Optics express最新文献

Conventional iterative numerical modeling of chirped pulse amplification (CPA) systems requires a large temporal simulation window to accommodate the heavily chirped pulses. Simultaneously, maintaining the high temporal resolution certainly improves the computational complexity, posing challenges for CPA system design and optimization based on numerical simulations. To overcome this limitation, we propose a cascaded long-short-term memory (LSTM) model with a downsampling strategy trained for efficient and accurate modeling of a multi-stage optical fiber system. This approach delivers full-field simulation of the heavily chirped pulse with 10-nm spectral bandwidth at the pulse energy reaching 14.9 μJ. Through aggressive downsampling in the time domain, the proposed framework reduces the computational complexity by 929 times and achieves a remarkable 1,564-fold speedup compared to conventional numerical simulations, while maintaining prediction errors of the pulse energy and duration below 2%. Our work provides an efficient and high-fidelity CPA systems modeling alternative, which is particularly suitable for the inverse design and optimization of CPA systems for high-energy short pulses generation.

The abundance of carbon dioxide (CO₂) clumped isotopologues is an important tracer of environmental conditions in both atmospheric and paleoclimatic contexts. However, the conventional method for accurate CO₂ clumped isotope measurements, based on magnetic sector isotope ratio mass spectrometers (IRMSs), is time-consuming (hours per replicate) and requires large sample sizes (up to 100 µmoles CO₂). The recent development of isotope ratio laser spectrometers (IRLSs) determines CO₂ clumped isotope composition based on the infrared absorption spectra of corresponding CO₂ isotopologues and has significantly decreased the duration of clumped isotope measurements (minutes per replicate). However, existing IRLS instruments still require similar sample sizes to current IRMSs. Here, we present, to the best of our knowledge, a new IRLS prototype that demonstrates the feasibility of performing clumped isotope measurements using only nanomoles of CO₂. The instrument leverages hollow core fiber (HCF) technology and achieves a reduction in sample size of about four orders of magnitude compared to existing IRLSs. We successfully detect and quantify the clumped isotopologues ¹⁶O¹³C¹⁸O and ¹⁸O¹²C¹⁸O absorption using ∼17 nanomoles of CO₂ and measure their abundances to precisions of 0.7‰ and 1.0‰, respectively in 1-1.5 minutes. Combining them with three other measured isotopologue lines we are able to calculate the clumped isotope ratios Δ₆₃₈ and Δ₈₂₈, achieving precisions of 0.7‰ and 1.8‰ in 15-30 seconds. Our results demonstrate the potential of HCF technology for clumped isotope analyses of nanomoles of CO₂ with future technical improvements particularly in mid-infrared fiber technology.

Polarization-dependent aberrations, or polarization aberrations, arise in optical systems due to diattenuation and retardance effects induced by optical surfaces along the beam path. In exoplanet coronagraphy, polarization aberrations fundamentally limit imaging performance at small angular separations, and must be carefully analyzed for extremely high-contrast systems such as NASA's planned Habitable Worlds Observatory. In this paper, we derive a method for calculating the theoretical bound for coronagraph performance in the presence of polarization aberrations after correction by the coronagraph's deformable mirrors, and confirm via simulations that it bounds actual wavefront control loop performance. Due to its simplicity and computational efficiency, this method is highly useful for rapid analysis of telescope and coronagraph designs during concept development.

We present a comparative study of vertical and lateral loss estimation in photonic-crystal surface-emitting lasers (PCSELs), focusing on how finite-size effects depend on the choice of infinite-structure band model. To analyze these effects, we introduce a k-space weighted loss estimation (kSWLE) framework that can be applied to any infinite-structure band model, and we contrast its predictions with those of finite coupled-wave theory (finite-CWT), which inherently relies on the infinite-CWT bandstructure. The kSWLE approach provides a semi-analytical means of estimating radiative and lateral losses by integrating band-dependent quantities over a Gaussian k-space envelope determined by the device size. We apply kSWLE using both CWT and guided-mode expansion (GME) bandstructure models, enabling a direct comparison of how different infinite-structure descriptions influence the predicted losses and spectral properties. In regimes where the lasing mode is dominated by a single band and has a spectrally compact k-space distribution, kSWLE reproduces similar scaling trends as finite-CWT. However, for small devices or at specific fill factors, the mode has a broader k-space distribution with contributions from multiple bands, leading to ambiguous mode classification and increased deviation between models. These results highlight the strengths and limitations of each modelling strategy and establish kSWLE as a practical tool for evaluating finite-size effects in PCSELs.

