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Seminar 3/23/2011 - The Quest for a Room-temperature Terahertz Semiconductor Laser

Professor Sushil Kumar
Electrical and Computer Engineering
Lehigh University

The terahertz region of the electromagnetic spectrum (frequency ~ 0.5-10 THz, photon-energy ~ 2-40 meV, wavelength ~ 600-30 micrometers) has historically been underdeveloped due to lack of convenient and efficient sources of coherent radiation. The terahertz frequency range offers several applications. Terahertz remote-sensing in astrophysics has traditionally been utilized to understand star and galaxy formation.
More recently, several applications have been identified for terahertz spectroscopy and imaging, for example in the detection of concealed drugs and explosives in packages, or non-invasive biomedical imaging of the skin tissue or the teeth.

Out of several methods to generate terahertz radiation, "quantum-cascade" lasers (QCLs) are among the most promising. Terahertz QCLs provide significantly higher average optical power as compared to any other type of solid-state terahertz sources. However, in comparison to the mid-infrared QCLs that could operate at room-temperature with robust performance, terahertz QCLs are still required to be cryogenically cooled, which limits their practicability. Increasing the operating temperatures for such lasers therefore remains one of the primary goals in research.

In this talk we will discuss the primary challenges in obtaining laser action at terahertz frequencies as compared to the mid-infrared, and the various temperature degradation mechanisms. Several different design approaches for terahertz QCLs will be described. The designs leading to the lasers with highest operating temperatures at both low (163 K at 1.8 THz) and high (186 K at 4 THz) terahertz frequencies will be discussed.
Guiding the long-wavelength terahertz radiation in semiconductors also offers unconventional challenges. Unique methods in waveguide engineering had to be implemented to realize single-mode distributed-feedback lasers and to obtain continuous tunability of the single-mode output. Aspects related to waveguide engineering for terahertz semiconductor lasers will also be discussed.

Host: Prof. Claire F. Gmachl

Location: Bowen Hall Atrium

Date/Time: 03/23/11 at 12:00 pm - 03/23/11 at 1:00 pm

Category: PRISM/PCCM Seminar Series

Department: PRISM