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Multimode fiber (MMF) is extensively studied for its ability to transmit light modes in parallel, potentially minimizing optical fiber size in imaging. However, current research predominantly focuses on grayscale imaging, with limited attention to color studies. Existing colorization methods often involve costly white light lasers or multiple light sources, increasing optical system expenses and space. To achieve wide-field color images with typical monochromatic illumination MMF imaging system, we proposed a data-driven "colorization" approach and a neural network called SpeckleColorNet, merging U-Net and conditional GAN (cGAN) architectures, trained by a combined loss function. This approach, demonstrated on a 2-meter MMF system with single-wavelength illumination and the Peripheral Blood Cell (PBC) dataset, outperforms grayscale imaging and alternative colorization methods in readability, definition, detail, and accuracy. Our method aims to integrate MMF into clinical medicine and industrial monitoring, offering cost-effective high-fidelity color imaging. It serves as a plug-and-play replacement for conventional grayscale algorithms in MMF systems, eliminating the need for additional hardware.

With the rapid development of superconducting quantum computing and the implementation of surface code, large-scale quantum computing is emerging as an urgent demand. In a superconducting computing system, the qubit is maintained in a cryogenic environment to avoid thermal excitation. Thus, the transmission of control signals, which are generated at room temperature, is needed. Typically, the transmission of these signals to the qubit relies on a coaxial cable wiring approach. However, in a large-scale computing system with hundreds or even thousands of qubits, the coaxial cables will pose great space and heat load to the dilution refrigerator. Here, to tackle this problem, we propose and demonstrate a direct-modulation-based optical transmission line. In our experiment, the average single-qubit XEB error and control error are measured as 0.139% and 0.014% separately, demonstrating the feasibility of the optical wiring approach and paving the way for large-scale superconducting quantum computing.

In this article, a thorough model of linearly polarized fiber laser considering polarization coupling, mode coupling, SBS, and SRS effects is established. The output results of direct pumping and tandem pumping linearly polarized fiber laser under different SBS and SRS intensity settings are simulated. The results show that direct pumping is a better pumping scheme at present, and if the doping concentration of gain fiber can be further increased and the mode field quality of corresponding passive fiber can be optimized, the disadvantages of tandem pumping can be suppressed. To explore the potential of tandem pumping, a backward tandem pumped linearly polarized fiber amplifier is built and 875 W over 13 dB linearly polarized laser output is obtained.

Thermo-optic phase shifters (TOPSs) are commonly used in large-scale silicon photonic integrated optical phased arrays (OPAs). However, fast-response TOPSs consume relatively high power; the elevated temperature floor in the dense region of the TOPSs introduces thermal crosstalk between optical paths, which undermines the control accuracy. We propose a combined method that involves subarray design in the optical power distribution network and array control method to predict, optimize, and redistribute the phase shifts and mitigates thermal crosstalk. Thermal simulations and an array control method for generic OPA models are discussed. A silicon photonic chip prototype of a 4 × 4 OPA with three-level cascaded subarrays is fabricated to demonstrate the proposed method. The experimental and statistical results show that the method effectively reduces the average total power consumption by 31%, the maximum local temperature by 18.4%, and the thermal crosstalk within the OPA.

Laser lighting has great potential to be the next generation of general lighting due to its high brightness and directionality. However, the light extraction efficiency and luminous efficiency from the light exit surface are greatly limited since phosphor structure. Here, we design and optimize a phosphor structure by Monte Carlo method (MCM) with optimization algorithm. The results indicate that the optimized Ce:YAG single crystal phosphor is able to improve the extraction efficiency to 0.49, which is much higher than the conventional parallel phosphor. The luminous efficiency of the optimized phosphor can also reach 230 lm/W. In addition, the experiments and simulations show that the extraction efficiency and luminous efficiency will reduce to 0.41 and 190 lm/W if there is scattering in the optimized phosphor. The spatial distribution of the light intensity and thermal stability of the optimized phosphor are also measured. The optimized phosphor is helpful to the design of side heat dissipation structure. In general, the optimized phosphor may play a significant role in the high-flux laser lighting and the method also provides a universal tool for the phosphor design.

