Advanced Lasers, High-Power Lasers, and Applications XV

This presentation introduces a novel polishing methodology centered around robotic systems. Specifically, deterministic polishing technologies like computer controlled optical surfacing (CCOS) and magnetorheological finishing (MRF) are synergistically integrated with robotic platforms to realize a versatile and economically viable multi-axis polishing apparatus. The presentation delves into the advantages and disadvantages inherent in Robot CCOS&MRF systems, elucidating various compensation techniques designed to enhance the precision of the robotic polishing process. Empirical evidence underscores the capability of robot-based CCOS & MRF systems to attain nanometer-level accuracy in the fabrication of mid-sized aspherical or freeform optics, all while operating within a cost-effective framework.

The 14-meter off-axis deployable space telescope, Single Aperture Large Telescope for Universe Studies (SALTUS), is designed to serve as an exceptionally large far-infrared observatory in space. SALTUS aims to observe thousands of faint astrophysical targets, including the earliest galaxies, protoplanetary disks in different stages of evolution, and various solar system objects. Its architecture incorporates a radiatively cooled, unobscured 14-meter aperture and cryogenic instruments, enabling both high spectral and spatial resolution with unprecedented sensitivity across a wavelength range that is largely inaccessible to current ground-based or space observatories. The innovative SALTUS optical system, featuring a large inflatable off-axis primary mirror, offers exceptional sensitivity, angular resolution, and imaging performance at far-infrared wavelengths over a wide ±0.02° × 0.02° field of view. SALTUS' compact design allows it to fit within existing launch fairings and be easily deployed in orbit.

Non-destructive techniques are critical for understanding the body’s structure and function, for both scientific discovery and development of diagnostic procedures. Optical coherence tomography (OCT) is outstanding for cross-sectional mapping of the microstructure of tissue up to 2 mm in depth. Variants of OCT can show blood flow, quantify tissue stiffness, and visualize movement of cellular structures. I will discuss two examples of how OCT has positively impacted medicine. First, monitoring tumor growth in mouse models of colon cancer is critical for understanding the value of chemopreventive and therapeutic compounds. Miniature endoscopes allow alterations in crypt structure and tumor size to be visualized. Second, the understudied fallopian tube is a significant imaging challenge, but careful ex vivo studies and development of flexible sub-mm diameter endoscopes allow elucidation of the complex microstructure of the FT including the coordinated movement of cilia. These insights can be used for understanding infertility and the development of ovarian cancer.

Harnessing integrated quantum photonic circuits for the generation, manipulation, and detection of quantum states of light offers a pathway towards implementing advanced quantum technologies for applications spanning quantum computation, quantum simulation, and quantum communication. In this presentation, we will show recent advancements in the large-scale integrated photonic devices and circuits for quantum computation, networking, and simulations. Our discussion will delve into the on-chip processes involved in creating, manipulating, and measuring complex entanglement structures, such as multidimensional and multiphoton entanglement. We will discuss quantum computing and networking with integrated photonics, highlighting several aspects of chip-based entanglement distribution, teleportation, Gaussian Boson sampling, qudit-based and cluster-state quantum computations. We will also discuss photonic simulations of topological physics on a lattice of coupled microresonators, by which we have observed topologically-protected entanglement and fast topological non-Hermitian phase transitions, and we implemented a fully programmable photonic insulator within this framework.

We have experimentally removed most of the discrete pre-pulses generated by the post-pulses within a few hundred picoseconds around the main pulse with wedged optics. We have achieved orders of magnitude enhancement of the pedestal within a few tens of picoseconds around the main pulse by improving the optical quality of a key component in the stretcher. For the complete elimination of the remaining pre-pulses, the femtosecond optical parametric amplifier based on the utilization of the idler pulse and, in parallel, nonlinear sum-frequency generation with the signal and idler of an OPA is also being investigated. We have successfully installed the single plasma mirror system and confirmed three orders of magnitude further enhancement. We are planning the double plasma mirror configuration for a further three orders of magnitude improvement.

Recent years, high power femtosecond laser has been rapidly developing and widely used in industry, medicine as well as scientific research. As high as kilowatt level average power of femtosecond lasers have been realized in all the thin-disk, fiber and slab geometries. However, the most wide used gain material for thin-disk and slab geometry is Yb:YAG crystal, whose narrow emission bandwidth limits the pulse duration after the amplification. Yb:CYA with a much broader bandwidth seems to be a potential candidate for high power femtosecond amplifiers with short pulse duration. In this talk, we present our recent work on femtosecond amplifers based on the Yb:CYA crystal, as high as 65 W of average power and 6.5 mJ of pulse energy with pulse duration shorter than 200 fs was demonstrated. The report provides an outlook on the amplification of 100-200 W power and subsequent nonlinear frequency conversion.

We present an integrated repetition rate tunable Yb-fiber laser system delivering micro-joule pulses with compressed pulse duration below 350 fs. The system used a chirped fiber Bragg grating as fiber stretcher, which was specially designed to match the 2nd and 3rd order dispersion of transmission grating compressor with a groove density of 1740 l/mm. 1 μJ pulse in 266 fs and 10 μJ pulse in 325 fs pulse duration were obtained at repetition rate of 2 MHz and 200 kHz, respectively. The pulse repetition rate can be tuned from 200 kHz to 2 MHz while maintaining <350 fs microjoule pulses output. This compact fiber laser source was built for applications in ophthalmology, such as cornea flap cutting and tissue vaporization.

