The cross-correlation method for temporal characterization is investigated using simulations of the twocolor above threshold ionization (ATI) on He induced by a vacuum ultraviolet (VUV) free-electron laser (FEL) in the presence of an infrared (IR) field. Non-linear dependencies of the sideband structure produced in the two-color ATI process are expressed as a function of IR laser intensity by considering the spatial distributions and temporal jitter of both lasers. The temporal properties of the FEL pulse can be characterized accurately using the cross-correlation method at a low IR laser intensity of ~3 \times 10^{10} W/cm2 but with low cross-correlation signals. When the dynamic range of sidebands is increased to high IR intensity, the accuracy of the cross-correlation method becomes crucially dependent on the actual nonlinear index. An approach of determining this index is proposed here to improve the accuracy of temporal characterizations.

This letter demonstrates an efficient high-power high-brightness 2-\mu m continuous-wave (CW) laser with double-end, diffusion-bonded Tm, Ho:YVO4 crystal cooled with liquid N2. The reduction in thermal stress in the composite Tm, Ho:YVO4 rod enabled the laser to achieve a laser output power of 23.4 W at 2.05 \mu m, which is 1.37 times higher than that of the non-composite Tm, Ho:YVO4 rod. The corresponding slope efficiency is 37.3% and the optical–optical conversion efficiency is 35.4%. The beam quality M2 factor is about 1.85 at 20 W output level with circularly symmetric beam spot.

Cu-doped borate glass co-doped with SnO2 nanoparticles is fabricated by melt quenching. The structure and morphology of the samples are examined by X-ray diffraction and field emission scanning electron microscopy. Up-conversion enhancement is observed in the photoluminescence (PL) and thermoluminescence (TL) intensities of the glass. PL emission spectra are identified in the blue and green regions, and a fourfold increase in emission intensity may be observed in the presence of embedded SnO2 nanoparticles. The glow curve is recorded at 215 oC, and fourfold increases in TL intensity are obtained by addition of 0.1 mol% SnO2 nanoparticles to the glass. Higher TL responses of the samples are observed in the energy range of 15–100 KeV. At energy levels greater than ~0.1 MeV, however, flat responses are obtained. The activation energy and frequency factor of the second-order kinetic reaction are calculated by the peak shape method.

Twin photon generation at various emission angles is observed. It is found that different kinds of twin photons using only one crystal under different conditions are obtained. Twin photon generation is more effective at smaller emission angles. Two-photon entanglement is also achieved after compensation.

Higher-band self-trapping and oscillation (rotation) of nonlinear quadruple beams in two-dimensional (2D) square photonic lattices are numerically demonstrated. Under appropriate conditions of nonlinearity, a quadruple-like beam can self-trap into localized modes that reside in the second Bragg reflection gap through single-site excitation. By changing the initial orientation of the incident quadruple beam related to the lattices, periodic oscillations of the localized quadruple mode may be obtained. The localized quadruple state becomes a rotating doubly charged optical vortex (DCV) during rotation and should undergo charge-flipping when the rotating direction is reversed.

Analysis of glass homogeneity using the attaching interferometric data model neglects body distribution. To improve analysis accuracy, we establish the three-dimensional gradient index (GRIN) model of glass index by analyzing fused silica homogeneity distribution in two perpendicular measurement directions. Using the GRIN model, a lithography projection lens with a numerical aperture of 0.75 is analyzed. Root mean square wavefront aberration deteriorates from 0.9 to 9.65 nm and then improves to 5.9 nm after clocking.

We present a digital holographic microscope wherein the sample is illuminated by structured light to enable the capture of additional object spatial frequencies. Reconstructed images with increased spatial resolution are obtained by separating and synthesizing bandwidths of different frequency regions in the Fourier domain. The theoretical analysis and experimental results are presented.

A compact multipass cell with low fringes and high thermal stability is described. This cell is formed by two twisted cylindrical mirrors. The optical parameters are determined based on the selection criteria, which include mirror filling efficiency, interference fringes, and pattern stability. With a pattern of 174 passes, this cell gives a 22-m path length in a volume of 0.55 L. The results of an absorption measurement of oxygen at 13 091.7 cm-1 show that the fringe noise is lower than 6.54×10-4. The maximum allowed temperature change to keep the beam from exiting is 33 K, which indicates high stability against thermal drift.

