Abstract
We report a terahertz quantum-cascade vertical-external-cavity surface-emitting laser (QC-VECSEL) emitting around 1.9 THz with up to 10% continuous fractional frequency tuning of a single laser mode. The device shows lasing operation in pulsed mode up to 102 K in a high-quality beam, with the maximum output power of 37 mW and slope efficiency of 295 mW/A at 77 K. Challenges for up-scaling the operating wavelength in QC metasurface VECSELs are identified.
Highlights
Terahertz (THz) quantum-cascade (QC) lasers have so far been demonstrated as sources of radiation at frequencies between 1.2 THz and 5.6 THz [1,2,3], among which, high performance QC-lasers at frequencies below 2 THz are considered of particular interest
The VECSEL cavity was constructed by pairing the QC-metasurface with planar inductivemesh output couplers (OCs) of the type that has been used in previous QC-VECSEL
By stepping the piezoelectric stage, continuous tuning of single lasing mode was observed between 1.81 THz and 1.95 THz (Fig. 3(b)). This 140 GHz tuning range is limited by the free-spectral range (FSR) of the external cavity and an estimated cavity length around 1.1 mm is indicated from the FSR
Summary
Terahertz (THz) quantum-cascade (QC) lasers have so far been demonstrated as sources of radiation at frequencies between 1.2 THz and 5.6 THz [1,2,3], among which, high performance QC-lasers at frequencies below 2 THz are considered of particular interest. The gain provided by the QC-active material suffers, as obtaining a population inversion between closely spaced subbands (hν ≈ 8 meV at 2 THz) reduces the selectivity of injection and removal of electrons This tends to reduce the dynamic range between the threshold current Ith and the maximum achievable current Imax, which in turn reduces the operating temperature and maximum output power [2,12,13,14,15,16,17]. QC-VECSELs have been demonstrated in the frequency range of 2.5-4.6 THz, with the best performance (i.e. highest powers and efficiencies) in the 3-4 THz range [21,22,23] In this demonstration, we have re-scaled the metasurface design to operate at a lower frequency, while preserving 10% continuous fractional frequency tuning of a single lasing mode by using intracryostat piezoelectric control of the cavity length
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