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Micropatterning and defect engineering of colloidal photonic crystals <i>via</i> laser direct writing
摘要： Micropatterning and defect engineering of colloidal photonic crystals (CPCs) play a significant role in the functionality of photonic crystals as they are crucial for optical chip integration, microcavity lasing, chemical sensing, etc. However, obstacles have arisen in recent years especially due to the lack of a general, cost-effective and versatile strategy to make these functional structures in one step. Traditional micro-/nanofabrication techniques may work for one structure but fail for another and the fabrication process is mostly complicated, which potentially incurs reproducibility issues. Here, point defects, waveguides and micropatterns with variable feature sizes (4B500 nm) can be easily created in polystyrene (PS)/SiO2 CPC films via laser direct writing, which is based on selective photodegradation of PS beads. By applying different laser powers or irradiation times, different coloured micropatterns and images with high resolution can be generated, which has great implications for image displays and anti-counterfeiting.
关键词： photodegradation,Micropatterning,colloidal photonic crystals,anti-counterfeiting,defect engineering,laser direct writing,image displays
更新于2025-09-16 10:30:52
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Ambient atmosphere laser-induced local ripening of MoS <sub/>2</sub> nanoparticles
摘要： Transition metal dichalcogenide (TMDC) ultrathin layers have attracted considerable interest in the recent years. Their peculiar functional properties can be exploited in electronics, spintronics, optoelectronics, photonics, energy production, harvesting and storage. The availability of cost-effective, green, and efficient growth processes is of paramount importance and significant effort has been made in the research on various production methodologies. Here we report on a simple laser-based process which allows the direct writing of thin TMDC layers. In detail, by direct exposure to laser irradiation of a dip-coated MoS2 precursor, we obtained a three-dimensional arrangement of MoS2 nanoparticles in the form of platelets with a lateral dimension of about 50 nm and thickness down to bilayers. The characterization was assessed by AFM and Raman spectroscopy. The platelets are formed only in the central region of the laser spot, confirming that the material out of the spot is indeed an unprocessed precursor. By tuning the precursor deposition, we demonstrate the fabrication of MoS2 patterns with designed layer numbers. The proposed approach is highly versatile and can be applied also for the controlled growth of other TMDCs, as proved by the successful generation of WS2 layers.
关键词： Transition metal dichalcogenide,MoS2,direct writing,laser-induced,Raman spectroscopy,AFM
更新于2025-09-16 10:30:52
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New Strategy to Achieve Laser Direct Writing of Polymers: Fabrication of the Color-Changing Microcapsule with Core-Shell Structure
摘要： This paper proposed an efficient and environmentally friendly strategy to prepare a new color-changing microcapsule with core-shell structure for laser direct writing of polymers, and only the physical melt blending of polymers was employed. The laser absorber (SnO2) and the easily carbonized polymer (PC) were designed as the “core” and the “shell” of the microcapsule, respectively. The microcapsules were in situ formed during melt blending. SEM, TEM, and EDS confirmed the successful preparation of SnO2/PC microcapsules with core-shell structure. Its average diameter was 2.2 μm, and the “shell” thickness was 0.21?0.24 μm. As expected, this SnO2/PC microcapsule endowed polymers with an outstanding performance of NIR laser direct writing. The Raman spectroscopy and XPS indicated that the color change ascribed to the polymer carbonization due to the instantaneous high temperature caused by the SnO2 absorption of NIR laser energy. Optical microscopy observed a thick carbonization layer of 234 μm. Moreover, Raman depth imaging revealed the carbonization distribution, confirming that the amorphous carbon produced by the carbonization of the PC “shell” is the key factor of SnO2/PC microcapsules to provide polymers an outstanding performance of laser direct writing. This color-changing microcapsule has no selectivity to polymers due to providing a black color source (the carbonization of PC) itself, ensuring the high contrast and precision of patterns or texts after laser direct writing for all general-purpose polymers. We believe that this novel strategy to achieve laser direct writing of polymers will have broad application prospects.
关键词： microcapsule,core-shell structure,carbonization,polymer,laser direct writing,near-infrared pulsed laser
更新于2025-09-16 10:30:52
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Mass Producible Low-Loss Broadband Optical Waveguides in Eagle2000 by Femtosecond Laser Writing
摘要： Optical waveguides were fabricated in alkaline earth boro-aluminosilicate glass, by femtosecond laser direct writing, with varying pulse energy and scan velocity. A spectral characterization, from 500 nm to 1700 nm, was made in order to determine their losses and understand its dependence on the processing parameters. Three major loss mechanisms were identified. At longer wavelengths, loss is mainly due to weak coupling. On the other hand, the behavior at shorter wavelengths is governed by propagation loss due to Rayleigh scattering, which was shown to be practically eliminated (<0.05 dB· cm?1· μm4) at higher scan velocities. Bulk absorption was also found to have an influence in the propagation losses at higher wavelengths. The combination of intermediate pulse energies (between 125-250 nJ) and high scan velocities (above 6 cm/s) allowed the fabrication of optical waveguides offering low losses across the entire range of wavelengths tested, facilitating applications that require larger wavelength working bands. Furthermore, since optimal fabrication conditions are achieved at higher scanning velocities, mass production with reduced fabrication times can be achieved.