We have used an active ytterbium double-clad spun fiber with a mode field diameter of 35 µm and an intrinsic birefringence of 1.45×10⁻⁸ rad/m in our MOPA scheme for a high-power fiber laser. The optical source operates at a wavelength of 1040 nm in the frequency range of 1 to 20 MHz (pulse duration of 50 ps), with an average power of 160 W and a peak power of 160 kW (8 µJ per pulse), delivering high beam quality (M² = 1.15).

This paper presents all-fiber master oscillator-power amplifier systems that deliver high average power picosecond pulses with durations of 6 to 50ps, a tunable repetition rate within 360 kHz to 1 GHz range, and peak powers of up to 2 MW. The experimental investigations incorporate two Yb-doped spun tapered double-clad fibers gain modules with 60 μm and 92 μm core diameters. Utilizing the 92 μm core module picosecond pulses with high average power of 625 W average power at 20 MHz, and 645 W at 1 GHz were achieved. The gain module with 60 μm core diameter enabled to deliver a high peak power pulsed- signal with 2 MW peak power at 360 kHz and 50 ps pulse duration, while 26 MHz and 6 ps pulses reached 1 MW peak power. In all configurations, near-diffraction-limited beam quality, M² < 1.4, was maintained without any traces of transverse mode instability (TMI). These compact, TMI-free, high-power amplifiers offer a promising platform for high-power ultrafast fiber lasers for the vast majority of industrial applications.

This paper presents the development and performance evaluation of a four-channel fiber amplifier system, achieving an average power of more than 800 W before compression. The average power of 724 W and a single pulse energy of 0.9 mJ at a repetition rate of 800 kHz is obtained after a grating-based compressor. The system demonstrates a beam spot ellipticity of 96% and a root-mean-square error of power fluctuation of 0.59%. By optimizing the gain of each channel amplifier and analyzing the time-domain characteristics of the compressed pulse, effective dispersion pre-compensation is achieved, reducing the pulse duration from 445 fs to 227 fs without requiring pulse shaping or spectral modulation. Utilizing nonlinear post-compression techniques, the laser pulse duration is further shortened to several tens of femtoseconds.

A Kerr lens mode-locked (KLM) thin-disk laser oscillator with a promising broad-gain bandwidth medium, Yb:KLuW (Yb3+:KLu(WO4)2), has been developed and ultrashort pulse laser oscillation demonstrated. The pulse width, spectral width and time-bandwidth product obtained under OC transmittance of 0.6% and GDD-1400 fs2 conditions were 57.5 fs, 20.0 nm and 0.326, respectively. The KLM thin-disk laser was the first demonstration of this material and its family (Yb-doped tungstate-based gain medium) in the world, and the pulse width obtained was the smallest ultrashort pulse laser using the same material reported so far. The average power, however, was limited to 425 mW by the low OC transmittance. In CW laser oscillation experiments, an average output power of 139 W and a slope efficiency of 62% were also obtained.

We present the design and construction of a mode-locked master oscillator power amplifier (MOPA) laser system, featuring a passive mode-locked oscillator operating at 1064 nm and a novel single-stage power amplifier with up to 40 dB gain. The amplifier delivers over 500 W peak power through a single-mode, 6 µm core polarization-maintaining (PM) fiber, producing 10 ps pulses with an ideal Gaussian beam profile. Amplified spontaneous emission (ASE) is effectively suppressed to -50 dB relative to the laser signal in the output spectrum. The system has demonstrated stable operation for over 10,000 hours, including continuous operation and intermittent on-off cycling. Throughout this period, no variations in self-starting behavior, output power, wavelength, or spectral bandwidth were observed.

In order to obtain sub-nanosecond microchip laser with low timing jitter, a scheme of injection seeding assistant laser pulses was designed in this work, which actively bleaches the Cr:YAG crystal and so that the sub-nanosecond laser pulses are locked and synchronized. The temporal stability of the sub-nanosecond laser was improved by nearly three orders of magnitude. Adjusting the peak pump power and ΔtQ can realize tunable sub-nanosecond laser power, eliminate the pulse tailing in the time-domain waveform, improve the beam quality and power stability, and regulate the beam spots. The sub-nanosecond microchip laser in this scheme has a simple structure and synchronized timing sequence, which could be used in high-resolution laser ranging, lidar, etc.

We report a long-wave infrared source driven by a 1-kHz Yb:YAG thin-disk laser, which comprises two parallel multi-cycle optical parametric chirped-pulse amplifiers (OPCPAs) operating at 2.3 and 3.1 μm, respectively, alongside a stage of ZnGeP2-crystal-based difference-frequency generation (DFG). The resulting 9-μm DFG pulses have an energy of 0.21 mJ, a 3-cycle duration, a 1-kHz repetition rate, and long-term energy stability. The simultaneous output of three synchronized intense lasers at short-wave infrared (2.3 μm), mid-wave infrared (3.1 μm), and long-wave infrared (9 μm), renders the source particularly appealing for multi-color ultrafast applications.