The exact modeling of light transport in scattering media is critical in biological imaging, free-space communication, and phosphor-converted lighting. Angular spectrum is proved to be a fast and effective approach to reconstructing the wavefront dynamics during the propagation in scattering media, however, finding it difficult in acquiring the wavefront and energy change simultaneously. Besides, conventional methods for energy tracing, such as the Monte Carlo method, are inefficient in speed and hard to simulate the wavefront change. Here, we propose an extended angular-spectrum modeling (EASM) approach using tenuous scattering approximate solutions to obtain a time-efficient and accurate method for reconstruction of energy and wavefront dynamics in various scattering media. The generality of our method is numerically simulated and experimentally verified with a set of scattering media with different properties. EASM has a time advantage under the guarantee of calculation accuracy, especially when calculating several thickness changes after the calculation model is established. Furthermore, multi-layered media can also be simulated by EASM with a good precision. The results suggest that EASM performs certain computations more efficiently than the conventional method and thus provides an effective and flexible calculation tool for scattering media.

This paper presents an approach that combines the generalized multimode nonlinear Schrodinger equation with a transmission model to analyze spatiotemporal characteristics of multimode interference in single mode/large mode area fiber-graded-index multimode fiber-single mode fiber (SMF/LMA-GIMF-SMF) structures for the first time. Approximated self-imaging (ASIM) behavior in GIMF and the study of the latter structure used in spatiotemporal mode-locked fiber lasers are first demonstrated. Simulations show that these structures can work as saturable absorbers enabling high-energy pulse output due to nonlinear intermodal interactions and intensity-dependent multimode interference. Otherwise, underlying ASIM is proven that it can perturb the transmission of SMF/LMA-GIMF-SMF, causing instability of their saturable-absorption characteristics. This paper provides a theoretical guide for many applications, such as beam shaping, mode conversion, and high-energy ultrafast fiber laser.

With the presence of complex background noise, parasitic light, and dust attachment, it is still a challenging issue to perform high-precision laser-induced damage change detection of optical elements in the captured optical images. For resolving this problem, this paper presents an end-to-end damage change detection model based on siamese network and multi-layer perceptrons (SiamMLP). Firstly, representative features of bi-temporal damage images are efficiently extracted by the cascaded multi-layer perceptron modules in the siamese network. After that, the extracted features are concatenated and then classified into changed and unchanged classes. Due to its concise architecture and strong feature representation ability, the proposed method obtains excellent damage change detection results efficiently and effectively. To address the unbalanced distribution of hard and easy samples, a novel metric called hard metric is introduced in this paper for quantitatively evaluating the classification difficulty degree of the samples. The hard metric assigns a classification difficulty for each individual sample to precisely adjust the loss assigned to the sample. In the training stage, a novel hard loss is presented to train the proposed model. Cooperating with the hard metric, the hard loss can up-weight the loss of hard samples and down-weight the loss of easy samples, which results in a more powerful online hard sample mining ability of the proposed model. The experimental results on two real datasets validate the effectiveness and superiority of the proposed method.

Nanostructured fiber devices enabling mode conversion between arbitrary fiber modes are proposed and numerically validated. The intra-fiber nanostructures are optimized by the inverse design algorithm. We demonstrate a set of designs of nanophotonic fibers that can facilitate high-purity conversion from the fundamental mode to higher-order modes up to 3 orders for both LP and OAM modes inside the fibers. The purity values of the output modes can reach 98% with an ultra-wide operation band exceeding 400 nm around the telecom wavelengths. These devices can be fabricated by technique of thermal drawing of assembled preforms, making them suitable for mass production.

In this paper, we study the emerging 1535 nm Er: Yb codoped fiber MOPA with high power and high brightness. To characterize the interstage influence of this ASE-sensitive system, we conduct an interstage numerical model based on steady energy transfer model, where the seed and amplifier converge together. We analyze the amplifier setup, the seed pumping scheme, and feedback from inner reflection based on the model. Afterwards, we experimentally demonstrate a 1535 nm all fiber large mode area Er: Yb codoped fiber MOPA with the output power of 174.5 W, the brightness of 13.97 W/μm 2 sr, and ASE suppression ratio of 45 dB. To the best of our knowledge, this is the highest power and brightness of 1535 nm fiber lasers to date.

The amplification of random fiber lasers (RFLs) attracts much attention due to their unique characteristics such as wavelength flexibility and low coherence. We present that, in the kilowatt-level amplification of RFL operating near its lasing threshold, a broad and flat spectral pedestal can co-exist with the narrow spectral peak of RFL. This phenomenon is different from the case in the amplification of fixed-cavity laser seeds. Time-domain measurements show that the broad and flat spectral pedestal, which extends to long wavelengths, is composed of temporal pulses, while few temporal pulses exist in the narrow spectral peak. We attribute the spectral pedestal to intensity fluctuations from the random seed laser and modulation instability in the amplification stage. Control experiments reveal that the working status of the random seed laser and the effective length of the amplifier can influence the spectral bandwidth. By taking advantage of this phenomenon, we propose a novel approach to achieve a high-power broadband light source through the amplification of RFLs operating near the lasing threshold.

