Two-photon lithography and nanoscale 3D printing

In plain language

Most 3D printers build objects from relatively coarse layers. Two-photon lithography works at a much finer scale. A liquid resin is exposed to a tightly focused laser beam, and the resin only hardens at the very centre of the beam, where the light is most intense. By moving the focus through the resin in three dimensions, a designer can draw structures that are too small to see without a microscope.

The method has been used to make tiny optical and mechanical parts. In 2001, a team at Osaka University led by Satoshi Kawata printed a micro-bull about 10 micrometres long, showing that the approach could make detailed three-dimensional objects at a very small scale.

Technical explanation

Two-photon lithography, also called two-photon polymerisation, relies on two-photon absorption. A photoinitiator in the resin only absorbs light when it receives two photons at once, and that happens only where light intensity is high enough, which is the tight focal volume of the laser. Polymerisation is therefore confined to a small volume, and the printed feature can be far smaller than the wavelength of the light used. Maruo, Nakamura and Kawata (1997) reported three-dimensional microfabrication by photopolymerisation stimulated by two-photon absorption in Optics Letters.

Physics World reported in 2001 that the Kawata group's method reached a spatial resolution of about 120 nanometres, with a demonstration micro-bull about 10 micrometres long made in commercially available resin. The Nature paper's standfirst states that micromachines can be created with higher resolution using two-photon absorption. Jaiswal and colleagues (2023) describe two-photon lithography as a versatile technology for making two- and three-dimensional micro and nanostructures, and they note that the results depend on process parameters and on the photoinitiator and resin formulation.

The review by Jaiswal and colleagues identifies the main constraint on the field: the lack of two-photon polymerisable resins is described as a bottleneck to its growth, so much of the research effort is on developing efficient resin formulations. Their review also covers applications in microelectronics, photonics, optoelectronics, microfluidics and plasmonic devices. The sources reviewed here do not give verified throughput, build volume or cost figures for commercial systems, so the trade-off between resolution and practical output cannot be quantified from them.

What the evidence says

Each statement is typed by the strength of its evidence and linked to the source that supports it.

Limitations and open problems

• The lack of two-photon polymerisable resins is described as a bottleneck to the growth of the technique (Jaiswal and colleagues, 2023).
• Published demonstrations are micrometre-scale objects, and the sources reviewed here do not show scaling to larger parts.
• Resolution depends on process parameters and on the photoinitiator and resin formulation (Jaiswal and colleagues, 2023).
• The sources reviewed here do not give verified throughput or cost figures for commercial systems, so practical output cannot be judged from them.

Possible future uses

Timeline

1. 1997Maruo, Nakamura and Kawata publish three-dimensional microfabrication by two-photon-absorbed photopolymerisation in Optics Letters. Sources: [1]
2. 16 Aug 2001The Kawata group at Osaka University reports a micro-bull about 10 micrometres long, with about 120 nanometres resolution, printed in commercially available resin. Sources: [2], [3]
3. 11 Mar 2023Jaiswal and colleagues publish a two-decade review of two-photon lithography in iScience, highlighting resin availability as the main bottleneck. Sources: [4]

Futures this could help bring about

How far away?

Printing features smaller than a cell

Pilots · 4 of 8 steps done

Related breakthroughs

• Grayscale projection two-photon lithography reports 55 nm nanowires and 1.7 billion voxels per second (29 May 2026)
• Metalens arrays split one femtosecond laser into more than 120,000 focal spots for parallel nanoscale 3D printing (17 Dec 2025)

Glossary

Two-photon absorption

A process in which a molecule absorbs two photons at once, which only happens efficiently where light intensity is very high, such as at the focus of a laser.

Photoinitiator

A chemical in a resin that starts the hardening reaction when it absorbs light.

Diffraction limit

The smallest detail that conventional focused light can resolve, which is roughly set by the light's wavelength.

Photopolymerisation

A reaction in which light turns a liquid monomer resin into a solid polymer.

Sources

1. peer reviewed paper
   Three-dimensional microfabrication with two-photon-absorbed photopolymerization
   Shoji Maruo, Osamu Nakamura, Satoshi Kawata. Optics Letters, 1997. DOI: 10.1364/OL.22.000132. Accessed 21 Oct 2026.
2. peer reviewed paper
   Finer features for functional microdevices
   Satoshi Kawata, Hong-Bo Sun, Tomokazu Tanaka et al.. Nature, 16 Aug 2001. DOI: 10.1038/35089130. Accessed 21 Oct 2026.
3. news
   New nano-technique hits the bull's-eye
   Physics World, 16 Aug 2001. Accessed 21 Oct 2026.
4. peer reviewed paper
   Two decades of two-photon lithography: Materials science perspective for additive manufacturing of 2D/3D nano-microstructures
   Arun Jaiswal, Chandresh Kumar Rastogi, Sweta Rani et al.. iScience, 11 Mar 2023. DOI: 10.1016/j.isci.2023.106374. Accessed 21 Oct 2026.

Revision history

3 changes since this profile was created.