Combining the advantages of spatio-spectral multiplexing and computational imaging, we proposed a self-referenced single-shot spatiotemporal measurement technique called coherent modulation imaging for the spatio-spectrum (CMISS). Experimentally, CMISS acquired the multi-dimensional amplitude and phase information of an ultrashort pulse in a single frame, with femtosecond-scale temporal resolution, micron-scale spatial resolution, and 0.04 rad phase accuracy. Furthermore, this spatiotemporal measurement technique was applied to the single-shot ultrafast diagnosis of laser plasma evolution. An arbitrary time-wavelength-encoded biprism interferometer (TWEBI) was demonstrated with a temporal resolution of 200 fs, a spatial resolution of 4 μm, an effective frame rate of 5 trillion fps, and freely adjustable temporal range. By using plug-and-play biprisms, TWEBI experimentally realized the convenient switching between shadow-recording mode and phase-measurement mode for the dynamic characterization of femtosecond laser induced air filamentation process.

We experimentally investigated the build-up dynamics of single-cavity dual-wavelength-comb pulses emitted from a ring fiber cavity with Lyot filter configuration. When the pump powers of the bidirectional pumps are set as 132.2 mW and 142.0 mW respectively, dual-wavelength pulses with the center wavelengths of 1532.2 nm and 1553.2 nm and spectral bandwidths of 1.1 nm and 1.8 nm are obtained. To measure the single-shot build-up process by using dispersive Fourier transform spectroscopy, a 10-kilometer-long single-mode fiber with a group dispersion velocity of 17.8ps/nm/km, i.e. the time delay of 178 ps/nm, is added between the output of laser and optical detector. When switching on the pump diode, the two-step build-up process of dual-wavelength pulses is experimentally verified. These results provide a deep understanding of single-cavity dual-wavelength-comb pulse generation and contribute to the design and control of single-cavity dual-comb pulses.

High field ultrafast laser pulse can instantaneously generate intense electromagnetic fields at a very small scale of focus, in which microscale region it is expected to generate compact electron accelerators and new radiation sources. Here we present a principle of quasi particle coherent radiation amplification using a free electron pumping. When an ultrafast laser focus on a metal wire waveguide, the excited electron pulse pumps surface plasmon polaritons and achieves coherent amplification, which is observed by the ultrafast optical pump-probe method. Using this quasiparticle source with natural surface modes, we have demonstrated a new method of waveguide-coupled terahertz electron acceleration with electron energy gain exceeding MeV at an acceleration distance of 5 mm within the waveguide. The electrons locked phase with laser are crucial for the direct acceleration and pulse control of electrons. We propose a scheme to generate attosecond electron pulse (~260 as) from solid surface under relativistic laser field.

a scheme called advanced dual-chirped optical parametric amplification (DC-OPA) that employs two kinds of nonlinear crystal (BiB3O6 and MgO-doped lithium niobate) was demonstrated to generate high-energy, single-cycle mid-infrared laser pulses. Based on the advanced DC-OPA scheme, we achieved carrier-to-envelope phase-stable mid-infrared laser pulses with a bandwidth of 1.4–3.1 μm and an output pulse energy of 53 mJ. After temporal compression, the pulse duration was down to 8.58 fs, which corresponds to 1.05 cycles with a central wavelength of 2.44 μm and indicates a peak power of 6 TW. To our knowledge, the obtained pulse energy and peak power are the highest achieved for optical parametric amplification of single-cycle mid-infrared laser pulses.

Current ultra-intense ultrashort lasers have achieved peak powers of 10 Petawatt and focused intensities of 10^23 W/cm^2. Next, considering a 10^26 W/cm^2 focused intensity and a single-wavelength focal spot, the peak power should be at least 1 Exawatt. Single-cycle Exawatt-class lasers require the lowest energy, which can reduce the size and cost of the project. However, to achieve single-cycle Exawatt-class laser pulses, near-octave ultra-broadband high-energy amplification is required. For this purpose, the wide-angle non-collinear optical parametric chirped pulse amplification (WNOPCPA) method was proposed, and the first experimental demonstration is introduced here. At the same time, a near-octave ultra-broadband grating for pulse stretching and compression of WNOPCPA has been successfully developed. To focus almost all the energy of a single-cycle Exawatt-class laser into a single-wavelength focal spot, a two-step focusing method with the combination of a parabola and a hyperbola is introduced here, and the focal spot size can be reduced from several-wavelength to single-wavelength.

Optical parametric amplification (OPA) is a promising method of producing extremely intense light. In this study, we propose an amplification scheme known as crossed-Fabry–Perot–cavity OPA (XOPA). It is based on the principle of periodic idler elimination,resulting in a monotonically increasing overall conversion efficiency. Using signal pulses at 808 nm and pump pulses at 532 nm, we experimentally demonstrated a chirped pulse XOPA with a conversion efficiency of 56.28% and a gain bandwidth of 120 nm. Further investigations revealed several advantages. Stable pulse shaping in the spatial, temporal, and frequency domains was realized by actively attaching a spatiotemporal modulation to the pump pulse. Pulse contrast adjustability on the front edge of the signal pulse was verified in the XOPA using different Fabry-Perot cavity lengths. These results indicate the astringency and precise regulation of output in nonlinear processes. Because there are numerous crystals suitable for noncollinear configurations from the near-infrared to mid-infrared regions, XOPA has a universal potential for use in laser systems with extreme intensity, few-cycle duration, and ICF drivers.

