Exploring and Utilizing Laser-Material Interaction for Engineering, Biotechnology, and Medicine

At the Terakawa Laboratory of Keio University's Department of Electronics and Electrical Engineering, research is being conducted on technology that explores and utilizes laser-material interaction to contribute to engineering, biotechnology, and medicine.

Here, keywords of the research are laser processing, micro- and nano-structure, and biomedical applications.

In particular, the laboratory is focused on processing with a femtosecond laser that enables them to achieve more precise processing than with lasers currently used broadly in industry.

"Most lasers currently used in industry are continuous wave, or what are known as nanosecond lasers, that have a longer interaction time. When this type of laser is used, the energy imparted during the laser irradiation diffuses to the surrounding area, which means that energy cannot be localized to the desired area of interaction. But if the laser pulse is in a femtosecond time-scale, the energy is completely transferred before heat can diffuse into the surrounding area, which makes little heat-affected zone, and extremely precise processing is possible."

By combining this perspective of extremely short "time" with the perspective of "space" of interaction, micro- and nano-processing that overcomes the diffraction limit becomes possible. For example, by arranging dielectric particles on a substrate and just illuminate uniformly with a femtosecond laser pulse without lens focusing, numerous small nanoscale holes can be created simultaneously. On the other hand, by using a propagating scattered field, a nanoscale periodic surface structure can be easily created.

"That is to say, in terms of time we emphasize an extremely short interaction time. As for space, more precise processing becomes possible by confining or controlling the area of interaction. So we are researching the fabrication of various small structures and patterning as well as periodic structure by merger of such concepts of short interaction time and the unique spatial distribution of light."

The Terakawa Laboratory is also conducting research on future biotechnology and medical technology by utilizing the various characteristics of laser light. By exposing focused- and enhanced-optical field with femtosecond laser processing, onto a cell membrane, small multiple holes in the membrane can be created. With this technology, it becomes possible to introduce drug molecules or genes into targeted cells by using selectively conjugated dielectric particles to the cell.

"By opening up a hole in the cell membrane without damaging the cell, drug molecules or genes can be inserted into the cell from outside the cell. The cell membrane typically acts as a barrier to the cell and prevents anything from entering from the outside, but by opening up a small hole in the membrane it becomes a passageway into the cell. This can then be used for therapies such as gene therapy or regenerative medicine."

With its small thermal impact, femtosecond laser processing can be used to perform local cell surgery on a living cell. In addition, because femtosecond laser processing can also be applied to transparent materials, the Terakawa Laboratory is performing processing on low toxicity materials such as biodegradable polymers.

"There are still many things that we need to do. One challenge is to perform processing with greater precision. As for applications of such processing, by achieving a level of processing technology previously unattainable, new opportunities will emerge, and we will discover potential future applications that were not even imagined because they were impossible. This is our challenge."