Femtosecond Laser Micro- and Nanofabrication: From Fundamentals to Applications

Table of Contents

Femtosecond laser micro- and nanofabrication links ultrafast energy deposition to transparent-material modification, three-dimensional polymerization, pulse shaping, parallel processing, and functional device integration. This article follows that path from physical mechanisms to applications.

Ultrafast interaction Transparent materials Two-photon polymerization 3D / 4D microfabrication

First page of the review Femtosecond laser micro nano processing from fundamental to applications — Primary review used in this article: “Femtosecond laser micro/nano processing: from fundamental to applications.”

Application background

A femtosecond laser produces pulses with durations on the order of femtoseconds, where \(1\ \mathrm{fs}=10^{-15}\ \mathrm{s}\). Its combination of extremely short duration and very high peak power creates four core capabilities:

01Cold processing

Interaction ends before picosecond-scale thermal relaxation, minimizing the heat-affected zone.

02Nonlinear absorption

Even transparent materials absorb through multiphoton and tunneling ionization.

03Three-dimensional writing

A focus can be positioned inside transparent matter to create buried 3D structures.

04New induced states

The process can create LIPSS, nanogratings, color centers, and nanocrystals.

In “cold” processing, the pulse ends before electron–phonon coupling and other thermal-relaxation processes spread energy. Material can therefore be modified or removed with little melting, recast, or cracking. Nonlinear absorption also removes the normal wavelength-selectivity constraint, allowing metals, semiconductors, dielectrics, polymers, and biological tissues to be processed with one broadly adaptable platform.

Representative applications include:

Microelectronics and photonics: waveguides, photonic crystals, microresonators, integrated optical circuits, and sensors.
Micro- and nanoelectromechanical systems: microsensors, actuators, and micromotors.
Biomedicine: microfluidic chips, drug-delivery systems, tissue-engineering scaffolds, biosensors, and microneedle arrays.
Functional materials and surfaces: superhydrophobic or superhydrophilic surfaces, antireflection textures, and catalytic structures.
Data storage: five-dimensional optical storage.
AI photonics: optical neural networks and photonic computing units.

Applications of femtosecond laser microfabrication in photonics microfluidics biomedicine robotics and data storage — Application landscape for femtosecond laser micro- and nanofabrication.

Femtosecond laser–matter interaction

Energy intensity and femtosecond picosecond nanosecond time scales in pulsed laser matter interaction — Pulsed laser–matter interaction viewed by energy intensity and characteristic time scale.

Femtosecond scale: the field excites optically active electronic states, causing electron heating, electronic nonequilibrium, nonthermal phase transitions, and Coulomb explosion.
Picosecond scale: excited electrons transfer energy to atomic motion, and nonequilibrium transformations such as homogeneous melting develop.
Nanosecond scale: the irradiated zone cools and solidifies; heterogeneous melting, melt flow, resolidification, and microstructural modification dominate.

Ionization mechanisms

The central feature of femtosecond interaction is its nonlinearity: photons are concentrated into a very short time and a small focal volume.

Multiphoton ionization: an electron absorbs several photons nearly simultaneously and reaches the conduction band. This is especially important in transparent materials.
Tunneling ionization: a strong electric field bends and narrows the Coulomb barrier, allowing a bound electron to tunnel into a free state.
Avalanche ionization: existing free electrons gain energy from the field and collisionally ionize additional bound electrons, creating a multiplying cascade.

Multiphoton tunneling and avalanche photoionization mechanisms — Three photoionization routes: multiphoton ionization, tunneling ionization, and avalanche ionization.

Energy transfer and phase transformation

Metals: free electrons absorb photons and heat rapidly, then transfer energy through electron–electron collisions and electron–phonon coupling, raising lattice temperature and causing melting or vaporization.
Nonmetals: dielectrics and semiconductors first generate free carriers through ionization. The carrier plasma absorbs additional energy and later transfers it to the lattice.
Nonthermal melting and ablation: strong electronic excitation destabilizes the lattice before conventional thermal equilibrium is reached. This is one physical basis of cold processing.
Thermal melting and ablation: energy reaches the lattice through electron–phonon coupling and drives familiar melting, vaporization, and removal.
Coulomb explosion: rapid electron removal leaves a positively charged surface whose ion–ion repulsion ejects material explosively.
Photomechanical spallation and phase explosion: confined pressure creates voids and layer separation, or superheated matter decomposes explosively near a critical state.

Comparison of heat effects and damage in femtosecond picosecond and nanosecond laser ablation — Femtosecond ablation confines thermal damage, whereas longer pulses more readily create melt, recast, and surrounding defects.