Vortex beams have been applied in multiple engineering and scientific applications due to their distinctive orbit angular momentum and vortex phase characteristics. Traditional methods suffer from complicated setup for the generation of vortex beams not only costly but also non-scalable. In this study, we propose a novel approach for the direct generation of vortex beams and coaxial muti-vortex beams through the use of laser resonator mirror. We have designed a diffractive output mirror of the laser resonator using Gerchberg-Saxton (GS) algorithm inspired by the mode matching theory and optical diffraction principles. Through the analysis of the pumping power in a four-level laser configuration, we have established correlations between ring-shaped pumping light and target vortex beam characteristics, thereby providing essential design guidelines for vortex beam generation within resonators.

The periodical pulse bundles were presented in a Yb-doped double-clad distributed Bragg reflector all-fiber configuration. To our best knowledge, this is the first reported periodical pulse bundles in the self-pulse fiber laser. We study the variation of repetition rate of pulse bundle, inner-separation, and other parameters via pumped power. With a pumped power of 529.2mW, the periodical pulse bundles is obtained. Furthermore, a single pulse bundle compose of 1 main pulse and 2 sub-pulses. The pulse width of the main pulse and the sub-pulse are 2.2s and7.7s, respectively. The separations of between main pulse, right sub-pulse and left are 22.70s and 22.15s, respectively. The average period of the pulse bundle is ~75s with repetition rate of 13.3kHz. The number of sub-pulses between adjacent main pulses decreases to 1 when the pumped power does to 450.2mW. When the pumped power increases to 594.4mW, The number does to 3.

Frequency stability of laser sources is critical in ensuring laser-based measurement accuracy and reliability. In this paper, we report a method to assure high frequency stability of multi-wavelength lasers through the Pound-Drever-Hall technique. Three lasers with wavelength spacing of about 5G and 15nm around 1.55μm were simultaneously locked to the same Fabry-Pérot cavity with free spectral range of 5G. When locked, the laser frequencies were observed to drift all within 200 kHz, validating the feasibility of the system design. Frequency-locking of more lasers with different wavelengths can be realized to satisfy the requirement of different applications in this way.

The spectrum of 1 micron femtosecond laser is broadened according to the principle of dispersion balance. By balancing the positive dispersion in the 1 micron laser, the total dispersion of the entire laser is 0 or in the near 0 dispersion region, so as to achieve the purpose of broadening. Firstly, 1 micron single-mode fiber is added in the cavity to reduce the positive dispersion in the cavity to a certain extent. Then two gratings with negative dispersion are used outside the cavity to further balance the dispersion of the laser. After equilibrium, the dispersion is in the near zero dispersion region, extending the original spectral width of 5nm by nearly 6 times. This is a promising light source that is widely used in biomedical imaging and other applications.

Precise dispersion measurement is important for various applications, including optical communications, laser cavity design, and nonlinear optics. In this work, we present a dispersion measurement method for the fiber under test inside the Fourier domain mode-locked (FDML) laser by locating the sweet spot regime under the different driving frequencies of the Fabry-Perot tunable filter. The group delay resolution achieved is 2.88 ps, an order of magnitude higher than other dispersion measurement methods based on phase shift or pulse delay. The proposed dispersion measurement method has high resolution and simple configuration, making it promising for measuring the dispersion of special fibers or conventional fibers near their zero-dispersion wavelengths.

Title:Nonlinear optical response and their laser modulation properties of CsPbBr1.8I1.2 quantum dots at 1 µm. Authors:Mengqi Lv, Jin Zhao，Endi Dai，Yanxu Zhang，Maorong Wang*， Xia Wang Abstract:CsPbBr1.8I1.2 perovskite quantum dots were prepared by thermal injection method. The quantum dots were characterized for their morphology and nonlinear optical properties. The nonlinear absorption coefficient of -1.8610-6 was attained by fitting the experimental data. The central wavelength of the photoluminescence spectra was 585.5nm with a full width at half maxima (FWHM) of 33.9nm. The saturable absorber mirror (SAM) was formulated by spin-coating method. A semiconductor laser pumped passively mode-locked Nd:YVO4 laser was successfully implemented in a W-type cavity with a length of 1.9m. The maximum average output power and the repetition frequency obtained at the absorbed pump power 3.3W were 287mW and 80.645MHz respectively.

In this paper we report on a simple method for characterizing ultrashort vortex laser pulses generated from Erbium-doped fiber laser. The single-mode fiber oscillator can produce mode-locked pluses with duration of 316 fs around 1550 nm. By passing linearly polarized TEM00 Gaussian mode-locked pulses through vortex retarders, ultrashort vortex laser pulses are created, and the topological charge numbers of the vortex beams are characterized through far field multi-pinhole interferometer. The experiment results agree well with simulation. This diagnostic method will benefit vortex beam generation and advance its application for ultrafast science.

