Femtosecond laser micromachining can be used either to remove materials or to change a material's properties, and can be applied to both absorptive and transparent substances. Over the past decade, this technique has been used in a broad range of applications, from waveguide fabrication to cell ablation. This review describes the physical mechanisms and the main experimental parameters involved in the femtosecond laser micromachining of transparent materials, and important emerging applications of the technology. Interactions between laser and matter are fascinating and have found a wide range of applications. This article gives an overview of the fundamental physical mechanisms in the processing of transparent materials using ultrafast lasers, as well as important emerging applications of the technology.

Femtosecond laser micromachining in transparent materials

Micromachining technology was used to prepare chemical analysis systems on glass chips (1 centimeter by 2 centimeters or larger) that utilize electroosmotic pumping to drive fluid flow and electrophoretic separation to distinguish sample components. Capillaries 1 to 10 centimeters long etched in the glass (cross section, 10 micrometers by 30 micrometers) allow for capillary electrophoresis-based separations of amino acids with up to 75,000 theoretical plates in about 15 seconds, and separations of about 600 plates can be effected within 4 seconds. Sample treatment steps within a manifold of intersecting capillaries were demonstrated for a simple sample dilution process. Manipulation of the applied voltages controlled the directions of fluid flow within the manifold. The principles demonstrated in this study can be used to develop a miniaturized system for sample handling and separation with no moving parts.

Micromachining a miniaturized capillary electrophoresis-based chemical analysis system on a chip

The unique characteristics of ultrafast lasers, such as picosecond and femtosecond lasers, have opened up new avenues in materials processing that employ ultrashort pulse widths and extremely high peak intensities. Thus, ultrafast lasers are currently used widely for both fundamental research and practical applications. This review describes the characteristics of ultrafast laser processing and the recent advancements and applications of both surface and volume processing. Surface processing includes micromachining, micro- and nanostructuring, and nanoablation, while volume processing includes two-photon polymerization and three-dimensional (3D) processing within transparent materials. Commercial and industrial applications of ultrafast laser processing are also introduced, and a summary of the technology with future outlooks are also given. Scientists in Asia have reviewed the role of ultrafast lasers in materials processing. Koji Sugioka from RIKEN in Japan and Ya Cheng from the Shanghai Institute of Optics and Fine Mechanics in China describe how femtosecond and picosecond lasers can be used to perform useful tasks in both surface and volume processing. Such lasers can cut, drill and ablate a variety of materials with high precision, including metals, semiconductors, ceramics and glasses. They can also polymerize organic materials that contain a suitable photosensitizer and can three-dimensionally process inside transparent materials such as glass, and are already being used to fabricate medical stents, repair photomasks, drill ink-jet nozzles and pattern solar cells. The researchers also explain the characteristics of such lasers and the interaction of ultrashort, intense pulses of light with matter.

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Ultrafast lasers—reliable tools for advanced materials processing

Driven by functionality and purity demand for applications of inorganic nanoparticle colloids in optics, biology, and energy, their surface chemistry has become a topic of intensive research interest. Consequently, ligand-free colloids are ideal reference materials for evaluating the effects of surface adsorbates from the initial state for application-oriented nanointegration purposes. After two decades of development, laser synthesis and processing of colloids (LSPC) has emerged as a convenient and scalable technique for the synthesis of ligand-free nanomaterials in sealed environments. In addition to the high-purity surface of LSPC-generated nanoparticles, other strengths of LSPC include its high throughput, convenience for preparing alloys or series of doped nanomaterials, and its continuous operation mode, suitable for downstream processing. Unscreened surface charge of LSPC-synthesized colloids is the key to achieving colloidal stability and high affinity to biomolecules as well as support materials,...

Laser Synthesis and Processing of Colloids: Fundamentals and Applications

This paper reviews a new field of direct femtosecond laser surface nano/microstructuring and its applications. Over the past few years, direct femtosecond laser surface processing has distinguished itself from other conventional laser ablation methods and become one of the best ways to create surface structures at nano- and micro-scales on metals and semiconductors due to its flexibility, simplicity, and controllability in creating various types of nano/microstructures that are suitable for a wide range of applications. Significant advancements were made recently in applying this technique to altering optical properties of metals and semiconductors. As a result, highly absorptive metals and semiconductors were created, dubbed as the “black metals” and “black silicon”. Furthermore, various colors other than black have been created through structural coloring on metals. Direct femtosecond laser processing is also capable of producing novel materials with wetting properties ranging from superhydrophilic to superhydrophobic. In the extreme case, superwicking materials were created that can make liquids run vertically uphill against the gravity over an extended surface area. Though impressive scientific achievements have been made so far, direct femtosecond laser processing is still a young research field and many exciting findings are expected to emerge on its horizon.

