Short pulses offer long-term gains

You might think laser pulse lengths measured in nanoseconds—that is, billionths of a second—are short. But they’re long compared to those of picosecond (a trillionth of a second) and femtosecond (a quadrillionth of a second) lasers, which are known as ultrashort-pulse lasers.

Once confined mainly to laboratories and medical facilities, USPLs have become increasingly popular machining options over the last decade, thanks to lower prices and more-rugged designs intended for industrial settings.

For machining applications, one of the main selling points of USPLs is that they shrink—and sometimes eliminate—the heat-affected zone. “The pulses are so short that heat doesn’t have time to be absorbed significantly, or at all, into either the material you’re cutting or adjacent structures,” explained Ramsey Cook, business development manager for the micro-processing group at Trumpf Inc., Farmington, Conn., a USPL manufacturer.

If a manufacturer cuts a thin line into steel with a USPL, Cook said, the laser vaporizes steel molecules, leaving little melt or debris along the cut.

Cut by a TruMicro picosecond laser from Trumpf, this “bicycle” is dwarfed by a 2€ coin. Image courtesy Trumpf.

The idea is to eliminate secondary operations. “If you’re cutting metal heart stents, for example, you would prefer not to do any post-process operations to clean them because that improves throughput,” said Jimmie Bates, director of operations and business development for Altos Photonics Inc., a USPL seller in Bozeman, Mont. “So you make the cut with a femtosecond laser, and you’re good to go.”

Another advantage of ultrashort laser pulses is they cut transparent materials. “If you use a long pulse in glass, the beam might go right through it because there’s no absorption,” said Ronald Schaeffer, CEO of PhotoMachining Inc., Pelham, N.H., which uses USPLs for micromachining. “When you get down to very short pulses, you actually have absorption in some of these otherwise transparent materials.”