In high-power laser systems, we propose a new single-shot spatiotemporal measurement method combining compressed sensing (CS) and quadri-wave lateral shearing interferometry (QWLSI) to address the challenges of characterizing ultrashort broadband lasers. Our technique accurately determines wavefront characteristics across spectral and spatial dimensions, and is optimized using TWIST-TV and Fourier modal expansion. The study evaluates the impact of regularization parameters, channel numbers, and frames on measurement accuracy. We find that multiframe models outperform single-shot models, particularly in broadband applications, with improvements in Peak-Signal-to-Noise Ratio (PSNR) and Root-Mean-Square Error (RMSE). This method successfully recovers wavefronts over a 100 nm range with 100 channels achieving average recovery accuracy of 0.012λ and 30.27 dB.The findings confirm the method in precisely measuring broadband laser, making it foundational for future large-scale implementations.

The transition of operational states in lasers has always been a pivotal issue in laser technology. Various modulation methods and techniques can achieve diverse forms of pulse outputs to cater to the requirements of different application scenarios. In our work, we constructed an Er-doped fiber laser with PbS-carbon nanotube saturable absorbers, achieving the transition between Q-switched and mode-locking pulses by adjusting pump power and polarization controller states. The research results provide a new perspective for the design and implementation of laser devices capable of switching output pulse types, offering fresh insights into the design and optimization of fiber lasers.

In multimode fiber, nonlinear multimodal interference is sensitive to external perturbation, such as bending, temperature. Based on this feature, rich nonlinear dynamic could be captured in mode-locked fiber laser, when a piece of multimode fiber is incorporated in cavity. Based on the structure of single mode fiber-multimode fiber-single mode fiber, two distinct-type spectral sideband and adjustable width of sidebands are demonstrated in a Er-doped fiber laser. The numerical simulation displays the effect of filtering, high-order dispersion, polarization modal dispersion on spectral sidebands. Our work supports a promising solution for exploring nonlinear dynamics in fiber lasers.

High-quality, ultrafast fiber lasers have long been favored by both research and industry for many desirable properties. Here, we present an Yb-doped fiber laser system by utilizing a directly spliced photonic crystal fiber to amplify a seed source, and sub-100 fs ultrashort pulses are obtained with an average power of 6.55 W and at a repetition rate of 100.15 MHz. The M2 factors are measured to be about M_x^2=1.13 an M_y^2=1.12, respectively. These results demonstrate the promising potential of this compact fiber laser system for both research and industrial applications.

In response to the significant demand for high damage threshold, broadband high reflection films for high power laser systems. The composite high-reflection films combines the advantages of high damage threshold and high refractive index materials. The effect of the numbes of cycle of Al₂O₃/SiO₂ protective layer on the damage resistance of Al₂O₃/Ta₂O₅/SiO₂ composite high-reflection films at 532 nm band is investigated. There is no significant distinction in the laser damage threshold of the composite high-reflection films with three or six cycles of protective layer, which is mainly due to various impurities and defects in the thin films. Six cycles of protective layer protection was more effective, all the laser damage occur within the protective layer. And the interface between Al₂O₃/SiO₂ and Ta₂O₅/SiO₂ is the weak region of composite films.This study provides a valuable reference for the subsequent application of composite dielectric films in high-power laser systems.

This article establishes a theoretical model for designing a surface grating compressor, the compressor has advantages such as large dispersion adjustable range, high diffraction efficiency, compact structure, and strong power tolerance. The ns level four pass transmission surface grating compressor has a diffraction efficiency of 73.2%, reaching 94% of the theoretical value, and an output pulse width of 459fs.

Molecular alignment and orientation are two special rotation states of gaseous molecules. Nowdays, molecular alignment and orientation has been a hot topic of atoms, molecules and optical physics since they not only can reveal the deep quantum mechanisms of the molecules in the external field but also pave a way for the quantum information science, and intense field physics. Here, we investigate the molecular alignment of gaseous carbon monoxide (CO) induced by the near-infrared few-cycle laser pulses through nonresonant process by numerical methods. The Hamiltonian of the molecules in the ultrashort laser pulses is obtained based on the rigid rotor approximation theory, then the time-dependent Schrodinger equation of the system is solved by split-step Fourier transform. It is found that the momentum of the molecules increases rapidly in a very short time, and then keeps stably for a long time; the alignment degree of molecules is an oscillation signal in the time domain even the

A 101.3 μJ single-frequency linear-polarized pulsed laser at 1550 nm was demonstrated from a 12-μm core diameter fiber amplifier. The pulse width and repetition rate were 387 ns and 10 kHz, respectively, corresponding to a pulse peak power of 262 W. Narrow linewidth of 780 kHz was measured with a delayed self-heterodyne method and the optical signal-to-noise ratio was over 45 dB without the observation of the ASE around 1 μm.

Neodymium-doped fiber lasers (NDFL) that operate on the three-level transition offer emission within the range of approximately 860 nm to 940 nm. Coupled with their inherent advantages of compactness and beam quality, NDFLs have garnered significant interest from researchers and are increasingly preferred for generating DUV light. However, realizing high-power high energy lasing around the 900 nm band still remains a challenge. This is attributed to the notably higher stimulated emission efficiency of the four-level conversion at around 1060 nm in neodymium-doped fibers compared to the efficiency of the three-level conversion of 4F3/2-4I9/2. In this work, we introduce and demonstrate a high energy all-fiberized nanosecond pulsed neodymium-doped master oscillator power amplifier (MOPA) system that emits light at 905 nm, the unwanted ASE and parasitic lasing at around 1060 nm have been successfully suppressed in out system and ultimately achieves an output pulse energy of 0.15 mJ.

