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Micromachines
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Ultrafast Laser Micro- and Nanoprocessing
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Ultrafast Laser Micro- and Nanoprocessing

A special issue of Micromachines (ISSN 2072-666X). This special issue belongs to the section "D：Materials and Processing".

Deadline for manuscript submissions: closed (31 October 2023) | Viewed by 12075

Special Issue Editor

Dr. Xin Zhao

E-Mail Website
Guest Editor
Department of Mechanical Engineering, Clemson University, Clemson, SC 29634-0921, USA
Interests: laser–matter interaction; ultrafast laser nano-/micromachining; laser shock peening; ultrafast laser surface texturing; dissimilar materials joining
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Ultrafast laser-based manufacturing and materials processing has attracted substantial interest in recent decades. The ultrashort duration and extremely high peak laser intensity of ultrafast laser pulses allow for localized laser heating/ablation and a reduced heat-affected zone, making it a promising tool for high precision micro- and nanoscale materials processing. In addition, the unique characteristics of ultrafast laser pulses result in novel laser–matter interaction processes, heralding a new era of fundamental study into the underlying mechanisms. Compared to longer laser pulses, the mechanisms of laser absorption, carrier dynamics, heat transfer, phase shift, and material removal are fundamentally unique yet poorly understood. Therefore, we are announcing this Special Issue to provide a platform to showcase research papers, communications, and review articles focused on nano- and microscale ultrafast laser materials processing. The scope of this issue covers, but is not limited to, ultrafast laser–matter interaction, ultrafast laser ablation, nano-/micromachining, surface texturing, refractive index modifications, additive manufacturing by ultrafast lasers, two/multi-photon polymerization and reduction, thin film processing, beam/pulse shaping for ultrafast laser processing, laser shock peening, laser cleaning, ultrafast lasers in biomedical applications, and numerical modeling of ultrafast laser materials processing.

Dr. Xin Zhao
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Micromachines is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • ultrafast lasers
  • materials processing
  • nano- and microscale
  • laser–matter interaction
  • laser ablation
  • laser machining
  • surface texturing
  • two/multi-photon polymerization/reduction
  • beam/pulse shaping
  • numerical modeling

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Related Special Issue

Published Papers (7 papers)

