Tunable quantum-cascade VECSEL operating at 1.9 THz

Wu, Yu Sheng; Yue, Shuai; Addamane, Sadhvikas; Reno, John L.; Williams, Benjamin S.

doi:10.1364/oe.438636

Cited by 14 publications

(7 citation statements)

References 30 publications

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“…This is uniquely important for a QC-VECSEL, in which the wings of the cavity mode are expected to interact with the unbiased metasurface; this will introduce extra cavity loss as well as cause the cavity mode to "gain-guide" and try to confine itself to the biased area. 23 This is a phenomenon which is not typically observed with a ridge waveguide THz QC-laser. Future metasurface designs can potentially accommodate this both by optimizing the metasurface antenna design in the unbiased area to reduce this loss, as well as by redesigning active regions to ensure that lossy ISB transitions don't couple with the metasurface.…”

Section: Please Cite This Article Asmentioning

confidence: 92%

THz time-domain characterization of amplifying quantum-cascade metasurface

Yue

Kim

Shahili

et al. 2021

Applied Physics Letters

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An amplifying quantum-cascade (QC) metasurface, the key component of the QC vertical-external-cavity surfaceemitting-laser (VECSEL), is studied as a function of injected current density using reflection-mode terahertz time domain spectroscopy. Nearly perfect absorption is measured at zero bias, which is associated with the transition from the weak to strong coupling condition between the metasurface resonance and an intersubband transition within the QC material. An increase in reflectance is observed as the device is biased, both due to reduction of intersubband loss and the presence of intersubband gain. Significant phase modulation associated with the metasurface resonance is observed via electrical control, which may be useful for electrical tuning of QC-VECSEL. These results provide insight into the interaction between the intersubband QC-gain material and the metasurface, and modify the design rules for QC-VECSELs for both biased and unbiased regions.

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Section: Please Cite This Article Asmentioning

confidence: 92%

THz time-domain characterization of amplifying quantum-cascade metasurface

Yue

Kim

Shahili

et al. 2021

Applied Physics Letters

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“…This quadratic dependence of ξ 0 with wavelength helps to compensate for the smaller QC-gain available at much lower frequencies (<2 THz) [32], [33], [34]. On the other hand, at higher frequencies, ξ 0 can drop low enough to prevent lasing.…”

Section: A Wavelength Scaling the Metasurfacementioning

confidence: 99%

“…As the QC-VECSEL is scaled to the extreme ends of the spectrum (<2 THz and >4.5 THz), it becomes a challenge to maintain the same level of device performance. We detail here Device A [32] and D as representative devices at these extremes, with center frequencies 1.9 THz and 4.5 THz respectively. At the low end, the QC gain material is more difficult to engineer, since the small photon energies (8 meV at 2 THz) necessitate more closely spaced subbands that make selective pumping of the upper state more difficult [33], [46].…”

Section: Experimental Survey Of Tunable Qc-vecselsmentioning

confidence: 99%

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Wavelength Scaling of Widely-Tunable Terahertz Quantum-Cascade Metasurface Lasers

Kim

Curwen

et al. 2023

IEEE J. Microw.

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Terahertz (THz) external-cavity lasers based on quantum-cascade (QC) metasurfaces are emerging as widely-tunable, single-mode sources with the potential to cover the 1-6 THz range in discrete bands with milliwatt-level output power. By operating on an ultra-short cavity with a length on the order of the wavelength, the QC vertical-external-cavity surface-emitting-laser (VECSEL) architecture enables continuous, broadband tuning while producing high quality beam patterns and scalable power output. The methods and challenges for designing the metasurface at different frequencies are discussed. As the QC-VECSEL is scaled below 2 THz, the primary challenges are reduced gain from the QC active region, increased metasurface quality factor and its effect on tunable bandwidth, and larger power consumption due to a correspondingly scaled metasurface area. At frequencies above 4.5 THz, challenges arise from a reduced metasurface quality factor and the excess absorption that occurs from proximity to the Reststrahlen band. The results of four different devices -with center frequencies 1.8 THz, 2.8 THz, 3.5 THz, and 4.5 THzare reported. Each device demonstrated at least 200 GHz of continuous single-mode tuning, with the largest being 650 GHz around 3.5 THz. The limitations of the tuning range are well modeled by a Fabry-Pérot cavity which accounts for the reflection phase of the metasurface and the effect of the metasurface quality factor on laser threshold. Lastly, the effect of different output couplers on device performance is studied, demonstrating a significant trade-off between the slope efficiency and tuning bandwidth.

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“…Recent theoretical studies pave the way toward such goals [6,7], using both intra-series [17] and inter-series [38,39] Rydberg exciton transitions, including the non-trivial role of phonons [14]. With promising new results for intra-series coupling in the microwave domain [23] and recent advances in THz sources [40,41] enabling to explore transitions in the 1 ∼ 10 meV range, experimentally probing two-photon strategies is likely to soon yield important results for solid-state Rydberg physics.…”

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confidence: 99%