We demonstrate a magneto-optical trap (MOT) with counter-propagating two-color cooling beams in a cesium 6S1/2 6P3/2 8S1/2 (852.3+794.6 nm) atomic system. Based on the conventional MOT due entirely to the 852.3 nm cooling laser’s scattering forces, we replace one of the six 852.3 nm cooling beams with a 794.6 nm cooling beam. Our two-color MOT can efficiently cool and trap atoms from the red to blue detuning sides of two-photon resonance without pre-cooling. The technique is promising for the direct generation of correlated photon pairs in a two-color MOT based on diamond-configuration four-wave mixing.

The threshold of a laser-induced breakdown of air is determined experimentally and theoretically. We find that the ionization of air has two steps: the first step is a multi-photon ionization process, which provides enough “seed electrons” to initiate the next step, and the second one is predominated by cascade ionization, which continues to produce free electrons geometrically until the critical free-electron density for breakdown is reached. So a two-step model based on the Morgan ionization model is established to describe the breakdown process. It is found that the time node dividing the two steps is about 9.8 ns in atmospheric air, and the threshold derived from the two-step model proposed here is more consistent with the experimental results than traditional ionization model.

Ghost imaging and diffraction, inspired by the Hanbury Brown and Twiss effect, have potential in both classical and quantum optics regimes on account of their nonlocal characteristics and subwavelength resolution capability, and therefore have aroused particular interest. By extending the correspondence imaging scheme, we utilize the positive and negative intensity correlations in diffraction and perform subwavelength diffraction with pseudo-thermal light. In the experiment, a subwavelength (λ/2) resolution and a better signal-to-noise ratio (10.3% improvement) are simultaneously achieved. The scheme can be utilized as a complement to the existing ghost imaging scheme to improve image quality.

In this Letter, a simple and passively mode-locking Yb-doped all fiber laser using a nonlinear polarization rotation technique operating under dissipative soliton (DS) or dissipative soliton resonance (DSR) conditions is proposed. Furthermore, using a combination of a bandpass filter and a Loyt filter, tunable single-wavelength or dual-wavelength operation under two different conditions is realized, respectively. The tunable single-wavelength DS laser has a 5 nm tuning range from 1029 to 1034 nm with a pulse width of 110 ps. The tunable single-wavelength DSR operation laser has a range of 4 nm. In-depth research on the mechanism of the conversion between DS and DSR is carried out. Particularly, under dual-wavelength DSR operation, the obtained step-like pulses consist of two rectangular pulses with different energies. This work could help give a deeper insight into normal dispersion pulses.

We demonstrate an efficiency-enhanced picosecond (ps) mid-infrared radiation via optical parametric downconversion. Based on a cascaded periodically poled MgO-doped stoichiometric lithium tantalate crystal (MgO:sPPLT), a tandem optical parametric oscillation-optical parametric amplification (OPO-OPA) process is achieved. Compared with a single OPO process, the conversion efficiency obtains an enhancement of 71%.

Using a lithium niobate (LN) material, we propose a broadband polarization beam splitter (PBS) with high efficiency by employing a negative refractive photonic crystal (PhC) wedge slab with an angle of 60°. It can split the incident light into two parts at about 90° with TE and TM polarizations. The transmissions of polarized light for an LN-based PBS are more than 80% with a broad angle and wavelength bandwidth of 8° and 70 nm at 1.55 μm, while with a Si-based PhC, no PBS with high efficiency can be realized for the relatively lower transmission of TM output light.

Temperature-dependent photoluminescence (PL) of phase-separated InGaN quantum wells is investigated over a broader excitation power range. With increasing excitation power from 0.5 μW to 50 mW, the In-rich quasi-quantum dot (QD)-related PL peak disappears at about 3 mW, while temperature behavior of the InGaN matrix-related PL peak energy (linewidth) gradually evolves from a strong “S-shaped” (“W-shaped”) temperature dependence into a weak “S-shaped” (an approximately “V-shaped”), until becoming an inverted “V-shaped” (a monotonically increasing) temperature dependence. This indicates that, with increasing excitation power, the carrier localization effect is gradually reduced and the QD-related transition is submerged by the significantly enhanced InGaN matrix-related transition, while the carrier thermalization effect gradually increases to become predominant at high excitation powers.

