Integration of ridge array and Talbot cavity is an effective method for semiconductor laser optical power amplification. However, it is difficult for such designs to work stably in the fundamental supermode, resulting in the inability to achieve phase locking among the ridge arrays. Here, we report a phase-locked scheme that significantly increases the waveguide loss of high-order supermodes by adjusting the absorption boundary width of the ridge array, making the Talbot devices work stably in the fundamental supermode. Compared with the first-generation devices, the output power of the designed device is increased from 286 mW to 359 mW, and the central brightness is increased by twice. The demonstrated phase-locked high-brightness terahertz (THz) laser sources will have great application potential in THz spectroscopy and imaging.
We have made improvements for QCL in the thermal management to produce high output power. Unlike the previous literature, we use epilayer-down mounting and buried heterostructures to achieve high output power by improving the heat dissipation and reducing the thermal resistance. At 20 K, the continuous wave threshold current density is 110 A·cm-2 and the maximum current density is 210 A·cm−2. The maximum output power is about 250 mW at single facet. The central frequency is approximately ∼4 THz, which matches the energy band design. The thermal simulation shows that, compared with the traditional device, the heat removal performance of the optimized device is significantly improved, and the core temperature is reduced by about 20 K. It improves the heat extraction through epilayer-down mounting and buried heterostructures and leads also to significant lateral heat fluxes. The ways can facilitate the heat extraction in all in-plane directions. In conclusion, this method is beneficial to the development of high continuous wave power, especially for thick active region design. The demonstration of buried heterostructure terahertz quantum cascade lasers for epilayer-down mounting can promote the development of high-power terahertz source in continuous wave.
In this letter, we introduce a very long wave infrared Quantum Cascade Detector (QCD) with a peak response wavelength of 14.5 μm based on a twin-well coupled absorption region design. Different to standard, single transition well QCDs, the twin-well design effectively enhances the absorption strength of the device and broadens the response spectrum to a certain extent. At 77 K, we observed a responsivity of 3.51 mA / W and a Johnson noise limited detectivity of 1×108 Jones. Altogether, this design resulted in detection at temperatures of up to 140 K with a calibrated black-body source by light coupling using a 45° wedge. These high performance very long wave QCDs are expected to provide pollution monitoring, deep space exploration and other applications.
Spectral beam combining (SBC) is a regular approach of utilizing semiconductor laser arrays, as it can greatly improve output power and maintain the beam quality. External cavity spectral beam combining based on the six elements quantum cascade laser (QCL) array, with a 10μm ridge width and a pitch of 60μm, was realized. The divergence of the light from output coupler is 0.6mrad and 3.8mrad, for fast axis (perpendicular to the array) and slow axis (parallel to the array), respectively. Under a condition of 10kHz repetition frequency and 1μ s pulse width, the array’s peak power is 2.9W without SBC system. The peak power of 0.9W and 1.34W is achieved when utilizing a output coupler based on Ge without anti-reflection (AR) coating or with AR coating, respectively. Corresponding the beam combining efficiency is 31.0% and 46.2%, respectively. We recorded the cross-locking phenomenon when tuning array by rotating the external cavity output coupler angle, as a relatively close element spacing results in mutual locking of adjacent elements. The system could tuning over 99cm-1 (1904cm-1--2003cm-1).
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