Science & Technology, Singapore (Commonwealth Union) – A team of scientists, led by Nanyang Technological University, Singapore (NTU Singapore), has devised an innovative approach to generate intense and ultra-fast lasers, holding great potential for the development of precise devices that can expedite the detection of trace amounts of pollutants and hazardous gases.
Currently, lasers utilizing invisible light within the mid-infrared range can rapidly analyze the composition of the air, identifying greenhouse gas pollutants, toxic substances, explosives, or gases associated with diseases in a person’s breath within minutes.
Scientists of the study indicate that the significance of high-powered mid-infrared lasers generated in ultra-fast pulses lies in their capacity to support highly sensitive devices capable of remotely detecting even minute quantities of substances that might otherwise escape notice or prove challenging to identify.
They further pointed out that the existing methods for producing such lasers have limitations. One approach demands pristine laboratory conditions devoid of disturbances, such as vibrations and fluctuations in temperature and humidity, which can disrupt finely calibrated equipment, rendering the lasers impractical for use outside the lab.
An alternative method can withstand environmental interferences like vibrations but falls short in producing lasers with intensities sufficient for accurately detecting minuscule amounts of substances.
The aforementioned challenges have been effectively addressed through recent research led by NTU Singapore. The scientists employed specially crafted optical fibers with hollow cores, adjusting the thickness of sub-structures in the fibers to generate highly luminous lasers in the mid-infrared range of the electromagnetic spectrum.
“Our method paves the way for developing portable, powerful and fast mid-infrared laser generators that don’t need well-controlled and vibration-free environments to work,” explained Nanyang Assistant Professor Chang Wonkeun, of the NTU, School of Electrical & Electronic Engineering, who was the lead of this latest study.
“This means we can pair them with a detector and use them in the field to help test and identify a wide variety of unknown substances on the spot and at the same time, even in trace amounts, without spending extra time sending samples to labs for testing.”
Hollow-core fibers, a key focus of the study, offer distinct advantages in the realm of mid-infrared lasers, which operate within the wavelength range of 2-20 micrometers. In comparison to lasers at other wavelengths, mid-infrared lasers exhibit enhanced capabilities for substance detection.
Molecules of various types absorb mid-infrared lasers uniquely, allowing for more precise identification of unknown substances compared to lasers at different wavelengths. Moreover, the accuracy of substance identification using mid-infrared lasers remains unaffected by the presence of water molecules, a notable advantage over other laser types.
One approach to rapidly generate high-powered mid-infrared lasers involves directing intense and ultra-fast near-infrared radiation, characterized by a shorter wavelength, through optical fibers. However, fibers with solid glass cores typically yield mid-infrared lasers with insufficient power, posing challenges for accurate detection of small substance quantities.
Achieving high-intensity mid-infrared lasers conventionally needs an interference-free environment, confining their utility to laboratory settings. Assistant Professor Chang addressed these restrictions by making use of glass fibers with hollow cores. By utilizing computer simulations, he determined the types of radiation formed when near-infrared radiation went through these hollow-core fibers. Unlike traditional optical fibers, these tube-like structures feature inner walls adorned with a ring of smaller glass tubes around the hollow center.
Via adjustments to the wall thickness of the fiber’s miniature tubes, simulations carried out by Assistant Professor Chang showed that it was possible to change a near-infrared laser into a potent, ultra-fast mid-infrared laser.
Subsequently, the research team executed experiments that involved filling the centers of the hollow-core fibers with argon gas, validating the predictions made during the simulations. The outcome was the generation of mid-infrared lasers with wavelengths ranging from 3 to 4 micrometers, achieving peak power in the megawatt range—approximately a million times more powerful than a standard light bulb.
This conversion of the laser’s characteristics occurs as the near-infrared laser interacts with the shape of the fiber, energizing the argon gas molecules and prompting the laser to shift to the mid-infrared spectrum.