We present a method that accurately measures large optical surfaces before polishing using a laser tracker. Using the scanning mode of the laser tracker considerably improves measurement efficiency and minimizes the dominant errors caused by environmental change. We use this method to measure a \Phi 1.3-m aspheric mirror and obtain a measurement uncertainty of 0.72 \mu m (root mean square, RMS).

A piece-wise transition detection algorithm that performs displacement measurements for self-mixing sensors is developed. The algorithm can correctly detect self-mixing fringes at a low signal-to-noise ratio in the presence of disturbances without filtering. Displacement reconstructions by the phase unwrapping method based on this algorithm are experimentally validated, with laser subject to the moderate feedback regime.

Transient thermal impedance of GaN-based high-power white light emitting diodes (LEDs) is created using a thermal transient tester. An electro-thermal simulation shows that LED junction temperature (JT) rises to a very low degree under low duty cycle pulsed current. At the same JT, emission peaks are equivalent at pulsed and continuous currents. Moreover, the difference in peak wavelength when a LED is driven by pulsed and continuous currents initially decreases then increases with increasing pulse width. Thus, selecting an appropriate pulse width decreases errors in JT measurement.

The quantum cascade laser (QCL), a potential laser source for mid-infrared applications, has all of the advantages of a semiconductor laser, such as small volume and light weight, and is driven by electric power. However, the optical power of a single QCL is limited by serious self-heating effects. Therefore, beam combination technology is essential to achieve higher laser powers. In this letter, we demonstrate a simple beam combination scheme using two QCLs to extend the output peak power of the lasers to 2.3 W. A high beam combination efficiency of 89% and beam quality factor of less than 5 are also achieved.

Core-diameter adjustment, in analogy to doping management, is proposed in this letter for balancing thermal load and nonlinear effects. In this scheme, the core-to-cladding ratio increases with increasing core diameter along the direction of signal and pump propagation. An all-fiber-integrated Yb-doped master oscillator power amplification (MOPA) is successfully demonstrated. Two segments of fiber with different core diameters but same inner-cladding diameters and doping levels are spliced together and used as gain fibers in the last stage. A maximum average output power of 200 W at an overall slope efficiency of 71% is achieved from the MOPA with a pulse energy of 2 mJ and peak power as high as 80 kW.

A domain-level gradient-based routing (DLR) algorithm for heterogeneous optical networks with synchronous digital hierarchy and optical transport network domains is proposed and experimentally validated. This algorithm classifies domains into groups with incremental levels on the basis of domain-level partitioning, and guides paths level by level along a gradient on the basis of interdomain routing tree evolution. The proposed algorithm is implemented in the hierarchical path computation element-based control architecture for connection provisioning. Testbeds with commercial and emulated nodes are established to verify the feasibility and performance of the algorithm. Experimental and emulation results show that DLR effectively performs in terms of network blocking probability, real time characteristics, and scalability.

An optical bandpass filter (OBF) is an important element whose properties considerably influence the output performance of a single side band multicarrier source based on a re-circulating frequency shifter. The influence of the OBF in the loop on the output spectrum is theoretically analyzed. Numerical simulations and experiments are also carried out. Results show that the steepness and deepness of a nonflat-top filter influence the stability of the spectrum of an output multicarrier. To obtain multicarrier output with tone to noise ratio (TNR) >26 dB and error vector magnitude (EVM) <0.25, the steepness ratio of the filter should be greater than 0.75 and deepness should be larger than 0.99.

A high-power pulsed pump method is proposed to obtain a high-energy output with an improved signaltonoise ratio (SNR) during pulse amplification. Based on numerical analysis, the ytterbium-doped fiber amplifiers are compared under different pumping conditions. At the same signal gain, the output using the high-power pulsed pump shows great SNR improvement and reduced output signal distortion, compared with a continuous-wave pump and a low-power pulsed pump. By adjusting the pump parameters, the amplifier can achieve the optimal output SNR without sacrificing the signal gain. We believe that the high-power pulsed pump scheme is very suitable for the high-energy nanosecond pulse amplification, which has a high SNR requirement.

A doubly cladding single-mode fiber humidity sensor is fabricated by agarose. The sensor has an insertion loss of -0.08 dB and a power change of -17.83 dB. The responses of the sensor to a relative humidity (RH) range form 30% to 100% at a temperature range form 25 to 34 oC are validated. The experiments demonstrate that the absorbability of agarose gel to moisture decreases with increasing RH in measured gas. We propose a calibration method that uses lookup tables and construct a corresponding calibration matrix. Using the sensor, we conduct real-time monitoring of RH in fresh concrete during its hardening process.

