A femtosecond laser with an infrared wavelength (1030 nm) and a pulse duration of 200 femtoseconds (fs) was utilized to directly induce graphene tracks on rough 3D-printed polyetherimide (ULTEM-9085) substrates. The inherent surface roughness of the 3D-printed sample and the print defects leads to significant challenges in achieving uniform and continuous graphene formation, which could be overcome through the regulation of the laser focus. By precisely overlapping multiple laser-induced graphene (LIG) tracks, a continuous LIG area was successfully produced, demonstrating the feasibility of large-area graphene patterning on rough polymeric substrates. Moreover, a secondary laser scan at lower laser fluence was applied to the preformed LIG, leading to an enhancement in the electrical conductivity. This improvement is attributed to further structural re-organization, defect reduction, and potential removal of insulating polymer residues. The proposed approach provides an efficient and scalable strategy for fabricating conductive graphene patterns on complex polymeric surfaces, with potential applications in flexible electronics, sensors, and energy storage devices.

This article presents the simulation and experimental study of quartz-enhanced photoacoustic spectroscopy (QEPAS) technical. This technique has gained interest in the area of gas sensing in the recent few years due to its highly selective and sensitive measurements offered by the quartz tuning fork (QTF). The experimental study is conducted using a quantum cascade laser (QCL) source operating in 8 μm for measuring acetone (C3H6O), ammonia (NH3), and methane (CH4) in low and high concentrations. The voltage produced for different concentrations of gases by the QTF due to the piezoelectric effect is experimentally obtained and recorded. The Opto-acoustic module consisting of the QTF and the pressure generation by the gas molecules is modelled and designed using the COMSOL Multiphysics software. The photoacoustic pressure generated by gas induces potential in the quartz material and causes the prongs to displace symmetrically. The prong displacement and the potential generated for different concentrations are captured and presented. The proposed system offers ultralow sensitivity in the parts-per-billion (ppb) order, which makes it an ideal candidate for human exhale breath (HEB) gas analysis for non-invasive disease diagnosis.

The Triboelectric Nanogenerator (TENG) can be an ancillary device for scavenging mechanical energy ubiquitous in industries. However, enhancing the output of TENG is a key area of research in energy harvesting. Conventional methods such as lithography and sandpaper replication require molds for surface area improvement, while Laser Scribing (LS) has revolutionized the fabrication of TENGs by enabling the production of complex patterns over large areas in a short time without additional requirements. In this work, we report novel LS technology for the output enhancement of TENGs. The Nd3+: YAG pulse laser with optimized parameters was used to etch the Aluminum (Al) layer of an Al-Polytetrafluoroethylene (PTFE) TENG. The LS parameters (laser fluence and spot overlap) were optimized to create micro/nano structures on the Al layer of the TENG, which increased its output. Among various combinations of TENG, the most optimal one achieved significantly higher values for peak-to-peak open circuit voltage, short circuit current, and power density, measuring 480 V, 22.7 µA, and 708 µW/cm2, respectively. These values were ∼45%, ∼61%, and ∼56% higher than those measured in the pristine TENG. Moreover, the most optimal TENG demonstrated its capability by charging a 10 µF capacitor up to 10.2 V in just 200 s while exhibiting mechanical robustness and consistent performance over 25,000 cycles. This top-performing TENG was then utilized to harness vibrational energy from a compressor, effectively serving as an energy harvester and a vibration monitoring sensor during loading conditions.

A hollow-core fiber (HCF) combined with a broadband supercontinuum laser-based direct absorption spectroscopy technique is pro-posed and demonstrated for concentration measurements of gas mixtu-res. A dual-wavelength technique is used to eliminate gas interference in multigas sensing. The concentrations of methane (CH4) in two bands, 1.6 and 2.3 μm, ammonia (NH3) in two bands, 2 and 2.3 μm, and carbon dioxide (CO2) in the 2-μm band are measured. The measurements were performed using 0.5, 1, 5, and 10 m long HCF covering multiple absorption lines in the given band. The minimum detection limit (MDL) is improved as the signal-to-noise ratio was enhanced up to 3.9 dB by considering cumulative absorbance obtained from multiple absorption lines in the broadband measurement. The MDL were 13 and 15 parts-per-million (ppm) for CH4 at 1.6 and 2.3 μm, respectively; 13 and 17 ppm for NH3 at 2 and 2.3 μm, respectively; and 154 ppm for CO2 at 2 μm band. The proposed dual-wavelength measurement technique was further extended to measure concentrations of gases in biogas samples. CH4, CO2, and hydrogen sulfide were measured to be 54.7%, 46.1%, and 2.1%, respectively, and atmospheric CO2 of 421 ppm was also measured using a 10-m long HCF. The system offers excellent long-term stability for over continuous measurement of 4 h.