A stable and broadband microwave photonic phase shifter based on the combined use of a linear chirped fiber Bragg grating and optical single-sideband (OSSB) modulation is proposed and experimentally demonstrated. The quality of the radio frequency (RF) signal is improved by the spectral separation delay processing. The theoretical fundamentals of the scheme are explained and the phase shift can be controlled linearly by the wavelength of the light source. In the experiment, a full 360° phase shift with a 10 GHz bandwidth can be achieved and tuned dynamically, continuously, and stably.

We demonstrate flexible multidimensional modulation formats, polarization multiplexed k-symbol check quadrature phase shift keying (PM-kSC-QPSK), based on PM-QPSK constellations for elastic optical networks. The experimental results show a significant optical signal noise ratio (OSNR) tolerance improvement for PM-2SC-QPSK and PM-4SC-QPSK over PM-QPSK in both back-to-back and 500 km transmission scenarios at the expense of spectral efficiency reduction. This flexible modulation method can be used in elastic optical networks to provide a trade-off between the spectral efficiency and OSNR tolerance.

The number of layers and the resolution of liquid crystal displays (LCDs) limit the reconstruction fidelity of near-eye light field displays based on multilayer LCDs. Because the eye’s resolution capability is different for central vision and peripheral vision, the fidelity can be improved by setting different weights for different areas. First we employ the eye’s modulation transfer function (MTF) to acquire the limiting resolution angle. Then, due to the inverse relationship between the limiting angle and the weight values, the weighted function related to retinal eccentricity is calculated. In combination with the linear least-squares algorithm, the peak signal-to-noise ratio (PSNR) of the reconstructed scene is raised. The simulation results indicate that the weighted optimization algorithm can improve the image fidelity and reconstruction accuracy.

The fluorescence of graphene oxide quantum dots (GOQDs) that are infiltrated into porous silicon (PSi) is investigated. By dropping activated GOQDs solution onto silanized PSi samples, GOQDs are successfully infiltrated into a PSi device. The results indicate that the intensity of the fluorescence of the GOQD-infiltrated multilayer with a high reflection band located at its fluorescence spectra scope is approximately double that of the single layer sample. This indicates that the multilayer GOQD-infiltrated PSi substrate is a suitable material for the preparation of sensitive photoluminescence biosensors.

Based on the geometrical optics approximation, we analyze the effects of non-Kolmogorov turbulence on the spiral spectrum of the orbital angular momentum (OAM) of Airy–Schell beams. Our numerical results of Airy–Schell beams on the horizontal path show that the beam spreading due to diffraction is smaller for shorter wavelengths, a smaller OAM quantum number, a larger radius of the main ring, and a higher arbitrary transverse scale in weak turbulence. The oscillation frequency of the mode probability density of Airy–Schell beams in the radial direction is much lower than that of Hankel–Bessel beams. The mode probability densities of Airy–Schell and Hankel–Bessel beams are remarkably dependent on the wavelength and OAM quantum number. In order to improve the mode probability density, Airy–Schell beams with shorter wavelengths and lower OAM quantum numbers may be the better choice, which is diametrically opposite to Hankel–Bessel beams. Our research provides a reasonable basis for selecting light sources and precise tracking.

Molybdenum (Mo) thin films, most commonly used as electrical back contacts in Cu(In,Ga)Se2 (CIGS) solar cells, are deposited by rf and dc magnetron sputtering in identical systems to study the discrepancy and growth mechanisms of the two sputtering techniques. The results reveal that though different techniques generally deposit films with different characteristic properties, Mo films with similar structural and physical properties can be obtained at respective suitable deposition conditions. Highly adhesive and conductive Mo films on soda lime glass are further optimized, and the as-fabricated solar cells reach efficiencies as high as 9.4% and 9.1% without an antireflective layer.

We experimentally demonstrate the application of MoSe2 thin film as a nonlinear medium and stabilizer to generate a multi-wavelength erbium-doped fiber laser. The cooperation of a photonic crystal fiber and a polarization-dependent isolator induces unstable multi-wavelength oscillations based on the nonlinear polarization rotation effect. A MoSe2 thin film is further incorporated into the cavity to achieve a stable multi-wavelength. The laser generates 7 lasings with a constant spacing of 0.47 nm at a pump power of 250 mW. The multi-wavelength erbium-doped fiber laser is stable with power fluctuations of less than 5 dB over 30 min.

