物理与天体物理最新文献

Chemical biosignatures, if present, are exposed to ultraviolet (UV) radiation at several locations in the solar system, including the martian surface. Solid thin-layer samples are commonly used to study the effect of UV irradiation on the stability of potential organic biosignatures in the laboratory and in space. Given the limitations of the layer deposition techniques previously used in astrobiology experiments, such as sublimation-recondensation and casting, antisolvent precipitation (i.e., crystallization from solution by addition of a poor solvent) offers a promising alternative. We applied the latter technique to deposit optically opaque crystalline layers of 1-methylnicotinamide chloride ((MNA)Cl) for use in subsequent UV irradiation experiments. The 1-methylnicotinamide cation in (MNA)Cl serves as a model of hypothetical extraterrestrial nicotinamide-based redox cofactors related to NAD(P)⁺. Under UV irradiation (λ ≥ 224 nm), decomposition of (MNA)Cl occurred, but it ceased after ∼14 days, leaving a large fraction of the material intact. This behavior is attributed to the shielding effect of a photoproduct layer on the crystal surfaces and can be kinetically described by a first-order bounded decay model. Such "self-preservation" may enhance the survivability of certain organic biosignatures provided they form sufficiently thick (opaque) layers or crystals. The presence of either synthetic gypsum (CaSO₄·2H₂O) or halite (NaCl) had a minimal effect on the kinetic parameters of the UV decomposition of (MNA)Cl.

We present polarization entanglement distribution over an operator-owned, metropolitan-scale fiber network, employing standard wavelength-division multiplexing components to achieve coexistence of O-band photons and C-band classical light. First, we demonstrate dynamic path switching by alternating between 15-km and 30-km deployed fiber loops, enabled by automated polarization compensation achieving sub-second recovery and time-averaged CHSH S-values exceeding 2.65 over 21 hours. We then assess the impact of co-propagating 100-Gbit/s C-band classical signals by varying launch powers up to 6 dBm. Finally, by combining path switching and classical co-propagation, we achieve stable entanglement distribution over 30 km of deployed fiber, validating the feasibility of hybrid quantum-classical transmission and paving the way for entanglement-based quantum networking on existing metropolitan infrastructure.

Computational color constancy (CCC) aims to recover the canonical appearance of scenes, yet current spectral-based approaches are hindered by the scarcity of hyperspectral data. This limitation compels reliance on suboptimal two-stage strategies, restricting the potential of deep learning. To overcome this, we propose a physically accurate spectral data augmentation strategy that expands the training set five-fold using real-world illuminants. Leveraging this, we introduce the Hierarchical Physics-Injection Network (HPI-Net). Experiments demonstrate that, within the full-multispectral-input setting, HPI-Net achieves a 20% reduction in mean recovery angular error relative to the strongest compared baseline, validating the effectiveness of our end-to-end physics-injection architecture.

High-repetition-rate X-ray free-electron laser facilities impose stringent requirements on the thermal stability and wavefront preservation of beamline mirrors. In this work, a coupled thermal-optical optimization method is developed for the first reflective mirror of the FEL-III beamline at the SHINE facility under an absorbed heat load of up to 11.12 W at a photon energy of 15 keV and a repetition rate of 200 kHz, with a peak absorbed power density of 0.0718 W/mm². The cooling length and cooling-groove distance from the optical surface are jointly optimized, and their effects on residual height error, slope error, and focal-plane Strehl ratio are evaluated using thermal-structural analysis and X-ray tracing. The results show that the mirror performance is governed by the coupled cooling geometry rather than by either parameter alone. Compared with the initial full-length cooling design, the optimized design reduces the RMS residual height error by 73.7% and the RMS slope error by 68.9%. The system-level Strehl ratio increases from 0.45 to 0.993, exceeding the target value of 0.96, while stray-light features are suppressed and a compact focal intensity distribution is recovered at the sample plane. These results demonstrate that deformation-based thermal optimization, when combined with system-level X-ray tracing, provides an effective thermal-optical design route for preserving wavefront quality in high-heat-load grazing-incidence X-ray optical systems.

