In nanometric displacement measurement, laser interferometry exhibits high sensitivity to sub-period displacements. However, the interferometric signals are often incomplete in period and limited in amplitude, making them susceptible to high-frequency noise and drift. Therefore, an improved nanoscale displacement measurement method is proposed, combining band-limited dynamic-noise-assisted complete ensemble empirical mode decomposition with adaptive noise (CEEMDAN) with sinusoidal-regression demodulation. By constraining the noise band and adaptively tuning the noise amplitude during injection, the low-frequency trend component is effectively purified. Based on the prior parameters, such as laser wavelength and displacement rate, to constrain the fitting solution space, the linear least squares fitting method is used to process the trend signal to achieve high-precision phase recovery and quantitative displacement measurement. Experiments show that the method remains stable under electromagnetic interference and impulse noise conditions, improving the signal-to-noise ratio by about 2.6 dB. The measurement error is 1-3 nm within the 20-300 nm range, and the stability is improved by approximately 62%, while also satisfying real-time feasibility. Overall, the method achieves nm-level accuracy with enhanced robustness to industrial noise and real-time computational efficiency.

Spatio-spectral measurement of ultrashort-pulse beam is very important for the performance optimization of laser facilities. A reference-free, spectrally resolved measurement method based on ptychography with an advanced iterative algorithm for high-precision synthesis of full-spectrum data is proposed. We designed an integrated measurement device with robust implementation and high reliability. The device was successfully applied in a target chamber of a terawatt-class ultrashort-pulse laser facility. The spatio-spectral complex amplitude of a complicated pulsed laser was accurately reconstructed with high spatial resolution of 11 μm and some wavelength-dependent spatial phase characteristics in the laser pulse were identified. This method offers a promising approach for advanced beam characterization of high-power femtosecond laser system.

Despite considerable progress in multi-stage laser wakefield acceleration (MSLWFA), efficient coupling between stages and the impact of laser-beam injection delay remains open challenges. A two-stage LWFA scheme is demonstrated using particle-in-cell (PIC) simulations, capable of producing multi-GeV electron beams over millimeter-scale propagation lengths. In the first stage, a high-intensity laser pulse (with [Formula: see text] [Formula: see text], [Formula: see text]= 800 [Formula: see text] and [Formula: see text]) propagates through a neutral helium (He) gas target inside a gas cell, with ionization modeled self-consistently to produce a fully ionized plasma at a plateau density [Formula: see text], generating a high-quality 1 GeV electron beam. This beam is then injected into a second stage inside the same gas cell, where systematically varying the injection delay enhances the injected bunch energy to 2.5 GeV and boosts background trapped electrons to 3 GeV, while reducing energy spread and preserving charge. These findings underscore the critical role of synchronization and plasma tailoring strategies relevant for future multi-pulse and flying-focus LWFA configurations.

The conjugated image is the main source of artifacts of coherent diffraction imaging (CDI) and was widely studied in the long past. However, there is no rigorous analysis to illustrate how it was mathematically generated in iterative reconstructions. By writing diffraction intensities into a linear equation set, in this paper, we show that real coefficients of these linear equations were the mathematic reason for the existence of conjugated image and related artifacts in conventional CDI algorithms and that complex coefficients of these linear equations were critical to obtain conjugated image free constructions. Dual-illumination was adopted as a simple example to show how to get complex coefficients in conventional CDI algorithms and to improve reconstruction quality. In this paper, theoretical analysis and experimental studies build a strong mathematical foundation as well as an accurate strategy for conjugate-image suppression in CDI and offer valuable guidance for optical alignment optimization.