We report the measurements of Brillouin gain coefficients in FC-770, FC-40, FC-43, and FC-70 using a Brillouin oscillator and amplifier system. In contrast to the traditional way, the novel method provides direct measurements of these coefficients with the medium electro-strictive coefficient or with the phonon lifetime absent. Additionally, the Brillouin gain coefficient of FC-70 in this experiment is different from the theoretical work.

The aim of this work is to provide an analytical method based on experimental measurements in order to obtain the prismatic film deformation for different curvatures of hollow cylindrical prismatic light guides (CPLGs). To conform to cylindrical guides it is necessary to bend the film to guide the light; changes induced by curving the film give rise to deformation shifts. Light losses affected by deformation are experimentally evaluated and numerically analyzed. The effect of deformation on prism angle is especially increased for CPLGs of curvatures higher than 20 m 1. An experimental method for the accurate transmittance of measurements related to bending is presented.

This Letter presents an optical design method based on the Seidel aberration theory for dynamic refocus systems. The function of a dynamic refocus system is to increase the amount of return photons when a pulsed laser travels over an extended height range. In this study, the dynamic refocus system is a short focal image system. The aberrations of the dynamic refocus system are calculated individually. Aplanatic lenses are used to eliminate the main spherical aberration. A field lens is used to change the stop position in order to eliminate comas and astigmatism. The effectiveness of the initial design results are confirmed, and the designed dynamic refocus objective with an aperture of F-number 0.98 and a focal length of 14.325 mm is achieved. The total motion of the dynamic refocus mirror is approximately 216 μm at heights that ranged from 8 to 18 km. The optimum result shows that the dynamic refocus system is an ideal optical image system at each conjugating height with 10 km sample thicknesses.

We propose an ultra-broadband and fabrication-tolerant polarization rotator-splitter (PRS) based on a waveguide with an L-shaped cross section and a Y-junction. The proposed PRS is based on the 220 nm silicon-on-insulator platform, and it shows less than 0.27 dB insertion losses and larger than 14 dB polarization extinction ratios over a wavelength range from 1200 to 1700 nm. To the best of our knowledge, the PRS working in the whole optical communication band is proposed for the first time.

We experimentally investigate the effects of the surface roughness of gold thin films on the properties of surface plasmon resonance. By annealing at different temperatures, film samples with different surface morphologies are obtained. Specifically, due to the diffusion of the gold atoms towards the films’ surface, the surface root-mean-square roughness decreases with the increasing annealing temperature. Then, we measure the surface plasmon resonance of the samples. The results show that the resonance angle of the surface plasmon resonance is sensitive to the root-mean-square roughness, and it gradually decreases by reducing the surface root-mean-square roughness.

This Letter introduces a trigger-controlled Geiger-mode avalanche photodiode (GM-APD). A hierarchical look-back-upon tree recurrence method is given to predict the performance of trigger-controlled GM-APDs under different trigger-count upper limits. In addition, the normalized detection probability is defined to evaluate the detection performance of trigger-controlled GM-APDs in typical weak optical signal detection (impulse noise and continuous noise situations). Theoretical analyses show that the trigger-controlled GM-APD improves the detection performance of GM-APDs in weak optical signal detection via the optimization of the trigger-count upper limit, compared with single-trigger and multi-trigger GM-APDs.

The electroluminescent characteristics of blue organic light-emitting diodes (BOLEDs) fabricated with doped charge carrier transport layers are analyzed. The fluorescent blue dopant BCzVBi is doped in an emissive layer, hole transport layer (HTL) and electron transport layer (ETL), respectively, to optimize the probability of exciton generation in the BOLEDs. The luminance and luminous efficiency of BOLEDs made with BCzVBi-doped HTL and ETL increase by 22% and 17% from 11,683 cd/m2 at 8.5 V and 6.08 cd/A at 4.0 V to 14,264 cd/m2 at 8.5 V and 7.13 cd/A at 4.0 V while CIE coordinates of (0.15, 0.15) of both types of BOLEDs remained unchanged. The electron mobility of BCzVBi is estimated to be 1.02×10 5 cm2/Vs by TOF.