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New mid infrared laser diode conversion efficiency over 50%

Researchers at Northwestern University have developed a small mid infrared laser diode with a conversion efficiency of more than 50%. It is reported that this achievement is a major breakthrough in the research of quantum cascade laser (QCL), which makes quantum cascade laser take an important step in practical application in many fields, including remote detection of hazardous chemicals. The relevant research results are published in the latest online edition of nature photonics.

Quantum cascade laser is a new type of diode laser with different light-emitting mechanism from the traditional semiconductor laser. According to the principle of quantum mechanics, its light-emitting wavelength can cover the mid infrared region. Different from the traditional diode laser, quantum cascade laser is a monopole device, which only needs electrons to operate. It uses the transition of electrons between one-dimensional quantized conduction bands to realize luminescence. After years of research and industrial development, the conversion efficiency of modern near-infrared (wavelength is about 1 μ m) laser diode is close to the extreme value, while that of mid infrared (wavelength is more than 3 μ m) laser diode is difficult to reach the extreme value. Previous reports have shown that the conversion efficiency of high efficiency quantum cascade laser will not be higher than 40% even if it is cooled to a low temperature state.

Researchers at the center for quantum device research (CQD) of Northwestern University have made a breakthrough in the efficiency of quantum cascade lasers by optimizing the material quality of laser equipment. They eliminate the unnecessary design elements in the operation of the laser at low temperature. When the temperature of the new laser cools to 40 Kelvin, the conversion efficiency of 4.85 μ m wavelength light reaches 53%.

Manij razeji, a professor of electrical engineering and computer science at Northwestern University's McCormick School of engineering and Applied Sciences and the leader of the research team, believes that the advent of this high-efficiency laser is a major breakthrough, which is the first time that scientists have made the laser emit more light than heat. She stressed that the laser conversion efficiency of the threshold of 50%, is a milestone achievement.

It is reported that improving the conversion efficiency is still the primary goal of laser research. The high efficiency of the new device can greatly expand the power calibration range of quantum cascade laser. Recent research shows that with the development of quantum cascade lasers, the output power of monopulse lasers has reached 120 watts, compared with 34 watts a year ago.

The research was co funded by the advanced research projects agency of the Department of Defense's efficient mid infrared laser (Emil) program and the U.S. Naval Research Institute.