January 20, 2023
Not every institution sends laser pulses blazing down a corridor that are strong enough to burn paper and skin. But that's exactly what occurred in UMD's Energy Research Facility, a plain-looking structure in the campus' northeast corner. As long as you don't peek behind a cork board and see the metal plate concealing a hole in the wall, the utilitarian white and grey hallway appears to be any other university hall when you visit it today.
However, for a few nights in 2021, UMD Physics Professor Howard Milchberg and his team converted the hallway into a laboratory: the shiny surfaces of the doors and a water fountain were covered to avoid potentially blinding reflections; connecting hallways were blocked off with signs, caution tape, and special laser-absorbing black curtains; and laboratory apparatus and cables took up the normally open walking space.
A cracking noise alerted team members to the laser's potentially lethal route down the hallway as they went about their job. There would occasionally be stronger pops and a metallic tang in the air as the beam's path halted at a white ceramic block. Each night, a researcher worked alone on the laser modifications while seated at a computer in the neighbouring lab while using a walkie-talkie.
They attempted to temporarily turn a fibre optic cable, or more precisely, an air waveguide, that would direct light for tens of metres, out of thin air. An air waveguide prescribes a channel for light, much like a fibre optic internet connection does for efficient highways for streams of optical data.
These air waveguides might be used for a wide range of light-related tasks, including the detection of light generated by air pollution, long-range laser communication, and even laser warfare. Instead than having to unspool solid wire and worry about gravity's limitations, an air waveguide allows the cable to develop quickly and unsupported in the air.
The researchers outlined how they broke a record by directing light through 45-meter-long air waveguides and discussed the physics underlying their technique in a manuscript approved for publication in the journal Physical Review X.
To avoid bothering (or zapping) coworkers or unaware pupils during the workday, the researchers carried out their ground-breaking atmospheric alchemy at night. Before they could use the hallway for another purpose, they had to acquire approval for their safety protocols.
The project's primary author and doctoral student in electrical and computer engineering at the University of Maryland, Andrew Goffin, says it was a "very unusual experience." "When you discharge lasers within the lab, you don't have to deal with any of the labour that goes into setting up curtains for eye protection, for example. It was undoubtedly exhausting."
The goal of all the effort was to see how far they could take the technique. A comparable technique has previously been proven to be effective for measuring distances of under a metre by Milchberg's lab. But because their facility is too tiny and transferring the laser would be difficult, the researchers were unable to expand their tests beyond tens of metres. As a result, a corridor and a hole in the wall were converted into a lab.
There were significant difficulties: the enormous scale-up to 50 metres compelled us to reevaluate the basic physics of air waveguide creation, and the desire to send a high-power laser down a 50-meter-long public hallway naturally raises significant safety concerns, according to Milchberg. "Fortunately, the physicists and the Maryland environmental safety office provided us with good collaboration."
A light beam—whether from a laser or a flashlight—will continually grow as it travels in the absence of fibre optic cables or waveguides. A beam's intensity may decrease to useless levels if allowed to expand uncheckedly. It pays to guarantee effective, focused light delivery, whether you're trying to reproduce a science fiction laser blaster or detecting pollution levels in the atmosphere by using a laser to pump them full of energy and catching the emitted light.
Milchberg suggests that more light—in the form of extremely brief laser pulses—could be the answer to the problem of containing light. This project was based on earlier work from his group that showed they could use these laser pulses to carve waveguides in the air in 2014.
The short pulse method makes use of a laser's capacity to provide such a strong intensity down a filament-like channel that it generates plasma—a state of matter in which electrons have been ripped loose from their atoms. The air is heated along this energy route, which causes it to expand and form a low-density air channel in the laser's aftermath. The popping noises the researchers heard along the beam path were the tiny cousins of thunder. This process is similar to lightning and thunder in that the energy of the lightning bolt converts the air into a plasma that eruptively expands the air to produce the thunderclap.
However, the scientists didn't require these low-density filament routes by themselves to direct a laser. The researchers desired a core with a high density (the same as internet fibre optic cables). They therefore designed a system of several low-density tubes that naturally disperse and combine to form a moat around a denser core of undisturbed air.
The new experiment took advantage of a novel laser setup that automatically scales up the number of filaments depending on the laser energy; the filaments naturally distribute themselves around a ring. The 2014 experiments only used a fixed arrangement of four laser filaments.
In order to increase the power they could transmit to a target at the end of the corridor, the researchers demonstrated how the approach might expand the length of the air waveguide. By the time the laser reached its destination, the waveguide had retained around 20% of the light that would have otherwise been lost from the intended region. The distance exceeded their previous record by a factor of roughly 60. The team believes that significantly better guiding efficiencies should be easily possible with the technology in the future because their calculations indicate that they are not yet close to the theoretical limit of the technique.
Our findings suggest that the laser might have been modified for a longer waveguide if we had a longer corridor, according to Andrew Tartaro, a doctoral student in physics at the University of Maryland who worked on the experiment and is an author on the publication. But our guide is accurate for the hallway we have.
The researchers also conducted shorter eight-meter tests in the lab where they more thoroughly examined the physics at play in the procedure. They were able to send around 60% of the possibly lost light to their target for the shorter test.
They conducted tests that made advantage of the plasma formation's popping sound. It not only revealed the location of the beam but also gave the researchers information. To determine the waveguide's length and strength along its length, they employed a line of 64 microphones (more energy going into making the waveguide translates to a louder pop).
The scientists discovered that the waveguide only existed for a brief period of time before dissolving back into nothingness. But for the laser bursts the researchers were transmitting through it, that's aeons: In that period, light may travel more than 3,000 kilometres.
The team is preparing tests to further increase the length and effectiveness of its air waveguides based on what they learnt from their calculations and experiments. Additionally, they intend to channel various hues of light and test the hypothesis that a waveguide for a continuous high-power beam may be created via a quicker filament pulse repetition rate.
Milchberg claims that the achievement of the 50-meter scale for air waveguides "actually paves the way for considerably longer waveguides and numerous uses." "We have the formula to expand our guidance to one kilometre and beyond," the researcher said, "based on new lasers we will shortly get."
Under the terms of a Creative Commons licence, this article has been taken from PHYSOORG. Go here to read the original article.
.webp)
.jpeg)
If you have any doubts, please let me know