Physical modification by femtosecond pulses

Surface modification

Laser-induced periodic surface structures (LIPSS): periodicity is usually near or below the wavelength. Interference between incident light and surface plasmon polaritons or scattered waves creates textures that tune reflection, structural color, wetting, and friction.
Light-trapping structures: micro- and nanotextures on silicon and other absorbers can increase optical path length and improve solar-cell absorption.

Laser induced periodic surface structures on silica and ZnSe — LIPSS formed on silica and ZnSe surfaces.

Bulk modification

Refractive-index change: supports waveguides and gratings in transparent media and may appear as smooth index increase, birefringent nanogratings, or microvoids.
Crystallization: localized heating and rapid cooling alter the crystalline state.
Microvoids and microchannels: high-energy focusing produces a confined microexplosion inside transparent matter, enabling buried fluidic channels and cavities.

Microscale removal and deposition

Nanosecond drilling is often limited by poor edge quality, stress cracking, recast layers, and fragmentation. Femtosecond pulses strongly limit heat diffusion and control deposition more precisely, producing high-resolution features with fewer defects. Cutting and scribing are particularly valuable for hard brittle materials such as semiconductors, glass, and sapphire.

Formation stages of a microhole drilled in silicon by femtosecond laser ablation — Microhole formation during femtosecond ablation of silicon.

Surface ablation deep ablation and termination stages in femtosecond percussion drilling of glass — Three percussion-drilling stages in glass: free plume expansion at the surface, wall-confined deep ablation, and slowing when bottom fluence falls below threshold.

In deposition, a femtosecond pulse ablates a target and the ejected species condense on another substrate as a thin film or nanoparticle layer.

Two-photon polymerization and photochemistry

Two-photon polymerization (TPP), also called two-photon lithography, is a major additive-manufacturing use of femtosecond lasers. A photoinitiator absorbs two or more photons and triggers polymerization, so liquid resin solidifies only within the focal voxel. Because two-photon probability scales approximately with the square of intensity, curing is tightly localized and true three-dimensional features below the diffraction-limited focal size can be produced.

The main advantages are free-form 3D fabrication and high resolution, with feature sizes reaching hundreds or tens of nanometers under optimized conditions.

Comparison of one photon and two photon absorption and localized polymerization voxels — One-photon absorption excites a larger axial region; two-photon absorption confines the reaction around the intensity maximum.

Three dimensional microstructures fabricated by two photon polymerization — Representative structures fabricated by TPP.

Other induced phenomena

Photoluminescence: ultrafast writing can generate upconversion fluorescence and persistent afterglow in rare-earth-doped glass and crystals.

Long afterglow phosphorescence induced by 800 nanometer femtosecond irradiation in rare earth doped glass and crystals — Persistent phosphorescence induced by 800 nm femtosecond irradiation.

Color centers: femtosecond modification can create nitrogen-vacancy centers in diamond, which are important building blocks for quantum sensing and quantum information.

Nitrogen vacancy centers induced in diamond by femtosecond laser processing — Laser-induced NV centers in diamond.

Nanogratings: periodic nanoscale structures written inside transparent materials are birefringent and can serve polarization optics, data storage, and sensors.

Polarized image of a miniature world map written inside fused silica by a femtosecond laser — A miniature world map encoded as birefringent nanostructure inside fused silica.

Nanocrystals: localized high temperature and pressure can nucleate perovskite and other nanocrystals in glass for emitters, solar cells, and optical data storage.

Tunable colored perovskite nanocrystals and patterns directly written by a femtosecond laser — Tunable perovskite nanocrystals and color patterns generated by direct writing.

Tailored optical properties: processing parameters can induce controllable optical chirality even in initially achiral materials such as silica.

On demand tuning of optical chirality in silica by femtosecond laser writing — On-demand tuning of optical chirality.

Micro- and nanofabrication of transparent materials

Glass and fused silica

Glass is among the most widely processed materials because of its optical transparency and chemical stability. Different modification regimes can form buried channels, volume gratings, and waveguides. Fused silica, with its high damage threshold and excellent ultraviolet transmission, is a benchmark material for femtosecond research and applications.

Birefringent patterning in fused silica by femtosecond laser writing — Birefringent patterning inside fused silica.

Femtosecond induced microcracks used to enhance glass waveguide performance — Controlled microcracks can be integrated into a waveguide design rather than treated only as defects.

Polymers

Polymers require relatively little processing energy, are inexpensive and formable, and can be chemically doped. They support optical storage, microchannels, gratings, and waveguides. TPP in polymers is highly mature, although thermal stability and mechanical strength can be lower than in glass or crystals.

Four dimensional optical data storage written in a polymer by a femtosecond laser — Four-dimensional optical storage written in a polymer.

