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1. Recent Advances in Room Temperature, High-Power Terahertz Quantum Cascade Laser Sources Based on Difference-Frequency Generation

   https://doi.org/10.3390/photonics3030042  

   Lu, Quanyong; Razeghi, Manijeh (September 2016, Photonics)

   We present the current status of high-performance, compact, THz sources based on intracavity nonlinear frequency generation in mid-infrared quantum cascade lasers. Significant performance improvements of our THz sources in the power and wall plug efficiency are achieved by systematic optimizing the device’s active region, waveguide, and chip bonding strategy. High THz power up to 1.9 mW and 0.014 mW for pulsed mode and continuous wave operations at room temperature are demonstrated, respectively. Even higher power and efficiency are envisioned based on enhancements in outcoupling efficiency and mid-IR performance. Our compact THz device with high power and wide tuning range is highly suitable for imaging, sensing, spectroscopy, medical diagnosis, and many other applications. 

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2. Widely tunable room temperature semiconductor terahertz source

   https://doi.org/10.1063/1.4902245  

   Lu, Q Y; Slivken, S; Bandyopadhyay, N; Bai, Y; Razeghi, M (November 2014, Applied Physics Letters)

   We present a widely tunable, monolithic terahertz source based on intracavity difference frequency generation within a mid-infrared quantum cascade laser at room temperature. A three-section ridge waveguide laser design with two sampled grating sections and a distributed-Bragg section is used to achieve the terahertz (THz) frequency tuning. Room temperature single mode THz emission with a wide tunable frequency range of 2.6–4.2 THz (∼47% of the central frequency) and THz power up to 0.1 mW is demonstrated, making such device an ideal candidate for THz spectroscopy and sensing. 

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3. Room temperature single-mode terahertz sources based on intracavity difference-frequency generation in quantum cascade lasers

   https://doi.org/10.1063/1.3645016  

   Lu, Q Y; Bandyopadhyay, N; Slivken, S; Bai, Y; Razeghi, M (September 2011, Applied Physics Letters)

   We demonstrate room temperature single-mode THz emission at 4 THz based on intracavity difference-frequency generation from mid-infrared dual-wavelength quantum cascade lasers. An integrated dual-period distributed feedback grating is defined on the cap layer to purify both mid-infrared pumping wavelengths and in turn the THz spectra. Single mode operation of the pumping wavelengths results in a single-mode THz operation with a narrow linewidth of 6.6 GHz. A maximum THz power of 8.5 μW with a power conversion efficiency of 10 μW/W2 is obtained at room temperature. 

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4. High power, room temperature, terahertz sources and frequency comb based on difference-frequency generation at CQD

   https://doi.org/10.1117/12.2635322  

   Razeghi, Manijeh (September 2022, Terahertz Emitters, Receivers, and Applications XIII)

   Razeghi, Manijeh; Baranov, Alexei N. (Ed.)

   Quantum cascade laser (QCL) is becoming the leading laser source in the mid-infrared and terahertz range due to its rapid development in power, efficiency, and spectral covering range. Owing to its unique intersubband transition and fast carrier lifetime, QCL possesses strong nonlinear susceptibilities that makes it the ideal platform for a variety of nonlinear optical generations. Among this, terahertz (THz) source based on difference-frequency generation (DFG) and frequency comb based on four wave mixing effect are the most exciting phenomena which could potentially revolutionize spectroscopy in mid-infrared (mid-IR) and THz spectral range. In this paper, we will briefly discuss the recent progress of our research. This includes high power high efficiency QCLs, high power room temperature THz sources based on DFG-QCL, room temperature THz frequency comb, and injection locking of high-power QCL frequency combs. The developed QCLs are great candidates as next generation mid-infrared source for spectroscopy and sensing. 

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5. Mid-infrared rainbow light-emitting diodes

   https://doi.org/10.1063/5.0129196  

   Muhowski, Aaron J.; Kamboj, Abhilasha; Mansfield, Noah C.; Wasserman, Daniel (December 2022, Applied Physics Letters)

   We demonstrate a room-temperature all-epitaxial guided-mode resonance light-emitting diode operating in the mid-wave infrared. The device comprises a dielectric waveguide with an AlGaAsSb p−i−n diode core, below a layer of grating-patterned GaSb and above a highly doped, and thus, low index, InAsSb layer. Light emitted from the device active region into propagating modes in the waveguide scatters into free space via the GaSb grating, giving rise to spectrally narrow features that shift with emission angle across much of the mid-wave infrared. For collection angles approaching 0°, we are able to obtain linewidths of ∼2.4 meV across the spectral/angular emission of the LED, corresponding to λ/Δλ∼570. Fine control of emission wavelength can be achieved by tuning the applied current, which causes a redshift of approximately 20 nm due to the thermo-optic effect. The presented device has the potential for use in compact, high bandwidth, and low-cost mid-wave infrared sensing applications requiring spectral discrimination. 

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