High-gain free-electron lasers (FELs) have been a great success as the fourth generation light sources. In the last decade, tremendous progress has been made in both theoretical understandings and successful constructions and operations of large-scale FEL facilities all over the world. To generate fully coherent, ultrafast X-rays with high brightness, various novel seeded FEL schemes have been proposed and experimentally demonstrated in recent years. This paper gives an overview of recent advances and prospects for future developments in the seeded high-gain FELs.

This paper is focused on an introduction to the mechanism of nonlinearity enhancement by field confinement and magnification effects of surface plasmon polariton (SPP). By coupling the incident electromagnetic field with the coherent motion of free-electron plasma in the metal, SPP is excited near the metal surface, providing field confinement in nanoscale, which results in the enhancement of electrical field and nonlinearity magnitude. The light intensity required for nonlinear process is dramatically reduced and the occurrence of weak light nonlinear process in nanoscale is possible. Starting from the situation of metallic nanoparticle system, the basic principle of enhancement of electric field and nonlinearity by surface plasmon resonance is introduced. A theory for the evaluation of third-order optical susceptibility of nonlinear nano-composites is presented, which is further used to analyze the nonlinear property of an asymmetric split ring metamaterial. Finally, the surface plasmon resonance is used to enhance the magnitude of nonlinear optical activity effect. The nonlinearity enhancement by surface plasmon is proved to pave a way for the development of weak light nonlinearity in nanoscale.

Femtosecond laser two-photon (multi-photon) micro/nano-processing technology gets the extensive and in-depth research, and is more specifically applied in many frontier fields because of its excellent designable three-dimensional (3D) processing capacity, high spatial resolution, and low additional damage. In this review, we introduce the latest concrete applications and progress of femtosecond laser direct writing (fsLDW) technology in diverse fields with various materials, emphatically, the related work on biological materials′ fsLDW processing. Especially, by combining with the advanced fsLDW technology, protein-based materials have been studied and explored in various functional bio-related micro/nano-devices and systems based on their unique physical, chemical, and biological characteristics.

Terahertz (THz) emission from plasma filament driven by ultra-short laser pulses attracts intense interests for revealing the microscopic dynamics of THz generation and providing new THz sources for applications. This review covers the recent progress in the areas including: the generation of carrier envelope phase (CEP) stabilized infrared (IR) few-cycle laser pulses, the models of THz generation from plasma filament by intense few-cycle laser field, the propagation of few-cycle laser pulses in air plasma, the waveform controlled THz emission and its application in the measurement of actual value of CEP.

Rapid developments and wide applications of optical coherence tomography (OCT) have been achieved since its first coming into being. Doppler OCT is an important functional extension of existing OCT imaging modality. Spectral domain OCT (SD-OCT) system and its applications in dynamic monitoring of blood flow in a rat brain model and three-dimensional flow-field measurement of a microfluidic chip are presented. Recent advances in Doppler imaging method and system developments are reported, including sensitive phase retrieval for Doppler imaging through higher-order cross-correlation, vector-velocity quantification by two-zone beam divider and transit-time analysis, ultralong-range orthogonal dispersive SD-OCT system and its application in phase-sensitive imaging.

1.6 μm single-frequency lasers have important applications in laser wind lidars, differential absorption lidars, optical communication and pumping optical parametric oscillators. We introduce the main techniques to get single-frequency output in solid-state lasers, including micro-chip cavity, twisted mode cavity, the cavity with F-P etalons inside, traveling wave ring cavity, coupled cavity and the non-planar ring resonator. The research progress of 1.6 μm single-frequency lasers in China and abroad are summarized.

The entangled states of light with quantum correlations of quadrature amplitude and phase components are the key resources for realizing the continuous variable quantum communication and quantum calculation. With the rapid development of quantum information science, researching and establishing practicable quantum information networks have become the main goal pursued by scientists in this field. For developing the long-distance transfer of quantum information via quantum repeaters, it is essential to prepare multipartite entangled states consisting of multi-color optical sub-modes respectively at fiber transmission and atomic transition frequencies. We briefly introduce the concept and the development of the continuous variable entangled optical fields firstly, then summarize the generation experiments of two-color and three-color entangled optical fields. At last the generation principle and the experimental method of three-color entangled optical fields at the atomic transition frequency and the communication window of optical fibers accomplished by our group recently are presented detailedly.

