Registration of image feature points using differential evolution

This paper introduces a robust global nonlinear optimizer—differential evolution(DE),which is a simple evolution algorithm to search for an optimal transformation that makes the best alignment of two sets of feature points.To map the problem of matching into the framework of DE,the objective function is proportional to the registration error which is measured by Hausdorff distance,while the parameters of transformation are encoded in floating-point as the functional variables.Three termination criteria are proposed for DE.A simulation of 2-dimensional point sets and a similarity transformation are presented to compare the robustness and convergence properties of DE with genetic algorithm’s (GA).And the registration of an object and its contour model have been demonstrated by using of DE to natural images.

Imaging Internuclear Separation of H^＋2 in Configuration Space： Reduced Dimensionality Model

We present a method for obtaining the internuclear separation of diatomic molecular ion H^＋2 irradiated by attosecond-duration laser pulse, by computing the probability flux of wavefunction pattern of photoelectron in configuration space. In contrast to earlier means of attosecond-scale time-gating or taking ratio of image data in momentum space, our alternative is characterized by experimental feasibility. The numerical results of a reduceddimensionality model on hydrogenic ions corroborated our method are obtained and can be generalized to more complex molecular systems for inferring bond length or bond angle information.

Research and Remote Implementation of Program Updation of DSP System by Ethernet

Based on the structure and bootloader principle of DSP system, a method for the remote updation, debugging and self-loading of DSP system is developed by Ethernet. Hardware circuit and DM9000 driven program are presented and TCP/IP protocol is embedded into DSP. Through the re-mapping of external memory address, it is easy to implement the load of program section selectively and DSP self-boot. The experimental results show that the problem of high cost in system maintenance by conventional field debugging by emulator and the limitation in chip-level boot are resolved.

Profound Carrier-Envelope-Phase-Difference Effect on Photoionization Rate： Numerical Results on a Model Hydrogen Atom

We discuss importance of the carrier-envelope phase difference （CEPD） effect which would be encountered in real short laser pulses. By numerically simulating photoionization rate of a one-dimensional atomic hydrogen model irradiated by short light pulses, a profound CEPD effect on the photoionization rate is revealed, which might shed light on laser-atom interaction investigation. We also suggest that photoionization process might be exploited in return to measure CEPD values.

Generation of multi-freedom controllable helical beam through high-order Bessel beams[Invited]

In this Letter,we propose a scheme to generate helical optical fields with multi-freedom controllable features.High-quality helical lobes with adjustable radii,chirality,and lobe numbers can be generated by tuning the phase term of two paired highorder Bessel beams.Furthermore,the pitch of the helical beam can be controlled by combining another rotational phase term.The validity of our scheme is demonstrated in both simulations and experiments.Our scheme is promising to facilitate the rapid fabrication of helical structures with diverse parameters,which are critical in various applications,such as optical metamaterials,biology,and particle transport.

All-fiber few-mode erbium-doped fiber amplifier supporting six spatial modes

Using the few-mode erbium-doped fiber(FM-EDF)with a simple two-layer erbium-doped structure,we demonstrate an all-fiber FM-EDF amplifier.The gain equalization among the six spatial modes supported by the FM-EDF is achieved when only the pump in the fundamental mode(LP01)is applied.When the signals in six spatial modes are simultaneously amplified,the average modal gain is about 15 dB,and differential modal gain is about 2.5 dB for the signal at 1550 nm.

Two-photon polymerization of femtosecond high-order Bessel beams with aberration correction

In the femtosecond two-photon polymerization(2PP)experimental system,optical aberrations degrade the fabrication quality.To solve this issue,a multichannel interferometric wavefront sensing technique is adopted in the adaptive laser processing system with a single phase-only spatial light modulator.2PP fabrications using corrected high-order Bessel beams with the above solution have been conducted,and high-quality microstructure arrays of microtubes with 20μm diameter have been rapidly manufactured.The effectiveness of the proposed scheme is demonstrated by comparing the beam intensity distributions and 2PP results before and after aberration corrections.