Metasurface has achieved fruitful results in tailoring optical fields in free space. However, a systematic investigation on applying meta-optics to completely control waveguide modes is still elusive. Here we present a comprehensive catalog to selectively and exclusively couple free space light into arbitrary high-order waveguide modes of interest, leveraging silicon metasurface-patterned silicon nitride waveguides. By simultaneously engineering the matched phase gradient of the nanoantennas and the vectorial spatial modal overlap between the antenna near-field and target waveguide mode profile, either single or multiple high-order modes are successfully launched with high purity reaching 98%. Moreover, on-chip twisted light generators are theoretically proposed with configurable OAM topological charge ℓ from -3 to +2. This work may serve as a comprehensive framework for guided mode meta-optics and motivates further applications such as versatile integrated couplers, multiplexers, and mode-division multiplexing-based communication systems.

Energy transfer is an essential light-matter interaction. The transfer efficiency is critical for various applications such as light-emitting, optical modulation, and the photoelectric effect. Two primary forms of light-matter energy transfer, including absorption and emission, can be enhanced in optical cavities. Both forms can reach an extremum inside the cavity according to the coupled-mode theory. Graphene conductivity at the terahertz frequency can be tuned from positive to negative, providing a suitable material to study switchable extremums of these two forms. We integrate graphene with a nested cavity where an infrared cavity is inserted in a terahertz cavity, thereby achieving terahertz perfect absorption at the static state and optimal gain under photoexcitation. Leveraging an inserted infrared cavity, we can elevate the working efficiency by strongly absorbing the infrared pump. We also numerically show the feasibility of electrically tunable extreme energy transfer. Our concept of the nested cavity can be extended to different materials and even to guided modes. A switchable synergy of loss and gain potentially enables high-contrast dynamic modulation and photonic devices with multiplexing functions.

Stray light is a known strong interference in spectroscopic measurements. Photons from high-intensity signals that are scattered inside the spectrometer, or photons that enter the detector through unintended ways, will be added to the spectrum as an interference signal. A general experimental solution to this problem is presented here by introducing a customized fiber for signal collection. The fiber-mount to the spectrometer consists of a periodically arranged fiber array that, combined with lock-in analysis of the data, is capable of suppressing stray light for improved spectroscopy. The method, which is referred to as fiber-based periodic shadowing, was applied to Raman spectroscopy in combustion. The fiber-based stray-light suppression method is implemented in an experimental setup with a high-power high-repetition-rate laser system used for Raman measurements in different room-temperature gas mixtures and a premixed flame. It is shown that the stray-light level is reduced by up to a factor of 80. Weak spectral lines can be distinguished, and therefore better molecular species identification, as well as concentration and temperature evaluation, were performed. The results show that the method is feasible and efficient in practical use and that it can be employed as a general tool for improving spectroscopic accuracy.

Epsilon-near-zero (ENZ) materials have recently been suggested as excellent candidates for constructing all-optical and electro-optical switches in the infrared. The performance of previously reported ENZ material-based optical switches, however, has been greatly hampered by the low quality- (Q-) factor of the ENZ cavity, resulting in a large required optical pump fluence or applied voltage, a large insertion loss, or a small modulation depth. Here, we propose a solution by integrating the ENZ material into a Bragg microcavity, such that the Q-factor of the coupled cavity can be dramatically enhanced. Using high-mobility Dysprosium-doped cadmium oxide (CdO) as the prototype ENZ material, we numerically show an infrared all-optical switch with its reflectance modulated from near-zero to 94% under a pump fluence of only 7 μJ cm -2 , about a 59-time-reduction compared with a state-of-the-art Berreman-type cavity. Moreover, the high-Q coupled cavity can also be adopted to realize a reflective electro-optical switch. Its reflectance can be switched from near-zero to 89%, with a bias electric field well below the breakdown field of conventional gate dielectrics. The switching operation can further be extended to the transmission mode with a slightly modified cavity geometry, with its absolute transmittance modulated by 40%.

