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Tuning a terahertz wire laser


Tunable terahertz lasers are desirable in applications in sensing and spectroscopy because many biochemical species have strong spectral fingerprints at terahertz frequencies. Conventionally, the frequency of a laser is tuned in a similar manner to a stringed musical instrument, in which pitch is varied by changing the length of the string (the longitudinal component of the wave vector) and/or its tension (the refractive index). However, such methods are difficult to implement in terahertz semiconductor lasers because of their poor outcoupling efficiencies. Here, we demonstrate a novel tuning mechanism based on a unique ‘wire laser’ device for which the transverse dimension w is λ. Placing a movable object close to the wire laser manipulates a large fraction of the waveguided mode propagating outside the cavity, thereby tuning its resonant frequency. Continuous single-mode redshift and blueshift tuning is demonstrated for the same device by using either a dielectric or metallic movable object. In combination, this enables a frequency tuning of 137 GHz (3.6%) from a single laser device at 3.8 THz.

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Figure 1: Illustration of different tuning mechanisms.
Figure 2: The concept of tuning a wire laser.
Figure 3: Experimental setup and simulation results.
Figure 4: Tuning results from device T114.
Figure 5: Continuous tuning spectra.

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This work was supported by the Air Force Office of Scientific Research, National Aeronautics and Space Administration, and National Science Foundation. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under contract no. DE-AC04-94AL85000.

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Correspondence to Qing Hu.

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Qin, Q., Williams, B., Kumar, S. et al. Tuning a terahertz wire laser. Nature Photon 3, 732–737 (2009).

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