tripod scheme to create a lattice of degenerate dark states opens new possibilities for spin ordering and symmetry breaking.

OPTICAL BISTABILITY IN A DEGENERATE TWO-LEVEL EIT MEDIUM UNDER THE INFLUENCE OF AN EXTERNAL MAGNETIC FIELD: AN ANALYTICAL APPROACH

We investigate the behavior of optical bistability in a degenerate two-level atomic medium using an external magnetic field to separate the lower level into two distinct levels that both connect to an upper level by the probe and coupling laser fields. Based on analytical solutions, the absorption spectrum and behavior of optical bistability in an electromagnetically induced transparency regime under an external magnetic field are investigated. By controlling the external magnetic field, we find that the appearance and disappearance of the optical bistability can be easily controlled according to the strength of the magnetic field in the transparent window domain. Furthermore, the effects of the intensity of the coupling laser field and the parameters of the system on the behavior of optical bistability are also considered. The proposed model is useful for applications in all-optical switches and magneto-optic storage devices.

The multi-photon induced Fano effect

The ordinary Fano effect occurs in many-electron atoms and requires an autoionizing state. With such a state, photo-ionization may proceed via pathways that interfere, and the characteristic asymmetric resonance structures appear in the continuum. Here we demonstrate that Fano structure may also be induced without need of auto-ionization, by dressing the continuum with an ordinary bound state in any atom by a coupling laser. Using multi-photon processes gives complete, ultra-fast control over the interference. We show that a line-shape index q near unity (maximum asymmetry) may be produced in hydrogenic silicon donors with a relatively weak beam. Since the Fano lineshape has both constructive and destructive interference, the laser control opens the possibility of state-selective detection with enhancement on one side of resonance and invisibility on the other. We discuss a variety of atomic and molecular spectroscopies, and in the case of silicon donors we provide a calculation for a qubit readout application.

High-speed, multicolor, structured illumination microscopy using a hexagonal single mode fiber array

Structured Illumination Microscopy (SIM) is a widely used imaging technique that doubles the effective resolution of widefield microscopes. Most current implementations rely on diffractive elements, either gratings or programmable devices, to generate structured light patterns in the sample. These can be limited by spectral efficiency, speed, or both. Here we introduce the concept of fiber SIM which allows for camera frame rate limited pattern generation and manipulation over a broad wavelength range. Illumination patterns are generated by coupling laser beams into radially opposite pairs of fibers in a hexagonal single mode fiber array where the exit beams are relayed to the microscope objective’s back focal plane. The phase stepping and rotation of the illumination patterns are controlled by fast electro-optic devices. We achieved a rate of 111 SIM frames per second and imaged with excitation patterns generated by both 488 nm and 532 nm lasers.

Observation of an Electromagnetically Induced Grating in Cold 85Rb Atoms

Electromagnetically induced grating (EIG) is extensively investigated as an artificial periodic structure in recent years owed to its simple reconfiguration and flexible adjustability. We report the experimental observation of EIG in cold rubidium atoms. The coupling and probe lasers are corresponding to the 5S1/2−5P1/2 and 5S1/2−5P3/2 transitions of a V-type electromagnetically induced transparency (EIT) configuration, respectively. A clear spatial intensity distribution of the probe laser with distinguished third-order diffraction pattern is recorded to character the EIG. The influence of the pertinent experimental parameters, such as coupling laser intensity and two-photon detuning on the diffraction pattern is investigated in detail. This is the first observation in visual form of the EIG in cold rubidium atoms. These results may potentially provide a nondestructive method to image cold atoms and pave the way for investigating non-Hermitian physics and the control of light dynamics.

Precise Measurement of Hyperfine Structure of Cesium 7S1/2 Excited State

We present a precise measurement of the hyperfine structure of cesium 7 S 1 / 2 excited state by employing electromagnetically induced spectroscopy (EIS) with a cesium three-level cascade ( 6 S 1 / 2 − 6 P 3 / 2 − 7 S 1 / 2 ) atom in a room temperature vapor cell. A probe laser, λ p = 852 nm, was coupled to a transition | 6 S 1 / 2 ⟩ → | 6 P 3 / 2 ⟩ , related frequency locked to the resonance hyperfine transition of | 6 S 1 / 2 ⟩ → | 6 P 3 / 2 ⟩ with a Fabry–Perot (FP) cavity and an electro-optic modulator (EOM). A coupling laser, λ c = 1470 nm, drove the | 6 P 3 / 2 ⟩ → | 7 S 1 / 2 ⟩ transition with the frequency scanned over the | 6 P 3 / 2 ⟩ → | 7 S 1 / 2 ⟩ transition line. The hyperfine level interval was extracted to be 2183.61 ± 0.50 MHz by analyzing EIS spectroscopy. The optical–optical double-resonance (OODR) spectroscopy is also presented for comparison, with the corresponding value of the hyperfine level interval being 2183.48 MHz ± 0.04 MHz, and the measured hyperfine splitting of excited 7 S 1 / 2 state is shown to be in excellent agreement with the previous work.