Pulse contrast is an important specification of high-intensity laser, reflecting the technical level of the laser system. As such lasers generally operate in a very low repetition rate and even in a single-shot mode, real-time single-shot measuring techniques are necessary for diagnosing pulse contrast. Compared with time-scanning measurement, the techniques for single-shot measurement are very deficient and more difficult. We present a new measuring scheme supporting high dynamic range and large temporal window simultaneously. Integrating the series of innovative technologies, we make a practical measuring prototype whose feasibility and reliability as well as the main performance have been examined by the proof-of-principle experiments. The pulse contrast can now been measured with high resolution and high fidelity at a dynamic range of about 109 within a temporal window of 50～100 ps. The invented measuring prototype has been applied successfully in the national petawatt laser system.

Recently, gradient meta-surface has become an important and hot sub-branch in electromagnetic metamaterial research. In this paper, we review some recent progresses in this area, such as using gradient meta-surfaces as a bridge to link propagating waves and surface waves and the conversion efficiency issue related to such conversion, high efficiency broadband anomalous reflection by optical gradient meta-surfaces, the development of a mode-expansion theory for studying the scattering properties of inhomogeneous meta-surfaces, flat meta-surfaces to focus electromagnetic waves in reflection geometry and the comparison of reflective and transmissive gradient meta-surfaces. Finally, we present our perspectives on the future direction of this research field.

By their unique and excellent optical properties, femtosecond lasers have brought novel developments and methodologies in biophotonics researches. In researches of cell and molecular biology, femtosecond lasers can perform precise stimulations and operations to cells at the subcellular or diffraction limit level. In this article, calcium signal modulation in human cells by femtosecond lasers is reviewed, possible mechanism of optical release of cellular calcium store is discussed, and physical and physiological processes of the release are analyzed. The hypothesis of cellular responses to femtosecond lasers is investigated at cellular and molecular level, with demonstrations of following molecular and physiological processes. This all-optical modulation of molecular signals is very important to the researches of cellular signaling pathways, which can be further applied in optical regulation of gene expression and stem-cell differentiation.

The progress of new concept small-size satellite atomic clock in Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, is introduced. Base on the pulsed optically pumping (POP) and the orthogonal polarization detection technology, the contrast of the transition signal of atomic clock is improved from 30% in absorption detection to about 100%. The detected result reflects the variation of amplitude and phase of incident light. Therefore, the detection sensitivity and the signal-to-noise ratio are improved effectively, which leads to the improvement of the frequency stability of the atomic clock. Under the same experimental condition, POP atomic clock with orthogonal polarization detection technology has a frequency stability about an order of magnitude higher than the result of POP atomic clock using absorption detection. Above all, when the stabilities of the temperature of physics system, the current of magnetic field, and the intensity of laser are improved by about an order of magnitude, the stability of this atomic clock could reach 1×10-13 for 1s and 1×10-15 for a day, which means that this type of POP atomic clock might become a good substitute of the H-maser.

Laser-plasma experiments about magnetic reconnection have been used to investigate characteristics of activities of the solar magnetic field and the magnetosphere. In our recent laser plasma experiments, two side-by-side thin target layers, instead of a single one, are used. It is found that at one end of the elongated current sheet (CS), a fanlike electron outflow region including three well-collimated electron jets appears. These laboratory experimental observations of three electron diffusion regions (EDRs) reproduce the characteristics of magnetic reconnection sites at the Earth's magnetotail，which was observed by the Cluster satellites in 2003 and 2005, separately. The higher than 1 MeV tail of the jet energy distribution exhibits a power-law scaling. The enhanced electron acceleration is attributed to the intense inductive electric field in the narrow electron dominated reconnection region, as well as additional acceleration as electrons are trapped inside the rapidly moving plasmoid formed in and ejected from the CS. The plasmoid ejection also induces a secondary CS. The experimental results mimic the formation process of solar coronal mass ejections and flares, and also confirm the theory and model predictions about the CS-born anomalous plasmoid as the initial stage of coronal mass ejections, and the behavior of moving-away plasmoid stretching the primary reconnected field lines into a secondary CS conjoined with two bright ridges identified. We compare the parameters of plasmas in the transition region between solar corona and chromosphere, at the reconnection site of the magnetotail, and that produced by the giant lasers, and find that all three plasma systems have Euler-Alfven similarity, meaning that the physics underlying current laser-plasma phenomena can be applicable to that of solar flares and substorms of magnetosphere.

Glaucoma is the second leading cause of blindness worldwide. Though the pathogenesis of glaucoma is not yet fully understood, the high intraocular pressure (IOP) is the leading reason for the formation of glaucoma. But the resistance points of aqueous humour out flow in primary open angle glaucomatous eyes is still unknown. The research in animal and donor eyes demonstrated that the collapse of Schlemm′s canal (SC) at higher IOP might be a cause of primary open angle glaucoma (POAG). We have established a tailored anterior segment swept source optical coherence tomography to measure SC morphometric values in living normal and POAG human eyes, and carried out a series of statistical comparison. This paper reviews the research progress and proposes the research prospects in future.