We carry out in situ single-molecule measurements of the specific interaction between apolipoprotein A-I (apoA-I) and ATP binding cassette transporter A1 (ABCA1) on THP-1 cells. Single-molecule force spectroscopy shows that similar to normal apoA-I, the dysfunctional apoA-I from diabetes patients interacts with ABCA1 via two different binding sites on the cells. The strength of dysfunctional apoA-I binding to a high-capacity binding site is 26.5+(-)4.9 pN. The minor direct apoA-I/ABCA1 binding strength is 56.7+(-)4.1 pN. These results facilitate a pathological understanding of the mechanisms that underlie the specific interaction of apoA-I and ABCA1 at the single-molecule level.

Activating mutants in rat sarcoma (RAS) and B-rapid accelerated fibrosarcoma (BRAF) are found in at least a third of cases of human tumors and melanoma; hence, numerous therapeutic treatments target this pathway. In this letter, we study the adhesion force of RAS-coated beads with BRAF-coated beads, BRAF (A246P) mutant–coated beads, and GST-coated beads using optical tweezers. One full and two fractional RAS–BRAF specific binding modes are identified using the rupture force distribution. The koff (0) of the full binding mode in RAS–BRAF is 3.71×10-4/s and 1.16×10-4s-1 in RAS–BRAF (A246P), whereas the xb is around 3 \times 10-10 m in both groups.

A Yb-doped silica glass fiber laser with a core made by sol-gel method is reported. The maximum power of 1.14 W is obtained with a pump power of 5.46 W at a wavelength of 976 nm. The slope efficiency is 34%. The refractive index fluctuation across the core is below 5×10-4 at a doping level of Yb 0.15 mol%, A2O3 4.0 mol%, and P2O5 2.0 mol%. High background attenuation of 6 dB/m at 1 053 nm limites the slope efficiency and maximum output power.

Based on two-step coordinate transformation along the radial direction, an optical device with three functions is proposed. The proposed device functions as a transparent device, a vision-enabling internal cloak, and a movement-allowing external cloak. The general expressions of material parameters for the optical device are determined, and each function of the device is confirmed using full-wave simulation. The effect of material loss on device performance is also investigated. Future applications for the proposed device include antenna protection and military stealth.

The structural, morphological, optical, and nonlinear optical properties of a lead sulfide (PbS) thin film grown by chemical bath deposition (CBD) are investigated by X-ray diffraction (XRD), scanning electron microscope (SEM), ultraviolet-visible (UV-Vis), and open aperture Z-scan experiments. The band gap energy of the PbS nanocrystalline film is 1.82 eV, higher than that of bulk PbS at 300 K. The nonlinear absorption properties of the film are investigated using the open aperture Z-scan technique at 1064 nm and pulse durations of 4 ns and 65 ps. Intensity-dependent switching of the film from nonlinear absorption to saturable absorption is observed. The nonlinear absorption coefficient increases monotonically with increasing pulse duration from 65 ps to 4 ns.

We investigate the angular distribution and average kinetic energy of ions produced during ultrafast laser ablation (ULA) of a copper target in high vacuum. Laser produced plasma (LPP) is induced by irradiating the target with Ti:Sapphire laser pulses of ～50 fs and 800 nm at an angle of incidence of 45o. An ion probe is moved along a circular path around the ablation spot, thereby allowing characterization of the time-of-flight (TOF) of ions at different angles relative to the normal target. The angular distribution of the ion flux is well-described by an adiabatic and isentropic expansion model of a plume produced by solid-target laser ablation (LA). The angular width of the ion flux becomes narrower with increasing laser fluence. Moreover, the ion average kinetic energy is forward-peaked and shows a stronger dependence on the laser pulse fluence than on the ion flux. Such results can be ascribed to space charge effects that occur during the early stages of LPP formation.

We present an analysis of the impact of afluctuating-loss channel on free-space quantum key distribution (QKD). Considering the characteristics of the fluctuating-loss channel, a scintillation discriminator that acts according to the information of instant channel loss is proposed to help improve the performance of a free-space QKD system, which suffers from the influence of atmospheric turbulence. Theoretical and numerical results show that this discriminator is a useful tool for increasing secure key rates, especially for long-range free-space QKD.

We discuss the efficiency of an electro-optic (EO) polymer sensor with interdigitated coplanar electrodes. The developed EO sensor is used to detect terahertz radiation via EO sampling. Results show that the sensor improves more significantly detection sensitivity than does a sensor with sandwich configurations.