2 µm ultra-fast fiber laser has wide applications in polymer material processing and space communications. Our researches focused on the automatic control of a 2 μm thulium doped fiber laser system (TDFL) based on optimization algorithms. By constructing a NPR mode-locked based closed-loop control system and adaptive genetic algorithm (GA) searching, a typical noise like pulses(NLP) was searched with recovery time of ~2 minutes. Further by constructing a power-self adjustment and optical-spectrum feedback technology, the fine identification and search of femtosecond pulsing states including single , bounded, multiple soliton states, as well as soliton molecules in this band were achieved using GA. Stable single soliton states were firstly obtained through fully automatic searching, with a pulse duration of 2.6 ps and a typical Kelly sideband and time consuming of ~ 20 minutes. The result will provide a new idea for mid-infrared ultra-fast laser dynamics and multi-dimensional characteristics control.

Beam quality is an important performance of high power laser facility. In order to further reduce the wavefront distortion and improve the laser spot shape, the wavefront control method of "real-time detection and dynamic correction" is studied in this paper. During data collection, We collect three-frequency analog light in the same optical path as the main laser, and deduct the interference of background light and bad points of CCD camera, for improving the accuracy of wavefront measurement. Additionally, we comprehensively measure the correction effect by the energy concentration, spot shape and spot flatness of the laser. The results show that after hundreds of real-time dynamic closed-loop, the beam quality of laser is obviously improved.

In this study, the current-voltage(IV) curve before and after irradiation by 1-μm continuous and short pulse laser separately are analyzed contrastively. The experimental results showed that both sub-nanosecond pulse and continuous wave lasers can induce damage on solar cells with an increasing deposition energy, mainly manifested as melting ablation caused by thermal diffusion and fragmentation caused by thermal and mechanical stress. After irradiation with continuous lasers, the short-circuit current, open-circuit voltage, and energy conversion efficiency decrease significantly, while the short-circuit current of the solar cells irradiated by pulsed laser shows a differentiated performance of not decreasing but increasing. Integrating the equivalent circuit model of the solar cells with the degradation mechanism of the IV curve, the change in the series and parallel resistances caused by the increase of internal defects and the melting of grid line, is not the primary causes of the increase of short-circuit current, but rather the current limit layer shift induced by the different degrees of damage in the 3 sub-cells.

We present a novel laser isotope separation (LIS) system using a 423-nm single-frequency diode laser based on gallium nitride (GaN) for enriching 48Ca, essential for neutrinoless double beta decay studies. This system features 23 injection-locked lasers, achieving over 2 watts of power, crucial for matching the narrow isotope shift of 48Ca. Utilizing the Pound-Drever-Hall technique for frequency stabilization, we maintain a relative frequency variation below 1 MHz rms, demonstrating the system’s potential for precise and scalable isotope separation. This advancement offers a significant leap toward practical large-scale applications of LIS in scientific research.

Broadband low-coherence light is considered to be an effective way to suppress laser plasma instability in inertial confinement (ICF) research.In this work, we propose the use of a random fiber laser (RFL) as the seed source. The spectral features of this RFL can be carefully tailored to provide a good match with the gain characteristics of the laser amplification medium, thus enabling efficient amplification while maintaining low coherence. A theoretical model is constructed to give a comprehensive description of the output characteristics of the spectrum-tailored RFL, after which the designed RFL is experimentally realized as a seed source. Through precise pulse shaping and efficient regenerative amplification, a shaped random laser pulse output of 28 mJ is obtained, which is the first random laser system with megawatt-class peak power that is able to achieve low coherence and efficient spectrum-conformal regenerative amplification.

Here, a theoretical analysis and an experimental demonstration of high-quality laser amplification are reported. The results show that the addition of a 2 ×2 tiled-Ti:sapphire amplifier to the today’s 10 PW ultra-intense laser is a viable technique to break the 10 PW limit and increase the highest peak power recorded to few tens PW, further approaching the Exawatt-class (EW).

Silica sol-gel film is coated on the surface of optical elements used in high power laser system, which will absorb molecular contamination during storage time, resulting in optical transmission loss and photothermal absorption enhancement. Under the influence of laser and particle existence, it is easy to cause surface damage, which is not conducive to the maintenance of optical performance and the stable operation of the facility. It is proposed to filter the air in the optical storage environment. Through the data analysis of the optical effect test after filtering, it is found that the chemical filter is an important device to ensure the long-term maintenance of optical performance, and it is suggested to arrange it in the key process links of the laser system.

Through the first-order Stokes light as signal light and pump light propagating together, the atomic polarization field of air can be effectively excited in a short distance, and the spectrum can be effectively broadened, which is based on stimulated rotational Raman scattering (SRRS) of gas. 1% ultraviolet spectrum broadening at kilojoule level is realized by using SRRS effect under signal light injection in experiment. It is also proved that the beam quality can be maintained after broadening, especailly nearfield and time waveform. The instantaneous spectral broadening can be controlled by precise design of temporal waveform evolution of signal laser.

