Abstract
The dynamical tuning due to rear facet illumination of single-mode, terahertz (THz) quantum-cascade lasers (QCLs) which employ distributed feedback gratings are compared to the tuning of single-mode QCLs based on two-section cavities. The THz QCLs under investigation emit in the range of 3 to 4.7 THz. The tuning is achieved by illuminating the rear facet of the QCL with a fiber-coupled light source emitting at 777 nm. Tuning ranges of 5.0 and 11.9 GHz under continuous-wave and pulsed operation, respectively, are demonstrated for a single-mode, two-section cavity QCL emitting at about 3.1 THz, which exhibits a side-mode suppression ratio better than −25 dB.
Highlights
Frequency tuning is an important prerequisite for state-of-the-art spectroscopy
A fast and continuous tuning of multi-mode terahertz (THz) quantum-cascade lasers (QCLs), independent of a specific active region design, has been demonstrated by illuminating their rear facets with a nearinfrared diode laser.[14]. These THz quantumcascade lasers (QCLs) are based on single-plasmon waveguides, and the frequency tuning was attributed to a change of the optical length of the Fabry-Perot cavity.[14]
Based on the illumination arrangement presented in Ref. 14, we have improved the illumination of the rear facet of the THz QCL using a diode laser (DL) by coupling the light through an optical fiber instead of mounting the DL on the THz QCL submount
Summary
Frequency tuning is an important prerequisite for state-of-the-art spectroscopy. It allows for the adjustment of the emission frequency over a certain range, e.g., for modulation spectroscopy techniques.[1,2,3] In addition to intrinsic frequency tuning mechanisms for terahertz (THz) quantumcascade lasers (QCLs) via current and temperature change, additional concepts have been tested during the last decade. Continuous tuning of two-section, singlemode terahertz quantum-cascade lasers by fiber-coupled, near-infrared illumination Germany (Received 17 February 2017; accepted 24 April 2017; published online 4 May 2017; publisher error corrected 9 May 2017)
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