Although optical microscopy is a widely used technique across various multidisciplinary fields for inspecting small-scale objects, surfaces or organisms, it faces a significant limitation: the lateral resolution of optical microscopes is fundamentally constrained by light diffraction. Dielectric micro-spheres, however, offer a promising solution to this issue as they are capable of significantly enhancing lateral resolution through extraordinary phenomena, such as a photonic nanojet.Building upon the potential of dielectric micro-spheres, this paper introduces a novel approach for fabricating 3D micro-devices designed to enhance lateral resolution in optical microscopy. The proposed 3D micro-device comprises a modified coverslip and a micro-sphere, facilitating easy handling and integration into any existing optical microscope. To manufacture the device, two advanced femtosecond laser techniques are employed: femtosecond laser ablation and multi-photon lithography. Femtosecond laser ablation was employed to create a micro-hole in the coverslip, which allows light to be focused through this aperture. Multi-photon lithography was used to fabricate a micro-sphere with a diameter of 20 µm, along with a cantilever that positions the above the processed micro-hole and connect it with the coverslip. In this context, advanced processing strategies for multi-photon lithography to produce a micro-sphere with superior surface roughness and almost perfect geometry (λ/8) from a Zr-based hybrid photoresist are demonstrated. The performance of the micro-device was evaluated using Mirau-type coherence scanning interferometry in conjunction with white light illumination at a central wavelength of 600 nm and a calibration grid (Λ = 0.28 µm, h > 50 nm). Here, the 3D micro-device proved to be capable of enhancing lateral resolution beyond the limits achievable with conventional lenses or microscope objectives when used in air. Simultaneously, it maintained the high axial resolution characteristic of Mirau-type coherence scanning interferometry. The results and optical properties of the micro-sphere were analyzed and further discussed through simulations.
The field-of-view (FOV), depth of field, and resolution of conventional microscopes are constrained by each other; therefore, a zoom function is required. Traditional zoom methods lose real-time performance and have limited information throughput, severely limiting their application, especially in three-dimensional dynamic imaging and large-amount or large-size sample scanning. Here, an adaptive multiscale (AMS) imaging mechanism combining the benefits of liquid lenses and multiscale imaging techniques is proposed to realize the functions of fast zooming, wide working distance (WD) range and large FOV on a self-developed AMS microscope. The design principles were revealed. Moreover, a nonuniform-distortion-correction algorithm and a composite patching algorithm were designed to improve image quality. The continuous tunable magnification range of the AMS microscope is from 9× to 18×, with the corresponding FOV diameters and resolution ranging from 2.31 to 0.98 mm and from 161 to 287 line-pairs/mm, respectively. The extended WD range is 0.8 mm and the zoom response time is 38 ms. Experiments demonstrated the advantages of the proposed microscope in pathological sample scanning, thick-sample imaging, microfluidic process monitoring, and the observation of living microorganisms. The proposed microscope is the first step towards zoom multiscale imaging technology and is expected to be applied in life sciences, medical diagnosis, and industrial detection.
One of the challenges in the field of multi-photon 3D laser printing lies in further increasing the print speed in terms of voxels/s. Here, we present a setup based on a 7 × 7 focus array (rather than 3 × 3 in our previous work) and using a focus velocity of about 1 m/s (rather than 0.5 m/s in our previous work) at the diffraction limit (40×/NA1.4 microscope objective lens). Combined, this advance leads to a ten times increased print speed of about 108 voxels/s. We demonstrate polymer printing of a chiral metamaterial containing more than 1.7 × 1012 voxels as well as millions of printed microparticles for potential pharmaceutical applications. The critical high-quality micro-optical components of the setup, namely a diffractive optical element generating the 7 × 7 beamlets and a 7 × 7 lens array, are manufactured by using a commercial two-photon grayscale 3D laser printer.
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 SZ2080TM 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.
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.