With the development of special fiber fabrication technology and the pumping technology with high brightness laser diode, the average output power of supercontinuum source increases dramatically to hundred watt level in recent years. Based on the introduction of recent developments in high power supercontinuum fiber source, the key technologies of high power supercontinuum generation are analyzed. The up-to-date progress on high power supercontinuum fiber source in the National University of Defense Technology is presented: 101 W supercontinuum average output power is extracted from a homemade photonic crystal fiber by using a pulsed fiber laser as the pump; 177 W near-infrared supercontinuum power is obtained directly from a large-mode-area double-cladding fiber amplifier; 10 W mid-infrared supercontinuum is achieved from a ZBLAN fiber with a 2 μm pulse pump.

Radially polarized beam is one of the present hotspots and has great potential applications in many fields due to its special focus properties and polarization state. It becomes a hot technology to acquire radially polarized beam by use of photonic crystal grating as the mode selector. We summarize the recent research progress on radially polarized solid-state laser. Concerning the previous research on microchip radially polarized laser, in which the output power is limited due to the strong thermal effects of the lasing material at intensive pumping, a bonded crystal is chosen as the lasing material to weaken the temperature gradient in the lasing area and thereafter the thermal lens effect at the presence of intensive pumping. And the recent progress of lasers based on bonded crystal such as continuous wave radially polarized solid-state laser, passively Q-switched radially polarized laser and actively Q-switched radially polarized laser is summarized.

Laser weapon is playing a more and more important role in modern warfare. This paper discusses the damage mechanism, development situation and future development trend of laser weapon. Laser weapons can be divided into chemical laser weapon, free-electron laser weapon, solid state laser weapon, etc. according to the laser generation method. The latest status of high-energy laser programs, including technology, subsystem and prototype demonstrations, is assessed in detail. The key technology of laser weapon is also analyzed.

The better-controllable laser-induced cavitation bubbles are widely used in scientific research and industrial applications. This paper describes the mechanism of the laser-induced cavitation bubbles: vapor bubble and plasma bubble. Effects on the process of bubbles′ expanding and collapsing by liquid properties and environmental conditions are analyzed. Finally, the applications of laser-induced cavitation bubbles in the fields of microelectronics, biomedicine, preparation of nanomaterial ands surface modification are discussed.

Graphene has unique mechanical, thermal, electrical and optical properties, excellent thermal stability and chemical stability. It is one of the most promising materials for fabricating high conductive films in LED industry. This article mainly introduces the fabrication and characterization of graphene, as well as the research progress for graphene as conductive electrodes used in GaN-based light emitting diodes (LEDs). In addition, the application prospect of graphene electrodes is also discussed.

Optical parametric chirped pulse amplification (OPCPA) is the most promising key technology to achieve the large ultra-high power and ultrashort pulse laser system. However, parametric fluorescence is still an important factor affecting the temporal contrast of the system. We review the theoretical and experimental research of the parametric fluorescence, discuss the mechanism of its generation and point out the parameters which affect the spatial-temporal pattern and spectrum distribution. Based on that, we summarize the suppression of parametric fluorescence in the aspects of the input energy and the saturated or over-saturated amplification. Temporal contrast of the OPCPA system can be improved by the means mentioned above, and it satisfies the requirements of high quality physical experiments.

Surface enhanced Raman scattering (SERS) has emerged as a new vibrational spectrum technology for the single-molecule detection and the imaging of samples. It has a great promise in studying the screening of early cancer for its high sensitivity, good specificity and rapidly noninvasive detection. Recently, the application of SERS in cancer detection has been a new research focus. In this review, we provide a brief introduction to the latest research achievements in tumorous tissues, tumorous cells and blood of cancer patients. Then we give a comprehensive discussion of the difficulties, limitations and applications of these works. The prospect of SERS technology for cancer detection is discussed.

Phase-sensitive optical time domain reflectometer φ-OTDR is one of the most important means of distributed sensing and monitoring for intrusion and vibration due to its excellent overall performance. This paper explains the research progress of the source technology, the sensing technology and the signal demodulation technology of the distributed optical fiber sensing and monitoring system based on φ-OTDR, reviews the newest research results, and analyzes their innovativeness and existing problems. The principles of differential amplitude detection and direct phase demodulation are explained, and the difference between these two kinds of demodulated methods are compared. It is hard to demodulate the phase signal only from the speckle using differential amplitude detection, and this scheme is just an indirectly and qualitatively measuring method. Direct phase demodulation is a directly and quantitatively measure method, and can be use in dynamic measurement or fiber hydrophone, etc., but the influence of fading noise resulting from the inner pulse interference of Rayleigh scattering beams is obvious. Finally, the prospect of distributed optical fiber sensing and monitoring technology based on φ-OTDR is set forth.

