High-throughput microchannel fabrication in fused silica by temporally shaped femtosecond laser Bessel-beam-assisted chemical etching

Wide-Size Range and High Robustness Self-Assembly Micropillars for Capturing Microspheres

Capillary force driven self-assembly micropillars (CFSA-MP) holds immense promise for the manipulation and capture of cells/tiny objects, which has great demands of wide size range and high robustness. Here, we propose a novel method to fabricate size-adjustable and highly robust CFSA-MP that can achieve wide size range and high stability to capture microspheres. First, we fabricate a microholes template with an adjustable aspect ratio using the spatial-temporal shaping femtosecond laser double-pulse Bessel beam-assisted chemical etching technique, and then the micropillars with adjustable aspect ratio are demolded by polydimethylsiloxane (PDMS). We fully demonstrated the advantages of the Bessel optical field by using the spatial-temporal shaping femtosecond laser double-pulse Bessel beams to broaden the height range of the micropillars, which in turn expands the size range of the captured microspheres, and finally achieving a wide range of capturing microspheres with a diameter of 5-410 μm. Based on the inverted mold technology, the PDMS micropillars have ultrahigh mechanical robustness, which greatly improves the durability. CFSA-MP has the ability to capture tiny objects with wide range and high stability, which indicates great potential applications in the fields of chemistry, biomedicine, and microfluidics.

Investigation on hybrid laser ablation and its application in fused silica damage mitigation

We present and investigate a hybrid laser-based method of surface shaping for damage mitigation on fused silica surfaces. Damage sites were removed and precisely shaped into an optically-benign cone by a procedure of femtosecond laser ablation with a subsequent CO₂ laser polishing process. The morphology of the cone rim was quantitatively predicted by a numerical model. Since the heat-affected zone (HAZ) of the laser polishing process was effectively confined by the optimization of ablation parameters, the dimensions of the raised rim were reduced by an order of magnitude. The intensity of the on-axis hotspot was positively related to the dimensions of the raised rim, and thus an inapparent downstream intensification was achieved by the rim reduction. Laser-induced damage threshold (LIDT) of the cone was tested to be ∼14 J/cm² on the input surface. Therefore, the presented method is appropriate to mitigate damage and also provides a promising approach to manufacturing functional microstructures for high-power applications.

Polarization-independent microchannel in a high-speed-scan femtosecond laser-assisted etching of fused silica

Microchannels fabricated by femtosecond laser-assisted chemical etching are of great use in biochemical analysis. In this paper, we study the morphology change of etched microchannels in fused silica by controlling the laser scan speed, and we find a significant difference between the chemical etched length and volume. The fabricated microchannels would gradually become tapered along the scan direction, which influences the flow of the hydrofluoric (HF) reagent and the etching rate. As a result, the difference ratios of the etched length and volume, respectively, reach -5.56% and -41.83% followed by the scan speed increasing from 5 to 200 µm/s. Microchannels with polarization independence and better aspect ratio could be obtained in a high-speed-scan mode. We suggest that laser-induced structural transformation from interconnected microcracks to nanogratings could be responsible for this change. Aforementioned results offer a feasible approach to achieve polarization-independent microchannels, which is in favor of accelerating the fabrication of three-dimensional microfluidic devices.

Femtosecond laser hybrid processing strategy of transparent hard and brittle materials

With high hardness, high thermal stability, chemical inertness and excellent optoelectronic properties, transparent hard and brittle materials have drawn significant attentions in frontier domains such as aerospace, photoelectric detection, and high-intensity lasers. Femtosecond laser processing technology demonstrates great potential for transparent hard and brittle materials processing due to its outstanding advantages such as non-contact, true 3D processing and programmable design. However, high-energy laser ablation usually causes severe damage to the surface of the materials, resulting in low processing accuracy, low processing efficiency and poor surface quality. Femtosecond laser hybrid processing strategies have been proven to be an effective solution to solve the above problems. This mini-review summarizes the fundamentals and research progress of femtosecond laser hybrid processing strategies of transparent hard and brittle materials in recent years. Moreover, the challenges and application prospects of these techniques are discussed.