Laser polishing (LP) is considered an effective method for generating ultrasmooth surfaces owing to its precision, flexibility, and material compatibility. However, a lack of understanding of the evolution of surface topography during LP significantly limits the achievable surface roughness in practice. In this work, for the first time, by employing optical time-stretch quantitative interferometry (OTS-QI), we recorded the entire evolution of surface topography during LP with nanosecond-level temporal resolution, providing insight into the mechanisms involved in the surface roughness evolution, such as the Marangoni effect and the formation mechanism of mid-frequency waviness (MFW). Assisted by numerical calculations, we reveal that a ‘perfect polishing point’ exists, i.e., the optimal interaction time for LP at a specific laser power density, at which the surface roughness can be minimised without the formation of an MFW owing to the Marangoni effect and non-uniform removal. This OTS-QI system harnesses the rapid repetition rate of femtosecond lasers, achieving a remarkable measurement speed exceeding 100,000,000 times per second while preserving a measurement accuracy comparable to that of existing white light interferometers (WLIs), setting a new benchmark as the fastest recorded roughness measurement. In addition to LP, the proposed method can be applied for real-time and in situ monitoring of many machining scenarios involving highly dynamic phenomena.
To fulfill the requirements of high-precision common baseline measurement for multiple parameters, such as surface profiling and the curvature radius of large-aperture optical elements on the same instrument, this paper proposes a research on a high-precision large-aperture laser differential confocal-interferometric measurement method. This method is based on the principle of laser differential confocal combined with interferometry. It utilizes a Galilean double-reflection collimation system to generate well large-aperture collimated beams and employs mechanical phase-shifting technology for large-aperture and heavy-load reference lenses to overcome the flaws of existing large-aperture wavelength-tuning phase shifting technology in theory, thus achieving high-precision and high-stable phase-shifting interference in large-aperture surface profiling measurements. By utilizing the laser differential confocal method with anti-scattering and anti-interference properties, high-precision common baseline measurements are achieved for the multiple-parameter of optical elements such as ultra-long focal lengths and ultra-large curvature radii. The measurements of large-aperture surface profiles, the mean PV was 46 nm. For the ultra-long focal length, the relative standard deviation was 0.019%, whereas for the ultra-large curvature radius, the relative standard deviation was 0.0036%. This method enables high-precision, high-stable, and high-efficient common baseline measurements for the multiple parameters of optical elements with large, medium, and small apertures thereby providing an effective technical approach for improving the detection and machining precision of optical elements.
The transport of intensity equation (TIE) is a well-established deterministic 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 the pixel super-resolution technique, TI-AC is made compatible with sensors that have a large pixel size 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 on the quantitative phase target and unstained biological cells demonstrate that the half-width imaging resolution can be improved to ~345 nm (2-fold gain) 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.
In the past several decades, photonic integrated circuits (PICs) have been investigated using a variety of different waveguide materials and each excels in specific key metrics, such as efficient light emission, low propagation loss, high electro-optic efficiency, and potential for volume production. Despite sustained research, each platform shows inherit shortcomings that as a result stimulate studies in hybrid and heterogeneous integration technologies to create more powerful cross-platform devices. This is to combine the best properties of each platform; however, it requires dedicated development of special designs and additional fabrication processes for each different combination of material systems. In this work, we present a novel hybrid integration scheme that leverages a 3D-nanoprinted interposer to realize a photonic chiplet interconnection system. This method represents a generic solution that can readily couple between chips of any material system, with each fabricated on its own technology platform, and more importantly, with no change in the established process flow for the individual chips. A fast-printing process with sub-micron accuracy is developed to form the chip-coupling frame and fiber-guiding funnel, achieving a mode-field-dimension (MFD) conversion ratio of up to 5:2 (from a SMF28 fiber to 4µm×4µm mode in polymer waveguide), which, to the best of our knowledge, represents the largest mode size conversion using non-waveguided 3D nanoprinted components. Furthermore, we demonstrate such a photonic chiplet interconnection system between silicon and InP chips with a 2.5 dB die-to-die coupling loss, across a 140 nm wavelength range between 1480 nm to 1620 nm. This hybrid integration plan can bridge different waveguide materials, supporting a much more comprehensive cross-platform integration.
