Room temperature high-power terahertz semiconductor laser with high-quality beam shape and stable spectral emission

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This project seeks to develop compact and high power THz sources in order to close an important gap in technology between microwave and optical devices. This is a transition area between electronics and optics as well as a transition area between classical mechanics and quantum physics. The specific location of THz waves in the electromagnetic spectrum also gives them a plethora of unique properties. For an example, THz waves can pass through a variety of substances, including synthetics, textiles, paper, and cardboard. Also, many biomolecules, proteins, explosives or narcotics feature characteristic absorption signatures at the frequencies between 1 and 5 THz. Therefore, two major applications of THz radiation are imaging, sensing and spectroscopy. Besides, unlike X-rays, THz waves do not have any ionizing effects and are generally considered biologically innocuous. This makes THz waves much safer and healthier than X-rays when used for security checks and medical diagnosis. In addition, as the THz frequency is orders of magnitude higher than tht used for traditional wireless internet, there is the potential to apply THz technology for the next-generation of high-speed wireless communications. Unfortunately, current commercial sources of THz radiation are either extremely large or require cryogenic cooling, neither of which are desirable traits for widespread use. By integrating quantum device engineering, nonlinear optics, optical phased arrays, and photonic integrated circuit technology, it may now be possible to realize a compact, mass-producible, and room temperature THz source with high output power in continuous operation. This source will represent an enabling technology for all of the applications mentioned above.The proposed THz frequency source is based on difference frequency generation (DFG) in a dual-wavelength quantum cascade laser (QCL) that has been configured as an optical phased array (OPA) for coherent, high power operation. The utility of the OPA is to both manage waste heat and provide near diffraction limited beam quality for THz emission. With proper heat management and packaging, this will be the first room chip-based semiconductor laser with 1 mW CW THz output power at room temperature. This type of THz source inherits all of the advantages of the mid-infrared QCLs, such as room temperature operation, electrical pumping, compact size, stable emission, and the potential for mass production. This multidisciplinary project is a combination of both theory and experiment covering diverse fields, including semiconductor physics, material science, quantum mechanics, optoelectronics, nonlinear optics, thermal management, and micro/nanotechnology. In additional to the practical use of the technology that will be developed, project details also make an excellent case study for integrated device development, which will be explored as part of the Solid State Engineering curriculum at Northwestern University.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.