高功率高重复频率飞秒掺镱光纤激光频率梳的研究(特邀)

飞秒光学频率梳在精密计量学和光谱学中扮演着革命性的推动角色,成为近二十年超短脉冲激光技术及应用研究领域最活跃的前沿方向之一。文中基于250 MHz重复频率(frep)的掺镱(Yb)光纤激光器,研究了不同腔内色散以及锁模机制对飞秒脉冲序列载波包络相位偏移频率(fCEO)噪声的影响。通过对飞秒光梳细节的优化,得到了49 d B信噪比的fCEO拍频信号并获得了秒稳3.2×10^(-10)的锁定结果,同时frep的锁定结果也达到了到了秒稳3.4×10^(-13)的精度。此外文中还研究了不同啁啾状态的种子光飞秒脉冲对基于大模场面积双包层Yb光子晶体光纤放大器输出光脉冲宽度的影响。以携带-3.8×10~4fs2预啁啾量的光脉冲作为种子光,在60 W 976 nm半导体激光泵浦下,获得了250 MHz重复频率、23 W平均功率和66 fs压缩后脉冲宽度的激光输出。

Integrated sources of photon quantum states based on nonlinear optics

The ability to generate complex optical photon states involving entanglement between multiple optical modes is not only critical to advancing our understanding of quantum mechanics but will play a key role in generating many applications in quantum technologies.These include quantum communications,computation,imaging,microscopy and many other novel technologies that are constantly being proposed.However,approaches to generating parallel multiple,customisable bi-and multi-entangled quantum bits(qubits)on a chip are still in the early stages of development.Here,we review recent advances in the realisation of integrated sources of photonic quantum states,focusing on approaches based on nonlinear optics that are compatible with contemporary optical fibre telecommunications and quantum memory platforms as well as with chip-scale semiconductor technology.These new and exciting platforms hold the promise of compact,low-cost,scalable and practical implementations of sources for the generation and manipulation of complex quantum optical states on a chip,which will play a major role in bringing quantum technologies out of the laboratory and into the real world.

Near-infrared lasing and tunable upconversion from femtosecond laser inscribed Nd,Gd:CaF_(2)waveguides

Optical channel waveguides with depressed cladding configurations have been produced in Nd,Gd∶CaF_(2)laser crystals by using ultrafast laser inscription.Waveguide properties are investigated in terms of guiding behaviors and localized laserinduced lattice damages.Under an optical pump of 808 nm light,continuous-wave waveguide lasing at 1.06μm is achieved,with a single-mode operation and a minimum lasing threshold of 98.8 m W.Furthermore,the visible emissions of Nd^(3+)with short wavelengths ranging from 415 nm to 550 nm and long wavelengths from 550 nm to 625 nm are observed upon 808 nm laser excitation via the up-converted process.The intensity ratios of two wavelength ranges are proved to be tunable through changing the pumping polarizations.

Electronic structure, optical properties, and lattice dynamics in atomically thin indium selenide flakes

The progressive stacking of chalcogenide single layers gives rise to two- dimensional semiconducting materials with tunable properties that can be exploited for new field-effect transistors and photonic devices. Yet the properties of some members of the chalcogenide family remain unexplored. Indium selenide （InSe） is attractive for applications due to its direct bandgap in the near infrared, controllable p- and n-type doping and high chemical stability. Here, we reveal the lattice dynamics, optical and electronic properties of atomically thin InSe flakes prepared by micromechanical cleavage. Raman active modes stiffen or soften in the flakes depending on which electronic bonds are excited. A progressive blue-shift of the photoluminescence peaks is observed for decreasing flake thickness （as large as 0.2 eV for three single layers）. First-principles calculations predict an even larger increase in the bandgap, 0.40 eV, for three single layers, and as much as 1.1 eV for a single layer. These results are promising from the point of view of the versatility of this material for optoelectronic applications at the nanometer scale and compatible with Si and III-V technologies.

Power efficiency of time-stretch imaging system by using parallel interleaving detection

A 38.88 MHz time-stretch line-scan imaging system with parallel interleaving detection is experimentally dem- onstrated. Since only half-chromatic dispersion is used to stretch optical pulses for wavelength-to-time mapping, the power efficiency is significantly improved by 6.5 dB. Furthermore, the theoretical analysis indicates that the power loss can be efficiently reduced for scan rates less than 100 MHz. In addition, a mathematical model for signal-to-noise evaluation is derived, including amplified spontaneous emission noise in the power compensation. Thanks to the improvement of the power efficiency by using parallel interleaving detection, the signal quality is enhanced.