We demonstrate a diode-pumped Yb:LLF laser that combines multi-watt semiconductor saturable absorber mirror (SESAM) mode locking with record continuous-wave (CW) tuning. Using a compact cavity pumped by a single-emitter 10 W multimode diode at 960 nm, the laser provides up to 3.2 W CW output with a tuning range from 996 to 1073 nm and a slope efficiency of 42%. In mode-locked operation, it delivers up to 2.8 W of average power with 180 fs pulses (10.9 nJ at 257.5 MHz) in a high-power regime, and up to 570 mW with 110 fs pulses (2.6 nJ at 214.1 MHz) in a short-pulse regime. Compared to previous work, this represents more than an order-of-magnitude increase in usable mode-locked power and pulse energy together with a substantially extended CW tuning span, and we outline straightforward routes to further broaden the tuning, shorten the pulses, and scale the usable average power. Taken together with earlier results on Yb:YLF, these findings indicate that Yb:LLF can serve as a competitive sister host and a strong candidate for future high-power and cryogenic Yb-based laser and amplifier studies.

Projector-camera nonlinearity produces carrier-locked phase ripple in four-step fringe projection profilometry. We introduce second-harmonic injection, whose coefficient controls the third-fifth harmonic imbalance through nonlinear intermodulation, while the injected harmonic is rejected by ideal four-step demodulation. A two-stage spatial-reuse calibration selects the coefficient directly from measured ripple, evaluating 22 candidates using eight images. Across eight independent reference-plane projection-capture repetitions, the method achieved a phase RMSE of 0.00617 ± 0.00009 rad (mean ± sample standard deviation), compared with 0.02243 ± 0.00038 rad without correction. Sculpture-model measurements further demonstrated ripple suppression on a complex surface. The method provides efficient active predistortion for repeated four-step profilometry under a stable, calibrated response.

Advances in optical atomic clocks and the forthcoming redefinition of the SI second are pushing for ultra-stable lasers with extremely low short-term instability and predictable drift. Cryogenic silicon Fabry-Perot cavities are promising candidates for this purpose. Here, we report the lowest operating temperature achieved for a laser-stabilized Fabry-Perot cavity, and the most precise measurement of the silicon coefficient of thermal expansion (CTE) to date. Measurements were performed from 655 mK to 16 K using a laser stabilized to an 18 cm single-crystal silicon cavity. Below 1 K, the CTE lies in the 10^-13K^-1 range, reaching a minimum of 3.5(4)×10^-13K^-1 at 655 mK. We also develop a model based on Debye and Einstein approaches that reproduces the measured CTE in this range. These results show reliable ultra-stable operation at sub-Kelvin temperatures and open new perspectives for optical clocks and fundamental physics tests.

Photonic extreme learning machines use random optical propagation, detection nonlinearity, and a trained linear readout for energy-efficient and scalable optical computing. However, conventional intensity readout with CCD or CMOS cameras constrains the dimensionality of the hidden representation space. Here, we experimentally replace intensity detection with an event-based camera, whose thresholded log-intensity response provides alternative pixel-wise hidden representations: first-event time, binary activation, and event count. In a nonlinear two-spiral classification task, we obtain accuracies of 93±3% with strong intrinsic generalization, and comparable ridge and pseudo-inverse performance indicating sample-limited effective dimensionality. Regression results reveal sensitivity to systematic representation drift, identifying stability requirements for future event-based PELMs. These results establish event-based detection as an alternative nonlinear optical-to-digital measurement that provides informative representations for the considered tasks while clarifying current limitations.

We present a combined experimental and theoretical study of high-harmonic generation driven by an ω+4ω two-color bicircular laser field. By exploiting the circularly polarized components of the driving field, we generate extreme-ultraviolet radiation consisting predominantly of harmonics with the same helicity, resulting in a strongly chiral harmonic spectrum. Individual harmonics exhibit ellipticities of up to 0.8, demonstrating the feasibility of generating elliptically polarized attosecond pulse trains. We further show that varying the ellipticity of the 4ω driving field provides an effective means of controlling both the spectral distribution of the emitted radiation and the polarization state of the generated harmonics. Theoretical simulations are in good agreement with the experimental results, providing insight into the harmonic-generation mechanism and elucidating the role of contributions from the magnetic quantum numbers m=±1.

We propose and demonstrate an ultra-broadband mode converter based on phase-shifted long-period gratings operating at the dispersion turning point. The device employs a sidewall-etched LPG in a polymer few-mode waveguide, where two optimized π-phase shifts broaden the resonant dip. Simulations show a -10 dB bandwidth of 745 nm for conversion between the E₁₁ and E₂₁ modes. The fabricated device shows a mode conversion efficiency higher than 15.6 dB over the wavelength range from 1285 to 1825 nm for both TE and TM polarizations. The proposed device provides a compact and fabrication-tolerant solution for mode-division multiplexing and broadband optical interconnects.