In this study, a ray tracing model based on the law of reflection in vector form was developed to obtain the design parameters of multipass cells (MPC) with dense spot patterns. Four MPCs with distinct patterns were obtained using an established mathematical model. An MPC with a four-concentric-circle pattern exhibited the longest optical path length (OPL) of approximately 38 m and an optimal ratio of optical path length to volume (RLV) of 13.8 cm^-2. A light-induced thermoelastic spectroscopy (LITES)-based methane (CH₄) sensor was constructed for the first time using the developed optimal MPC and Raman fiber amplifier (RFA). A novel trapezoidal-tip quartz tuning fork (QTF) was used as the detector to further improve the sensing performance. The CH₄-LITES sensor exhibited an excellent linear response to optical power and CH₄ concentration. The minimum detection limit (MDL) of the CH₄-LITES sensor reached 322 ppb when the output optical power of the RFA was 350 mW. The Allan deviation of the system indicated that the MDL decreased to 59.5 ppb when the average time was increased to 100 s.

Femtosecond laser fabrication technology has been applied to photonic-lantern mode (de)multiplexers owing to its 3D fabrication capability. Current photonic-lantern mode (de)multiplexer designs based on femtosecond laser fabrication technology mostly follow a fibre-type photonic lantern design, which uses trajectory-symmetry structures with non-uniform waveguides for selective mode excitation. However, non-uniform waveguides can lead to inconsistent waveguide transmission and coupling losses. Trajectory-symmetry designs are inefficient for selective-mode excitation. Therefore, we optimised the design using trajectory asymmetry with uniform waveguides and fabricated superior ultrafast laser-inscribed photonic-lantern mode (de)multiplexers. Consistent waveguide transmission and coupling losses (0.1 dB/cm and 0.2 dB/facet, respectively) at 1550 nm were obtained on uniform single-mode waveguides. Based on the trajectory-asymmetry design for photonic-lantern mode (de)multiplexers, efficient mode excitation (

,

, and

) with average insertion losses as low as 1 dB at 1550 nm was achieved, with mode-dependent losses of less than 0.3 dB. The photonic-lantern design was polarisation-insensitive, and the polarisation-determined losses were less than 0.2 dB. Along with polarisation multiplexing realised by fibre-type polarisation beam splitters, six signal channels (

,

,

,

,

, and

), each carrying 42 Gaud/s quadrature phase-shift keying signals, were transmitted through a few-mode fibre for optical transmission. The average insertion loss of the system is less than 5 dB, while its maximum crosstalk with the few-mode fibre is less than −12 dB, leading to a 4-dB power penalty. The findings of this study pave the way for the practical application of 3D integrated photonic chips in high-capacity optical transmission systems.

Lunar sample return missions are crucial for researching the composition and origin of the Moon. In recent decades, several lunar sample return missions have been conducted, yielding abundant and valuable lunar samples. As the latest development in lunar sample returns, the Chang’e-6 mission aimed to implement lunar farside sampling. The shorter time available for sampling requires higher sampling efficiency. In this study, the main factors in the sampling site selection and sampling process are introduced and a vision-based sampling implementation is designed for the Chang’e-6 mission to significantly simplify manual operation while maintaining high sampling quality. By sufficiently leveraging the point cloud data reconstructed from the binocular camera images, autonomous terrain analysis and sample point selection are achieved. A 6D pose estimation pipeline based on point cloud registration provides a robust method for sampler pose measurement, replacing the previous manual fine-tuning process and achieving better accuracy. Owing to the well-analyzed sample points and accurate fine-tuning, the proposed approach demonstrates high accuracy in controlling the scooping depth, while significantly reducing the time cost of the sampling implementation, effectively supporting the Chang’e-6 lunar sample mission.

Laser direct writing employing multi-photon 3D polymerisation is a scientific and industrial tool used in various fields such as micro-optics, medicine, metamaterials, programmable materials, etc., due to the fusion of high-throughput and fine features down to hundreds of nm. Some limitations of technology applicability emerge from photo-resin properties, however any material modifications can strongly affect its printability, as photoexcitation conditions alter as well. Here we present wavelength-independent 3D polymerisation using low peak power laser oscillators. High pulse repetition rate and fast laser direct writing was employed for advancing additive manufacturing out of the SZ2080^TM photo-resist without any photo-initiator. Wavelengths of 517 nm, 780 nm, and 1035 nm are shown to be suitable for producing 300 nm polymerized features even at high – up to 10⁵ µm/s– writing speeds. Variation of organic-inorganic ratio in hybrid material results in shift and decrease of the dynamic fabrication window, yet not prohibiting the photo-structuring. Controlled energy deposition per focal volume is achieved due to localized heating enabling efficient 3D printing. Such spatio-selective photo-chemical cross-linking widens optical manufacturing capacity of non-photo-sensitive materials.

As the most fundamental, efficient frequency-mixing technology, second-order nonlinear optical effects have been extensively applied in the fields of advanced laser technology, microscopic imaging, and optical communication. However, overcoming the limitations of the centrosymmetric nature of traditional optical fibres and exciting second-order nonlinearity remains challenging. In this study, we demonstrate a functionally doped polymer microfibre to implement second-order nonlinear processes in an optical fibre system. Few-layer gallium selenide (GaSe) nanosheets with high nonlinear susceptibility χ⁽²⁾ are doped in polyvinyl alcohol (PVA) to fabricate the hybrid polymer microfibre, which enables strong second harmonic generation (SHG) and sum-frequency generation (SFG) with sub-milliwatt pump power. When pumped by a continuous-wave (CW) laser, the observable SHG signal was excited in the 1500–1630 nm wavelength range, exhibiting a theoretically predicted power dependence. The SFG response was also validated in the GaSe-doped PVA microfibre with the excitation of two CW pumps, with the signal intensity corresponding to the theoretical evolution tendency when the power and wavelength of the pump light were adjusted. Hence, developing GaSe-doped polymer microfibres provides a novel approach toward the fabrication and application of nonlinear optical fibre devices.

