Optics letters最新文献

Quantitative phase imaging of transparent samples with large phase variations is fundamentally challenged by the nonconvex nature of phase retrieval from intensity-only measurements. In this regime, conventional algorithms with random initialization often converge to nonphysical solutions and fail to recover meaningful phase information, even when the forward model is accurately known. Here, we present a phase-gradient-based initialization strategy for coded ptychographic imaging that exploits the fact that local phase gradients remain stably encoded as lateral displacements in coded intensity patterns. By extracting displacement-derived phase-gradient information from measured intensities and constructing a globally consistent initial phase, the proposed initialization introduces essential first-order physical constraints prior to optimization. Simulations and experiments demonstrate that this strategy enables stable and physically correct reconstruction in large-phase regimes where random initialization breaks down, without increasing measurement redundancy.

Harmonic mode-locking (HML) in soliton fiber lasers provides a practical approach to generating multi-gigahertz pulse trains; however, simultaneous control of the pulse repetition rate (PRR) and optical spectrum width (OSW) remains a challenge. Here, we experimentally demonstrate wide and continuous tunability of both PRR and OSW in an HML soliton fiber laser mode-locked through nonlinear polarization evolution (NPE). This is the first, to the best of our knowledge, report presenting a two-dimensional map of HML laser states forming a connected domain in the coordinates [pump power; PRR], enabling smooth transitions between different regimes without loss of mode-locking. Experimentally, limited by the available pump power, we achieved maximum repetition rates of approximately 4.2 GHz and 18 GHz for pulses with spectral widths of about 4 nm and 1.7 nm, respectively.

Wavefront aberration (WAE) is a major source of error in cold atom gravimeters (CAGs). In conventional CAGs, due to the limited range of modifiable parameters, it is challenging to obtain sufficient samples to determine the truncation order (TO) of the Zernike polynomials in WAE assessment. To address this, this paper proposes an approach combining Leave-One-Out Cross-Validation (LOOCV) with F-statistic to determine the TO: LOOCV pre-screens candidate orders with optimal generalization performance, followed by F-statistic to validate whether the higher-order model yields significant improvements, ultimately balancing model complexity and predictive performance. We conduct modulated Raman beam aperture experiments under three different system wavefront conditions. The results demonstrate that our approach can accurately evaluate the TO of the Zernike polynomial model in the conventional CAG, whereas the conventional approach fails. Moreover, we performed a joint fitting of the data from these three sets of wavefronts. Compared to the individual fitting, the joint fitting reduced the evaluation uncertainty by approximately 64% on average.

A chiral drug with different enantiomers exhibits different pharmacological activities. Structure identification, quality control, and accurate quantitation are all important issues for chiral drugs. So far, these concerns can be studied only by different techniques solely; one method that can investigate all the abovementioned issues simultaneously is needed. Such an approach can definitely promote the development of the drug industry. Raman spectroscopy has long been used for quantitation and has been utilized for chirality study in recent years, thanks to its molecular fingerprints and the optical activity of chiral molecules. In this study, we firstly investigate the polarization sensitivity of racemic ibuprofen and its (S)-enantiomer using our home-built polarized Raman microscope then successfully distinguish the racemic and its (S)-enantiomer by Raman optical activity (ROA) spectra and its principal component analysis (PCA) scatter plot. Notably, the combination of polarized Raman spectroscopy (PRS) and partial least squares regression (PLSR) is proposed to achieve accurate quantitation of commercial ibuprofens. The experimental results of the coefficients of determination (R²) are 0.957 for racemic ibuprofen and 0.988 for (S)-ibuprofen, and their root mean square error of prediction (RMSEP) values are 0.126% and 0.049%, respectively. These preliminary results give a hint that polarized Raman spectroscopy (PRS) is a powerful non-destructive analytical tool for drug applications. These preliminary results give a hint that polarized Raman spectroscopy (PRS) is a powerful non-destructive analytical tool for drug applications.

