Two-photon polymerization (TPP) is a direct laser writing technology. With TPP, the light-matter interaction only takes place within the volume of a focused laser spot.
The simultaneous absorption of two photons in the focused spot triggers the locally confined polymerization of an exposed photoresist.
The laser focus can be moved through the volume of the photoresist along all three spatial dimensions. Complex 3D structures are written along the laser’s trajectory, using light like a brush.
Thanks to its versatility, TPP fabrication has applications in many fields, including microoptics, photonics, micromechanics, and biomedicine.
High resolution and real 3D printing capabilities set TPP apart from alternative technologies and enable novel applications in different industries.
Complex Structures in One Process Step
Very complex structures can be fabricated in one single process step without the need for subsequent deposition of fresh material as in conventional 3D printing technologies (e.g. metal 3D printing or stereolithography).
Resolution below the Diffraction Limit
Non-linear absorption enables a resolution below the diffraction limit as opposed to conventional laser scanning methods. The right picture shows a metalens for visible light with smallest feature sizes in the range of 100 nm.
Accuracy and Scalability
Very accurate structures can be realized, ranging from the sub-micrometer to the centimeter scale. TPP bridges the gap between nano- and microfabrication tools and conventional 3D printing.
Stitching-free Fabrication Capability
Stitching defects can be avoided with Infinite Field of View (IFoV) writing mode, enabled by the synchronized 5-axes movement in Multiphoton Optics' LithoProf3D TPP equipment. In IFoV writing mode, the limited scan area of the microscope objective (< 1 mm) is enlarged throughout the travelling range of the sample stage (100 mm x 100 mm).
The upper picture shows a cylindrical microlens array fabricated without stitching by using IFoV writing mode.
The below picture shows the cylindrical microlens array fabricated with stitching. Major drawbacks of this technique are unwanted stitching artefacts at the borders thereby introducing optical artefacts which are undesired for many applications.
Integration into Nano- and Microfabrication Processes
Since the technology uses the same materials (photoresists and solvents) as in standard nano- and microfabrication, integration into conventional workflows is seamless.
Structures can be printed directly on active (LEDs, photodiodes, EELs, VCSELs) or passive (fibers, irregular substrates) devices.
This eliminates time intensive legacy processes such as active alignment of individual components.
Microoptics for various applications
Microlens arrays with varying sizes and shapes can be used for imaging and sensor applications.
TPP fabrication process -
based on three steps
To achieve high quality results, deep knowledge on structure formation induced by the exposure strategy is crucial. Over the years, Multiphoton Optics has developed and optimized exposure strategies for printing results in accordance with customer requirements.