A common-path interferometer for the real-time measurement of the liquid-crystal (LC) optic-axis angle and effective refractive index distribution is proposed. This method involves adding a polarizer and polarization camera to a general optical microscope. This requires only single-exposure imaging without changing any optical elements, and greatly simplifies the measurement process and system. In addition, the measurement results are unaffected by light-source power fluctuations or a non-uniform spatial distribution. Therefore, this method is suitable for measuring the LC optic-axis angle and effective refractive index of electrically controlled LC devices. Finally, the feasibility and validity of the proposed method are verified by simulation and experimentation.

In this paper, pulsed output with pulse-widths approaching the round-trip time were generated by utilizing a cavity-less high-gain Nd:GdVO 4 bounce geometry. By adopting an EOQ (electro-optics Q-switch) device, pulse-widths of 1.36 ns, 1.82 ns, and 2.39 ns were achieved at three effective cavity lengths, respectively. All these pulse-widths were close to the round-trip time of corresponding effective cavity lengths. Moreover, watt-level output power at kHz-level repetition rate was achieved, as well as the good beam quality with M 2 factor less than 1.3. The output had a time-averaged continuous spectrum with 10 dB linewidth of 0.2 nm.

While metasurfaces are now widely considered in free-space optics, their potential for coupling and tailoring guided waves is not fully explored. Here we transfer the Jones matrix method to target versatile on-chip coupling using metasurface-patterned photonic waveguides around the telecommunication wavelength of 1.55 μm, which can accommodate both propagation and Pancharatnam-Berry phase metasurfaces for guided waves. One can either encode two arbitrary and independent phase profiles to any pair of orthogonal polarizations or deploy complete control over both the phase and polarization of coupled modes. A set of design scenarios synergizing silicon nanoantennas and low-loss silicon-nitride waveguides are proposed, including directional couplers with mode-selectivity and polarization splitters with directionality ranging from 10 to 20 dB. Furthermore, our optimization method can be further extended to cover multiple working wavelengths. Exemplary on-chip color routers are also numerically demonstrated. This chip-integrated metasurface platform further translates the concept of a metasurface into photonic integrated circuits, serving as a positive paradigm for versatile and complete control over waveguide optical signals and motivating chip-scale applications such as polarization/wavelength demultiplexers, optical switches, and multifunctional mode converters.

The growth and laser amplifier performance of a large-aperture Nd:LuAG ceramic are reported. Using the vacuum sintering and high-temperature insostatic pressing (HIP) methods, three pieces of a 50 mm-aperture Nd:LuAG ceramic are fabricated and used as the gain medium in a diode-pumped nanosecond distributed active mirror amplifier chain (DAMAC). The energy storage capacity of large-aperture Nd:LuAG is investigated and compared with that of Nd:YAG. Energy amplification up to 10.3 J at 10 Hz is achieved, which, to the best of our knowledge, produces the highest peak power (1 GW) using Nd:LuAG. The excellent energy storage and extraction performance confirm the great potential of Nd:LuAG in high-energy scaling.

In this paper, we demonstrated a monolithic fiber-Bragg-grating-based (FBG-based) master oscillator power amplification configuration fiber laser with a narrow linewidth at high-power level. Several approaches were implemented to reduce the seed laser linewidth and the magnification of spectrum broadening in order to achieve a narrow output linewidth. The narrow seed laser linewidth was obtained by restricting the reflection bandwidth of the FBG. To reduce the magnification of spectrum broadening, a backward pumping scheme was employed in the amplifier stage after its capacity to suppress laser spectrum broadening was preliminarily investigated experimentally. Further, by intentionally shortening the length of the active fiber in the amplifier and sharing the backward pumping power with the oscillator, the spectrum broadening was further inhibited without sacrificing optical efficiency. A maximum output power of 2.19 kW was achieved with a 3 dB spectrum bandwidth of only 86.5 pm. The beam quality at the maximum power was measured to be M 2 ~1.46. No sign of transverse mode instability was shown during the experiments.

We propose a new method of phase-singularities manipulation in optical vortices carrying orbital angular momentum (OAM), namely, quadrant-separable multi-singularity manipulation (QSMSM). In QSMSM, the positions of partial vortices in a quadrant region can be manipulated, while the singularities in other regions remain unchanged. The basic model of the multi-singularity OAM beam is obtained by the principle of coherent superposition of two Hermite-Gaussian modes with spatial mismatch. The actual multi-singularity beams are generated by external modulation with a spatial light modulator. The distribution of vortices trajectory can be controlled by the energy mismatch degree and the spatial mismatch degree. The vortices in a quadrant region can be independently manipulated by partially controlling the energy mismatch degree. The technology of partially tuning singularities in QSMSM improves the flexibility of vortices control and has great potential in applications of optical tweezers and optical modulators.

