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In this letter, quantum cascade lasers (QCLs) based on excited-states injection are presented. The operating voltage is significantly reduced compared with the conventional groundstate injection design. Devices emitting at ~5.25 μm were fabricated through standard buried-heterostructure processing. Stable single-mode emission was observed by implementing a buried first-order distributed feedback (DFB) grating. The maximum output power of the DFB QCL with 2-mm cavity length was more than 300 mW at 10 °C with a high wall-plug efficiency of 5.6% in continuous-wave mode. [ABSTRACT FROM AUTHOR]

We demonstrate a buried grating coupled substrate emitting distributed-feedback quantum cascade laser with high power room temperature continuous wave (cw) operation at 4.97 μm. A second-order semiconductor/semiconductor grating is used for in-plane feedback and vertical out-coupling. A surface emitting power of 248 mW is attained in cw operation at 20 °C. Single-mode operation is obtained with a good linear wavelength tuning with injection current. The far field shows a low divergence about 0.14° × 16°, indicating that the device operates in symmetric mode. [ABSTRACT FROM PUBLISHER]

High-power broad area substrate-emitting distributed feedback (DFB) quantum cascade laser emitting at λ ~ 4.6 μm is reported. Proper second-order DFB grating coupling, low waveguide loss mechanism, and epilayer-down mounting bring about a high vertical radiative optical power. The maximum peak power is as high as 1.82 W at 20 °C and still 1.22 W at 50 °C operated in pulsed mode with a pulsed width of 1 μs and duty cycle of 0.2%. A single-lobed radiation far-field with a divergence angle of 7.9 ° in the ridge-width direction and two-lobed radiation far-field with a divergence angle of 0.61 ° in the cavity-length direction are achieved by depositing the high-reflection coatings on both facets. Robust single-mode emission is continuously tunable by the heat sink temperature up to 115 °C. [ABSTRACT FROM PUBLISHER]