Friedrich-Alexander-Universität Erlangen-Nürnberg

Optical Trap Assisted Near field Nanostructuring

Optical Trap Assisted Near-field Nanostructuring

The laser is considered to be a very precise manufacturing tool which is capable of easily generating structures on a micrometer scale. However, it becomes very challenging to decrease features sizes below one micrometer in case of direct-write laser processing. This is due to the optical diffraction limit, which does not allow laser radiation to be focused much smaller than its wavelength.

Fortunately, it is possible to overcome this limitation by utilizing non-linear effects with ultrafast lasers or by using optical near-fields. A near-field arises for instance when an electromagnetic wave transmits from one material to another with a different index of refraction. It is called near-field, because the amplitude of the electromagnetic field decays exponentially and thus it does not propagate farther than approximately one wavelength. The diffraction limit does not apply in the optical near-field so that it can be focused smaller than far-field radiation.

To utilize this effect, small transparent micro-particles are irradiated by laser pulses. The particles act as micro-lenses, focus the pulses and give rise to electromagnetic near-fields underneath themselves, which can be strong enough to modify or ablate the underlying surface. If the particles are small enough, i.e. below one micrometer in diameter, the resulting structures can be below diffraction limit.

Figure 1: Contacting Particle Lens Array Nanostructuring: micro-particles condense in a hexagonal grid and are irradiated with laser pulses (a). Near-field focusing underneath the particles then leads to periodical nano-holes (b). [QUE11]

To enable generating arbitrary surface structures instead of arrays of nano-holes, a single particle can be moved around on the substrate. This is achieved by so-called optical tweezers: a tightly focused cw laser beam can confine a micro-particle in three dimensions and therefore move and position it very precisely. The trapped particle then can be irradiated by a second, ultrashort pulsed laser. The resulting near-field focus processes the substrate material and continuous structures of any shape can directly be written.

This project is funded by the German National Research Foundation (DFG) within the Priority Programme 1327 “Optically Produced Nano-structures for Biomedical and Technical Applications”.

Figure 2: Principle of Optical Trap Assisted Nanostructuring: A tightly focused cw laser beam (red) confines and positions a micro-particle. The particle is used to focus ultrashort laser pulses (blue), which leads to nanoscale surface structures. [QUE12]
Figure 3: Generated surface structure on polyimide. [QUE12]


 [LEI10]     Leitz, K.-H.; Quentin, U.; Hornung, B.; Otto, A.; Alexeev, I.; Schmidt, M.: Microsphere near-field nanostructuring using picosecond pulses. In: Physics Procedia, Vol. 5, Part 1, S. 237–244, 2010.

[LEI11a]     Leitz, K.-H.; Quentin, U.; Hornung, B.; Otto, A.; Alexeev, I.; Schmidt, M.: Ultrafast Microsphere Near-field Nanostructuring. In: Photonics West 2011, Proc. SPIE 7925, 792518 (2011).

[LEI11b]    Leitz, K.-H.; Redlingshöfer, B.; Reg, Y.; Otto, A.; Schmidt, M.: Metal Ablation with Short and Ultrashort Laser Pulses. In: Physics Procedia, Vol. 12, S. 230–238, 2011.

[Li11]         Li, L.; Hong, M., Schmidt, M.; Zhong, M.; Malshe, A.; Huis int’Veld, B.; Kovalenko, V.: Laser Nano-manufacturing – State of the Art and Challenges. In: CIRP Annals - Manufacturing Technology, Vol.60/2, 2011

[LEI09]      Leitz, K.-H.; Otto, A.; Schmidt, M.: Sub-Wellenlängen-Strukturierung mit nahfeldverstärkten, ultrakurzen Laserpulsen. In: Laser in der Elektronikproduktion und Feinwerktechnik - Tagungsband des 12. Erlanger Seminars LEF 2009. S. 47–63.

[SCH09]     Schmidt, M.; Leitz, K.-H.; Otto, A.: Sub-Wavelength Structuring using Microsphere Near-Field Enhancement. In: Proceedings of the DFG-NSF Research Conference (14.-17.10.09), New York, 2009.

[QUE11]    Quentin, U.; Leitz, K.-H.; Alexeev, I; Schmidt, M.: Application of Gaussian optical tweezers for ultrafast laser assisted direct–write nanostructuring. In: Proceedings of LPM 2011

[QUE12]    Quentin, U.; Leitz, K.-H.; Deichmann, L.; Alexeev, I; Schmidt, M.: Optical trap assisted laser nanostructuring in the near-field of micro-particles. In: Journal of Laser Applications (submitted)

[Tsa12]      Tsai, Y.-C.; Leitz, K.-H.; Fardel, R.; Otto, A.; Schmidt, M.; Arnold, C.B.: Array-based optical trap assisted nano-patterning on rough surfaces. In: IOP Nanotechnology (submitted)



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