Fiber-based endoscopes are promising for minimally invasive in vivo biomedical diagnostics. Multicore fibers offer high resolution imaging. However, to avoid image deterioration induced by inter-core coupling, significant spacing between cores is required, which limits the active image guiding area of the fiber. Thus, they suffer from low light collection efficiency and decreased signal-to-noise ratio. In this paper, we present a method to increase the collection efficiency by thermally expanding the cores at the facet of a multicore fiber. This expansion is based on the diffusion of doping material of the cores, thus the fiber’ s original outer diameter is preserved. By enlarging the core diameter by a factor of 2.8, we increase the intensity of the transmitted light by a factor of up to 2.3. This results in a signal-to-noise ratio increase by a factor of up to 4.6 and significant improvement in the image contrast. The improvement increases with increasing working distance but is already prominent for as small working distance as 0.5 mm. The feasibility of the method is proved experimentally by lensless single-shot imaging of a test chart and incoherent light reflected from clusters of microbeads. The demonstrated approach is an important tool especially in imaging of biological specimens, for which phototoxicity must be avoided, and therefore, high collection efficiency is required.

Herein, we have explored the recombination dynamics and defect concentration of a mixed cation mixed halide perovskite Cs_0.17FA_0.83PbI_1.8Br_1.2 with 1.75 eV bandgap after exposure to a gamma-ray source (2.5 Gy/min). We used photoluminescent spectroscopy to observe changes in recombination dynamics on perovskite films, impedance spectroscopy to reveal the contribution of interface recombination, and admittance spectroscopy to define the activation energy and concentration of defects. It was revealed that moderate doses (up to 10 kGy) passivate defects with activation energy ≈ 0.5 eV and at the same time form new defects that cause dramatic growth of the diffusion coefficient and migration of mobile ions. These two processes with opposite direction result in high radiation tolerance of the studied material and solar cells up to 10 kGy. Doses above 10 kGy are detrimental for perovskite solar cells, mainly due to the growing role of interface recombination. The results encourage the use of the wide bandgap perovskite Cs_0.17FA_0.83PbI_1.8Br_1.2 as a material for tandem solar cells with potential applications in a space environment.

Early diagnosis of brain tumors is often hindered by non-specific symptoms, particularly in eloquent brain regions where open surgery for tissue sampling is unfeasible. This limitation increases the risk of misdiagnosis due to tumor heterogeneity in stereotactic biopsies. Label-free diagnostic methods, including intraoperative probes and cellular origin analysis techniques, hold promise for improving diagnostic accuracy. Polarimetry offers valuable information on the polarization properties of biomedical samples, yet it may not fully reveal specific structural characteristics. The interpretative scope of polarimetric data is sometimes constrained by the limitations of existing decomposition methods. On the other hand, dynamic laser speckle analysis (DLSA), a burgeoning technique, not only does not account for the polarimetric attributes but also is known for tracking only the temporal activity of the dynamic samples. This study bridges these gaps by synergizing conventional polarimetric imaging with DLSA for an in-depth examination of sample polarization properties. The effectiveness of our system is shown by analyzing the collection of polarimetric images of various tissue samples, utilizing a variety of adapted numerical and graphical statistical post-processing methods.

Water monitoring, environmental analysis, cell culture stability, and biomedical applications require precise pH control. Traditional methods, such as pH strips and meters, have limitations: pH strips lack precision, whereas electrochemical meters, although more accurate, are fragile, prone to drift, and unsuitable for small volumes. In this paper, we propose a method for the optical detection of pH based on a multiplexed sensor with 4D microcavities fabricated via two-photon polymerization. This approach employs pH-triggered reversible variations in microresonator geometry and integrates hundreds of dual optically coupled 4D microcavities to achieve the detection limit of 0.003 pH units. The proposed solution is a clear example of the use-case-oriented application of two-photon polymerized structures of high optical quality. Owing to the benefits of the multiplexed imaging platform, the dual 4D microresonators can be integrated with other microresonator types for pH-corrected biochemical studies.

The transport of intensity equation (TIE) is a well-established phase retrieval technique that enables incoherent diffraction limit-resolution imaging and is compatible with widely available brightfield microscopy hardware. However, existing TIE methods encounter difficulties in decoupling the independent contributions of phase and aberrations to the measurements in the case of unknown pupil function. Additionally, spatially nonuniform and temporally varied aberrations dramatically degrade the imaging performance for long-term research. Hence, it remains a critical challenge to realize the high-throughput quantitative phase imaging (QPI) with aberration correction under partially coherent illumination. To address these issues, we propose a novel method for high-throughput microscopy with annular illumination, termed as transport-of-intensity QPI with aberration correction (TI-AC). By combining aberration correction and pixel super-resolution technique, TI-AC is made compatible with large pixel-size sensors to enable a broader field of view. Furthermore, it surpasses the theoretical Nyquist-Shannon sampling resolution limit, resulting in an improvement of more than two times. Experimental results demonstrate that the half-width imaging resolution can be improved to ~345 nm across a 10× field of view of 1.77 mm² (0.4 NA). Given its high-throughput capability for QPI, TI-AC is expected to be adopted in biomedical fields, such as drug discovery and cancer diagnostics.