Femtosecond Laser-assisted Etching Research Articles

Scanning strategy-dependent etching rate in the formation of through-via holes by femtosecond laser-assisted etching

In this study, we used femtosecond laser-assisted etching (FLAE) to drill through glass vias (TGVs) in 0.3 mm thick non-alkali glass substrates. In FLAE, the focus of the femtosecond laser pulses is scanned to modify the material along a preprogrammed pattern, and the modified region is preferentially removed by chemical etching. We found that the scanning strategy affected the etching rate along the laser-modified lines. Among four types of scanning strategies tested, the strategy 〈du〉—that is, scanning in a downward direction followed by an upward direction—obtained the highest etching rate. In this case, the etching rate along the laser-modified line was approximately 10 times larger than that of the unmodified region.

Room-temperature NH3 gas sensing of S-hyperdoped silicon: Optimization through substrate resistivity

Sulfur-hyperdoped black silicon (S-BSi) prepared by femtosecond laser-assisted etching in SF6 atmosphere has dual characteristics of large specific surface area and super-doped impurities, and its physics and applications have attracted extensive attention. The room-temperature NH3 gas sensing capability of the samples is studied in the conductance mode. The S-BSi-based sensors exhibit a response to NH3 gas. Interestingly, their responsivity varies with the substrate resistance, and the sensor based on an appropriate substrate resistance shows the optimal responsivity. Additionally, the device demonstrates fast response and recovery speed, as well as good selectivity. The evolution of the responsivity and response/recovery time is recorded with natural aging for two months, showing acceptable long-term durability. The mechanism by which the responsivity of S-BSi-based sensors varies with resistivity is discussed. Based on this mechanism, there is an optimal substrate resistivity that maximizes the responsivity. The results show that S-BSi is a potential material for the fabrication of conductivity gas sensor with good NH3 detection performance.

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 200µm/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.

Low-loss optofluidic waveguides in fused silica enabled by spatially shaped femtosecond laser assisted etching combined with carbon dioxide laser irradiation

We demonstrate the fabrication of low-loss optofluidic waveguides encapsulated in fused silica glass using femtosecond laser microfabrication followed by carbon dioxide laser irradiation. Spatially-shaped femtosecond laser-assisted chemical etching is first used to fabricate microchannels with circular cross-sections and a string of open extra-access ports in the glass. Further, the carbon dioxide laser direct writing on the glass surface is used to create a thermal reflow effect of etched glass microstructures for simultaneously polishing all internal surfaces of channels and sealing the extra-access ports. With this effect, the inner surface roughness of the etched microchannels can be reduced to ∼ 40 nm. Finally, a single-mode microfluidic optical waveguide with a propagation loss of ∼ 0.78 dB/cm at 1310 nm is obtained inside the glass by filling a mixture solution of decane and liquid paraffin into a laser-polished microchannel.

Laser-Scanning Direction Effect in Femtosecond Laser-Assisted Etching

In this study we examined how the laser-scanning direction during the inscription of modified lines affects to the etching rate along the lines in the femtosecond laser-assisted etching. An isotropic material (silica) was used as the sample. Circular polarization was used for inscribing modified lines, in order to avoid a direction effect arising from polarization. Scanning direction dependence was observed in the etching rate along the modified lines. The relation between the occurrence of a scanning direction effect and the other inscribing parameters (pitch and pulse energy) was examined.

Heating Effect of Etchant on Femtosecond Laser-Assisted Etching

Heating Effect of Etchant on Femtosecond Laser-Assisted Etching

Fabrication of diffractive microlens array by femtosecond laser-assisted etching process

Graphical abstractDisplay Omitted Highlights? The diffractive microlens array is fabricated by the femtosecond laser and chemical etching process. ? The effect of micro-grating forming is studied upon laser power and etching ratio. ? The quasi-crystal diffraction patterns with the types of cross and octagon can be achieved. The study presents the fabrication of diffractive microlens array on glass substrate by using the femtosecond laser (FS-laser) and chemical etching process. Here, the laser is based on an all-in-one FS-laser system with the central wavelength of 517?2.5nm for fabricating the embedded grating structures inside glass substrate. The laser beam focused distance between the surface and sample is 25µm. The repetition rate and pulse duration of FS-laser are 100kHz and 350fs, respectively. The attenuated laser beam is directly into objective lens (20i?) with the numerical apertures (NA=0.4). Hence, the microstructures can be patterned by the routes of X-Y motion stage. The glass sample is then etched by hydrofluoric acid (HF) in an ultrasonic bath for 15min for developing structures. Finally, the results show a successful process for forming the microlens array of the diffractive patterns, in which two types of cross and octagon are obtained from the single and double diffraction, respectively.

Femtosecond Laser-Assisted Etching of Fluoride Crystals

Femtosecond laser-assisted etching is a technique for internal micro removal processing of transparent materials. In the present study, we applied this technique to fluoride crystals of CaF2 and MgF2. In the case of CaF2, selective etching of a femtosecond laser-modified region was observed with etchants of aqueous solutions of nitric acid, sulfuric acid, and hydrogen chloride, while no signature of etching was observed for MgF2. Microchannels were fabricated in CaF2 substrates. At the inlet, the microchannel showed polygonal shapes, which may be related to anisotropy in the etching rate.

Femtosecond laser-assisted etching of Pyrex glass with aqueous solution of KOH

A femtosecond laser-assisted etching technique was applied to Pyrex glass, a kind of borosilicate glass, to perform removal processing with three-dimensional arbitrarity in design and micrometer-order spatial resolution. An aqueous solution of potassium hydroxide (KOH) was adopted as a highly selective etchant. The rate and selectivity of etching were evaluated from in situ images, and fabrication of three-dimensional microchannels was demonstrated.

Laser Fabrication and Manipulation of an Optical Rotator Embedded inside a Transparent Solid Material

We report the fabrication and rotation of an optical rotator confined in a microcavity inside silica glass material, based on the techniques of femtosecond laser-assisted etching and laser manipulation. The rotator thus prepared may act as a micropump and micromixer. The material of this rotator is identical to that of the host substrate, because femtosecond laser-assisted etching is an internal removal process. As a result, the rotator as well as substrate has high chemical stability and good optical transparency. We also describe tests in which we demonstrated that this fabrication technique is versatile enough to allow one to parepare two types of rotators with different shapes.

Three-Dimensional Residue-Free Volume Removal inside Sapphire by High-Temperature Etching after Irradiation of Femtosecond Laser Pulses

We applied the femtosecond laser-assisted etching technique, that is, irradiation of focused femtosecond laser pulses followed by selective chemical etching, to volume removal inside sapphire. At room temperature, volume etching only slightly advanced while residue remained inside the volume. By increasing the etching temperature, complete volume etching without residue was achieved. Complete etching was, however, accompanied by undesirable phenomena of surface pits or cracks, which are expected to be excluded through further improvement of processing.