We report, for the first time to the best of our knowledge, a truncated diffraction with a triangular aperture of the SU(2) geometric modes and propose a method to detect the complicated orbital angular momentum (OAM) of an SU(2) wave-packet. As a special vortex beam, a nonplanar SU(2) mode carrying special intensity and OAM distributions brings exotic patterns in a truncated diffraction lattice. A meshy structure is unveiled therein by adjusting the illuminated aperture in the vicinity of the partial OAM regions, which can be elaborately used to evaluate the partial topological charge and OAM of an SU(2) wave-packet by counting the dark holes in the mesh. Moreover, through controlling the size and position of the aperture at the center region, the truncated triangular lattice can be close to the classical spot-array lattice for measuring the center OAM. These effects being fully validated by theoretical simulations greatly extend the versatility of topological structures detecting special beams.

Experimental amplification of 10-ns pulses to an energy of 12.2 J at the repetition rate of 1-10 Hz is reported from a diode-pumped room-temperature distributed active mirror amplifier chain (DAMAC) based on Nd:YAG slabs. Efficient power scaling at the optical-optical efficiency of 20.6% was achieved by suppressing the transverse parasitic oscillation with ASE absorbers. To the best of our knowledge, this is the first demonstration of a diode-pumped Nd:YAG active-mirror laser with nanosecond pulse energy beyond 10 joules. The verified DAMAC concept holds the promise of scaling the energy to a 50 J level and higher by adding 10-12 more pieces of active mirror in the chain.

Crosstalk is the main challenge for active collision avoidance LIDAR. Conventional strategy on static discrimination threshold and unified number of accumulated pulses is not valid against crosstalk with varying number of sources and varying intensity. This paper presents an adaptive strategy to distinguish the target echo from dynamic crosstalk with unknown intensity in the scenario of intelligent vehicles and autonomous ground vehicles. The adaptive strategy is theoretically and experimentally verified to have much better performance on dynamic crosstalk than conventional strategy, and the detection rate is enhanced by 82.4% as well.

In this paper, a 933 W amplified spontaneous emission (ASE) source with a full width at half maximum (FWHM) of 50.4 nm is presented. The broadband source is generated by a 1271 W ASE amplifier together with 140m ordinary passive fiber for nonlinear transformation. With multi-wavelength rate equations and a nonlinear Schrödinger equation (NLSE), spectral evolution of the ASE source is analyzed theoretically.

SPM is an important limitation in some fiber lasers and amplifier systems. In this paper, the influence of gain saturation on the SPM-induced spectral broadening for coherent and incoherent nanosecond pulses is discussed. The models of SPM-induced spectral broadening for coherent and incoherent nanosecond pulses are generalized to the amplification with gain saturation. Experiments are conducted to validate our theoretical analysis for incoherent nanosecond pulses in a super-luminescent diode seeded cascaded fiber amplifier system where pulses with high peak power and high pulse energy are generated and gain saturation occurs. Excellent agreements between theoretical analysis and experimental results are obtained, and the influence of higher order nonlinear terms on the SPM effect is observed and analyzed .

Stimulated Raman scattering (SRS) is an important limiting factor for achieving high peak power intensity in fiber amplifier systems. It was proposed to use partially coherent light to increase the SRS threshold significantly. In this paper, the SRS threshold of partially coherent light in silica fibers is investigated by both experiments and theoretical analysis, which show that the SRS threshold is independent on light coherency when the bandwidth of the light is much narrower than 30 nm.

A numerical modeling is developed for 30-kW class liquid-convection-cooled elastically-mounted Nd:YAG multi-slab laser resonator configuration. The modeling exhibits the thermal effects and resultant wavefront aberration of the gain module under flow cooling and CW pumping at 100-kW level, the self-reproducing oscillating mode within the large-aperture cavity, as well as the beam quality enhancement by adaptive optics. The simulation results predict a CW output power of 31 kW with the optical-optical efficiency of 26.1% obtained from a modified resonator configuration with dual gain modules that have opposite flow directions, while the beam quality can be improved to β<2 after the correction of a deformable mirror.