Development of lab-on-chip biosensor for the detection of toxic heavy metals: A review

Recently, a decrease in water availability and quality has been raised due to rapid industrialization, unsustainable agricultural activities and anthropogenic activities. Heavy metals are considered significant pollutants in the water environment, cause environmental hazards and health effects to humans. For monitoring water contaminants utilized different conventional techniques. Still, they have some drawbacks, such as cost expensive, ecological issues, and processing time, requiring technicians and researchers to operate them effectively. Biosensors have become reasonable devices for screening and identifying environmental contaminants because of their different benefits contrasted with other detecting techniques. This review summarizes the toxic effect of heavy metal and their source, occurrence. A detailed discussion is provided on the heavy metal recognition materials for detecting heavy metals in wastewater. Lab on chip (LOC) is an emerging micro-electrical mechanical system (MEMS) device that intakes liquid and makes it move through the micro-channels, to accomplish fast, cost-effective and profoundly sensitive analysis with significant yield. LOC also provided a discussion on numerous laboratory functions on a single platform. This article attempts to discuss the detection of heavy metals using lab on a chip by suitable recognition materials. Further, the design and fabrication mechanism and their recognition abilities of LOC were also reviewed. The review mainly focuses on the application of LOC biosensors, pros, and cons, and suggests a roadmap towards future development to enhance the practical use in pollutant monitoring.

Investigating focus elongation using a spatial light modulator for high-throughput ultrafast-laser-induced selective etching in fused silica

Ultrafast-laser-induced selective chemical etching is an enabling microfabrication technology compatible with optical materials such as fused silica. The technique offers unparalleled three-dimensional manufacturing freedom and feature resolution but can be limited by long laser inscription times and widely varying etching selectivity depending on the laser irradiation parameters used. In this paper, we aim to overcome these limitations by employing beam shaping via a spatial light modulator to generate a vortex laser focus with controllable depth-of-focus (DOF), from diffraction limited to several hundreds of microns. We present the results of a thorough parameter-space investigation of laser irradiation parameters, documenting the observed influence on etching selectivity and focus elongation in the polarization-insensitive writing regime, and show that etching selectivity greater than 800 is maintained irrespective of the DOF. To demonstrate high-throughput laser writing with an elongated DOF, geometric shapes are fabricated with a 12-fold reduction in writing time compared to writing with a phase-unmodulated Gaussian focus.

Femtosecond Laser Assisted 3D Etching Using Inorganic-Organic Etchant

Selective laser etching (SLE) is a technique that allows the fabrication of arbitrarily shaped glass micro-objects. In this work, we show how the capabilities of this technology can be improved in terms of selectivity and etch rate by applying an etchant solution based on a Potassium Hydroxide, water, and isopropanol mixture. By varying the concentrations of these constituents, the wetting properties, as well as the chemical reaction of fused silica etching, can be changed, allowing us to achieve etching rates in modified fused silica up to 820 μm/h and selectivity up to ∼3000. This is used to produce a high aspect ratio (up to 1:1000), straight and spiral microfluidic channels which are embedded inside a volume of glass. Complex 3D glass micro-structures are also demonstrated.

Femtosecond laser double pulse Bessel beam ablation of silicon

Here, a double pulse Bessel beam was acquired by modulating a femtosecond laser Gaussian beam from both spatial and temporal scales. The double pulse Bessel beam ablation of silicon was studied systematically. The experimental results showed that when the time delay was 0.5 ps, the ablation efficiency slightly increased. As the time delay increased from 0.5 to 100 ps, the ablation rate was significantly suppressed, which could be attributed to the fact that the time delay was longer than the time for free electron density reaching its maximum value approximately 150 fs. Moreover, the morphology of the ablation spot indicated that the time delay had a significant effect on the changes in morphology. More importantly, a different time delay affected the percentage of oxygen on the processed spot. Finally, using the double pulse Bessel beam ablation of silicon, controllable antireflection and superhydrophobic functional surfaces could be easily obtained.

Drilling high aspect ratio holes by femtosecond laser filament with aberrations

A near-infrared femtosecond laser is focused by a 100 mm-focal-length plano-convex lens to form a laser filament, which is employed to drill holes on copper targets. By shifting or rotating the focusing lens, additional aberration is imposed on the focused laser beam, and significant influence is produced on the aspect ratio and cross-sectional shape of the micro-holes. Experimental results show that when proper aberration is introduced, the copper plate with a thickness of 3 mm can be drilled through with an aspect ratio of 30, while no through-holes can be drilled on 3-mm-thickness copper plates by femtosecond laser with minimized aberration. In addition, when femtosecond laser filament with large astigmatism is used, micro-holes that had a length to width ratio up to 3.3 on the cross-section are obtained. Therefore, the method proposed here can be used to fabricate long oval holes with high aspect ratios.