Diamond, sapphire, and functional crystals

Diamond: femtosecond lasers can create NV centers, waveguides, microfluidic structures, and quantum sensors. Processing is difficult, but diamond’s hardness, thermal conductivity, wide band gap, and biocompatibility make it valuable in extreme environments and quantum technology.

Femtosecond writing of nitrogen vacancy centers LIPSS and waveguides in diamond — NV centers, LIPSS, and waveguides fabricated in diamond.

Sapphire: high hardness, thermal stability, and transparency make it an important optical and substrate material, but uncontrolled processing can readily generate cracks.

Subwavelength ripples and biomimetic structures formed on sapphire by a femtosecond laser — Subwavelength ripples and biomimetic structures on sapphire.

Functional crystals: YAG, Nd:YAG, LiNbO₃, quartz, and TeO₂ can host nanostructures, waveguides, index-modified zones, birefringent regions, and microholes. LiNbO₃ is especially important for electro-optic, acousto-optic, and nonlinear-optical devices; direct-written waveguides and periodic structures add new functionality without conventional wafer processing.

Gels, liquids, and photoresists

TPP commonly uses liquid or gel photoresists:

Negative resists: irradiated regions cross-link and remain after unexposed material is washed away. Examples include acrylates, SU-8 epoxy, Ormocer® hybrid sol–gels, and SZ2080.
Positive resists: irradiation makes exposed material soluble so it is removed during development.
Critical properties: transparency, two-photon absorption cross-section, polymerization shrinkage, mechanical strength, and biocompatibility.

Microstructures fabricated by two photon polymerization — Microstructures produced by TPP.

Photonic crystal fabricated in SZ2080 photoresist by femtosecond laser writing — A photonic crystal fabricated in SZ2080.

Pulse shaping and high-throughput processing

Femtosecond pulse shaping

Temporal shaping controls how energy is distributed in time. Pulse trains can improve removal efficiency, reduce heat accumulation, and tune quality. Implementations include beam splitters, acousto-optic modulators, Fourier-domain pulse shapers, and thin-film resonators.

Temporal pulse shaping system based on a Michelson interferometer — A Michelson-interferometer approach to temporal pulse shaping.

Pulse train generator and femtosecond laser experimental setup — Pulse-train generator and femtosecond processing setup.

Spatial shaping changes the transverse energy distribution to form flat-top, Bessel, or vortex beams. Diffractive optical elements, birefringent lens groups, and spatial light modulators are common tools.

Gaussian square flat top circular flat top vortex and Bessel beam profiles — Representative spatial profiles: Gaussian, square and circular flat-top, vortex, and Bessel beams.

Spatial pulse shaping with birefringent lenses and a liquid crystal spatial light modulator — Spatial shaping using a birefringent lens group or liquid-crystal SLM.

Frequency shaping changes wavelength through nonlinear processes such as second-harmonic generation and optical parametric amplification.

Pulse shaping expands the process window. Temporally shaped bursts can improve glass cutting and drilling; spatial shaping, especially Bessel beams and programmable SLMs, increases depth tolerance, parallelism, and three-dimensional flexibility.

High-throughput femtosecond processing

Point-by-point scanning is inherently slow. Three strategy families increase throughput:

Source and motion improvements: higher average power, higher repetition rate, faster galvanometers, and more accurate stages.
Multifocus and multi-beam interference: microlens arrays or diffractive optics generate many foci, while interference creates periodic patterns over a large area.
Holographic pattern processing: an SLM or DMD displays a computed hologram and projects a target pattern for area-wise exposure.

Multifocus multi beam interference and holographic parallel femtosecond laser processing — Parallel strategies: multifocus exposure, multi-beam interference, and holographic patterning.

High speed projection two photon polymerization using a digital micromirror device — DMD projection TPP for high-throughput fabrication.

4D printing and nanoscale resolution

Micro- and nanoscale 4D printing

4D printing combines a printed 3D structure with time-dependent response. The structure changes shape, properties, or function under temperature, pH, light, magnetic field, solvent, or another stimulus.

Difference between static 3D printing and stimulus responsive 4D printing — Static 3D printing compared with stimulus-responsive 4D printing.

Magnetic microplate array actuated for droplet transport as a 4D printing example — Magnetically actuated microplates for droplet transport.

pH responsive hydrogel microstructures as a 4D printing example — pH-responsive hydrogel structures that change configuration after fabrication.

These systems point toward reconfigurable microdevices for soft robotics, biomedical tools, and adaptive sensors.

Super-resolution nanofabrication

The goal is to move beyond the conventional diffraction limit toward features of tens of nanometers or, in specialized demonstrations, only a few nanometers. Two different metrics matter: linewidth, the smallest feature that can be produced, and writing resolution, the smallest spacing at which two adjacent features remain distinct.