Polymethyl methacrylate (PMMA) is widely used in optical systems due to its excellent optical and mechani cal properties, so its performance in laser systems is of great interest, especially in laser-induced damage. In this study, the ultraviolet laser damage characteristics of PMMA optical plates were systematically investigated with a nanosecond-pulsed laser at 355 nm. The 1-on-1 laser-induced damage threshold (LIDT) of a 0.2-mm-thick PMMA optical plate exceeded 20 J/cm2, decreasing with increased thickness. Under multiple-pulse (S-on-1) test ing, the LIDT decreased progressively with the pulse number, reaching similar to 5 J/cm2 at seven shots. At fluences below 100%LIDT, the damage morphology was characterized as internal pinpoints in microns, whose density increased with fluence and was higher closer to the front surface. When the fluence exceeded 100%LIDT, an ablation crater formed on the front surface. Under single-shot irradiation, the area of the damage region increased logarithmi cally with increasing laser fluence. In contrast, the size of internal pinpoints had no significant correlation with fluence but was strongly influenced by the pulse number. Furthermore, plasma dynamics and temperature field simulations suggest that internal pinpoints potentially originate from localized absorption by sub-micron defects, with the resulting pinpoint size being primarily determined by the initial defect dimensions. To enhance optical performance, an anti-reflective coating was applied to the 0.2-mm-thick PMMA optical plates, yielding a trans mittance of 99.4% at 355 nm. Our results show the significant potential of PMMA optical plates for applications in high-power ultraviolet laser facilities.

Abstract Laser wakefield acceleration offers ultra-high accelerating gradients, enabling compact sources of multi-GeV electron beams with femtosecond duration and quasi-monoenergetic spectra. In this work, we investigated the nonlinear evolution of plasma bubbles and their effect on electron injection and energy gain, using high-fidelity, multi-dimensional particle-in-cell (PIC) simulations performed with the open-source code SMILEI. A relativistically intense laser pulse (a 0 =7.7, λ 0 =0.8 μm, w 0 =20 μm, E=30 J, and τ=30 fs) propagated through a helium gaseous medium with a plateau density of n e =7×10 18 cm -3 after complete ionization. The simulations revealed complex bubble dynamics, including initial formation, disruption, destruction, and bubble merging, strongly influenced by local longitudinal electric field E x approaching or exceeding the cold wave-breaking limit E WB . Exceeding the wave-breaking field E WB triggered bubble destabilization, while the bubble merging at the end of the plateau plasma density region extended the acceleration length, sustaining high longitudinal fields on the order of 1 TV/m and boosting continuous electron injection. This mechanism produced a dense, quasi-monoenergetic electron bunch with a charge of 1 nC, a peak energy of ~1 GeV, femtosecond-scale duration, energy spread below 10%, rms angular divergence θ y of 7 mrad, and a longitudinal rms beam size of σ x =10 μm. Comprehensive analysis of the wakefield structure evolution demonstrated that exploiting nonlinear bubble evolution and interactions near the wave-breaking limit can enhance both energy gain and electron beam quality, providing actionable strategies for next-generation compact LPAs.

To achieve accurate temporal characterization of broadband laser pulses, a sufficient phase-matching bandwidth is required. The problem is mainly solved by using third-order nonlinear effects or few-micrometer-thin secondorder nonlinear crystals. However, difficulties persist in enhancing signal conversion efficiency while ensuring sufficient bandwidth. In this work, we propose a bandwidth-extending method based on spectral filtering function and ptychographic algorithm, termed Spectral Correction and Trace Truncation (SCTT), for characterizing broadband pulses. In experiments, we achieved the characterization of 720-880 nm broadband pulses using a beta-barium borate (BBO) crystal with a thickness of up to 100 mu m-far beyond the scale of a few microns-under phase-matching configuration. The reconstructed pulses are consistent with the standard results obtained using a 5-mu m-thin BBO crystal, but the measurement sensitivity and signal-to-noise ratio are increased by a factor of similar to 18, and the minimum measurable pulse energy is less than 10 pJ.

Conjugate image is an inherent problem of coherent diffraction imaging (CDI) and direct analysis and research on them have long been incomplete. By writing diffraction intensities into linear equation set, it was demonstrated that the fundamental mathematical reason for the generation of conjugate image lies on the real-value coefficients of these linear equations, and then the conjugate image could be eliminated by adopting optical alignments that can lead to complex–value coefficients. While theoretical analysis was proposed its feasibility was verified both numerically and experimentally. The study provides new insights into the physical mechanism of CDI and new strategies to improve the image quality of other phase retrieval techniques.