Compact micro-spectrometers have gained significant attention due to their ease of integration and real-time spectrum measurement capabilities. However, size reduction often compromises performance, particularly in resolution and measurable wavelength range. This work proposes a computational micro-spectrometer based on an ultra-thin (~250 nm) detour-phased graphene oxide planar lens with a sub-millimeter footprint, utilizing a spectral-to-spatial mapping method. The varying intensity pattern along the focal axis of the lens acts as a measurement signal, simplifying the system and enabling real-time spectrum acquisition. Combined with computational retrieval method, an input spectrum is reconstructed with a wavelength interval down to 5 nm, representing a 5-time improvement compared with the result when not using computational method. In an optical compartment of 200 μm by 200 μm by 450 μm from lens profile to the detector surface, the ultracompact spectrometer achieves broad spectrum measurement covering the visible range (420 - 750 nm) with a wavelength interval of 15 nm. Our compact computational micro-spectrometer paves the way for integration into portable, handheld, and wearable devices, holding promise for diverse real-time applications like in-situ health monitoring (e.g., tracking blood glucose levels), food quality assessment, and portable counterfeit detection.
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.
Nano-kirigami technology enables the flexible transformation of two-dimensional (2D) micro/nanoscale structures into three-dimensional (3D) structures with either open-loop or close-loop topological morphologies, and has aroused significant interest in the fields of nanophotonics and optoelectronics. Here, we propose an innovative kissing-loop nano-kirigami strategy, wherein 2D open-loop structures can transform into 3D kissing-loop structures while retaining advantages such as large deformation heights and multiple optical modulations. Benefiting from the unidirectional deformation of the structures, the kissing-loop nano-kirigami exhibits significant asymmetric transmission under x-polarized light incidence. Importantly, the Pancharatnam-Berry geometric phase was experimentally realized in nano-kirigami structures for the first time, resulting in broadband anomalous reflection in the near-infrared wavelength region. The kissing-loop nano-kirigami strategy can expand the existing platform of micro/nanoscale fabrication and provide an effective method for developing optical sensing, spatial light modulations, and optoelectronic devices.
Carbon dots (CDs) have shown great potential for application in optoelectronics, owing to their merits of tunable fluorescence, biocompatibility, low toxicity, and solution processability. However, the intrinsic nature of CDs makes them prone to fluorescence quenching in the aggregated state. In addition, the emission peak width at half maximum of a single CD is usually greater than 60 nm, and the emission spectra may exhibit a multi-peak superposition state, resulting in poor monochromaticity. Further, the unsatisfactory quantum yield of CDs restricts their further application. Considering this, doping strategies have successfully improved the electrical, optical, and chemical properties of CDs. The intrinsic structure and electron distribution of CDs can be effectively adjusted by metal or nonmetal doping. Doping atoms generate n- or p-type charge carriers, changing the bandgap energy, and thereby improving the photophysical properties of the CDs. In this comprehensive review, we explore the intricate effects of various doping strategies on CDs and systematically categorize them. Notably, we elaborate on the diverse types of doped CDs and emphasize their photophysical properties, aiming to elucidate the fundamental mechanisms underlying the influence of doping on CD performance. Specifically, this review describes the extensive applications of doped carbon dots (X-CDs) in optoelectronic devices, information encryption, anti-counterfeiting measures, imaging techniques, and detection fields, to spur further X-CD exploration and application.
Side-pumping fibre combiners offer several advantages in fibre laser design, including distributed pump absorption, reduced heat load, and improved flexibility and reliability. These benefits are particularly important for all-fibre lasers and amplifiers operating in the mid-IR wavelength range and based on soft-glass optical fibres. However, conventional fabrication methods face limitations due to significant differences in the thermal properties of pump-delivering silica fibres and signal-guiding fluoride-based fibres. To address these challenges, this work introduces a design for a fuse-less side-polished (D-shaped) fibre-based pump combiner comprising multimode silica and double-clad fluoride-based fibres. The results demonstrate stable coupling efficiency exceeding 80% at a 980-nm wavelength over 8 hours of continuous operation under active thermal control. The developed pump combiner has also been successfully integrated into a linear Er-doped fibre laser cavity, showing continuous-wave generation at 2731 or 2781-nm central wavelength with an output power of 0.87~W. Overall, this innovative approach presents a simple, repeatable, and reproducible pump combiner design that opens up new possibilities for leveraging fibre-based component technology in soft glass matrices and other emerging fibres with unique compositions.