Pulse compressor has become the main obstacle on achieving 10s-100s PW lasers due to the damage limitation of diffraction gratings. Multistep pulse compressor (MPC) uses the “difficulty transforming” strategy by beam smoothing or spatiotemporally modified lasers. By using MPC, the laser peak power of PW lasers can be further increased by 2-10 times. Simple MPC method, like asymmetric four grating compressor (AFGC), can be applied in all the existed PW lasers by simply changing the grating pair distances. Enhanced by the self-compression technology in the post-compressor stage, exawatt-class laser beam is expected to be obtained by using this MPC method in the future, which will further extend the ultra-intense laser research fields.

Study on Rapid Quantitative Measurement Technology of the Nonvolatility Residue (NVR) on the Surface of Metal Structures for High-power Laser System (Jiang Yilan, Zhou Guorui, Niu Longfei, Miao Xinxiang): Cleaning control is crucial factor to ensure the stable operation of High-power Laser System (HPLS). The surface damages of the valuable optical elements were caused by different kinds of contaminants, seriously affecting the reliability and stability of the system. Therefore, the measurement technology for contaminants was particularly important. In this paper, the contact angle measurement method and the high precision solvent sampling method were used for off-line calibration, and the corresponding relationship between the contact angle of metal structure surface and the content of NVR was given. The rapid quantitative measurement of NVR on the metal surface was successfully realized, which provided a good support for the stable operation of HPLS.

Dynamic particle contamination during the operation of high-power laser devices is the major causal factor in reducing the damage resistance and service life of internal optical components; therefore, it is crucial to understand the dynamic particle contamination generation process caused by stray light to solve the problem. In this paper titled “Study on particles produced mechanism and influence to optics of aluminum alloy irradiated by stray light”, we theoretically and experimentally investigate the mechanism of particle contamination generation on the surface due to stray light for aluminum alloy materials commonly used in high-power laser devices，and the influence of generated particles on the damage performance of optical elements is evaluated. This research can provide technical foundation for the control of the clean level and stray light during the operation of high-power laser facility.

With the rapid advances in laser technology, optical fields with various topological features have attracted increasing attentions. In this talk I will review recently developed techniques that allows us to directly sculpt optical fields in the spatial and spatiotemporal domains. These spatiotemporal sculpturing techniques are employed to produce optical fields with various topological features. Wavepackets with these complicated topological structures exhibit many unique properties and may find important applications when interact with matters, opening tremendous potential opportunities for sculptured complex spatiotemporal wavepackets.

We demonstrate the sub-100 fs pulse generation from a dispersion-managed mode-locked Er:ZBLAN fiber laser at 2.8 μm. The coexistence of stretched pulses and dissipative soliton mode locking in the near-zero-dispersion region of fluoride fiber lasers has been demonstrated. With fine dispersion management, the shortest pulse of 95 fs was obtained from the stretched-pulse mode-locked Er:ZBLAN fiber laser. To the best of our knowledge, this is the shortest pulse to date directly generated from mid-infrared mode-locked fluoride fiber laser.

We proposed the triple-wavelength pulses across the 1530- and 1550-nm gain regions are emitted from a carbon nanotube mode-locked ring fiber laser by simultaneously exploiting intracavity loss based gain profile tuning, Lyot filter effect, and nonlinear polarization evolution. A polarization beam splitter with 2×1-m intracavity polarization-maintaining fiber pigtails is additionally introduced in a typical ring fiber cavity. Polarization-dependent loss is firstly adjusted to equalize the 1530- and 1550-nm gain regions. Except for the triple-wavelength pulses based on Lyot filter and loss based gain profile tuning, another type of triple-wavelength pulses, i.e. single-wavelength pulse centered at 1530-nm gain region and spectral-overlapping dual-wavelength pulses centered at 1550-nm gain region, are observed by additionally introducing nonlinear polarization evolution. These intriguing results show the feasibility of multi-wavelength pulse generation based on multiple soliton formation mechanisms and the high potential to construct a single-cavity multiple-comb source with versatile pulse characteristics.

Synchronously-pumped optical parametric oscillators (OPOs) can generate ultrafast mid-infrared pulses within a spectral range beyond the access of conventional mode-locked lasers, making them widely used in infrared photonics, biomedical examination, and molecular spectroscopy. This work has devised and implemented two novel variants for the FOPO system. Firstly, the pump threshold is significantly reduced by integrating an erbium-doped fiber as the additional gain medium for optical pulse formation. The stable and robust operation is evidenced by the large tolerance of cavity-length variation, which leads to a tight passive synchronization for the repetition rates of the involved pulse trains. In addition, by combining chirped polarized nonlinear crystals with fully polarization maintaining single-mode fibers, the spectral coverage range of signal and idler bands can be further expanded to 400 nm and 2000 nm, respectively.

