A research team led by 2014 Nobel laureate Hiroshi Amano at the Institute of Materials and Systems for Sustainability (IMaSS) of Nagoya University in central Japan, in collaboration with Asahi Kasei Corporation, has successfully conducted the world’s first welding continuous wave at room temperature of a deep-ultraviolet laser diode (wavelengths down to the UV-C region).
These results, published in Letters of applied physicsthey represent a step towards the widespread use of a technology with the potential for a wide range of applications, including sterilization and medicine.
Since their introduction in the 1960s, and after decades of research and development, the successful commercialization of diode lasers (LDs) has finally been achieved for a range of applications with wavelengths ranging from infrared to blue- violet. Examples of this technology include optical communication devices with infrared LDs and Blu-ray Discs that use blue-violet LDs.
However, despite the efforts of research groups around the world, no one has succeeded in developing LDs in the deep ultraviolet. A major breakthrough occurred only after 2007 with the emergence of the technology to fabricate aluminum nitride (AlN) substrates, an ideal material for growing aluminum gallium nitride (AlGaN) films for light-emitting devices UV.
Starting in 2017, Professor Amano’s research team, in collaboration with Asahi Kasei, the company that supplied 2-inch AlN substrates, started developing a deep ultraviolet LD. Initially, injecting sufficient current into the device was too difficult, preventing further development of UV-C laser diodes.
But in 2019, the research team successfully solved this problem using a polarization-induced doping technique. For the first time, they produced a short-wavelength ultraviolet-visible (UV-C) LD that works with short current pulses. However, the input power required for these current pulses was 5.2 W. This was too high for CW soldering because the power would cause the diode to heat up rapidly and cut out the laser.
But now, researchers at Nagoya University and Asahi Kasei have reshaped the structure of the device itself, reducing the drive power needed for the laser to operate to just 1.1W at room temperature. Earlier devices were found to require high levels of operating power due to the impossibility of effective current paths due to crystal defects occurring on the laser strip. But in this study, the researchers found that strong crystalline tension creates these defects.
By intelligently tailoring the sidewalls of the laser stripe, they suppressed the defects, resulting in efficient current flow in the active region of the laser diode and reducing operating power.
Nagoya University’s industrial-academic cooperation platform, called the Center for Integrated Research of Future Electronics, Transformative Electronics Facilities (C-TEF), has made possible the development of the new UV laser technology. Under the C-TEFs, researchers from partners like Asahi Kasei share access to state-of-the-art facilities on the Nagoya University campus, providing them with the people and tools they need to build high-quality, reproducible devices.
Zhang Ziyi, a representative of the research team, was in his second year at Asahi Kasei when he was involved in founding the project. “I wanted to do something new,” he said in an interview. “Everyone thought then that the deep ultraviolet laser diode was impossible, but Professor Amano told me, ‘We’ve come to the blue laser, now it’s time for the ultraviolet.'”
This research is a milestone in the practical application and development of semiconductor lasers in all wavelength ranges. In the future, UV-C LDs could be applied to health care, virus detection, particulate matter measurement, gas analysis, and high-definition laser processing.
“Its application to sterilization technology could be game-changing,” said Zhang. “Unlike current LED sterilization methods, which are inefficient in terms of time, lasers can disinfect large areas in a short time and over long distances.” This technology could particularly benefit surgeons and nurses who need sterilized operating rooms and tap water.
Positive results were reported in two articles in Letters of applied physics.
Hiroshi Amano et al, Local stress control to suppress dislocation generation for pseudomorphically grown UV-C AlGaN laser diodes, Letters of applied physics (2022). DOI: 10.1063/5.0124512
Hiroshi Amano et al, Temperature-dependent key characteristics of AlGaN-based UV-C laser diode and continuous wave laser demonstration at room temperature, Letters of applied physics (2022). DOI: 10.1063/5.0124480
Provided by Nagoya University
Citation: Scientists Demonstrate World’s First Continuous Wave Laser Diode Deep Ultraviolet Room Temperature (2022 Nov 24) Retrieved Nov 24, 2022 from https://phys.org/news/2022-11-scientists-world -continuous-wave -lasing-deep-ultraviolet.html
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