Triboelectric nanogenerators (TENGs) are promising cost-effective energy harvesters useful to scavenge vibration or mechanical movements from various domains. Ranging from condition monitoring of machines to motion sensing of humans, its applications are enormous in the internet of things scenario. Enhancing the performance of small-sized TENGs is of great demand, and pulsed laser-assisted texturing is an efficient and proven method to enhance the output of energy harvesters. This work studies simultaneous laser patterning of fluorinated ethylene propylene (FEP) dielectric material and the underneath copper electrode with three different wavelengths (355, 532, and 1064 nm) of the Nd3+:YAG laser and the device's electrical performance is analyzed. The maximum enhancement is observed in the case of 355 nm laser-assisted patterning on FEP and Cu electrode with a laser fluence of 10 J cm−2. The improvement is least in the case of 1064 nm laser-assisted patterning. Laser patterning on the underlying electrode with this new approach is able to produce an enhancement in the TENG output. However, patterning on the FEP top surface is critical in the process.

Hollow-core fiber and photoacoustic spectroscopy techniques are demonstrated for the measurement of atmospheric CO2 using a broadband supercontinuum laser at 2 µm wavelength range. The CO2 concentration was measured during the day and night time, was found to be around 420 ppm and 450 ppm respectively.

Hollow-core fiber and photoacoustic spectroscopy techniques are demonstrated for the measurement of atmospheric CO2 using a broadband supercontinuum laser at 2 µm wavelength range. The CO2 concentration was measured during the day and night time, was found to be around 420 ppm and 450 ppm respectively.

Hollow-core fiber and photoacoustic spectroscopy techniques are demonstrated for the measurement of atmospheric CO2 using a broadband supercontinuum laser at 2 µm wavelength range. The CO2 concentration was measured during the day and night time, was found to be around 420 ppm and 450 ppm respectively.

Graphene, is one of the prominent materials in device fabrication due to its high conductive and high flexural strength for electrodes/device applications. The latest technique for graphene synthesis i.e. carbonization of polyimide by laser patterning has received much attention because of its capability to create various functional materials and flexible devices. The requirement of graphene demands larger volume production where laser-induced graphene (LIG) by consideration of pulse overlap could prove to be the solution if a recipe is prepared through appropriate optimization. The present study focused on the CO2 laser (λ = 10.6 µm) interaction with polyimide by generating raster pattern with varying pulse overlap in linear direction. The raster pattern is fabricated at different laser energies and pulse overlap with a constant 30% line overlap between two consecutive lines, in the lateral direction, for synthesizing LIG at relatively low laser power. Various combinations of laser fluences (46 J cm−2, 56 J cm−2, 66 J cm−2) and pulse spot overlap (60%, 70%, and 80%) were used for the polyimide carbonization. Both experimental and numerical simulation (using ComsolTM) results present an insight that optimal control of laser pulse overlap shows significant effect on crystallinity and electrical resistivity of synthesized graphene. The macroscopic quality of the raster pattern is investigated through the optical microscope. Detailed Raman spectro-microscopic analysis is carried out to study the defect to graphenization ratio and its impact on the properties of graphene synthesized. Through Raman analysis, the average in-plane crystallite length of graphene synthesis was observed from 27.732 ± 4-37.132 ± 6 nm. At last, a resistive type strain sensor was fabricated to check the stability of LIG and its reliability for repetitive loading conditions. The pulse overlap photo-thermal model, and its finite element analysis implementation presents better understanding towards optimizing the promising technique towards synthesizing LIG.

In this work, micro-scribing of Cu film on a dielectric substrate with lasers having different pulse duration (6 ns, 500 ps, 1 ps, 120 fs) has been analyzed. The recast layer formation near the microchannel is clearly observed in the case of 6 ns and 500 ps laser-based scribing. On the other hand, 1 ps and 120 fs pulsed lasers were able to produce microchannel without observable recast layer. Based on the XRD analysis, compressive residual stresses are observed in the scribed region with the 6 ns and the 500 ps laser, whereas tensile residual stresses are measured in the scribed region with the 1 ps and the 120 fs lasers. Oxide layer formation was observed in the case of all the pule regimes. A theoretical simulation was developed to estimate the temperature on the dielectric substrate. Complete removal of Cu from the dielectric will resulted in thermal damage to the substrate. A hybrid micro-scribing technique, where the sample was immersed in NaCl solution during the final laser scan was demonstrated in the case of nanosecond laser. Finally, a frequency selective surface (FSS) was fabricated with the help of the hybrid scribing technique.

Pulsed laser-based material removal is a preferred micro-scribing technique for Copper (Cu) cladded onto an insulating substrate, such as a flame-retardant glass-reinforced epoxy resin (FR4), because of the less thermal diffusion as well as the process flexibility. This paper reports the pulsed laser-assisted micro-scribing of Cu (35 µm) from a dielectric material. The process was monitored by laser-induced breakdown spectroscopy technique (LIBS). For the complete removal of Cu from the substrate material, multiple laser scans were required. The Cu I line intensity in the LIBS spectra was decreasing with an increase in the microchannel depth. During the final laser scan, the FR4 substrate was getting ablated, and in the LIBS spectra, the characteristic emission lines from the substrate elements such as Calcium (Ca), Aluminum (Al), Sodium (Na) and Silicon (Si) were observed. The depth for a single laser pulse was estimated from a theoretical model, including the melt ejection due to the recoil pressure. Approximate microchannel depth was predicted based on the theoretical simulation.

