“You can do a lot of cool shit with lasers,” said Evan Peairs ’16, a physics senior who is using a laser in his thesis. “Lots of science.”
In addition to being prevalent in Science Fiction, lasers have an astounding variety of real world practical and scientific applications. From laser pointers to CD readers, cataract surgery and measuring the distance between atoms in molecules, laser technology is used in all kinds of fields, including Reed’s physics, art, and chemistry departments. Physical chemistry professor Dan Gerrity said, “You can burn things, cut things, blow air up into plasma; all sorts of stuff. In physics they’re using lasers to cool molecules down and analyze their behavior at very low temperatures. There’s such a vast array of applications.”
But how does a laser work, anyway? ‘Laser’ is an acronym for light amplification by stimulated emission of radiation. In other words, lasers are devices that take the energy stored in molecules that are excited by the laser and release it as a particular wavelength of light. The laser amplifies this light into a powerful, concentrated beam. The properties and color of the beam depend on the wavelength of light released by the molecules.
Gerrity’s enthusiasm for lasers and their various uses is contagious. Grinning in his office, he waves toward the laser lab next door, explaining how physical chemists use lasers. In Gerrity’s physical chemistry class, students use lasers to analyze chemical structures and measure incredibly tiny bond distances between atoms in different molecules. “It can get very technical — it’s even hard to explain to other chemists,” Gerrity said. “We can vaporize things, separate specific light and wavelengths to figure out which atoms are inside. We can measure the plasma emissions from what we’ve zapped, using lasers as analytical tools.”
Lasers with extremely short pulses of light allow chemists to capture freeze-frames of molecules, not unlike taking pictures with a strobe light. Chemists use these freeze frames to investigate transition states, black boxes in chemical reactions that happen too quickly to learn about using other methods.
Inside a laser, mirrors are placed on either side of a gas chamber containing molecules whose electronic and vibrational properties store energy. The mirrors allow the released photons to bounce back and forth, triggering the release of even more light from these molecules that travels on the same wavelength. One of the mirrors both reflects light and allows some to shine through, creating the laser beam.
In the past several decades, lasers have cropped up in almost every area of science and technology. Applications include clever new inventions like laser tweezers, tiny beams used to pick up and hold delicate specimens such as embryos and aerosol particles without disturbing their structure. A different kind of laser is being used to trap and cool molecules close to zero Kelvin, helping scientists working on confirming theories about how atoms behave when they’re extremely cold.
When asked if there were any misconceptions about lasers that he wanted to clear up, Gerrity paused and shook his head. “Probably most of what people think about lasers in pop culture is true. They can blind you if they’re strong enough, some can start fires. But there’s a lot more a diversity than people think.”
Peairs is working on a thesis using lasers to investigate acoustics. “My thesis is about taking pictures of instruments vibrating, and hopefully designing my own instruments too,” he said. Using the physics department laser and a special imaging program, Peairs has been analyzing the vibrations of instruments such as gongs and singing bowls by taking high-speed pictures that measure the changes in the instruments’ shapes as they make sound.
Peairs isn’t the only student using lasers for thesis work; chemistry senior Joohee Bang ’16, one of Gerrity’s advisees, is using lasers to analyze chemical structures. Lore about past laser-related theses abounds. Peairs commented, “Last year Dan Herman ’15 used a laser to do slow light. He built a beam through this wall into the lab next door through a ruby crystal. It slows the light down to about running speed. Trippy stuff.”
Like Gerrity, Peairs was very enthused by the many possibilities offered by laser technology. “You can make boson condensate, something colder than a solid, out of beryllium. You phase-shift a laser so the electrons headed toward it will red shift, compress and trap the beryllium. I think that was someone’s thesis. It basically makes an entirely new state of matter where the atoms pass through each other.”
In addition to scientific research, lasers are also useful for applied technology and manufacturing purposes. Jay Ewing ’97, supervisor of the physics department’s machine shop, trains students in how to use Reed’s laser cutter, located in the physics sub-basement.
“Our shop laser is a continuous cutting laser, for industrial engraving. It’s for making things, not so much learning about them,” Ewing explained. He studied physics at Reed, graduating in 1997, and has been working with the laser cutter for the past three years. The shop laser is free, open to the Reed community, and requires minimal training. Ewing believes the resource is underutilized.
“People are missing out by not using the shop laser,” he said. “You can make all kinds of things, and the materials here are free. You can engrave leather, wood, plastic… The only limits are two dimensions and creativity.” The shop laser is funded by the Dean of the Faculty’s Office, and is used by the art department, junior physics lab, and personal use among students and staff.
“There’s a tension at Reed between making things and learning things, “ said Ewing. “It’s a tricky balance.”
Evan Peairs also emphasized laser technology’s applications outside of scientific research.
“People can use lasers to do a lot of fun projects for themselves. You can take the lasers out of Blu-Ray players, those are powerful enough to pop balloons. Or even make your own laser-tag.” Peairs pulled out a piece of scrap paper and started drawing a diagram. “I’ve been thinking about taking a tall bike and mounting a laser onto the handlebars with sensors and a pin to make you fall off if you get hit.” He looked up from his drawing and grinned. “Yeah. Lasers are great.”