Constructing a one-dimensional (1D) core/shell heterostructure is a rational and efficient way to integrate multiple functional materials into a single device, in which a distinct and reliable interface and suitable energy-band alignment play important roles in optoelectronic applications. Here, using a typical magnetron sputtering system, we constructed a 1D ZnO/CdS/CdTe core/shell nanorod arrays radial heterojunction with a well-designed cascade type-II energy band alignment and improved the broadband photodetector (PD) performance. The well-formed shell layers compensated for the defect states on the ZnO surface and extended the photoresponse range from ultraviolet to visible and near-infrared. Moreover, reliable and distinct heterointerfaces with a cascade type-II energy band alignment can guarantee more stable carrier migration and reduce energy loss, promoting effective photogenerated charge carrier separation and resulting in an enhanced photoresponse. The optimised 1D ZnO/CdS/CdTe core/shell heterojunction PD exhibited a fast photoresponse at 0 V bias with high responsivity and detectivity. These results provide an important reference for the rational design and controllable synthesis of multifunctional optoelectronic nanodevices.
Selective laser melting (SLM) is a promising technology for fabricating complex components with W/Cu dual metal. To enhance the interfacial bonding of W/Cu dual metal, we propose a novel approach using laser texturing to fabricate micro/nanostructures on the W surface. The micro/nanostructures promoted the spreading of Cu in the liquid, inhibited defects, and considerably increased the contact area between W and Cu by mechanical interlocking. To the best of our knowledge, a W/Cu dual metal was successfully prepared by SLM without a transition layer the first time. The bonding strength of the two materials reached 123 MPa, close to that of a W/Cu dual metal joint prepared by diffusion bonding.
Optimizing laser processes is historically challenging, requiring extensive and costly experimentation. To solve this issue, we apply Bayesian optimization for process parameter optimization to laser cutting, welding, and polishing. We demonstrate how readily available Bayesian optimization frameworks enable efficient optimization of laser processes with only modest expert knowledge. Case studies on laser cutting, welding, and polishing highlight its adaptability to real-world manufacturing scenarios. Moreover, the examples emphasize that with suitable cost functions and boundaries an acceptable optimization result can be achieved after a reasonable number of experiments.
Silicon photonics is currently the leading technology for the development of compact and low-cost photonic integrated circuits. However, despite its enormous potential, certain limitations, such as the absence of a linear electro-optical (EO) effect because of the symmetric crystal structure of silicon remain. In contrast, barium titanate (BTO) exhibits a strong Pockels effect. In this study, we demonstrated a high-quality transferred barium titanate ferroelectric hybrid integrated modulator on a silicon-on-insulator platform. The proposed hybrid integration of BTO on silicon Mach-Zehnder interferometers exhibited EO modulation with a VπL as low as 1.67 V·cm, thereby facilitating the realisation of compact EO modulators. The hybrid integration of BTO with SOI waveguides is expected to pave the way for the development of high-speed and high efficiency EO modulators.
Measurements based on optical microscopy can be severely impaired if the access exhibits variations of the refractive index. In the case of fluctuating liquid-gas boundaries, refraction introduces dynamical aberrations that increase the measurement uncertainty. This is prevalent at multiphase flows (e. g. droplets, film flows) that occur in many technical applications as for example in coating and cleaning processes and the water management in fuel cells. In this paper, we present a novel approach based on adaptive optics for correcting the dynamical aberrations in real time and thus reducing the measurement uncertainty. The shape of the fluctuating water-air interface is sampled with a reflecting light beam (Fresnel Guide Star) and a Hartmann-Shack sensor which makes it possible to correct its influence with a deformable mirror in a closed loop. Three-dimensional flow measurements are achieved by using a double-helix point spread function. We measure the flow inside a sessile, oscillating 50-μl droplet on an opaque gas diffusion layer for fuel cells and show that the temporally varying refraction at the droplet surface causes a systematic underestimation of the flow field magnitude corresponding to the first droplet eigenmode which plays a major role in their detachment mechanism. We demonstrate that the adaptive optics correction is able to reduce this systematic error. Hence, the adaptive optics system can pave the way to a deeper understanding of water droplet formation and detachment which can help to improve the efficiency of fuels cells.