A deformable mirror with actuators of thermoelectric coolers (TECs) is introduced in this paper. Due to the bidirectional thermal actuation property of the TEC, both upward and downward surface control is available for the DM. The response functions of the actuators are investigated. A close-loop wavefront control experiment is performed too, where the defocus and the astigmatism were corrected. The results reveal that there is a promising prospect for the novel design to be used in corrections of static aberrations, such as in the Inertial Confinement Fusion (ICF).

Femtosecond pulse laser with tilted intensity front demonstrates the capability of rotating the writing of nanograting in glass in 3D space. Other than the light polarization, this phenomenon is also associated with the quill-writing effect, which depends on the correlation between the sample movement and the pulse front tilt. This is because a pondermotive force, perpendicular to the tilted intensity plane, can push the excited electron plasma forward towards the pulse front. This behavior further tilts the electrical field plane and eventually result in a forced rotation of nanograting in 3D space.

A 3kW liquid-convection-cooled Nd:YAG CW laser resonator with a novel design is developed and demonstrated, in which the straight-through geometry is adopted that the oscillating laser propagates through multiple thin slabs and multiple cooling flow layers in Brewster angle. Using the elastically-supported Nd:YAG single-crystal thin slabs at different doping levels, a multimode laser output with the output power of 3006 W is obtained from the stable cavity at the pump power of 19960 W, corresponding to an optical-optical efficiency of 15.1%, and a slope efficiency of 21.2%.

Deformable mirror (DM) is a common-used active freeform optical element. We introduce the concept of Woofer-Tweeter DM system for controlling focal-plane irradiance profiles. We firstly determine a freeform reflective surface for transforming a given incident laser beam into the desired focal-plane irradiance distribution by numerically solving a standard Monge-Ampère equation. Then, we use a low-bandwidth Woofer DM to approximate the required freeform reflective surface and a high-bandwidth Tweeter DM to compensate the residual error. Simulation results show that, compared with single DMs, the Woofer-Tweeter DM system brings the best focal-plane irradiance performances.

A laser-induced damage array composed of numerous pinpoints is generated in a large-aperture KDP crystal to suppress the transverse stimulated Raman scattering (TSRS). The 36 cm × 8.5 mm × 7 mm damage array is used to block the propagation of the TSRS photons within the crystal and decrease the TSRS gain length. Then several series of experiments were conducted on a large-aperture laser system to test this method and experimental results show that the amplification of TSRS is significantly suppressed by the laser-induced damage array.

We propose an improved double freeform-optical-surface design method for shaping a prescribed irradiance distribution whilst forming a desired wavefront from a given incident beam. This method generalizes our previous work [Opt. Exp. 21, 14728-14735 (2013)] to tackle non-separable beam irradiances. We firstly compute a proper ray mapping using an adaptive mesh method in the framework of the L2 Monge-Kantorovich mass transfer problem. Then, we construct the two freeform optical surfaces according to this mapping using a modified simultaneous point-by-point procedure which is aimed to minimize the surface errors. For the first surface, the modified procedure works by firstly approximating a value to the next point by only using the slope of the current point and then improving it by utilizing both slopes of the two points based on Snell's law. Its corresponding point on the second surface can be computed using the constant optical path length condition. A design example of producing a challenging irradiance distribution and a non-ideal wavefront demonstrates the effectiveness of the method.

Making use of the stretching effect of grazing incident laser beam, a novel method of wavefront correction was promoted. Without adding any extra beam expanding components, aberrations of wavefront could achieve satisfying correction by two grazing reflections along orthogonal directions on the deformable mirrors. The stretching effect expanded the beam size along grazing direction and the orientation dependent varying aberrations were well compensated as more actuators took effect in the correction process. Analysis showed that the fitting coefficient of all the first 30 order Zernike polynomials could be controlled within 5% by this method.

A numerical double-freeform-optical-surface design method is proposed for beam shaping applications. In this method, both the irradiance distribution and the wavefront of the output beam are taken into account. After numerically obtaining the input-output ray mapping based on Energy conservation using the variable separation method, the two freeform optical surfaces can be constructed simultaneously and point by point corresponding to the ray mapping based on Snell's law and the constancy of the optical path length. The method is only applicable for separable irradiance distributions. However, such a restriction is fulfilled by many practical laser beam shaping examples. Moreover, the restriction can simplify the computation considerably. Therefore, the method may be quite useful in practice, although it is not applicable to more general cases. As an example, the method was applied to design a two-plano-freeform-lens system for transforming a collimated 20 mm Gaussian laser beam (beam waist: 5mm) into a uniform 10 × 40 mm(2) rectangular one without changing the wavefront. Simulation results show that we can obtain a dual lens beam shaping system with the relative root mean square deviation of the irradiance ranging from 0.0652 to 0.326 and the power ratio concentrated on the desired region ranging from 97.5% to 88.3% as the output beam transfers from 0mm to 1000mm.