Direct femtosecond laser surface nano/microstructuring and its applications

The thermal conductivity of individual multiwalled carbon nanotubes was measured by utilizing the four-point-probe third-harmonic method, based on the fact that the third harmonic amplitude and pha...

Measurement of the thermal conductivity of individual carbon nanotubes by the four-point three-ω method

Ultra-short-pulse lasers have proved to be effective tools for micromachining a wide range of materials. When the ultra-short laser pulse is focused inside the bulk of a transparent medium, nonlinear absorption occurs only near the focal volume that is subjected to high intensity. Three-dimensional structures can be fabricated inside transparent materials by taking advantage of this volumetric absorption. In this paper, femtosecond laser pulses were used to fabricate straight and bent through-channels. Drilling was initiated from the rear surface to preserve consistent absorption of the laser pulse. When the debris was not removed efficiently, variation of the channel diameter and occasional termination of the drilling process were observed. Machining in the presence of a liquid and additional use of ultrasonic wave agitation facilitated the debris ejection. The machined channels had diameters on the order of tens of microns, high aspect ratios, and good wall-surface quality.

Liquid-assisted femtosecond laser drilling of straight and three-dimensional microchannels in glass

Ultrashort pulsed-laser radiation is an effective method for precision materials processing and surface nano-/micromodification because of minimal thermal and mechanical damage. This study demonstrates that controllable surface nanomachining can be achieved by femtosecond laser pulses through local field enhancement in the near-field of a sharp probe tip. Nanomachining of thin gold films was accomplished by coupling 800-nm femtosecond laser radiation with a silicon tip in ambient air. Finite-difference time-domain numerical predictions of the spatial distribution of the laser field intensity beneath the tip confirmed that the observed high spatial resolution is due to the enhancement of the local electric field. Possible structuring mechanisms and factors affecting this process are discussed. The present process provides an intriguing means for massive nanofabrication due to the flexibility in the substrate material selection, high spatial resolution of ∼10 nm (not possible with standard nanomachining techniques), and fast processing rates achievable through simultaneous irradiation of multiarray tips.

Femtosecond laser aperturless near-field nanomachining of metals assisted by scanning probe microscopy

Evaporation heat transfer of R-32, R-134a, R-32/134a, and R-32/125/134a inside a horizontal smooth tube

Control of one-dimensional (1D) nanostructures is demonstrated in this paper by selectively placing and aligning silicon carbide (β-SiC) nanowires (NWs). We developed a reliable and highly reproducible way of placing a single or double SiC NW on pre-patterned electrodes by using a focused ion beam and a nanomanipulator. 3-ω signals obtained by the four-point-probe method were used in measuring the thermal conductivity of the NWs. The thermal conductivities of the placed single and double β-SiC NWs were obtained at 82 ± 6 W mK − 1 and 73 ± 5 W mK − 1, respectively. The proposed technique offers new possibilities for manipulating and evaluating 1D nanoscale materials.

https://iopscience.iop.org/article/10.1088/0957-4484/21/12/125301/pdf

Focused ion beam-assisted manipulation of single and double β-SiC nanowires and their thermal conductivity measurements by the four-point-probe 3-ω method

Tae-Youl Choi

Papers

Measurement of the thermal conductivity of individual carbon nanotubes by the four-point three-ω method

Liquid-assisted femtosecond laser drilling of straight and three-dimensional microchannels in glass

Femtosecond laser aperturless near-field nanomachining of metals assisted by scanning probe microscopy

Evaporation heat transfer of R-32, R-134a, R-32/134a, and R-32/125/134a inside a horizontal smooth tube

Focused ion beam-assisted manipulation of single and double β-SiC nanowires and their thermal conductivity measurements by the four-point-probe 3-ω method