Two-photon polymerisation builds structures smaller than the beam that writes them
Polymerisation only happens where intensity is high enough for two photons to arrive together, which confines curing to a volume well inside the focal spot.
Conventional photopolymer printing cures resin wherever light of the right wavelength arrives. Resolution is therefore bounded by the optics. Two-photon polymerisation escapes that bound by relying on a process that only occurs at very high intensity.
The mechanism
The resin is transparent at the laser wavelength, so a single photon carries too little energy to initiate curing. Where intensity is extreme — at the focus of a tightly focused ultrafast beam — two photons can be absorbed effectively simultaneously, delivering their combined energy and triggering polymerisation.
The probability of that scales with the square of intensity. That non-linearity confines curing to a small volume around the focus, and by keeping intensity just above threshold the cured volume can be made considerably smaller than the focal spot itself.
Feature sizes of a few hundred nanometres, and in careful work below a hundred, are achievable.
What it enables
Micro-optics. Lenses and freeform optical elements printed directly onto fibre ends or detector surfaces, avoiding assembly and alignment.
Microfluidics. Channels, valves and mixers with genuinely three-dimensional geometry rather than layered approximations.
Scaffolds for cell culture. Structures with feature sizes matched to cells, used in tissue engineering and mechanobiology.
Mechanical metamaterials. Lattices whose bulk properties derive from geometry, printed at a scale where those properties are measurable.
Micro-robotics. Structures for micromanipulation and drug delivery research.
The throughput constraint
The process writes point by point. Producing a structure of a few hundred micrometres can take minutes to hours, which confines it to research, prototyping and low-volume high-value production.
Parallelisation is the active area: splitting the beam into many foci, using spatial light modulators to write many points at once, and combining with projection approaches for the bulk of a structure while reserving point writing for fine features.
Where it stands commercially
Systems are available from several suppliers and installed widely in research institutions, with a growing base in micro-optics production where the value per part supports the cycle time.
The honest position is that it is a manufacturing process for parts nothing else can make, rather than a faster or cheaper route to parts that can be made otherwise.
This article was produced by the LasersNews AI desk and reviewed by our editors.
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