Assaulting ink drops for science

View the video

This is what it looks like when a pulse of laser light obliterates a free-falling ink drop. The photograph is from an award-winning video in the American Physical Society’s 2014 Gallery of Fluid Motion competition. The image and others like it may help engineers build the next generation of computer chips.

The carnage was documented by physicist Hanneke Gelderblom of the University of Twente in Enschede, Netherlands, and her team, who fire nanosecond-long pulses of green laser light at drops of ink. A strobe light illuminates the action, allowing two cameras in tandem to capture about 10 million frames a second. This photo was taken microseconds after the laser made contact with a drop.

The laser delivers so much energy so quickly that some liquid transforms into a superheated gas called a plasma. That transformation is of particular interest to Gelderblom and ASML, the Dutch company that supports her research.

ASML builds lithography machines, which are used to produce computer chips. One device works by shooting a laser at drops of molten tin to produce plasma. The plasma then emits extreme ultraviolet light, which can imprint features less than 13.5 nanometers across onto chips. A smaller feature size would enable engineers to pack more transistors onto a single chip.

Gelderblom’s experiments provide insight into the first step of ASML’s laser-driven process. Her team studies the shape and fragmentation of the disturbed drops and analyzes how those features change depending on the laser energy and focus.

The splatter of an ink drop varies depending on the energy and focus of the laser pulse striking it, as explained in this video entry from the American Physical Society’s 2014 Gallery of Fluid Motion competition. Credit: Alexander L. Klein, Wilco Bouwhuis, Claas Willem Visser, Henri Lhuissier, Chao Sun, Jacco H. Snoeijer, Emmanuel Villermaux, Detlef Lohse, and Hanneke Gelderblom