Terahertz quantum cascade VECSEL with watt-level output power

Abstract

We report a terahertz quantum-cascade vertical-external-cavity surface-emitting laser (QC-VECSEL) whose output power is scaled up to watt-level by using an amplifying metasurface designed for increased power density. The metasurface is composed of a subwavelength array of metal-metal waveguide antenna-coupled sub-cavities loaded with a terahertz quantum-cascade gain material. Unlike previously demonstrated THz QC-VECSELs, the sub-cavities operate on their third-order lateral modal resonance (TM03), instead of their first-order (TM01) resonance. This results in a metasurface with a higher spatial density of the gain material, leading to an increased output power per metasurface area. In pulsed mode operation, peak THz output powers up to 830 mW at 77 K and 1.35 W at 6 K are observed, while a single-mode spectrum and a low divergence beam pattern are maintained. In addition, piezoelectric control of the cavity length allows approximately 50 GHz of continuous, single-mode tuning without a significant effect on output power or beam quality.

Photonic Engineering Technology for the Development of Terahertz Quantum Cascade Lasers

“…The lasing emission frequency, which is the eigenfrequency of the coupled microcavity, can be mechanically tuned by changing the external cavity length. [101] The tuning range is mainly determined by the free spectral range of the master cavity and thus the tunability was further improved to 260 GHz using a shorter cavity length. [100] More recently, THz VECSEL-a laser operating completely on the external FP cavity resonant mode, demonstrated single-mode lasing and continuous wavelength tuning over 50 GHz without significant influence on the output power.…”

“…Therefore, it is attainable to manipulate the outcoupling of mode energy by monolithically integrating side-emitter structures. [84] The configuration characteristics of THz VECSELs, that is, efficient energy outcoupling of the gain cavities and scalable array size, contribute to good performance including single-mode emission, small beam divergence (≈3° × 3°), [138,139] high power (1.35 W at 6 K and 830 mW at 77 K in pulse mode), [101] and high efficiency (PSE ≈ 767 mW A −1 and WPE ≈ 2%). [55,92] By coupling one reflector along with the antenna loop to control the lasing mode propagating direction, unidirectional emission was achieved along the waveguide with an enhancement of WPE (≈1%) in the predefined direction.…”

“…It was found that the power efficiency could be further improved (WPE ≈ 0.57% and PSE ≈ 450 mW A −1 ) when antenna loop structures were laterally integrated to the third-order DFB wire lasers to enlarge the effective emitting facet area. [101,140] [136] Alternatively, phase-locking of low-Q cavities is also an effective strategy to achieve high power efficiency while maintaining directional emission.…”

“…[100] More recently, THz VECSEL-a laser operating completely on the external FP cavity resonant mode, demonstrated single-mode lasing and continuous wavelength tuning over 50 GHz without significant influence on the output power. [101] The tuning range is mainly determined by the free spectral range of the master cavity and thus the tunability was further improved to 260 GHz using a shorter cavity length. [85] In addition, frequency tuning can also be realized by modulating k ⊥ , which is even more effective for broadband tuning.…”

“…In THz VECSELs, the external FP cavity ensures the phase coherence among the QC wires (work effectively as antenna emitters). [84] The configuration characteristics of THz VECSELs, that is, efficient energy outcoupling of the gain cavities and scalable array size, contribute to good performance including single-mode emission, small beam divergence (≈3° × 3°), [138,139] high power (1.35 W at 6 K and 830 mW at 77 K in pulse mode), [101] and high efficiency (PSE ≈ 767 mW A −1 and WPE ≈ 2%). [101,140]…”