A Babinet-principle-based coherent amplitude modulation imaging (BP-CAMI) method is proposed for accurate illumination characterization. It employs a random amplitude plate and a complementary constraint derived from the Babinet principle, establishing a dual-constraint framework that provides algorithmic rather than hardware redundancy. This approach effectively suppresses noise and artifacts during phase retrieval. Simulations and experiments on biomedical samples, resolution targets, and phase objects confirm substantial improvements in signal-to-noise ratio and spatial accuracy over conventional methods. Notably, BP-CAMI recovers richer high-frequency details than the ptychographic iterative engine, with quantitative gains of 2.85 dB PSNR and 7.81 μm resolvable linewidth, yet requires no hardware modifications. The work offers a practical, algorithm-driven route to enhance performance across coded-imaging systems.

In kilojoule-petawatt laser systems, grating mosaic is a common approach for fabricating meter-sized multilayer dielectric gratings (MLDGs) [11-14], but the imperfections such as mosaic gap increase the risk of damage to the final grating. It has been revealed that the short-pulse damage initiation in such grating exhibits a strong dependence on laser intensity [31,32,39]. In this paper, we investigate the three-dimensional near-field dynamics at the final grating of the mosaic grating compressors for both Fourier-transform-limited (FTL) and chirped pulses, based on the single-pass symmetric and asymmetric configurations. In the symmetric configuration, the near-field intensity fluctuations caused by errors of the second and third gratings (G2-G3) are effectively smoothed for FTL pulse, which is attributed to frequency-dependence of these fluctuations induced by the spatial dispersion between G2-G3. For chirped pulses, the instantaneous intensity distribution directly reflects the spatial profiles of corresponding chirped frequency components, thereby eliminating the smoothing effect, and the cross-influences of errors from all upstream gratings (G1-G2-G3) significantly deteriorated the intensity fluctuations. The asymmetric configuration introduces uncompensated spatial dispersion in the G4 near-field, results in frequency-dependence for the intensity fluctuations induced by G1 errors, hence the intensity distributions are smoothed for the FTL pulse. For the chirped pulse, this smoothing effect is similarly absent, and the intensity deterioration caused by cross-influences of G1-G2-G3 errors remains unmitigated. These results provide a crucial reference for configuration optimization of mosaic grating compressors.

Vortex dynamics are intriguing and challenging across multiple physics fields. In optics, customized spatiotemporally structured optical fields, especially spatiotemporal optical vortices (STOV), offer the potential to tailor light via coupled space-time degrees of freedom. However, the interaction mechanisms between multiple transverse orbital angular momentum singularities within a single wave packet remain elusive. This study explores the intrinsic dynamics of a STOV with three phase singularities, observing a pronounced vortex singularity oscillation phenomena by tuning the temporal dispersion. We show that these phenomena originate from the counterintuitive spatiotemporal attractive effect between vortices, which is closely related to the singularity distance. Furthermore, the stretching into filaments and annihilation behaviors is observed by introducing antivortex in the center of the wavepacket. Experimentally, we propose a Full Interferometric Retrieval of Spatiotemporal Tomography (FIRST) method that enables the complete, single-shot capture of wave packets, with excellent agreement between theoretical predictions and experimental results. To the best of our knowledge, the dynamics of transverse spatiotemporal singularities within a single wave packet are reported here for the first time. These findings confirm the existence of interesting interactions between STOV singularities, deepen our understanding of photonics and open a new direction for investigating the complex dynamics of vortex singularities in the spatiotemporal domain.

Laser-driven particle acceleration and related laser-matter interaction experiments require an ultrashort pulse laser with high temporal contrast. Here, we presented a plasma mirror (PM) temporal contrast enhancement system implemented at the SG-II 5PW laser facility, with a comprehensive investigation of spatiotemporal properties and physical applications. Key performance parameters of a PM were successfully obtained through single-shot online measurement by combining a spatiotemporally overlapped chirped pulse method. At a 45° incidence angle, the plasma reflectivity reached 84% for S-polarization and 48% for P-polarization, while the focal spot maintained excellent quality and the temporal contrast was improved by two orders of magnitude. The PM system was further applied in proton acceleration experiments under both polarization configurations. Supported by corresponding physical diagnostics, a significant reduction in optimum target thickness from 8 to 0.8 μm was achieved-clear evidence of effective pre-pulse suppression. Additionally, the PM and target installation were evaluated using a triple laser-damaged imaging method, based on the analysis of the three PM damage spots.