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Research

16 pages, 5553 KiB  
Article
A Computational Evaluation of Minimum Feature Size in Projection Two-Photon Lithography for Rapid Sub-100 nm Additive Manufacturing
by Rushil Pingali, Harnjoo Kim and Sourabh K. Saha
Micromachines 2024, 15(1), 158; https://doi.org/10.3390/mi15010158 - 21 Jan 2024
Cited by 1 | Viewed by 1648
Abstract
Two-photon lithography (TPL) is a laser-based additive manufacturing technique that enables the printing of arbitrarily complex cm-scale polymeric 3D structures with sub-micron features. Although various approaches have been investigated to enable the printing of fine features in TPL, it is still challenging to [...] Read more.
Two-photon lithography (TPL) is a laser-based additive manufacturing technique that enables the printing of arbitrarily complex cm-scale polymeric 3D structures with sub-micron features. Although various approaches have been investigated to enable the printing of fine features in TPL, it is still challenging to achieve rapid sub-100 nm 3D printing. A key limitation is that the physical phenomena that govern the theoretical and practical limits of the minimum feature size are not well known. Here, we investigate these limits in the projection TPL (P-PTL) process, which is a high-throughput variant of TPL, wherein entire 2D layers are printed at once. We quantify the effects of the projected feature size, optical power, exposure time, and photoinitiator concentration on the printed feature size through finite element modeling of photopolymerization. Simulations are performed rapidly over a vast parameter set exceeding 10,000 combinations through a dynamic programming scheme, which is implemented on high-performance computing resources. We demonstrate that there is no physics-based limit to the minimum feature sizes achievable with a precise and well-calibrated P-TPL system, despite the discrete nature of illumination. However, the practically achievable minimum feature size is limited by the increased sensitivity of the degree of polymer conversion to the processing parameters in the sub-100 nm regime. The insights generated here can serve as a roadmap towards fast, precise, and predictable sub-100 nm 3D printing. Full article
(This article belongs to the Special Issue Ultrafast Laser Micro- and Nanoprocessing)
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11 pages, 2132 KiB  
Article
Femtosecond Laser Machining of an X-ray Mask in a 500 Micron-Thick Tungsten Sheet
by Ebenezer Owusu-Ansah and Colin Dalton
Micromachines 2023, 14(11), 2071; https://doi.org/10.3390/mi14112071 - 7 Nov 2023
Viewed by 1191
Abstract
Femtosecond laser material processing (FLMP) was used to make an X-ray mask in a 500 µm thick tungsten sheet without the use of any chemical etch methods. The laser produced an 800 nm wavelength at a 1 kHz repetition rate and a pulse [...] Read more.
Femtosecond laser material processing (FLMP) was used to make an X-ray mask in a 500 µm thick tungsten sheet without the use of any chemical etch methods. The laser produced an 800 nm wavelength at a 1 kHz repetition rate and a pulse width of 100 fs. The laser beam arrival at the tungsten sheet was synchronized to a computer numerically controlled (CNC) stage that allowed for motion in the XYZθ directions. The X-ray mask design was made using CAD/CAM software (Alphacam 2019 R1) and it consisted of linear, circular, and 45° angle features that covered an area of 10 mm × 10 mm. A total of 70 laser beam passes at a moderate laser energy of 605.94 J/cm2 were used to make through-cut features into the tungsten sheet. The morphology of the top view (laser incident, LS) images showed cleaner and smoother cut edges relative to the bottom view (laser exit, LE) images. It was found that the size dimensions of the through-cut features on the LE surfaces were better aligned with the CAD dimensions than those of the LS surfaces. The focused laser beam produced inclined cut surfaces as the beam made the through cut from the LS to the LE of the tungsten sheet. The circular features at the LS surface deviated toward being oval-like on the LE surface, which could be compensated for in future CAD designs. The dependence of the CNC processing speed on the thickness of the etch depth was determined to have a third-order exponential decay relationship, thereby producing a theoretical model that will be useful for future investigators to predict the required experimental parameters needed to achieve a known etch depth in tungsten. This is the first study that has demonstrated the capability of using a femtosecond laser to machine through-cut an X-ray mask in a 500 µm thick tungsten sheet with no involvement of a wet etch or any other such supporting process. Full article
(This article belongs to the Special Issue Ultrafast Laser Micro- and Nanoprocessing)