Strain compensated robust semiconductor saturable absorber mirror for fiber lasers

We demonstrate a strain compensated long lifetime semiconductor saturable absorber mirror(SESAM) with a high modulation depth for fiber lasers.The SESAM was measured to have a damage threshold of 9.5 m J/cm^2, a modulation depth of 11.5%, a saturation fluence of 39.3 μJ/cm^2, and an inversed saturable absorption coefficient of 630 m J/cm^2.The SESAM has been applied to a linear cavity mode-locked Yb-doped fiber laser, which has been working for more than a year without damage of the SESAM.

Generation and application of structured beams based on double-phase holograms[Invited]

The manipulation of structured light beams requires simultaneous spatial modulation of amplitude and phase.Based on the double-phase holography(DPH)algorithm,we demonstrate an efficient reconstruction of Bessel beams with arbitrary onaxis intensity.Also,the off-axis DPH method enables more than doubled laser energy utilization compared with the widelyused off-axis phase wrapping modulation method.The DPH algorithm is also used in two-photon polymerization to enable the rapid fabrication of microtube arrays,ortho-hexagonal scaffolds,and 2D patterned microstructures.This work gives experimental proof to show the powerful feasibility of the DPH method in constructing economic adaptive laser processing systems.

Femtosecond laser microstructuring of nickel foil

We observe the morphological change and grain structure of Ni foil when it is ablated with femtosecond laser pulses. Scanning electron microscopy and field emission transmission electron microscopy are used to study the nature of the morphology and grain structure of nickel foil and determine the essential features. The results indicate that there are many random uanostructures in the center of the ablated region composed of nanocrystalline grains as well as some core-shell structures phase explosion and extremely high cooling rate are the for the formation of surface nanostructures. The observed morphologies seem to suggest that most probable physical mechanisms responsible

Ultra-flat dispersion in an integrated waveguide with five and six zero-dispersion wavelengths for mid-infrared photonics

We propose a new type of dispersion flattening technology, which can generate an ultra-flat group velocity dispersion profile with five and six zero-dispersion wavelengths(ZDWs). The dispersion value varies from-0.15 to 0.35 ps/(nm·km) from 4 to 8 μm, which to the best of our knowledge is the flattest one reported so far, and the dispersion flatness is improved by more than an order of magnitude. We explain the principle of producing six ZDWs. Mode distribution in this waveguide is made stable over a wide bandwidth. General guidelines to systematically control the dispersion value, sign, and slope are provided, and one can achieve the desired dispersion by properly adjusting the structural parameters. Fabrication tolerance of this waveguide is also examined.

Fiber-delay-line-referenced optical frequency combs:three stabilization schemes

We demonstrate the stabilization of an optical frequency comb(OFC) using a segment of fiber delay line as a reference. A mode-locked Er-doped fiber laser is phase locked to a kilometer-long fiber delay line using three different schemes. The short-term stability of the comb modes in the OFC stabilized by these schemes is obviously enhanced, down to the 10;level at millisecond average time. Among these three schemes, phase locking two bunches of comb modes in the OFC to the same fiber delay line exhibits the lowest residual phase noise. Fiber-delay-line-referenced OFCs can provide reliable laser sources in precise metrology owing to the advances of low cost, compactness, and high integration.

Ultra-broadband optical spectrum generation from a stretched pulse fiber laser utilizing zero-dispersion fiber

We investigate the effects of a piece of zero-dispersion fiber （ZDF） on the pulse dynamics of a passively mode-locked fiber laser operating in the stretched-pulse regime. Numerical simulation suggests that the proper location and length of ZDF facilitate spectrum broadening and pulse shortening in fiber lasers while maintaining constant net cavity dispersion. A nonlinear polarization evolution mode-locked Er-doped fiber laser with a dispersion map is built based on the simulation. Larger optical spectrum broadening is obtained by inserting a longer ZDF after the active fiber during single-pulse operation, which well agrees with the simulation.

Broadband athermal waveguides and resonators for datacom and telecom applications

The high-temperature sensitivity of the silicon material index limits the applications of silicon-based micro-ring resonators in integrated photonics. To realize a low but broadband temperature-dependent-wavelength-shift microring resonator, designing a broadband athermal waveguide becomes a significant task. In this work,we propose a broadband athermal waveguide that shows a low effective thermo-optical coefficient of1 × 10^(-6)∕K from 1400 to 1700 nm. The proposed waveguide shows a low-loss performance and stable broadband athermal property when it is applied to ring resonators, and the bending loss of ring resonators with a radius of >30 μm is 0.02 dB/cm.

