Using common electronics, NIST scientists have developed a laser that pulses 100 times more often than conventional ultrafast lasers. This newly developed laser is expected to enlarge the benefits of ultrafast science to new applications such as imaging of biological materials in real time.
Until now researchers have been unable to electronically switch light to make ultrafast pulses and eliminate electronic noise, or interference. But, now, scientists have developed a filtering strategy to lessen the heat-induced interference that generally would destroy the consistency of electronically integrated light.
Project leader Scott Papp said, “We tamed the light with an aluminum can, referring to the “cavity” in which the electronic signals are stabilized and filtered. As the signals bounce back and forth inside something like a soda can, fixed waves emerge at the strongest frequencies and block or filter out other frequencies.”
The conventional source of ultrafast light is an optical frequency comb, a precise “ruler” for light. Combs are usually made with sophisticated “mode-locked” lasers, which form pulses from many different colors of light waves that overlap, creating links between optical and microwave frequencies. Interoperation of optical and microwave signals powers the latest advances in communications, timekeeping and quantum sensing systems.
In contrast, NIST’s new electro-optic laser imposes microwave electronic vibrations on a continuous-wave laser operating at optical frequencies, effectively carving pulses into the light.
Lead author David Carlson said, “In any ultrafast laser, each pulse lasts for, say, 20 femtoseconds. In mode-locked lasers, the pulses come out every 10 nanoseconds. In our electro-optic laser, the pulses come out every 100 picoseconds. So that’s the speedup here—ultrafast pulses that arrive 100 times faster or more.”
Papp said, “Chemical and biological imaging is a good example of the applications for this type of laser. Probing biological samples with ultrafast pulses provides both imaging and chemical makeup information. Using our technology, this kind of imaging could happen dramatically faster. So, hyperspectral imaging that currently takes a minute could happen in real time.”
In order to develop this laser, scientists used an infrared continuous-wave laser to create pulses with an oscillator stabilized by the cavity. This provides the equivalent of a memory to ensure all the pulses are identical. The laser produces optical pulses at a microwave rate, and each pulse is directed through a microchip waveguide structure to generate many more colors in the frequency comb.
Papp said, “The electro-optic laser offers unprecedented speed combined with accuracy and stability that are comparable to that of a mode-locked laser. The laser was constructed using commercial telecommunications and microwave components, making the system very reliable. The combination of reliability and accuracy makes electro-optic combs attractive for long-term measurements of optical clock networks or communications or sensor systems in which data needs to be acquired faster than is currently possible.”
The study is published in the journal Science.