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14 pages, 10260 KiB  
Article
Productivity of Concentration-Dependent Conversion of Substitutional Nitrogen Atoms into Nitrogen-Vacancy Quantum Emitters in Synthetic-Diamond by Ultrashort Laser Pulses
by Sergey Kudryashov, Pavel Danilov, Evgeny Kuzmin, Nikita Smirnov, Alexey Gorevoy, Victor Vins, Daniil Pomazkin, Petr Paholchuk, Andrey Muratov, Alexey Kirichenko, Nikolay Rodionov and Evgeny Vasil’ev
Micromachines 2023, 14(7), 1397; https://doi.org/10.3390/mi14071397 - 9 Jul 2023
Cited by 4 | Viewed by 1443
Abstract
Tightly focused 515-nm, 0.3-ps laser pulses modify in a laser filamentation regime the crystalline structure of an Ib-type high-pressure, high-temperature (HPHT) synthesized diamond in a thin-plate form. The modified microregions (micromarks) in the yellow and colorless crystal zones, possessing different concentrations of elementary [...] Read more.
Tightly focused 515-nm, 0.3-ps laser pulses modify in a laser filamentation regime the crystalline structure of an Ib-type high-pressure, high-temperature (HPHT) synthesized diamond in a thin-plate form. The modified microregions (micromarks) in the yellow and colorless crystal zones, possessing different concentrations of elementary substitutional nitrogen (N) impurity atoms (C-centers), exhibit their strongly diminished local IR absorption (upon correction to the thickness scaling factor). Simultaneously, local visible-range (400–550 nm) absorption coefficients were increased, and photoluminescence (PL) yield was strongly enhanced in the broad range of 450–800 nm. The strong yellow-red PL enhancement saturates with laser exposure, implying the complete conversion of C-centers into nitrogen-vacancy (NV0,−) ones due to the laser-induced generation of Frenkel “interstitial-vacancy” I–V carbon pairs. The other emerging blue-green (>470 nm) and green-yellow (>500 nm) PL bands were also simultaneously saturated versus the laser exposure. The observed IR/optical absorption and PL spectral changes enlighten the ultrashort pulse laser inscription of NV0−-based quantum-emitter centers in synthetic diamonds and enable the evaluation of the productivity of their inscription along with the corresponding I–V generation rates. Full article
(This article belongs to the Special Issue Ultrafast Laser Micro- and Nanoprocessing)
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10 pages, 2566 KiB  
Article
An Integrated Pump-Controlled Variable Coupler Fabricated by Ultrafast Laser Writing
by David Benedicto, Juan C. Martín, Antonio Dias-Ponte, Javier Solis and Juan A. Vallés
Micromachines 2023, 14(7), 1370; https://doi.org/10.3390/mi14071370 - 4 Jul 2023
Viewed by 1564
Abstract
The design and fabrication of a integrated symmetric directional coupler dependent o the pumping power and operating at a 1534 nm wavelength is reported. The twin-core waveguide was inscribed into Er3+/Yb3+ co-doped phosphate glass by a femtosecond laser direct writing [...] Read more.
The design and fabrication of a integrated symmetric directional coupler dependent o the pumping power and operating at a 1534 nm wavelength is reported. The twin-core waveguide was inscribed into Er3+/Yb3+ co-doped phosphate glass by a femtosecond laser direct writing technique. By optical pumping, the coupling ratio can be modulated due to the changes induced in the refractive index of the material. The experimental results demonstrated that the coupling ratio can be tuned continuously from 100/0 to 50/50 by increasing the pump’s power from 0 to 350 mW. The developed twin-core coupler has promising applications for on-chip all-optical signal processing and communication systems. Full article
(This article belongs to the Special Issue Ultrafast Laser Micro- and Nanoprocessing)
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9 pages, 7376 KiB  
Article
Static Hydrophobic Cuprous Oxide Surface Fabricated via One-Step Laser-Induced Oxidation of a Copper Substrate
by Xi Yu, Yoshiki Tanaka, Tomoki Kakiuchi, Takafumi Ishida, Koh Saitoh, Fumihiro Itoigawa, Makoto Kuwahara and Shingo Ono
Micromachines 2023, 14(1), 185; https://doi.org/10.3390/mi14010185 - 11 Jan 2023
Cited by 2 | Viewed by 1729
Abstract
In this study, we developed a one-step method for fabricating hydrophobic surfaces on copper (Cu) substrates. Cuprous oxide (Cu2O) with low free energy was successfully formed after low-fluence laser direct irradiation. The formation of Cu2O enhanced the hydrophobicity of [...] Read more.
In this study, we developed a one-step method for fabricating hydrophobic surfaces on copper (Cu) substrates. Cuprous oxide (Cu2O) with low free energy was successfully formed after low-fluence laser direct irradiation. The formation of Cu2O enhanced the hydrophobicity of the Cu substrate surface, and the contact angle linearly increased with the proportion of Cu2O. The Cu2O fabricated by low-fluence laser treatment showed the same crystal plane orientation as the pristine Cu substrate, implying an epitaxial growth of Cu2O on a Cu substrate. Full article