The research on ferromagnetic materials, especially on ferromagnetic micro-nano materials in terahertz region, has made many achievements which have important potential applications. This article shows the research achievements of the terahertz emission in ferromagnetic thin films and ferromagnetic nanowires employing femtosecond laser pulses, and some ferromagnetic materials interaction with terahertz wave as well. These includes the influences of applied magnetic field and non-magnetic nano-coatings on the attenuation and time delay of terahertz wave transmitted through ferromagnetic particles such as Co and Ni, Faraday rotation in ferrofluid, the magnetic field of terahertz pulses interaction with magnetic moments and negative refraction index of some ferromagnetic thin films in terahertz region. Moreover, two kinds of terahertz functional devices controlled by magnetic field which are composed by artificially designed ferromagnetic materials are introduced. The prospect of the application of ferromagnetic materials in terahertz region is referred at last.

With the development of optical communication and optical networks, the optical data processing based on optical fiber has been investigated intensely. Several technologies of fiber dispersion based optical data processing are introduced, including time lens, time stretch based analog/digital (A/D) converter, fiber grating sensor′s wavelength demodulation, serial time-encoded amplified imaging, all optical integrator, convolution and correlation. Their principles, developments, advantages and disadvantages are discussed. The potential applications of optical data processing using modal dispersion are also discussed through comparing chromatic dispersion and modal dispersion and two kinds of modal dispersion based optical data processing are introduced.

As the crux technology of free-space communication, directed energy and many other application fields, beam scanning technology has been widely studied. This paper introduces the new development of beam scanning, analyzes the merits and faults of these technologies, especially makes an intensive study on liquid crystal optical phased array technology. Finally, the future development of beam scanning technologies is previewed.

Due to the inherent timing jitter of the electronic clocking circuits and comparator ambiguity, the traditional electronic analog-to-digital conversion (ADC) cannot fulfill the development of high bandwidth digital signal processing. Analog-to-digital conversion consists of sampling, quantizing and coding. Introducing photonic technologies for sampling and quantization of the electrical analog signal, all-optical ADC can improve the performance of the digital signal processing system to achieve high sampling rate and high resolution. Hence, it solves the bottleneck problem of electronic ADC. The main recently developed all-optical analog-to-digital converters, such as those based on Taylor scheme, interferometric and polarization interference, phase-shifted optical quantization (PSOQ), soliton self-frequency shift, long-period waveguide grating (LPWG) and arrayed waveguide grating (AWG), are introduced. Meanwhile, the characteristics of different methods are analyzed.

As the complexity of the mechanical system is increasing, designers need to give comprehensive consideration to the novelty, excellent performance and manufacturing feasibility of the structure in the design of the theoretical model of modern mechanism. However, the traditional manufacturing methods impose great restriction on the design. Selective laser melting (SLM) is one of the technologies that have most development potential, which can achieve direct manufacturing of metal functional parts from any complex computer-aided design (CAD) theoretical models in theory. Based on the characteristics of the freeform manufacturing of SLM, combining with the related research of South China University of Technology, we study the freeform design and direct manufacturing process of complex metal pieces with non-assembly, functional integration and lightweight characteristics, which provides effective reference for the innovative design and personalized manufacturing of products in the fields of aerospace, medical treatment and automobile.

According to the jamming principle and application method of laser decoy departure equipment, a hardware-in-the-loop (HWIL) simulation training system for laser decoy departure jamming is developed. The system is designed in conformity with the fundamental of “same principium and similar operation” firstly, and the key technologies are emphatically analyzed. Furthermore, the mode of operation and drilling is discussed based on the self-developed HWIL simulation training system. It is proved that the developed training system and contrived drilling means can simulate the whole process of laser decoy departure jamming, including threaten coming, task receiving and assignment, system spread and layout, cheating jamming countermeasure and equipments taking back. Consequently they can be used in essential operation and tactical drilling teaching for laser decoy departure jamming system.

The position and pose measurement for space non-cooperative target is an intractable problem of on-orbit servicing for space non-cooperative target, which has been a hotspot of research in recent years. In this paper, firstly, the characteristics of the position and pose estimation for space non-cooperative target are discussed. Secondly, the performance of the main position and pose estimation optics methods are comprehensively summarized. Finally, the vision sensor and estimation algorithm are analyzed, and their advantages, disadvantages and application area are concluded.