Multiphoton Optics’ Technology

Multiphoton Optics’ technology uses ultra-short pulsed laser light as manufacturing tool. The technology is based on a two- or multiple photon absorption (TPA / MPA) process in case of additive fabrication, initiated by ultra-short laser pulses. Due to the nature of the non-linear process, the intensity is only high enough to initiate a reaction in a material in the strongly confined focal volume. The method is known as  High-Precision 3D Printing on a sub-micrometer scale, where structures are created in the additive mode in photo-responsive materials such as polymers, hybrid polymers, or special glasses.

Dependent on the underlying material to be processed, this confinement cannot only be used for additive, but also for subtractive fabrication. A large variety of different materials can be processed by making use of the specific nature of the processes enabled by a femtosecond light source, also allowing to create structures in metals with very high precision.

In principle, the focal volume which is defined by the technical equipment and the optics determines the size of a created voxel (volume pixel) to a certain extent. However, the reaction kinetics of the underlying materials and other processes such as threshold processes related to the material composition also play a crucial role for the minimum size of a resulting voxel enabled by a material. This means that different interaction volumes have to be considered. While the technical interaction volume (red voxel) which is determined by the employed optics, by the stability of the laser, and by the stability and accuracy of the positioning system can be easily optimized, the chemical interaction volume (green voxel) is much more difficult to minimize, because this is dependent on many different factors such as, for example on the reaction kinetics of the material formulation and, consequently, on the laser-light initiated propagation and termination reactions in a material.

For example, in the additive fabrication mode (AFM) using polymers or inorganic-organic hybrid polymers, the laser pulses initiate a radical cross-linking of the C=C bonds or a cationic cross-linking of epoxide bonds. If the focal volume of the laser is scanned in three dimensions through the material, the material is directly cross-linked in 3D along the path of the focal volume. This enables Multiphoton Optics’ customers to fabricate 3D structures in the volume or on a surface of a material with highest precision directly, fast, and reliably from a CAD file or from files generated with LithoSoft3D. The degree of cross-linking in a polymer or hybrid polymer and thus the chemical and physical properties of the created material structures can be precisely controlled by the different accessible process parameters using Multiphoton Optics’ equipment.

The physical and chemical properties of the fabricated structures are directly related to the chosen parameters in the fabrication process. By varying these parameters, physical or chemical properties can be altered to create gradient structural properties which are interesting for many different applications in photonics or biomedicine. This is known as 4D printing, and Multiphoton Optics’ has done pioneer works in 4D structuring of materials in the last decade. For example, the mechanical stability of additively fabricated structures can be modified such that their Youngs modulus or mechanical strength differs within the structures or mechanically differently stable structures can be created. This is of particular interest in tissue engineering, since the cells prefer to adhere, differentiate, and proliferate on non-toxic structures which resemble the natural tissue in its mechanical properties.

Multiphoton Optics’ 3D structure fabrication is based on a continuous writing process on a large scale, layer-by-layer fabrication can be chosen if required, and a combination of processes is also possible. In its standard equipment, volumes up to 10 cm x 10 cm x 5 cm can be patterned with highest precision and – in most materials – with very large process windows, leaving nothing to be desired. This is possible due to the unique know how in process control with Multiphoton Optics’ LithoProf3D equipment which also can be used in the subtractive mode in customized versions of the equipment for patterning metals and special polymer modifications which are typically not accessible via direct standard lithography methods.