Output Power Of Quantum Cascade Lasers Research Articles

A QCL-based metrological-grade source at 6 μm

In view of high-precision molecular spectroscopy in the infrared, we realized a narrow-linewidth laser source at 5.8 $$\upmu$$m traceable to the second in the International System of Units by mixing two near-infrared lasers in an orientation-patterned GaP crystal. The generated radiation is traceable to a Cs fountain through an optical fiber-delivered carrier; its estimated linewidth is 2.3 kHz at 1 s integration time. A quantum cascade laser emitting at the same wavelength is used to boost the power of the mid-IR radiation up to few tens of mW. Thanks to a phase-locking loop, about 70% of the quantum cascade laser output power is within the linewidth of the difference-frequency radiation. This apparatus is used for absolute molecular spectroscopy in a region, above 5 $$\upmu$$m, where high-precision traceability and reliable operation are still challenging. In this paper, we provide the basic information to implement a powerful and metrological grade source in the mid-infrared for precision measurements.

Electrically-driven pure amplitude and frequency modulation in a quantum cascade laser

We present pure amplitude modulation (AM) and frequency modulation (FM) achieved electrically in a quantum cascade laser (QCL) equipped with an integrated resistive heater (IH). The QCL output power scales linearly with the current applied to the active region (AR), but decreases with the IH current, while the emission frequency decreases with both currents. Hence, a simultaneous modulation applied to the current of the AR and IH sections with a proper relative amplitude and phase can suppress the AM, resulting in a pure FM, or vice-versa. The adequate modulation parameters depend on the applied modulation frequency. Therefore, they were first determined from the individual measurements of the AM and FM transfer functions obtained for a modulation applied to the current of the AR or IH section, respectively. By optimizing the parameters of the two modulations, we demonstrate a reduction of the spurious AM or FM by almost two orders of magnitude at characteristic frequencies of 1 and 10 kHz compared to the use of the AR current only.

Scaling the output power of quantum-cascade lasers with a number of cascades

A series of quantum-cascade lasers emitting at λ≈11μm with different numbers of cascades in the active region – between 25 and 200 –grown by gas-source molecular beam epitaxy, is compared in terms of their room-temperature performance in pulsed mode as a function of the number of cascades. Within the given range of cascade number we observe a superlinear increase in both slope efficiency and differential quantum efficiency as functions of cascade number. The differential quantum efficiency scaled per number of cascades, however, shows a sublinear increase. A differential quantum efficiency of 17% per cascade and pulse power exceeding 7W per facet, both at room temperature, was demonstrated for quantum-cascade lasers with 200 cascades. All lasers with stripe width below 30μm are operated in the fundamental TEM00 spatial mode. This combination of high pulse power and TEM00 mode operation for room-temperature mid-infrared laser emission can be attractive for a number of applications.