The demand for optical glass has been rapidly increasing in various industries, where an ultra-smooth surface and form accuracy are critical for the functional elements of the applications. To meet the high surface-quality requirements, a polishing process is usually adopted to finish the optical glass surface to ensure an ultra-smooth surface and eliminate sub-surface damage. However, current ultra-precision polishing processes normally polish workpieces individually, leading to a low production efficiency and high polishing costs. Current mass-finishing methods cannot be used for optical glasses. Therefore, magnetic-field-assisted batch polishing (MABP) was proposed in this study to overcome this research gap and provide an efficient and cost-effective method for industrial use. A series of polishing experiments were conducted on typical optical components under different polishing parameters to evaluate the polishing performance of MABP on optical glasses. The results demonstrated that MABP is an efficient method to simultaneously polish multiple lenses while achieving a surface roughness, indicated by the arithmetic mean height (Sa), of 0.7 nm and maintained a sub-micrometer surface form for all the workpieces. In addition, no apparent sub-surface damage was observed, indicating the significant potential for the high-quality rapid polishing of optical glasses. The proposed method is highly competitive compared to the current optical polishing methods, which has the potential to revolutionize the polishing process for small optics.
Electromagnetic waves carrying orbital angular momentum (OAM), namely OAM beams, are important in various fields including optics, communications, and quantum information. However, most current schemes can only generate single or several simple OAM modes. Multi-mode OAM beams are rarely seen. This paper proposes a scheme to design metasurfaces that can generate multiple polarization-multiplexed OAM modes with equal intervals and intensities (i.e., OAM combs) working in the terahertz (THz) range. As a proof of concept, we first design a metasurface to generate a pair of polarization-multiplexed OAM combs with arbitrary mode numbers. Furthermore, another metasurface is proposed to realize a pair of polarization-multiplexed OAM combs with arbitrary locations and intervals in the OAM spectrum. Experimental results agree well with full-wave simulations, verifying a great performance of OAM combs generation. Our method may provide a new solution to designing high-capacity THz devices used in multi-mode communication systems.
Depth measurement and three-dimensional (3D) imaging under complex reflection and transmission conditions are challenging and even impossible for traditional structured light techniques, owing to the precondition of point-to-point triangulation. Despite recent progress in addressing this problem, there is still no efficient and general solution. Herein, a Fourier dual-slice projection with depth-constrained localization is presented to separate and utilize different illumination and reflection components efficiently, which can significantly decrease the number of projection patterns in each sequence from thousands to fifteen. Subsequently, multi-scale parallel single-pixel imaging (MS-PSI) is proposed based on the established and proven position-invariant theorem, which breaks the local regional assumption and enables dynamic 3D reconstruction. Our methodology successfully unveils unseen-before capabilities such as (1) accurate depth measurement under interreflection and subsurface scattering conditions, (2) dynamic measurement of the time-varying high-dynamic-range scene and through thin volumetric scattering media at a rate of 333 frames per second; (3) two-layer 3D imaging of the semitransparent surface and the object hidden behind it. The experimental results confirm that the proposed method paves the way for dynamic 3D reconstruction under complex optical field reflection and transmission conditions, benefiting imaging and sensing applications in advanced manufacturing, autonomous driving, and biomedical imaging.
Mode-division multiplexing technology has been proposed as a crucial technique for enhancing communication capacity and alleviating growing communication demands. Optical switching, which is an essential component of optical communication systems, enables information exchange between channels. However, existing optical switching solutions are inadequate for addressing flexible information exchange among the mode channels. In this study, we introduced a flexible mode switching system in a multimode fibre based on an optical neural network chip. This system utilised the flexibility of on-chip optical neural networks along with an all-fibre orbital angular momentum (OAM) mode multiplexer-demultiplexer to achieve mode switching among the three OAM modes within a multimode fibre. The system adopted an improved gradient descent algorithm to achieve training for arbitrary 3 × 3 exchange matrices and ensured maximum crosstalk of less than −18.7 dB, thus enabling arbitrary inter-mode channel information exchange. The proposed optical-neural-network-based mode-switching system was experimentally validated by successfully transmitting different modulation formats across various modes. This innovative solution holds promise for providing effective optical switching in practical multimode communication networks.
