We report terahertz quantum cascade lasers operating in pulsed mode at an emission frequency of 3 THz and up to a maximum temperature of 178 K. The improvement in the maximum operating temperature is achieved by using a three-quantum-well active region design with resonant-phonon depopulation and by utilizing copper, instead of gold, for the cladding material in the metal-metal waveguides.
Abstract:The terahertz (THz) frequency quantum cascade laser (QCL) is a compact source of high-power radiation with a narrow intrinsic linewidth. As such, THz QCLs are extremely promising sources for applications including high-resolution spectroscopy, heterodyne detection, and coherent imaging. We exploit the remarkable phase-stability of THz QCLs to create a coherent swept-frequency delayed self-homodyning method for both imaging and materials analysis, using laser feedback interferometry. Using our scheme we obtain amplitude-like and phase-like images with minimal signal processing. We determine the physical relationship between the operating parameters of the laser under feedback and the complex refractive index of the target and demonstrate that this coherent detection method enables extraction of complex refractive indices with high accuracy. This establishes an ultimately compact and easy-to-implement THz imaging and materials analysis system, in which the local oscillator, mixer, and detector are all combined into a single laser. References and links 1. B. Hu and M. Nuss, "Imaging with terahertz waves," Opt. Lett. 20, 1716Lett. 20, -1718Lett. 20, (1995 36, 2587-2589 (2011). 29. S. Donati, "Developing self-mixing interferometry for instrumentation and measurements," Laser Photon. Rev. 6, 393-417 (2012
Article:Dean, P, Lim, Y, Valavanis, A et al. (10 more authors) (2011) Terahertz imaging through self-mixing in a quantum cascade laser. Optics Letters, 36 (13 We demonstrate terahertz (THz) frequency imaging using a single quantum cascade laser (QCL) device for both generation and sensing of THz radiation. Detection is achieved by utilizing the effect of self-mixing in the THz QCL, and, specifically, by monitoring perturbations to the voltage across the QCL, induced by light reflected from an external object back into the laser cavity. Self-mixing imaging offers high sensitivity, a potentially fast response, and a simple, compact optical design, and we show that it can be used to obtain high-resolution reflection images of exemplar structures.
We investigate the implementation of surface emission via a second order grating in terahertz quantum cascade lasers with double-metal waveguides. Absorbing edge structures are designed to enforce anti-reflecting boundary conditions, which ensure distributed feedback in the cavity. The grating duty cycle is chosen in order to maximize slope efficiency. Fabricated devices demonstrate surface emission output powers that are comparable to those measured from edge-emitting double metal waveguide structures without gratings. The slope efficiency of surface emitting lasers is twice that of double-metal edge emitting structures. Surface emitting lasers show single mode behavior, with a beam divergence of approximately six degrees.
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