(This article belongs to the Special Issue Ultrafast Laser Micro- and Nanoprocessing)
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8 pages, 2846 KiB  
Article
Up/Down-Scaling Photoluminescent Micromarks Written in Diamond by Ultrashort Laser Pulses: Optical Photoluminescent and Structural Raman Imaging
by Pavel Danilov, Evgeny Kuzmin, Elena Rimskaya, Jiajun Chen, Roman Khmelnitskii, Alexey Kirichenko, Nikolay Rodionov and Sergey Kudryashov
Micromachines 2022, 13(11), 1883; https://doi.org/10.3390/mi13111883 - 1 Nov 2022
Cited by 6 | Viewed by 1687
Abstract
Elongated photoluminescent micromarks were inscribed inside a IaAB-type natural diamond in laser filamentation regime by multiple 515 nm, 0.3 ps laser pulses tightly focused by a 0.25 NA micro-objective. The micromark length, diameter and photoluminescence contrast scaled as a function of laser pulse [...] Read more.
Elongated photoluminescent micromarks were inscribed inside a IaAB-type natural diamond in laser filamentation regime by multiple 515 nm, 0.3 ps laser pulses tightly focused by a 0.25 NA micro-objective. The micromark length, diameter and photoluminescence contrast scaled as a function of laser pulse energy and exposure, coming to a saturation. Our Raman/photoluminescence confocal microscopy studies indicate no structural diamond damage in the micromarks, shown as the absent Raman intensity variation versus laser energy and exposition along the distance from the surface to the deep mark edge. In contrast, sTable 3NV (N3)-centers demonstrate the pronounced increase (up to 40%) in their 415 nm zero-phonon line photoluminescence yield within the micromarks, and an even higher—ten-fold—increase in NV0-center photoluminescence yield. Photogeneration of carbon Frenkel “interstitial–vacancy” (I–V) pairs and partial photolytic dissociation of the predominating 2N (A)-centers were suggested to explain the enhanced appearance of 3NV- and NV-centers, apparently via vacancy aggregation with the resulting N (C)-centers or, consequently, with 2N- and N-centers. Full article
(This article belongs to the Special Issue Ultrafast Laser Micro- and Nanoprocessing)
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13 pages, 5344 KiB  
Article
Controlled Continuous Patterning of Spherical Stainless Steel by Multi-Axis Linkage Laser Milling
by He Li, Junjie Zhang, Wenqi Ma, Yuan Liu, Xuesen Zhao, Zhenjiang Hu, Xiaohui Wang, Min Sheng and Tao Sun
Micromachines 2022, 13(8), 1338; https://doi.org/10.3390/mi13081338 - 18 Aug 2022
Cited by 1 | Viewed by 1847
Abstract
While laser surface texturing is promising for the fabrication of planar surface microstructures, the continuously patterning with micrometer accuracy of non-planar surface on miniature parts with large curvature by laser ablation is challenging. In the present work, we demonstrate the feasibility of applying [...] Read more.
While laser surface texturing is promising for the fabrication of planar surface microstructures, the continuously patterning with micrometer accuracy of non-planar surface on miniature parts with large curvature by laser ablation is challenging. In the present work, we demonstrate the feasibility of applying the proposed multi-axis laser milling in continuous patterning of 25 mm diameter spherical stainless steel with high uniformity and precision, based on a strategy of simultaneously adjusting the position and the posture of laser-surface interaction point for enabling the constant coincidence of laser beam with ablated surface normal. Specifically, a miniaturized five-axis platform for controlling workpiece motion with high degree-of-freedom is designed and integrated with a fixed nanosecond pulsed laser beam operating at 1064 nm. The precise path of laser-surface interaction point is derived based on the projection and transformation of pre-determined planar pattern on spherical surface. Meanwhile, a virtual prototype of the multi-axis laser milling with embedded interpolation algorithm is established, which enables the generation of NC codes for subsequent laser milling experiments. Furthermore, the sampling of laser processing parameters particularly for spherical surface is carried out. Finally, complex patterns are continuously structured on the spherical surface by employing the proposed multi-axis laser milling method, and subsequent characterization demonstrates both long range uniformity and local high accuracy of the fabricated patterns. Current work provides a feasible method for the continuous laser surface texturing of non-planar surfaces for miniature parts with large curvature. Full article
(This article belongs to the Special Issue Ultrafast Laser Micro- and Nanoprocessing)
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