Ultrafast Lasers Could Increase Accuracy of Mass Spectrometry

A workbench at Goddard is mounted with lasers and fiber connectors to test femtosecond-pulse laser technology.

Researchers at Goddard believe lasers that can pulse as quickly as one quadrillionth of a second could considerably improve the science of mass spectrometry by providing more accurate readings.

“The femtosecond laser has the advantage that you can achieve high peak power but the pulse width is so short, you don’t actually heat up your materials,” said Dr. Anthony Yu, co-investigator on this project.

Mass spectrometer technology requires a material to be disintegrated into atom-sized particles, which are then funneled between two magnets that sort the atoms by weight. Where the atoms hit on the detector can reveal their exact mass and therefore their specific element.

Yu is part of a Goddard engineering team led by Elisavet Troupaki that, collaborating with Goddard scientists led by Dr. Andrej Grubisic, is researching super-fast lasers that can precisely disassemble atoms from a solid material without heating or burning them. This will improve the accuracy of mass spectrometers.

An optimal power must be reached in order to properly break down materials, Yu said. To increase power in a laser you can increase the energy of the laser or shorten the laser pulse. Peak power and pulse width – or length of time – are inversely proportional, meaning as one of the two variables decrease, the other increases.

Studies are also being completed using nanosecond lasers, which are powerful, but do not allow for accurate spectrometry uses.

“When it goes into the nanosecond regime, although it sounds very short already, it is heating the material,” said Goddard engineer Steven Li. Heating can alter the material’s properties and reduce the precision of a cut, two things you do not want for mass spectrometry.

Not only does the femtosecond laser’s extremely short duration ensure that the materials won’t be heated, but the shorter pulse width also allows for a cleaner, more precise cut.

A femtosecond laser has a pulse duration of 10 -15 , or one quadrillionth of a second, compared to the 10 -9 , or one billionth of a second, for a nanosecond laser.

“This high-powered, extremely fast laser requires specific materials in the design and construction, and optical fiber is currently the best for this application,” Li said. Optical fiber has a core width of a few microns, or about the size of the diameter of a strand of hair. A few meters of coiled fiber is compact but reliable.

“Because everything is confined to fiber, there’s a low risk of anything being misaligned,” Yu said, “If you build a laser using larger optical components like mirrors and refractors, you have to align everything correctly. For fiber lasers, everything is spliced together, and that will make things a lot easier for space application.”

The Goddard team under Troupaki, previously led by Molly Fahey, received Internal Research and Development (IRAD) and Center Innovation Funding (CIF) grants for several years to explore the uses of ultrafast lasers.

The research team is passionate about their work as well as the possible avenues it can take them in the future.

“Existing instruments and concepts rely on nanosecond laser technology to enable laser desorption mass spectrometry LDMS,” said Project Scientist Dr. Grubisic. “The shorter pulse duration laser technology pursued here could dramatically enhance the analytical power of the LDMS due to its potential to minimize molecular fragmentation and sample fractionation. This improves sensitivity for fragile molecules, including potential molecular biomarkers that will continue to be of interest in astrobiology-focused planetary missions. It also opens the door to LDMS-based instruments for establishing the ages of rock formations – a key missing, planetary science technology identified in the last decadal survey”.

Ultrafast lasers also have applications in space travel and communication.

“We are looking at femtosecond lasers in particular” Yu said, “because the femtosecond laser can also be used for precision ranging. You have a series of pulses separated at a fixed period, and by detecting that series of pulses, you can actually have precision timing provided to you. For example, from Earth you can send that signal to a distant satellite, and when they receive it, they can use it for clock synchronization.”

CONTACT Elisavet.Troupaki-1@nasa.gov or 301-614-6119