A mode-locking fiber laser is not only a device that can generate ultrafast optical pulses, but also an ideal platform for investigating laser physics and nonlinear optics. As the design of a mode-locking fiber laser is for a specific application, researchers usually focus on how to stabilize the laser to generate a single type pulse output, such as soliton, dissipative soliton, similariton. In this work, we concentrate on the critical state or the semi-stable state, where several pulse types can be generated by parameter controls of the laser cavity.

We demonstrate a low threshold 0.5 at.%-doped Er: YAG micro-NPRO with a short round-trip path length designed to reduce the effects of energy-transfer upconversion (ETU) and reabsorption. Using a 1470 nm laser diode (LD) with a single emitter for resonantly pumping the Er: YAG micro NPRO, a single-frequency laser output of up to 354 mW at 1645 nm was achieved with a pump power of 3.5 W. This performance corresponds to a slope efficiency of 44.6% and a threshold power of 2.7 W, with a measured linewidth of 6 kHz for the Er: YAG micro-NPRO and a mode-hop-free frequency tuning range exceeding 10 GHz.

A high-energy 588nm yellow laser based on external-cavity frequency doubling of Raman amplifier was demonstrated. First, a 40mJ pure high-performance 1177nm first-order Stokes seed light was achieved with a KGd(WO4)2 (KGW) Raman oscillator pumped by 1064nm pulse laser. Then, a single-pass KGW Raman amplifier scheme was employed to obtain 152mJ 1177nm Raman output. Finally, by external-cavity frequency doubling with an LBO crystal, a 74.1mJ Raman yellow laser at 588nm with a pulse duration of 10.4ns was obtained under the total 1064nm pumping energy of 650mJ. The corresponding optical to optical conversion efficiency was 11.4%.

We experimentally demonstrated a fast and effective intelligent optimization algorithm to obtain the self-correcting ultrashort pulse emission from a nonlinear polarization rotation mode-lock fiber laser. The temporal trace corresponding to the optical spectrum is measured by the time-stretched dispersive Fourier transform technique, which functions as the monitoring signal. Subsequently, the genetic algorithm is proposed to finely control the electronic polarization controller for self-correcting pulse generation. The target state could be realized after 5 generations of iterations. By combining dispersive Fourier transform technique and genetic algorithms, the total adjustment time can be minimized to 6 seconds. These findings indicate an effective route to obtain robust and self-correcting ultrashort fiber lasers.

Airborne Molecular Contaminants (AMCs) are one of the key factors to improve the output performance of laser system. Under the strong laser irradiation, AMCs in the laser system condense into larger particles and adhere to the surface of optical elements to reduce the damage threshold, which lead to the lower transmission of the optical elements. In the work, a AMCs sensor based on optical microfiber decorated by Erbium-ytterbium co-doped silica film with fast desorption is proposed, and demonstrated experimentally to realize the cleanness level evaluation in laser system. In the experiment, the shapes and diameters of microfiber can be controlled precisely employing homemade ultrafine optical waveguide system, and the decorated Erbium-ytterbium co-doped silica film is fabricated by sputtering method. The sensing performance of the as-fabricated devices was evaluated. It provides for possible application in cleanness level evaluation in the laser system.

Notch filter serves as a vital optical filter, selectively blocking specific wavelength bands while transmitting both shorter and longer wavelengths. Traditional notch filter, designed by alternating layers of high and low refractive index materials, often suffer from undesired higher-order reflection bands. To address this problem, rugate filters with a sinusoidal variation in refractive index eliminate this issue. The refractive index distribution will affect the performance of the notch film. Therefore, the impact of refractive index distribution on the sidelobes of rugate filters was investigated using a developed software. The factors influencing the bandwidth and reflectance of rugate filters were also investigated. It was found that the sinusoidal index distribution modulation function was the most effective in sidelobe suppression. Furthermore, we found that index distribution modulation function decreases the reflectance of the reflection band, and the bandwidth was determined by maximum refractive index contrast. Additionally, we proposed a method for designing arbitrary multi-band rugate filters.

A multi-parameter comprehensive optimization analysis (MPCOA) method based on F-matrix theory is proposed to offer clear guidelines for fabricating high-performance chirped volume Bragg gratings (CVBGs). Experimental results show that high-DE CVBGs with a maximum relative diffraction efficiency (RDE) over 95% and a low absorption coefficient of 3×10^-4 cm^-1 have been successfully prepared.

An improved localized coupled wave method is proposed, which is suitable for the analysis of aperiodic volume holographic gratings. Simulation results of the diffracted electric field from the same volume holographic lens before and after the improvement of the localized coupled wave method are presented and discussed.

With the development of ultrashort pulse technology, the dispersion oscillations of the DMs become more stronger with the increase of the dispersion compensation bandwidth and target group delay dispersion(GDD) value. To reduce the GDD oscillation of dispersive mirrors, two pairs of chirped mirrors with a central wavelength of 800 nm and a bandwidth of about 200 nm are designed and fabricated, which provide about -100fs² and -200fs² GDD respectively in the wavelength range of 700-900 nm. The GDD oscillation is reduced from ±100 fs² for a single chirped mirror to nearly 0 fs² using chirped mirror pairs.To verify the compression performance, we simulated the propagation of a Gaussian pulse through our dispersive mirrors. The simulated results showed that the fabricated dispersive mirror pairs closely match the design specifications and effectively reduce the oscillation of group delay dispersion.