关键词： femtosecond laser direct writing,Rayleigh scattering,propagation loss,Coupling loss,Mie scattering,integrated optics,low-loss broadband optical waveguides,mass production
更新于2025-09-12 10:27:22
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Broadband Mid-Infrared Directional and Multimode Interference Couplers in GLS Glass Fabricated using Femtosecond Laser Direct-Writing
摘要： The first broadband directional and multimode interference couplers for the mid-infrared centred around 4 μm wavelength are demonstrated. The devices are inscribed into commercial chalcogenide glass (Gallium-Lanthanum-Sulfide, GLS) provided by the University of Southampton using a tightly focused 800 nm, 5.1 MHz repetition rate femtosecond laser. Low loss waveguides are formed by placing 3 individual laser written tracks next to each other, resulting in propagation losses as low as 0.22 dB/cm. These waveguides are used to create asymmetric directional couplers, where the propagation constant in one arm is tailored to flatten the chromatic response of the device. By locally changing the feedrate at which the sample is translated through the focus, a change in propagation constant is obtained in the coupling region of the device. This yields a 3 dB coupler with a wavelength flattened response over a 500 nm wavelength band for ±5% variation in the coupling ratio compared to < 200 nm for a symmetric directional coupler. Multimode interference couplers were created by placing 26 laser inscribed tracks next to each other to form a 140 μm wide multimode interference region with lengths ranging from 5 to 10 mm. Asymmetry inside the multimode interference regions induced by the sequential writing process results in port dependent cross coupling ratios. Yet, close to 3 dB coupling was found for an 8.1 mm long device when injecting into the left input. The device features nearly perfect achromaticity across 3.75 to 4.25 μm.
关键词： GLS glass,mid-infrared,multimode interference couplers,femtosecond laser direct-writing,directional couplers
更新于2025-09-12 10:27:22
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Maskless Micro/Nanopatterning and Bipolar Electrical-Rectification of MoS2 Flakes Through Femtosecond Laser Direct Writing
摘要： MoS2 micro/nanostructures are desirable for tuning electronic properties, developing required functionality, and improving existing performance of multilayer MoS2 devices. This work presents a useful method to flexibly microprocess multilayer MoS2 flakes through femtosecond laser pulse direct writing, which can directly fabricate regular MoS2 nanoribbon arrays with ribbon widths of 179, 152, 116, 98, and 77 nm, and arbitrarily pattern MoS2 flakes to form micro/nanostructures such as single nanoribbon, labyrinth array, and cross structure. This method is mask-free and simple, and has high flexibility, strong controllability, and high precision. Moreover, numerous oxygen molecules are chemically and physically adsorbed on laser-processed MoS2, attributed to roughness defect-sites and edges of micro/nanostructures that contain numerous unsaturated edge-sites and highly active centres. In addition, electrical tests of the field effect transistor fabricated from prepared MoS2 nanoribbon arrays reveal new interesting features: output and transfer characteristics exhibit strong rectification (not going through zero and bipolar conduction) of drain?source current, which is supposedly attributed to the parallel structures with many edge-defects and p-type chemical doping of oxygen molecules on MoS2 nanoribbon arrays. This work demonstrates the ability of femtosecond laser pulses to directly induce micro/nanostructures, property changes, and new device-properties of two-dimension materials, which may future enable new applications at electronic devices based on MoS2 such as logic circuits, complementary circuits, chemical sensors, and p?n diodes.
关键词： micro/nanopatterning,MoS2 flakes,oxygen bonding,femtosecond laser direct writing,electrical rectification
更新于2025-09-12 10:27:22
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Attachable micropseudocapacitors using highly swollen laser-induced-graphene electrodes
摘要： For powering wearable electronics, extensive research has been directed toward microscale flexible and stretchable energy-storage devices. Microsupercapacitors, though promising candidates, remain limited in terms of design flexibility, scalability, reusability, and compatibility with general substrates. This paper reports a high-performance sticker-type flexible microsupercapacitor using highly swollen reduced-graphene-oxide electrodes fabricated by an ultrashort-pulse laser to promote full active-site and durability of the electrodes. Our sticker-type flexible micropseudocapacitor provides a comparable volumetric energy density of 1.08 mWh cm-3 and 13 times higher volumetric power density of 83.5 mW cm-3 compared to conventional lithium thin-film batteries. Bio-inspired surface modifications are additionally applied to the reduced-graphene-oxide electrodes, which provides a six-fold increase (10.38 mF cm?2) of the areal capacitance. A 6 × 2 micropseudocapacitor array embedded in a sub-millimeter thin PDMS film adheres to safety goggles and successfully powers a μ-LED. The total capacitance of the array is maintained at ~97% of its original value after 200 repetitive attachments and detachments showing good durability. In addition, the sticker-type micropseudocapacitor array shows a stable performance under repeated deformation, and up to ~99% of capacitance retention after 200 bending cycles. This novel re-attachable flexible micropseudocapacitor will expedite the widespread use of flexible and wearable devices.