Phaeocystis globosa (P. globosa), a distinctive harmful algal bloom (HAB)-forming species, is capable of alternating between free-living cells and gelatinous colonies. Developing optical techniques for the rapid detection of this HAB-causing species requires knowledge of its inherent optical properties (IOPs), particularly in the form of intact colonies. However, these properties remain poorly understood for the giant colonies of P. globosa, given that measurements of them are challenging. Here, by modifying existing methods for IOPs measurements, we successfully obtained the absorption and scattering coefficients of intact P. globosa colonies up to 25 mm in size. Six strains were isolated from different regions of the China Seas: one collected in situ, and the others grown in culture. Our results show that the IOPs of intact colonies are similar to those of free-living cells, regardless of colony size (1-25 mm). A prominent absorption peak at 468-472 nm was consistently observed across all five colonial strains and the free-living cell strain, corresponding to chlorophyll-c₃ (Chl-c₃) absorption. Notably, although intracolonial fluid contains colored dissolved organic matter and the colony envelope consists of optically active particulate matter, their contributions to light absorption and scattering by colonies in the spectral range of 400-750 nm are negligible when the colony remains non-collapsed. Interestingly, broken colonies exhibit reduced chlorophyll-specific absorption compared to intact ones, suggesting that colony structure enhances light absorption. This result, combined with the fact that measurements of broken colonies via the traditional quantitative filter technique are compromised by uneven pad distribution, underscores the importance of measuring IOPs in intact P. globosa colonies rather than in filtered samples containing broken colonies. These findings will undoubtedly aid in the future development of bio-optical models for P. globosa colonies and enhance remote sensing algorithms for detecting P. globosa blooms.

We demonstrate the electrical control of topological interface modes at the interface between a graphene-based photonic superlattice and a uniform dielectric medium. Specifically, by integrating graphene sheets into the unit cell of metallodielectric superlattices, the presence or absence of topological interface modes can be dynamically controlled by tuning the permittivity of graphene via electrical gating. These topological modes emerge when the spatial average of the permittivity of the superlattices is negative and vanishes as the chemical potential of graphene is adjusted to render the averaged permittivity positive. The dependence of the existence of topological interface modes on the sign of the spatial average of the permittivity is fundamentally related to the emergence of a Dirac point, which arises when the averaged permittivity of the superlattices reaches zero and is accompanied by the Zak phase transition, thus resulting in the appearance and disappearance of topological interface modes. Furthermore, we find that the propagation constant of topological interface modes decreases when increasing the chemical potential of graphene. The robustness of such topological interface modes is also demonstrated. Our work provides clear physical insights and offers a promising approach to the dynamic control of topological interface modes.

By employing a pump-probe technique for enhanced spectral mapping of the dynamics in nonlinear frequency conversion, we demonstrate that photo-induced second-harmonic generation (SHG) in silicon nitride (Si₃N₄) microresonators can persist when transitioning from the preferred doubly resonant condition-where the resonances of the optical harmonics are required to be matched-to a highly detuned state where the generated second harmonic is significantly shifted away from its corresponding resonance. This results in an unconventionally broad conversion bandwidth. Other intriguing phenomena, such as detuning-dependent all-optical poling and nonlinear multi-mode interaction, are also presented, to the best of our knowledge, for the first time with direct experimental evidence. Our findings provide new insights into the physics of photo-induced second-order (χ⁽²⁾) nonlinearity, highlighting its potential applications for nonlinear χ⁽²⁾ photonics in an integrated Si₃N₄ platform.

Imaging multilayered hidden structures is challenging due to scattering, diffusion, and varied material responses. We demonstrate photothermal digital holography combining laser-induced heating with phase-sensitive holography for non-invasive imaging and characterization of hidden layers in multilayered samples. A low-power probe and an oblique high-power excitation beam enable simultaneous multilayer imaging. Absorption-induced heating caused refractive index changes in the multilayered structure, leading to phase shifts in the probe beam. Experiments on different materials revealed distinct thermal signatures. Oblique excitation enabled layer discrimination from a single hologram, and fitting spatial phase profiles with a thermal lensing model and temporal phase profiles with an error-function model yielded sample characterization.

An accurate determination of fluorescence lifetimes (FLs) provides valuable insights for various applications, from cell analysis to semiconductor characterization. While the FLs are commonly measured using time-correlated single photon counting (TCSPC), the accuracy is limited by pile-up deviation at high intensities and by statistical uncertainty at low count rates. To quantify the effects and identify the best compromise of low pile-up and high counting statistics, we present a theoretical model which analytically describes the TCSPC detection process and thus the accuracy of FL measurements. In addition, the theoretical model provides simple design rules for the maximum usable intensity and required photon counts. Furthermore, we utilize this findings in what we believe to be a novel method, which adjusts the signal intensity to the mentioned compromise by introducing a delay between excitation and detection. We applied and validated the method in single photon avalanche diode (SPAD) based FL measurements. In doing so, the delay method, applied with an algorithm, enables FL measurements with an accuracy of ±15% even at high detector saturations up to 99% with sub-ms measurement times. Unlike previous approaches, our model provides a detailed understanding of the TCSPC detection and the delay method enables robust and fast FL measurements.

Superimposing a pair of independent lasers is considered an incoherent process due to the inability to produce stable interference. However, here we show that stable interference can be recovered from transient interference through intensity correlation measurements. We demonstrate this by utilizing a pair of independent laser beams incident on separate slits of a Young's double-slit interferometer. This resulting stability enables the use of a pair of independent lasers in a correlation-based interferometric sensor that has the potential to be more robust to sources of phase noise, such as optical turbulence or vibrations.