We demonstrate the improvement and formation of UV-induced damage on LBO crystal output surface during long-term (130 h) high-power (20 W) high-repetition-rate (80 kHz) third-harmonic generation. The output surface was super-polished (RMS surface roughness <0.6 nm) to sub-nanometer scale super smooth roughness. The surface lifetime has been improved more than 20-fold compared with the as-polished ones (RMS surface roughness 4.0~8.0 nm). The damage could be attributed to the consequence of thermal effects resulted from impurity absorptions. Simultaneously, it was verified that the impurities originated in part from the UV-induced deposition.

A theoretical model as well as the experimental verification of the combined guiding mechanism for the transverse mode formation in the end-pumped laser resonator are investigated. The nonlinear Schrödinger-type wave equation in the gain medium is derived, in which the combined guiding mechanism: the thermal induced refractive index guiding effect as well as the gain guiding effect, is taken into account. The gain saturation and spatial hole burning are considered. The split step Fourier method is used to solve the nonlinear wave equation. A high power end-pumped Nd:YVO4 laser resonator is built up. After establishing the pump absorption model of our laser resonator, the temperature distribution in the gain medium is obtained by the numerical solving of the heat diffusion equation. The combined guiding effect is first observed in the end-pumped Nd:YVO4 laser resonator, and the experimental transverse mode profiles well agree with the theoretical prediction from the derived nonlinear Schrödinger-type wave equation. The geometric design criterion of the TEM00 mode laser is compared with our wave theory. The experimental- and theoretical- results show that our wave theory with the combined guiding mechanism dominates the transverse mode formation in high power end-pumped laser resonator.

We report a 12.2 W pulsed TEM(00) output from Q-switched quasi-concentric laser resonator with line-shaped end-pumping profile, with the repetition rate of 30 kHz and optical-optical efficiency of 27.1%. The laser output mode is symmetrized in two directions in terms of beam quality, waist radius, and waist position.

Corner pumping is a new pumping scheme for diode-pumped solid-state lasers, which has the advantages of high pump efficiency and favorable pump uniformity. A continuous-wave corner-pumped Nd:YAG/ YAG composite slab multi-wavelength laser at around 1.1 µm is demonstrated. The maximal output power is up to 12.06 W with an optical-to-optical conversion efficiency of 24%. At an output power of 10.3 W, the M(2) factors of beam quality at width and thickness directions are 7.71 and 2.44, respectively. With a LBO crystal inserted in the cavity, continuous-wave yellow-green laser with an output power of 841 mW is obtained. The experimental results show that a corner-pumping is a feasible scheme in the design of diode-pumped solid-state 1.1 µm lasers and their frequency-doubling to the yellow-green with low or medium output powers.

CdSe/ZnS colloidal quantum dots generally exist as blinking phenomena during the luminescence process that remarkably influences its applications. In this work, we used the surface plasmonic effect to effectively modulate single quantum dots. Obvious contrasts have been observed by comparing single quantum dots on silica and gold films. The surface plasmon is shown to obviously suppress the blinking of single quantum dots. With further demonstrated second- order correlation measurements, an anti-bunching effect was observed. The anti-bunching dip gives the smallest value of g(2)(0) = 0.15, and the lifetime of the exciton has been reduced. This method presents the application's potential towards tunable high-emitting-speed single photon sources at room temperature.

We report a diode-pumped Q-switched Nd:YAG-KGW Raman laser operating in two-color modulation. The output wavelength can be switched between 1159 nm and 1177 nm using an E-O switch, and the Raman output modulated in spectra-time domains was achieved. Raman pulse energy up to 114 mJ at 1177 nm and 98 mJ at 1159 nm were obtained respectively, corresponding to an overall Diode-Stokes conversion efficiency of 15.3% at 1177 nm and 13.2% at 1159 nm.

Ray-tracing algorithm was used to simulate the pump absorption efficiency and pump absorption distribution of LD corner-pumped laser with different parameters of Nd:YAG composite slab crystal. Resonator experiment was performed to suppress the oscillation of higher-order modes and realize TEM(00) operation. Experiment results showed that the output power was 11.94 W with an optical-optical efficiency of over 26%, and the M2 factors of beam quality at width and thickness directions were 1.18 and 1.34, respectively. It has been proven that the corner-pumped configuration could obtain laser output with good beam quality as a result of high pump efficiency and good pump uniformity.

