Terahertz (THz) frequency quantum cascade lasers emitting peak powers of >1 W from a single facet in the pulsed mode are demonstrated. The active region is based on a bound-to-continuum transition with a one-well injector, and is embedded into a surface-plasmon waveguide. The lasers emit at a frequency of ∼3.4 THz and have a maximum operating temperature of 123 K. The maximum measured emitted powers are ∼1.01 W at 10 K and ∼420 mW at 77 K, with no correction made to allow for the optical collection efficiency of the apparatus.

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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.

Multi-Watt high-power terahertz (THz) frequency quantum cascade lasers are demonstrated, based on a single, epitaxially grown, 24-μm-thick active region embedded into a surface-plasmon waveguide. The devices emit in pulsed mode at a frequency of ∼4.4 THz and have a maximum operating temperature of 132 K. The maximum measurable emitted powers from a single facet are ∼2.4 W at 10 K and ∼1.8 W at 77 K, with no correction being made for the optical collection efficiency of the apparatus, or absorption by the cryostat polyethylene window.Introduction: Terahertz (THz) frequency radiation has many potential applications, ranging from imaging, bio-and chemical-sensing, and non-destructive testing, through to security scanning, industrial process monitoring, and telecommunications [1,2]. However, one of the principal challenges is to develop compact, low-cost, efficient THz sources. In this respect, the development of the THz quantum cascade laser (QCL) provides a potential solid-state solution [3]. Nevertheless, for many remote sensing and imaging applications, for example, realtime measurement using a THz camera, high optical powers are desirable [4]. In addition, a high-power THz source is attractive for the investigation of non-linear physics at THz frequencies.In general, increased output powers can be obtained, in both conventional interband semiconductor lasers and mid-infrared QCLs, by using broader area cavities [5]. Relying on this strategy, we previously demonstrated 1.01 W peak output powers (P peak ) from a broad-area THz QCL [6]. However, scaling the device area to an even larger value leads to difficulties in managing the significant Joule heating and random filamentation [5]. As an alternative, the power can be increased by increasing the active region thickness, i.e. the number of cascade periods [7]. Indeed, THz QCLs with P peak of up to 470 mW per facet at 5 K have been demonstrated, using a direct wafer-bonding technique to stack two separate 10-μm-thick THz QCLs together, thereby increasing the active region thickness [8]. This approach, however, requires the QCL to have a symmetric active region, limiting widespread applicability of the technique. In this Letter, we demonstrate multi-Watt high-power THz QCLs with a 24-μm-thick active region, grown in a single epitaxial growth. The devices operate in pulsed mode with emission at a frequency of ∼4.4 THz and deliver P peak up to ∼2.4 W at 10 K and ∼1.8 W at 77 K.