03 Dec 2003
A pulsed ultraviolet laser shows potential for cutting patterns in cheese.
It seems that there’s no end to the type of materials that scientists will consider cutting with a laser. Researchers from the University of Wisconsin-Madison in the US astonished delegates at the recent ICALEO show in Florida when they announced that they had machined cheese into intricate shapes with a Q-switched Nd:YAG.
“Wisconsin is a big dairy and cheese making state and we were approached by a company that wanted to know if we could use a laser to cut thin slices of cheese at high speed,” Xiaochun Li, one of the researchers, told optics.org. “One motivation is the ability to cut cheese into fancy shapes that appeal to kids, such as a dinosaur or letters. The fast food industry is very interested in that idea.”
Li and his co-worker Hongseok Choi and assessed the suitability of an ultraviolet laser for cutting and drilling slices of mild cheddar that were a few millimeters thick. Central to the study was the investigation of which wavelength and energy fluence give the best results.
Experiments with the third (355 nm) and fourth (266 nm) harmonics of a Q-switched Nd:YAG laser demonstrated that a 266 nm beam is undoubtedly the preferred choice.
The 266 nm beam gave much deeper, cleaner cuts while signs of damage of burning can be seen in cuts made with a 355 nm beam, say Choi and Li in their ICALEO paper. The reason for the different cutting performance is the optical properties of the fat and protein in the cheese. The light absorption of protein is very strongly dependent on wavelength and about 100 times stronger at 150 nm compared to 300 nm.
“Basically, the cutting process is cold laser ablation, like that in laser eye surgery,” said Li. “At 266 nm it gives a very good clean cut, although going deeper than 10 mm is difficult.”
To date, the team has focused on making high quality intricate cuts in 2.5 mm thick mild cheddar. Patterns such as the University of Wisconsin-Madison motif were drawn on CAD software and then transferred to a workstation consisting of a flashlamp-pumped Nd:YAG laser and an xy table holding the cheese. The laser produced 10 ns long pulses with an average power of up to 10 W at 355 nm and 3.5 W at 266 nm.
The key limitation of the technique seems to be its slow cutting speed, less than 1 mm per second, which is restricted by the slow (20 Hz) repetition rate of the laser. Li says that a UV laser with a higher repetition rate and output power could significantly increase the depth and speed of the cutting.
He believes that the work could point to a new and lucrative market future for lasers. “The food industry could be a huge market for lasers just like the semiconductor industry,” Li said. “We’ve also been asked to cut meat and potato with a laser but we haven’t done that yet.”
• ICALEO is an annual laser materials processing show that is organized by the Laser Institute of America (LIA) and takes place each autumn. This year more than 450 attendees from 23 countries visited the event in Jacksonville, Florida, between 13-16 October. ICALEO 2004 will take place in San Francisco between 4-7 October.