Organic proteins are attractive owing to their unique optical properties, remarkable mechanical characteristics, and biocompatibility. Manufacturing multifunctional structures on organic protein films is essential for practical applications; however, the controllable fabrication of specific structures remains challenging. Herein, we propose a strategy for creating specific structures on silk film surfaces by modulating the bulging and ablation of organic materials. Unique surface morphologies such as bulges and craters with continuously varying diameters were generated based on the controlled ultrafast laser-induced crystal-form transition and plasma ablation of the silk protein. Owing to the anisotropic optical properties of the bulge/crater structures with different periods, the fabricated organic films can be used for large-scale inkless color printing. By simultaneously engineering bulge/crater structures, we designed and demonstrated organic film-based optical functional devices that achieves holographic imaging and optical focusing. This study provides a promising strategy for the fabrication of multifunctional micro/nanostructures that can broaden the potential applications of organic materials.
We describe how a direct combination of an axicon and a lens can represent a simple and efficient beam-shaping solution for laser material processing applications. We produce high-angle pseudo-Bessel micro-beams at 1550 nm, which would be difficult to produce by other methods. Combined with appropriate stretching of femtosecond pulses, we access optimized conditions inside semiconductors allowing us to develop high-aspect-ratio refractive-index writing methods. Using ultrafast microscopy techniques, we characterize the delivered local intensities and the triggered ionization dynamics inside silicon with 200-fs and 50-ps pulses. While similar plasma densities are produced in both cases, we show that repeated picosecond irradiation induces permanent modifications spontaneously growing shot-after-shot in the direction of the laser beam from front-surface damage to the back side of irradiated silicon wafers. The conditions for direct microexplosion and microchannel drilling similar to those today demonstrated for dielectrics still remain inaccessible. Nonetheless, this work evidences higher energy densities than those previously achieved in semiconductors and a novel percussion writing modality to create structures in silicon with aspect ratios exceeding ~700 without any motion of the beam. The estimated transient change of conductivity and measured ionization fronts at near luminal speed along the observed microplasma channels support the vision of vertical electrical connections optically controllable at GHz repetition rates. The permanent silicon modifications obtained by percussion writing are light-guiding structures according to a measured positive refractive index change exceeding 10−2. These findings open the door to unique monolithic solutions for electrical and optical through-silicon-vias which are key elements for vertical interconnections in 3D chip stacks.
Emission of THz radiation from air breakdown at focused ultra-short fs-laser pulses (800 nm/35 fs) was investigated for the 3D spatio-temporal control where two pre-pulses are used before the main-pulse. The laser pulse induced air breakdown forms a ~ 120 μm-long focal volume generate shockwaves which deliver a denser air into the focal region of the main pulse for enhanced generation of THz radiation at 0.1–2.5 THz spectral window. The intensity of pre- and main-pulses was at the tunnelling ionisation intensities (1–3) × 1016 W/cm2 and corresponded to sub-critical (transparent) plasma formation in air. Polarisation analysis of THz radiation revealed that orientation of the air density gradients generated by pre-pulses and their time-position locations defined the ellipticity of the generated THz electrical field. The rotational component of electric current is the origin of THz radiation.
Dwell time plays a vital role in determining the accuracy and convergence of the computer-controlled optical surfacing process. However, optimizing dwell time presents a challenge due to its ill-posed nature, resulting in non-unique solutions. To address this issue, several well-known methods have emerged, including the iterative, Bayesian, Fourier transform, and matrix-form methods. Despite their independent development, these methods share common objectives, such as minimizing residual errors, ensuring dwell time's positivity and smoothness, minimizing total processing time, and enabling flexible dwell positions. This paper aims to comprehensively review the existing dwell time optimization methods, explore their interrelationships, provide insights for their effective implementations, evaluate their performances, and ultimately propose a unified dwell time optimization methodology.
ISSN 2689-9620 EISSN 2831-4093
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2021, 2(3): 350-369. doi: 10.37188/lam.2021.024
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2021, 2(3): 313-332. doi: 10.37188/lam.2021.020
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2021, 2(4): 446-459. doi: 10.37188/lam.2021.028
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2021, 2(1): 59-83. doi: 10.37188/lam.2021.005
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2023, 4(3): 233-242. doi: 10.37188/lam.2023.023