Temporal visualization of femtosecond laser pulses with single-edge transport in turbid media via Monte Carlo simulation

We study the propagation of femtosecond laser pulses with a single (front or rear) edge or dual edge through turbid media via Monte Carlo simulation. The results show that both the transmitted pulses spread on the basis of the incident pulse width ${t_{p}} = {{100}}\;{\rm{fs}}$, arising from the scattering effect. Further, the broadening width of the incident laser with a dual-edge pulse is wider than that of the incident laser width a single-edge pulse. The effect of the scattering particles on the front edge and the rear edge of the femtosecond laser can be distinguished in the time domain for femtosecond laser pulses through turbid media with the optical depth (OD) less than 10. In this scattering regime, the front-edge pulse scattered by the particles contributes more to diffused photons, but the effect of the scattering particles on the front edge and the rear edge of the femtosecond laser cannot be discriminated in turbid media with the OD more than 10, where the scattering is dominated by multiple scattering.

Laser-induced structural modification in calcium aluminosilicate glasses using molecular dynamic simulations

Glass structures of multicomponent oxide systems (CaO–Al₂O₃–SiO₂) are studied using a simulated pulsed laser with molecular dynamics. The short- and intermediate-range order structures revealed a direct correlation between the transformation of Al^(IV) to Al^(V), regions of increased density following laser processing, inherent reduction in the average T–O–T (T = Al, Si) angle, and associated elongation of the T–O bonding distance. Variable laser pulse energies were simulated across calcium aluminosilicate glasses with high silica content (50–80%) to identify densification trends attributed to composition and laser energy. High-intensity pulsed laser effects on fictive temperature and shockwave promotion are discussed in detail for their role in glass densification. Laser-induced structural changes are found to be highly dependent on pulse energy and glass chemistry.

Bessel Beam: Significance and Applications-A Progressive Review

Diffraction is a phenomenon related to the wave nature of light and arises when a propagating wave comes across an obstacle. Consequently, the wave can be transformed in amplitude or phase and diffraction occurs. Those parts of the wavefront avoiding an obstacle form a diffraction pattern after interfering with each other. In this review paper, we have discussed the topic of non-diffractive beams, explicitly Bessel beams. Such beams provide some resistance to diffraction and hence are hypothetically a phenomenal alternate to Gaussian beams in several circumstances. Several outstanding applications are coined to Bessel beams and have been employed in commercial applications. We have discussed several hot applications based on these magnificent beams such as optical trapping, material processing, free-space long-distance self-healing beams, optical coherence tomography, superresolution, sharp focusing, polarization transformation, increased depth of focus, birefringence detection based on astigmatic transformed BB and encryption in optical communication. According to our knowledge, each topic presented in this review is justifiably explained.

High-speed drilling of alumina ceramic by sub-microsecond pulsed thin disk laser

The rapid development of optoelectronic components has demanded high-speed drilling for alumina ceramic substrate. However, the existing drilling speed cannot meet the demand due to the limitation of conventional laser system and drilling method. In this paper, by adopting a sub-microsecond pulsed thin disk laser that based on a multi-pass pumping module, a laser system with a pulse energy of 37.4 mJ and a peak power of 103.8 kW is developed, which helps us to achieve high processing efficiency. In addition, experimental and theoretical analysis suggest the positive defocusing method can be used to control the hole taper angle, and micro-holes with a hole diameter difference less than 6% is realized, which helps us to achieve high processing quality. Ultimately, it is reported that the drilling speed for micro-holes with a diameter of ∼150 µm reaches 30 holes per second, and for micro-holes with a diameter of ∼100 µm reaches as high as 66 holes per second. The performance of the sub-microsecond pulsed thin disk laser presented in this paper provides a reference in the field of high-speed laser processing.

Laser processing of alumina ceramic by a spatially superposing millisecond laser and a nanosecond laser with different beam shapes

Advanced combined pulse laser (CPL) processing technology with high processing efficiency is of interest for both academic and engineering prospects. However, the influence of the spatial superposition of the CPL on the processing quality is unclear. Here, we use a CPL composed of a nanosecond and millisecond laser with different beam shapes to drill alumina ceramic. Experimental and simulation results suggest that the CPL drilling process actively homogenizes the laser in the hole through multi-reflection of the laser, and thus holes with high circularity are obtained without the influence of the beam shape of the nanosecond laser. The research shows this to be a novel processing method, and that the processing quality is independent of the laser beam shape.