Near-field methods: adaptive scanning probes, near-field optical microscopy, and microsphere-assisted processing provide very high resolution but operate close to a surface.
Far-field threshold control: TPP can confine polymerization by tuning power, exposure, scan speed, initiator sensitivity, and diffusion so only the highest-intensity core crosses threshold.
STED-inspired lithography: a Gaussian excitation beam initiates polymerization while a doughnut-shaped depletion beam suppresses the excited state around it, shrinking the effective voxel.

Two beam STED inspired lithography shrinking a polymerization voxel for nanoscale fabrication — STED-inspired two-beam lithography compresses the active polymerization region.

Heterogeneous integration of functional materials

Heterogeneous integration combines materials and components with different functions in one device, creating capabilities that no single material can provide. It is especially important in photonic integrated circuits.

Monolithic integration: for example, epitaxial growth of compound semiconductors on silicon.
Hybrid integration: bonding and assembling separately optimized components.
Pulsed laser deposition: ablating a source target and depositing the vapor on a receiving substrate.
Femtosecond direct writing: writing waveguides and interconnects inside bulk material to connect existing structures.
Van der Waals integration: stacking two-dimensional materials or nanomembranes with weak interfacial bonding and relaxed lattice-matching requirements.

Multiple femtosecond fabricated microstructures integrated inside a Y shaped microchannel — Several functional microstructures integrated inside a Y-shaped channel.

Nanomembrane heterogeneously integrated inside a PDMS microfluidic channel — A nanomembrane integrated inside a PDMS microfluidic channel.

Protein microstructures integrated inside a closed microfluidic channel — Protein microstructures integrated inside a sealed microfluidic channel.

Three dimensional nanoscale printing of quantum dot functional microstructures — Three-dimensional nanoprinting of quantum-dot microstructures.

Applications in three-dimensional functional microdevices

Microfluidic chips

Femtosecond-assisted etching and water-assisted drilling can create complex three-dimensional lab-on-chip structures.

Three dimensional microfluidic lab on chip devices fabricated by femtosecond direct laser writing — Microdevices fabricated by femtosecond direct laser writing for lab-on-chip research.

Micro-optics

The process can form microlenses, micro-waveplates, and three-dimensional photonic crystals.

Fiber tip lenses spiral waveplates tunable microlens arrays and X ray compound refractive lenses — Micro-optics including fiber-tip lenses, a vortex-generating spiral waveplate, a tunable microlens array, and X-ray compound refractive lenses.

Micromechanics

Direct writing supports microresonators, compliant structures, and actuators.

Polymer microresonators for quantum photonics optical tuning gas sensing and ultrasound detection — Polymer microresonators used in quantum photonics, optical tuning, gas sensing, and ultrasound detection.

Microrobots

Many microrobots are 4D-printed structures whose geometry and material response convert external fields into motion.

Light driven walkers magnetoelectric swimmers and smart microflowers valves and claws — Light-driven liquid-crystal walkers, magnetoelectric swimmers, and smart microflowers, valves, and claws.

Microelectronics

Femtosecond lasers can print flexible electronic devices, sensors, electrodes, and heterogeneous circuit elements.

Hybrid femtosecond and continuous wave printing of Pt ZnO Ag diodes memristors and security circuits — Pt–ZnO–Ag diodes, memristors, and security circuits produced by hybrid femtosecond and continuous-wave laser printing.

Biomedical microdevices

Microneedle arrays: support minimally invasive drug delivery, vaccination, and biofluid sampling.
Biological scaffolds: provide three-dimensional environments for tissue engineering and cell studies.

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Artificial-intelligence photonics

Photonic devices can perform AI operations with high bandwidth and potentially low energy consumption.

Machine learning decoder and diffractive neural network integrated on CMOS chips — A TPP-integrated machine-learning decoder and a CMOS-integrated diffractive neural network for pupil-function retrieval.

PHYSICSNonlinear absorption

Ionization, plasma formation, and ultrafast energy transfer.

PROCESSRemoval and modification

Ablation, direct writing, polymerization, shaping, and parallel exposure.

DEVICEFunctional microdevices

Optical, mechanical, electronic, biological, and intelligent integration.

Reference

Gao, L., Zhang, Q., & Gu, M. “Femtosecond laser micro/nano processing: from fundamental to applications.” International Journal of Extreme Manufacturing, 7, 022010 (2025). DOI: 10.1088/2631-7990/ad943e.

The original Chinese edition was published by “Laser Insights” in Chongqing on May 23, 2025, at 07:26. View the original post