Unitary fermions and Lscher's formula on a crystal

We consider the low-energy particle-particle scattering properties in a periodic simple cubic crystal. In particular, we investigate the relation between the two-body scattering length and the energy shift experienced by the lowest-lying unbound state when this is placed in a periodic finite box. We introduce a continuum model for s-wave contact interactions that respects the symmetry of the Brillouin zone in its regularisation and renormalisation procedures, and corresponds to the nae continuum limit of the Hubbard model. The energy shifts are found to be identical to those obtained in the usual spherically symmetric renormalisation scheme upon resolving an important subtlety regarding the cutoff procedure. We then particularize to the Hubbard model, and find that for large finite lattices the results are identical to those obtained in the continuum limit. The results reported here are valid in the weak,intermediate and unitary limits. These may be used to significantly ease the extraction of scattering information, and therefore effective interactions in condensed matter systems in realistic periodic potentials. This can achieved via exact diagonalisation or Monte Carlo methods, without the need to solve challenging, genuine multichannel collisional problems with very restricted symmetry simplifications.

Compact multi-foci metalens spectrometer

A lightweight and portable spectrometer is desirable for miniaturization and integration.The unprecedented capability of optical metasurfaces has shown much promise to perform such a task.We propose and experimentally demonstrate a compact high-resolution spectrometer with a multi-foci metalens.The novel metalens is designed based on wavelength and phase multiplexing,which can accurately map the wavelength information into its focal points located on the same plane.The measured wavelengths in the light spectra agree with simulation results upon the illumination of various incident light spectra.The uniqueness of this technique lies in the novel metalens that can simultaneously realize wavelength splitting and light focusing.The compactness and ultrathin nature of the metalens spectrometer render this technology have potential applications in on-chip integrated photonics where spectral analysis and information processing can be performed in a compact platform.

Color-selective three-dimensional polarization structures

Polarization as an important degree of freedom for light plays a key role in optics.Structured beams with controlled polarization profles have diverse applications,such as information encoding,display,medical and biological imaging,and manipulation of microparticles.However,conventional polarization optics can only realize two-dimensional polarization structures in a transverse plane.The emergent ultrathin optical devices consisting of planar nanostructures,so-called metasurfaces,have shown much promise for polarization manipulation.Here we propose and experimentally demonstrate color-selective three-dimensional(3D)polarization structures with a single metasurface.The geometric metasurfaces are designed based on color and phase multiplexing and polarization rotation,creating various 3D polarization knots.Remarkably,different 3D polarization knots in the same observation region can be achieved by controlling the incident wavelengths,providing unprecedented polarization control with color information in 3D space.Our research findings may be of interest to many practical applications such as vector beam generation,virtual reality,volumetric displays,security,and anti-counterfeiting.

High-resolution grayscale image hidden in a laser beam

Images perceived by human eyes or recorded by cameras are usually optical patterns with spatially varying intensity or color profiles.In addition to the intensity and color,the information of an image can be encoded in a spatially varying distribution of phase or polarization state.Interestingly,such images might not be able to be directly viewed by human eyes or cameras because they may exhibit highly uniform intensity profiles.Here,we propose and experimentally demonstrate an approach to hide a high-resolution grayscale image in a square laser beam with a size of less than half a millimeter.An image with a pixel size of 300×300 nm is encoded into the spatially variant polarization states of the laser beam,which can be revealed after passing through a linear polarizer.This unique technology for hiding grayscale images and polarization manipulation provides new opportunities for various applications,including encryption,imaging,optical communications,quantum science and fundamental physics.

Solitons in One-Dimensional Bose–Einstein Condensate with Higher-Order Interactions

We model a one-dimensional Bose–Einstein condensate with the one-dimensional Gross–Pitaevskii equation(1 D GPE) incorporating higher-order interaction effects. Based on the F-expansion method, we analytically solve the1 D GPE, identifying the typical soliton solution under certain experimental settings within the general wave-like solution set, and demonstrating the applicability of the theoretical treatment that is employed.

Highly efficient THz four-wave mixing in doped silicon

Third-order non-linearities are important because they allow control over light pulses in ubiquitous high-quality centro-symmetric materials like silicon and silica.Degenerate four-wave mixing provides a direct measure of the third-order non-linear sheet susceptibility x^(3)(where L represents the material thickness)as well as technological possibilities such as optically gated detection and emission of photons.Using picosecond pulses from a free electron laser,we show that silicon doped with P or Bi has a value of x^(3)Lin the THz domain that is higher than that reported for any other material in any wavelength band.The immediate implication of our results is the efficient generation of intense coherent THz light via upconversion(also a x^(3)process),and they open the door to exploitation of nondegenerate mixing and optical nonlinearities beyond the perturbative regime.