We demonstrate the high-repetition rate acousto-optic Q-switching of a dual-rod Nd:YVO4 laser. Two thermally bonded composite YVO4-Nd:YVO4-YVO4 rod crystals were used as the gain medium to reduce the serious thermal effect. The pump mode and its influence on the laser mode were analyzed, and the effective pump radius was controlled by tuning the spectrum of laser diodes with adjustment on the temperature of laser diodes. Three different configurations of cavity optics were designed and the output performance using these cavities was investigated. In Q-switching operation, 73.2 W TEM00 mode average power at 650 kHz was obtained. The stable Q-switching range was from 80 kHz to 650 kHz with the pulse duration increasing from 17.5 ns to 80 ns. In CW operation, 78 W TEM00 mode and 93 W multi-mode output power was achieved with different cavity designs, corresponding to the optical-optical efficiency of 46.5% and 52.2% respectively.

The Zenneck THz surface wave (Z-TSW) on metals is discussed with respect to its difficulty in generation and measurement. The spatial collapse of the extent of the Z-TSW evanescent field, upon the addition of a sub-wavelength dielectric layer on the metal surface, is explained by a simple model, in good agreement with exact analytical theory. Experimental measurements of the THz surface wave on an aluminum surface covered with a 12.5 microm thick dielectric layer have completely characterized the resultant single-mode dielectric layer THz surface wave (DL-TSW). The measured frequency-dependent exponential fall-off of the evanescent wave from the surface agrees well with theory. The DL-TSW frequency-dependent absorption coefficient, phase velocity, group velocity and group velocity dispersion have been obtained. These guided-wave parameters compare favorably with other guided wave structures.

We report a high-power, high-repetition-rate TEM00 mode MOPA laser using acoustic-optic Q-switching. Seed laser from the dual-end- pumped Nd:YVO4 oscillator was scaled up to 183.5 W average power at 850 kHz after behind amplified by the four-stage power amplifiers. The stable Q-switching operation worked at different pulse repetition rate from 60 kHz to 850 kHz while the pulse duration increased from 12.8 ns to 72 ns. The beam quality was near diffraction-limit with M2 factors measured as M2x = 1.28 and M2y = 1.21. In CW operation, 195 W TEM00 mode output was achieved corresponding to the total optical-optical efficiency of 44.7% and the absorbed pump power to output power efficiency of 53.3% respectively.

An end-pumped ytterbium-doped all-fiber laser with 300 W output in continuous regime was reported, which was based on master oscillator multi-stage power amplifiers configuration. Monolithic fiber laser system consisted of an oscillator stage and two amplifier stages. Total optical-optical efficiency of monolithic fiber laser was approximately 65%, corresponding to 462 W of pump power coupled into laser system. We proposed a new method to connect power amplifier stage, which was crucial for the application of end-pumped combiner in high power MOPAs all-fiber laser.

We demonstrated a 103.5 W green laser with an extra-cavity second harmonic generation. The IR source was a high power Q-switched Nd:YVO(4) MOPA laser. The type I phase-matching LiB(3)O(5) was used as the nonlinear crystal in the second harmonic generation. The 103.5 W average power of 532 nm green laser was obtained at a repetition rate of 60 kHz with the beam quality factors of M2x <1.44 and M2y <1.23 in the orthogonal directions, corresponding to a peak power as high as 1.5 MW with the instability of pulse energy less than +/-4%. The optical frequency conversion efficiency from IR to green laser was up to 67%.

A high power, dual-end-pumped Nd:YVO(4) laser with a MOPA configuration was stably Q-switched at repetition rate up to 500 kHz. The thermally bonded Nd:YVO(4) crystal was used in our experiment. In acousto-optically Q-switching operation at repetition rate of 500 kHz, 35 W average power was produced by the oscillator, with optical-optical efficiency of 41.7%. 108 W average power was obtained by a master oscillator power amplifier (MOPA) configuration including two amplifier stages, corresponding to the total optical-optical efficiency of 42.2%. The pulse duration was 48 ns, with a stability of pulse peak value < 2.5%. The beam quality was better than two-times diffraction-limit (M(x)(2) = 1.99, M(y)(2) = 1.76).