Characterization of micro-holes drilled in alumina ceramic by the combined pulse laser technique

Nowadays, combined pulse laser (CPL) technology has shown obvious advantages in alumina ceramic drilling. However, the characterization of micro-holes drilled by the CPL is not clear. In this paper, micro-holes drilled by ns-ms and ns/ms CPLs are systematically compared from the aspects of hole diameter, cracks, spatter deposition, recast layer, re-solidified particles, grain size, and chemical composition. The results show that due to the synchronous output of the nanosecond laser, the ns/ms CPL can eject more melt through expelling of the plasma shock wave; thus, the recast layer, re-solidified particles, and oxygen vacancies are decreased, while the spatter deposition is increased. On the other hand, due to the higher temperature and larger temperature gradient introduced by the nanosecond laser, the hole diameter, cracks, and grain size are increased. Therefore, an ideal CPL method to optimize the drilling performance is proposed. The research results have important guidance for improving the processing quality of the CPL, especially for alumina ceramic laser processing.

Amplitude-phase optimized long depth of focus femtosecond axilens beam for single-exposure fabrication of high-aspect-ratio microstructures

Fabrication of high-aspect-ratio (HAR) micro/nanostructures by two-photon polymerization (TPP) has become a hot topic because of the advantages of ultra-high resolution and true 3D printing ability. However, the low efficiency caused by point-by-point scanning strategy limits its application. In this Letter, we propose a strategy for the rapid fabrication of HAR microstructures by combining TPP with an amplitude-phase optimized long depth of focus laser beam (LDFB). The optimization of the LDFB is implemented by modulating the amplitude and phase on a phase-only spatial light modulator, which can suppress the side lobe and smooth energy oscillations effectively. The LDFB is used for rapid fabrication of HAR micropillars and various microstructures, which greatly increases the fabrication efficiency. As a demonstration, several typical HAR microstructures such as assemblies, microchannels, microtubes, and cell scaffolds are prepared. Moreover, the microcapture arrays are rapidly fabricated for the capture of microspheres and the formation of microlens arrays, which show focusing and imaging ability.

Nanosecond-millisecond combined pulse laser drilling of alumina ceramic

A nanosecond-millisecond combined pulse laser (CPL) drilling method was proposed for drilling alumina ceramic. The total energy consumption of the CPL drilling was 1/7 of that of a conventional millisecond laser, and the drilling quality was better. The simulation results demonstrated that, due to the nonuniform reflection of the millisecond laser in the keyhole, the ellipse keyhole ablated by the off-axis incident nanosecond pulses had no effect on the circularity of the through hole. In addition, the multireflection of the laser in the keyhole enhanced the absorption, so the keyhole ablated by the nanosecond pulses could be used as a target for limiting the absorption of the subsequent millisecond pulses. In this context, the keyhole could be used to reduce the hole diameter if the subsequent millisecond laser had a bigger spot size, and this CPL drilling method could be used as an effective group hole drilling method.

Laser processing of alumina ceramic by spatially and temporally superposing the millisecond pulse and nanosecond pulse train

A novel combined laser pulses (CLPs) consisting of a millisecond (ms) pulse and an assisted nanosecond (ns) pulse train was proposed for drilling alumina ceramic. The processing efficiency and quality were well improved by spatially and temporally superposing the ms and ns laser beams. As a result, due to the multi-reflection of keyhole and ejection of melt, the temporally superposed CLPs could decrease the energy consumption of the drilling by an order of magnitude compared with the conventional ms pulse. On the other hand, the spatial distribution of the ns laser on the focal plane was elliptical due to the off-axis distortion of the optical system. However, since the reflection of the laser in the keyhole was non-uniform, the spatially superposed CLPs showed no dependence on the shape of the focused elliptical ns laser spot in terms of the drilling quality. The research results have an important guiding for improving the efficiency and quality of laser processing, especially for the alumina ceramic laser processing.

Experimental study on the optimum matching of CW-nanosecond combined pulse laser drilling

A combined pulse laser (CPL) drilling method that consisted of a continuous wave (CW) laser and an assisted nanosecond laser was used for drilling the Q235B steel. The influence of the repetition rate of the nanosecond laser on the CPL drilling efficiency was analyzed. The results show that the plasma screening threshold during the CPL drilling was about ${1.40} \times {{10}^9}\,\,{\rm W}/{{\rm cm}^2}$1.40×10⁹W/cm². When the peak power density of the nanosecond laser exceeded the plasma screening threshold, it still could not compensate for the energy loss caused by the plasma screening, even though the high-pressure shock wave introduced by the plasma could improve the drilling efficiency. On the other hand, when the peak power density of the nanosecond laser was lower than the plasma screening threshold, it was shown that the optimum matching between the CW laser and nanosecond laser could be obtained when the repetition rate of the nanosecond laser was between 10 and 25 kHz. Finally, the results show that the CPL drilling method had a better drilling efficiency and quality than conventional millisecond laser drilling.