The coupling alignment of single-mode fibers demands stringent optical mode matching accuracy, where micro-displacements and angular tilts drastically degrade coupling efficiency. Furthermore, traditional alignment processes frequently suffer from insufficient precision, slow convergence, and poor algorithmic stability. To overcome these limitations, this paper proposes a sensitivity matrix-based geometric particle swarm optimization (SG-PSO) algorithm. By introducing a sensitivity matrix to explicitly map the physical relationship between mechanical degrees of freedom and wavefront distortions, the proposed method provides clear geometric guidance to the particle swarm optimizer. The sensitivity matrix is seamlessly embedded into the PSO update rule to provide a deterministic search direction. The alignment process is comprehensively simulated using Zemax optical software and validated through physical experiments employing a 618 nm laser. Experimental results demonstrate that SG-PSO achieves a 50% reduction in eccentricity and tilt errors compared to traditional methods. Notably, the SG-PSO algorithm rapidly approaches the theoretical alignment limit, converging to a highly accurate solution within 15 iterations. Ultimately, SG-PSO exhibits substantial advantages in both positioning precision and convergence speed, offering a robust and highly efficient optimization paradigm for multi-degree-of-freedom fiber coupling alignment.

The suppression of ablative Rayleigh-Taylor instability (ARTI) by a spatially modulated laser in inertial confinement fusion (ICF) is studied through numerical simulations. The results show that in the acceleration phase of ICF implosion, the growth of ARTI can be suppressed by using a short-wavelength spatially modulated laser. The ARTI growth rate decreases as the wavelength of the spatially modulated laser decreases, and ARTI is completely suppressed after a certain wavelength has been reached. A spatially uniform laser is introduced to keep the state of motion of the implosion fluid consistent, and it is found that the proportion of the spatially modulated laser required for complete suppression of ARTI decreases as the wavelength continues to decrease. We also optimize the spatial intensity distribution of the spatially modulated laser. In addition, as the duration of the spatially modulated laser decreases, the proportion required for completely suppressing ARTI increases, but the required energy decreases. When the perturbation wavenumber decreases, the wavelength of the spatially modulated laser required for complete suppression of ARTI becomes longer. In the case of multimode perturbation, ARTI can also be significantly suppressed by a spatially modulated laser, and the perturbation amplitude can be reduced to less than 10% of that without a spatially modulated laser. We believe that the conclusions drawn from our simulations can provide the basis for new approaches to control ARTI in ICF.

Space-division and wavelength-division multiplexing require synchronous multiwavelength modal characterization in few-mode fibers, but single-wavelength methods are limited by spectral mixing, increased modal density, and wavelength-dependent distortions. We experimentally demonstrate synchronous multiwavelength mode decomposition in a few-mode fiber using a multimodal ptychographic iterative engine (SMW-MM-PIE). Using a static imaging system, the method reconstructs complex fields at four wavelengths from a single acquisition without mechanical realignment. Based on an established incoherent intensity-sum constraint, the framework integrates spectral decoupling, digital refocusing, scale compensation, and phase-guided cross-correlation registration for wavelength-resolved modal projection. The reconstructed fields show intensity correlation coefficients above 0.97 with their LP-basis projections at all wavelengths, including 21-mode cases, and agree with single-wavelength results under identical excitation conditions.

Abstract On-line wavefront measurement in real time is constrained by the susceptibility of multi-exposure interferometry to air turbulence and vibration. Here we propose a single-shot approach for a plane mirror based on wedge-induced lateral-shearing interferometry (W-LSI), by separating the first-order sidebands of the reference and test beams in the Fourier domain and then reconstructing them individually, so that the quasi-absolute wavefront is obtained in one exposure. For comparison, plane-mirror measurements were performed using a temporally separated quadriwave lateral shearing interferometry reference/test workflow and the proposed single-shot W-LSI method. Under the present non-isolated experimental conditions, the temporally separated reference/test acquisition in the conventional workflow was strongly affected by time-varying vibration and air turbulence, whereas the proposed W-LSI result agreed well with the Zygo interferometer measurement, with peak-to-valley values of 0.238 λ and 0.237 λ , respectively. The proposed method avoids phase-shifting operation and provides a single-shot, in-frame reference/test measurement scheme with reduced sensitivity to time-varying disturbances, making it suitable for quasi-absolute metrology of reflective elements under practical working conditions.