关键词： laser direct writing,attachable energy storage device,laser-induced graphene,pseudocapacitor,microsupercapacitor
更新于2025-09-12 10:27:22
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - An Increase in Refractive Index Contrast in a Waveguide Inscribed in Tellurite Glass by Means of Sub-Nanosecond Bursts of Femtosecond Pulses
摘要： Femtosecond laser direct writing (FLDW) of waveguides in dielectric glasses and crystals is well-recognized technique for manufacturing of compact laser sources, optical sensors, labs-on-a-chip and optical chips for quantum computing [1]. For this technology the main obstacle to compaction of optical circuits and an increase in the number of elements on an optical chip is constraint of the refractive index contrast Δn between the core and the cladding of a waveguide that is given by the nature of FLDW. Insufficient RIC also restricts application of the depressed cladding waveguides in mid-IR due to mode leakage [2]. The largest ever-obtained refractive index change is associated with ion migration in a phosphate glass under the thermal regime of laser writing, and it is as high as +0.03 [3]. Recently we found that simultaneous actions of rarefaction and electronic excitation lead to enhanced negative refractive index change in the laser modified spots in silica glass and sapphire [4], wherein the required conditions were produced by a sub-nanosecond burst of femtosecond laser pulses. Here we report on FLDW of a low loss waveguide with enhanced refractive index contrast in 70TeO2-22WO3-8Bi2O3 glass inscribed by bursts of pulses with exponentially decaying amplitudes in each burst and pulse separation of 10 ps. The depressed cladding waveguide composing of 14 parallel tracks with reduced refractive index was inscribed at wavelength of 1030 nm (Fig.1.(a)). The maximum refractive index change Δn produced by train of ordinary pulses in the investigated glass was as high as -0.002 [2]. Mapping of refractive index change in tracks inscribed by the bursts with different burst energies and pulse separation intervals is shown in Fig.1(c) The range of the parameters was found for which the burst produced smooth tracks of negative refractive index change, and its amplitude is increased by factor of 3 in comparison with tracks inscribed by ordinary pulses. The maximum index change Δn was obtained with pulse separation interval of 10 ps. Beside enhanced refractive index change the burst train inscribed tracks with reduced cross section. That is, the track height is less at least by a factor of 3 in comparison with one inscribed by ordinary pulses under the same energy for a burst and an ordinary pulse (Fig1(a),(b)). We consider that the enhanced index change and the reduced track height are inevitably accompanied by strong localization of energy deposition through a reduction in peak pulse intensity that allowed avoiding destructive Kerr self-focusing. We consider that the new technique of FLDW paves the way for better confinement of radiation in a depressed cladding waveguide writing waveguides with well deterministic architectures. The increase in the waveguide non-linearity and extension of operation range to mid-IR is inevitably expected.
关键词： sub-nanosecond bursts,tellurite glass,depressed cladding waveguide,refractive index contrast,Femtosecond laser direct writing
更新于2025-09-12 10:27:22
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Physical similarity of the processes of laser thermochemical recording on thin metal films and modeling the recording of submicron structures
摘要： Laser thermochemical recording is a flexible method for direct writing the binary planar structures (for instance, diffractive optical elements) by a local laser-induced oxidation of thin metal films. Unfortunately, due to excess of influencing parameters, search for regimes of high-resoluted recording could be complicated. The presented article proposes the way to analyze the hard-to-reach regimes of laser recording by modeling them with more convenient regimes (with different geometric and/or thermochemical parameters) based on their physical similarity.
关键词： Thin films,Laser direct writing,Laser thermochemical writing,Ultrahigh resolution,Laser-induced oxidation
更新于2025-09-11 14:15:04
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Optimization of ultrafast laser parameters for 3D micromachining of fused silica
摘要： We present an optimization study on laser parameters for 3D micromachining of fused silica to achieve critical goals for practical applications including high surface quality, high volume production, and complex surfaces by ultrafast laser direct writing assisted chemical etching. We conducted experiments on laser pulse width of 300 fs and 1 ps, pulse energy ranging from 0.1 μJ to 1.6 μJ, three different polarizations (circular, parallel and perpendicular) and number of overlapped pulses from 3 to 10,000 at 1030 nm with up to 2 MHz repetition rate to investigate their effect on nanogratings and one dimensional (1D) channel and two dimensional (2D) planar surface selective etching on 1 mm thick fused silica. In one configuration, we achieved 21.8 nm RMS surface roughness with 80 μm Gaussian filtering and in another configuration, we estimated the maximum writing speed to be 1.25 m/s for given 2 MHz repetition rate with less than 400 nm filtered root mean square (RMS) surface roughness at a 1 mm2 area which covers the thickness of the glass.
关键词： 3D microfabrication,Direct writing,Roughness,Chemical etching,Selectivity,Ultrafast laser
更新于2025-09-11 14:15:04