Micromachining soda-lime glass by femtosecond laser pulses

The physical process of forming a modified region in soda-lime glass was investigated using 1 kHz intense femtosecond laser pulses from a Ti： sapphire laser at 775 nm. Through the modifications in- duced by the femtosecond laser radiation using selective chemical etching techniques, we fabricated reproducible and defined microstructures and further studied their morphologies and etching prop- erties. Moreover, a possible physical mechanism for the femtosecond laser modification in soda-lime glass was proposed.

Observation of wave-breaking-free square pulses in a fiber ring laser

We experimentally and numerically demonstrate the generation of square pulses without any wave-breaking in a fiber ring laser. A segment of nonzero dispersion-shifted fiber is used to increase the laser cavity length and to optimize the parameters of the laser cavity. In the experiment, the pulse width can be tuned in a wide range from13.5 to 119.5 ns without wave-breaking while the peak power remains almost constant. The maximum singlepulse energy is up to 65.58 n J at a pump power of 508 m W. Numerical results are in good agreement with the experimental results. Numerical results also reveal the role of cavity length and nonlinearity in generating a square pulse without pulse breakup.

Flexible generation of femtosecond cylindrical vector beams (Invited Paper)

Femtosecond （fs） cylindrical vector beams （CVBs） have found use in many applications in recent years. However, the existing rigid generation methods seriously limit its development. Here, we propose a flexible method for generating fs-CVBs with arbitrary polarization order by employing half wave plates and vortex retarders. The polarization state, autocorrelation width, pulse width, and spectrum features of the input and generated CVB pulses are measured and compared. The results verify that the generated CVBs remain in the fs regime with no appreciable temporal distortion, and the energy conversion efficiency can reach as high as 96.5%, even for a third-order beam. As a flexible way to generate fs-CVBs, this method will have great significance for many applications.

High throughput direct writing of a mesoscale binary optical element by femtosecond long focal depth beams

Bessel beams have multiple applications owing to their propagation-invariant properties,including particle trapping,optical coherence tomography,and material processing.However,traditional Bessel-beam shaping techniques require bulky components,which limits the development of miniaturized optical systems for integration with other devices.Here,we report a novel femtosecond laser direct writing strategy for fabricating mesoscale(from submicrometer to subcentimeter)binary optical elements with microscale resolution.This strategy utilizes femtosecond beams with a long focal depth to increase throughput while reducing the constraints on critical sample positioning.As a demonstration,we manufactured and characterized a 2.2 mm diameter binary axicon.The experimentally measured quasi-Bessel beam intensity distribution and the numerical results were remarkably consistent,demonstrating a suitable tradeoff between the overall size,efficiency,and structural fidelity.Furthermore,a compact Bessel lens containing binary axicons was constructed and successfully used for femtosecond laser mask-less ablation of periodic grating-type surface plasmon polariton excitation units.The demonstrated approach shows significant potential for fabricating customizable integrated optical components.

Passive optimization of pump noise transfer function by narrow band-pass filtering in femtosecond fiber lasers

Fluctuation of pump power is one of the major sources of temporal and intensity noise in femtosecond fiber lasers.In this work,the transfer functions between the relative intensity noise(RIN)of the pump laser diode(LD)and the output RIN,between the RIN of the pump LD and timing jitter of femtosecond fiber lasers are systematically studied.It is demonstrated,for the first time to our knowledge,that the amplitude of the pump RIN transfer function can be effectively decreased by an intra-cavity narrow band-pass filter.In particular,for normal-dispersion lasers,the 3-d B bandwidth of the transfer function can also be narrowed by two-thirds,with a steeper falling edge.Furthermore,with the narrow band-pass filtering,the transfer function is almost independent of the net intra-cavity dispersion due to amplifier similariton formation.The proposed scheme can effectively isolate the pump-induced noise without the need of complex active pump LD control and intra-cavity dispersion management,thus providing an easy way for practical high-power,high-stability femtosecond fiber laser design and related high-precision applications outside the laboratory.