We present a deep learning driven computational approach to overcome the limitations of self-interference digital holography that is imposed by inferior axial imaging performances. We demonstrate learning by applying the prior knowledge of a sample, a 3D deep neural network model can simultaneously suppress the defocus noise and improve the spatial resolution and signal-to-noise ratio of conventional numerical back-propagation-obtained holographic reconstruction. 3D non-scanning volumetric fluorescence microscopy can be achieved, using a 2D self-interference hologram as input, without any mechanical and opto-electronic scanning and complicated system calibration. Our method offers a high spatiotemporal resolution 3D imaging approach, which can potentially benefit, for example, the visualization of dynamics of cellular structure and measurement of 3D behavior of high-speed flow field.

To enhance photodetector performance, transient absorption (TA) microscopy is employed for the first time, to the best of our knowledge, to investigate carrier diffusion in interface-passivated semiconductor polycrystalline films. TA analysis reveals that after passivation with DMMI-Cl, the carrier diffusion length in MASnBr₃ polycrystalline films increases from 109 nm to 123 nm, while the diffusion coefficient improves from 0.119 cm² s^-1 to 0.151 cm² s^-1. Furthermore, DMMI-Cl passivation suppresses carrier losses from monomolecular and Auger recombination and promotes bimolecular recombination. The resulting photodetector exhibits a nearly six-fold enhancement in responsivity (R = 4.09 AW^-1), giving it a strong standing among reported 3D hybrid Sn-based perovskite photodetectors. This work expands the application scope of TA microscopy, provides deeper insight into grain-boundary-modulated spatiotemporal carrier dynamics, and contributes significantly to the development of high-performance tin-based photodetectors.

Topological corner states (TCSs) enable localized energy at on-demand corners of a system and inherent defect immunity, making them highly promising for various applications such as communication, integrated optics, and sensing. However, traditional TCS-based sensors are designed for single-function detection, lacking the capability for multifunctional sensing. In this Letter, we propose a dual-function sensor that leverages TCSs within a composite photonic structure. Herein, the excitation of TCSs arises from near-field coupling assisted by topological edge states. By utilizing dual-band TCSs, the proposed sensor exhibits wavelength shifts in response to refractive index (RI) and temperature, achieving salinity sensitivity of 0.04 THz/‰ and temperature sensitivity of 0.021 THz/°C. This work establishes a new, to the best of our knowledge, paradigm for multifunctional sensing, paving the way for ultra-compact on-chip nanophotonic devices.

We present a low-cost, chip-scale spectrometer based on the principle of equal-thickness interference for spectral encoding. The design features a particularly simple structure, consisting of a plano-convex lens and a flat glass plate, both coated with silver on one side, while a charge-coupled device (CCD) captures the interferograms. The active chip is a square with a side length of 8.6 mm, and the overall spectrometer form factor is 7 cm. By employing an accompanying physics-constrained neural network (PCNN) to decode the interference images, the proposed micro-spectrometer achieves a spectral resolution of better than 4.8 nm across the 400-800 nm wavelength range. Calibration is significantly simplified by capturing the interferogram at 400 nm and using the scaling relationship. This approach offers a compact and practical solution for miniaturized spectral sensing.

Photolithography is essential for integrated circuit fabrication, where exposure determines pattern transfer and affects subsequent development and etching. Conventional methods like AFM and SEM are ex situ and cannot isolate exposure dynamics. To overcome these limitations, we introduce LithoPhase, an in situ monitoring system for photolithographic exposure that, to our knowledge, represents the first employment of quantitative phase imaging to track the photolithographic exposure process. Experimental results demonstrate that LithoPhase tracks phase evolution with micron-scale spatial and millisecond temporal resolution. Thus, LithoPhase enables real-time, in situ monitoring of exposure dynamics, offering a viable approach for advanced photolithography.

Temporal focusing (TF) is a key tool in wide-field two-photon excitation fluorescence microscopy for confining fluorescence excitation to a thin layer around the focal plane. TF is typically implemented with 100 femtosecond laser pulses and large microscope magnifications (>40). In this work, we demonstrate that performing TF with a random speckled illumination rather than a collimated beam significantly improves the optical sectioning for long pulses and small magnifications. We derive simple formulas of the optical sectioning as a function of speckle angular divergence, pulse bandwidth, and microscope parameters. Our approach paves the way for optically sectioned wide-field nonlinear imaging using >200 fs pulses and low magnifications enabling large fields of view.