Micro-scale removal of Cu from a dielectric substrate has applications in microelectronics, patch antenna fabrication and frequency selective surface (FSS) manufacturing. Pulsed laser-based micro-scribing of Copper (Cu) from a dielectric is a preferred technique to avoid the adverse effects of chemical etching, such as toxicity and corrosive nature of the etchant, difficulty in fabrication of mask etc. However, pulsed laser-assisted removal of Cu from a dielectric in the air will produce recast layer/ redeposit, oxide layer near the ablation zone and thermal damage to the dielectric is another challenge. In this study, a hybrid technique with nanosecond laser-activated electrochemical micro-scribing of Cu is demonstrated. The technique was extended to remove 35 μm Cu from Rogers-RO4003 dielectric with a thickness ≈0.75 mm to fabricate FSS samples in X-band. The Cu-deposited dielectric substrate was immersed in Sodium Chloride (NaCl) solution, the laser beam was directed through a negatively biased tool electrode and the sample was biased positively. In this hybrid technique, along with laser-assisted material removal, laser-activated electrochemical etching also removed Cu selectively. The laser irradiation coupled with the NaCl solution induced preferential micro-etching, resulting in improved surface morphology without re-deposition and recast layer and thermal protection to the dielectric substrate. The FSS sample produced with the laser-hybrid micro-scribing was working at 10.3 GHz.

The influence of a subnanosecond pulsed laser-based scribing of copper (Cu) and aluminum (Al) in salt solutions (NaCl and KCl) on the formation of microchannels is reported. This technique allows laser scribing along with selective etching of Cu and Al thin films. The focused laser beam can elevate the surface temperature on the sample and hence the chemical reaction rate, resulting in combined ablation with selective-area etching. The depth of microchannels in Cu and Al films is increased by 3-5 μm using the proposed hybrid technique. The average surface roughness values in the microchannel are decreased compared to that of scribing in water and air. The hybrid approach of laserbased scribing combined with electrochemical etching in neutral salt solutions allows uniform channel with almost no redeposit layer and debris on the channel edges. Further, an approach wherein, an application of direct current (DC) voltage (1.2 V) between the tool and the workpiece while laser scribing of Cu and Al in salt solution was demonstrated to improve the channel depth by few micrometers. This hybrid machining technique has also resulted in a reduction in the surface oxidation near the laser-ablated zone compared to that observed in air and water-based experiments.

A nanosecond laser ablation combined with LIBS is demonstrated for a micro-scribing of copper film on dielectric material. NaCl solution was used as a laser-activated etchant in the final scan for minimizing the thermal damage.

Laser scribing is carried out using a Q-switched (Brilliant B, Quantel) Nd3+:YAG laser system to scribe micro channels on copper coated on polyimide film, where copper thickness is approximately 35 microns and polyimide film thickness is 50 microns. Chemical etching is performed using FeCl3 solution for the laser scribed micro channels and from the experimental results it is observed that depth of the channel after etching is increasing with a reduction in the recast height. It is observed that with the increase in concentration of FeCl3 and the etch time, the material removed from the copper target increased. The height of recast for the 50 μm wide micro channel scribed using 20 mJ of energy and a laser wavelength of 532 nm reduced from 10 μm to 5 μm in case of 10% FeCl3 etched for 1 min. However the overall thickness of the copper thin film is observed to reduce from 35 μm to 30 μm. Hence a hybrid technique using NaCl as the scribing medium is developed, so that CuCl2 formed in the process of scribing helped in achieving a localized etching inside the channel without affecting the total target thickness.

Recently, there is an increasing interest to create micro-channels on metal thin films for diverse applications, such as biomedical, micro channel heat exchangers, chemical separation processes and microwave antenna. Nanosecond (ns) Nd3+:YAG laser has been studied for generating micro-channels on Cu thin film (35 μm) deposited on polyimide substrate (50 μm). A pulsed Nd3+:YAG laser (532 nm / 355 nm) based scribing was performed in air and water ambiancePlasma shielding phenomenon is observed to influence the depth of microchannel at higher energies. A novel pump-probe experiment has been conducted for verifying the plasma shielding effect in air. In underwater scribing the recast layer was reduced significantly as compared to that in air. Laser scribing of Cu thin film followed by chemical etching using FeCl3 was studied. However, the approach of chemical etching resulted in undercut and thinning of Cu film. Alternatively, laser material processing in NaCl solution was studied. Cl- ions present in the solution reacts with Cu which is removed from the sample via laser ablation and forms CuCl2. Formation of CuCl2 in turn improved the surface morphology of the channel through localized etching. The surface roughness parameter Ra was less than 400 nm for NaCl solution based scribing which is smaller compared to air and underwater based methods which are typically around 800 nm or above. Preliminary studies using femtosecond (fs) laser based Cu scribing in air with the fluence of 0.5 J/cm2 resulted in a crated depth of 3 μm without any recast layer.