Femtosecond Laser-Based Micromachining of Rotational-Symmetric Sapphire Workpieces

Kefer, Stefan; Zettl, Julian; Esen, Cemal; Hellmann, Ralf

doi:10.3390/ma15186233

Cited by 6 publications

(6 citation statements)

References 41 publications

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“…Two types of surface modification can be observed: the wide gray stripes of ~4 µm width indicate the removal of graphene, and the narrow dark lines with the width below 1 µm are due to the modified surface of the sapphire substrate. The laser fluence at the center of the Gaussian beam at the focal plane was ~9 J/cm 2 , which was significantly above the ablation threshold of both graphene (~70 mJ/cm 2 [ 16 ]) and sapphire (~2 J/cm 2 [ 24 ]). Changing the distance between the focusing lens and the sample surface led to laser beam defocusing and a larger spot diameter, which, in turn, produced lower laser fluence.…”

Section: Resultsmentioning

confidence: 99%

Epitaxial Lateral Overgrowth of GaN on a Laser-Patterned Graphene Mask

et al. 2023

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Epitaxial lateral overgrowth (ELO) of GaN epilayers on a sapphire substrate was studied by using a laser-patterned graphene interlayer. Monolayer graphene was transferred onto the sapphire substrate using a wet transfer technique, and its quality was confirmed by Raman spectroscopy. The graphene layer was ablated using a femtosecond laser, which produced well-defined patterns without damaging the underlying sapphire substrate. Different types of patterns were produced for ELO of GaN epilayers: stripe patterns were ablated along the and directions, a square island pattern was ablated additionally. The impact of the graphene pattern on GaN nucleation was analyzed by scanning electron microscopy. The structural quality of GaN epilayers was studied by cathodoluminescence. The investigation shows that the laser-ablated graphene can be integrated into the III-nitride growth process to improve crystal quality.

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Section: Resultsmentioning

confidence: 99%

Epitaxial Lateral Overgrowth of GaN on a Laser-Patterned Graphene Mask

et al. 2023

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“…The obtainable maximum length is currently limited by the employed laser scanner's working field. While stitching enables microstructuring of extended lengths with this approach, stitching compromise the physical integrity and practical usability of the machined workpiece 17 . Executing the process for overall four iterations, instead of three, results in a sapphire fiber exhibiting a diameter of 25 µm.…”

Section: Resultsmentioning

confidence: 99%

“…Macroscopic as well as microscopic images of the microstructured fiber are shown in Figure 3, which also includes a surface topography visualization obtained via WLI. Again, the process yields optical surface quality with an average Sa parameter of 249 nm over the whole fiber length 17 .…”

Section: Resultsmentioning

confidence: 99%

“…Laser radiation is generated by an ultrashort pulse laser system (Pharos-10-600 and Carbide, Light Conversion), whereas its fundamental emission wavelength of 1030 nm is frequency tripled to enable ultraviolet emission at a wavelength of 343 nm. This is done in order to minimize parasitic heat accumulation effects by exploiting the significantly reduced sapphire ablation threshold of UV radiation 17 . Throughout both processes, average output power, repetition rate as well as pulse duration and fluence are kept constant.…”

Section: Microstructuring Of Sapphire Rods Towards Photonic Applicati...mentioning

confidence: 99%

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High-precision micromachining of sapphire towards optical waveguiding structures using femtosecond lasers

Kefer

Zettl

Schmauß

et al. 2023

Laser-Based Micro- And Nanoprocessing XVII

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While sapphire is one of the most durable materials, its properties entail that high-precision machining, especially in the sub-millimeter regime, is still challenging. This contribution demonstrates and discusses novel femtosecond laser-based micromachining approaches for the fabrication of rotational-symmetric sapphire workpieces, specifically the generation of optical fibers by means of laser lathe of sapphire rods and the practical realization of windmill fibers. In addition, volume refractive index modification in planar sapphire substrates is presented to induce photonic crystal waveguides. The micromachined structures are comprehensively examined with respect to geometric fidelity, surface roughness, refractive index modification, and potential optical waveguiding properties. All micromachining approaches are done by means of frequency-doubled or frequency-tripled femtosecond laser radiation. Different laser optical setups including laser scanning head, spatial beam profilers including a spatial light modulator and axial rotatory movement of the specimen are employed for micro structuring and in-depth refractive index modifications. In particular for laser lathe, a sophisticated scanning pattern, in combination with an incremental axial rotatory movement of the specimen, allows for the precise diameter reduction of sapphire rods with 250 µm diameter to fibers with outer diameters of 25 µm. By supporting the workpiece with a V-groove fixture, multi-mode fibers with lengths up to 20 cm can be processed with an average surface roughness of 250 nm. Additionally, an adapted ablation scanning sequence enables the first practical demonstration of sapphire windmill fibers. Furthermore, using a spatial light modulator allows for the adaption of the laser propagation properties as to enable volume refractive index modifications with free-form arrangement. Hexagonal patterns of refractive index modifications surrounding a pristine waveguide core are fabricated and single-mode waveguiding at 1550 nm is verified. Finally, the possibility of integrating Bragg gratings into this photonic waveguide type is demonstrated.

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“…Non-contact, cold ablation enables the processing and manufacturing of work pieces without altering the surrounding material through excessive energy input, either through heat or through mechanical influences. Under these conditions, even hard to machine materials can be shaped and processed while conventional, mechanical approaches reach their limits [4][5][6]. This ultrashort pulsed laser processing approach has been adapted to several established machining methods like drilling [7,8], cutting [9,10] or milling [11,12] and is currently an increasing research subject for the use as a lathing tool [13][14][15][16].…”

Section: Introductionmentioning

confidence: 99%

Intensity distribution on cylindrical surfaces in ultrashort pulse laser turning

Zettl,

Esen,

Hellmann

2024

Laser-Based Micro- And Nanoprocessing XVIII

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Tangential laser turning is applied to generate rotationally symmetric parts on a micrometer scale. Due to the non-contact material ablation, this process is especially advantageous for machining brittle materials such as stellite, which tends to easily break during conventional lathe. Furthermore, the use of focused ultrashort laser pulses enables the process to machine a large variety of materials because of the low heat input into the work piece.By impinging a cylindrical work piece laterally, a distortion of the projected circular, focused laser beam on the material surface occurs. In order to predict the actual fluence and intensity distribution on the rotating work piece, fundamental calculations and experimental results are necessary.Against this background, we report on laser turning of cylindrical components using ultrashort laser pulses with attention to the geometrical conditions and the resulting intensity distribution on the work piece. Particularly, the laser spot formation on a cylindrical surface at an oblique angle is discussed. In addition, the use of a trepanning optic in the laser turning process and the resulting beam path on the surface will be issued. The superimposed motion of the work piece rotation, trepanning rotation and linear laser feed rate is subject to fundamental calculations and experimental results.

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Femtosecond Laser-Based Micromachining of Rotational-Symmetric Sapphire Workpieces

Cited by 6 publications

References 41 publications

Epitaxial Lateral Overgrowth of GaN on a Laser-Patterned Graphene Mask

Epitaxial Lateral Overgrowth of GaN on a Laser-Patterned Graphene Mask

High-precision micromachining of sapphire towards optical waveguiding structures using femtosecond lasers

Intensity distribution on cylindrical surfaces in ultrashort pulse laser turning

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