Abstract
We present an optically pumped terahertz gas laser, which is based on a mid-infrared quantum-cascade laser as a pump source, a transversely pumped standing wave resonator, and 15NH3 as a gain medium. We observe several laser lines around 4.5 THz, corresponding to rotational transitions in the ν2 band of ammonia. So far, these are the highest frequencies obtained from a QCL-pumped THz gas laser. The involved molecular transitions are unambiguously identified by high-resolution spectroscopy.
Highlights
Being highly brilliant continuous wave emitters, optically pumped terahertz (THz) gas lasers have been longstanding sources for a variety of applications from THz imaging, spectroscopy to detector characterization and calibration [1,2,3]
We present an optically pumped terahertz gas laser, which is based on a mid-infrared quantum-cascade laser as a pump source, a transversely pumped standing wave resonator, and 15NH3 as a gain medium
THz gas lasers have been even used in space and airborne applications such as the 2.5-THz local oscillator for the microwave limb sounder on NASA’s Aura satellite [4]
Summary
Being highly brilliant continuous wave emitters, optically pumped terahertz (THz) gas lasers have been longstanding sources for a variety of applications from THz imaging, spectroscopy to detector characterization and calibration [1,2,3]. In contrast to pumping with a CO2 laser, the frequency of mid-infrared QCLs can be continuously tuned over a range of typically several hundred GHz. Thanks to the maturity of mid-infrared QCL technology, continuous-wave devices with customer-specified emission range are nowadays commercially available. Thanks to the maturity of mid-infrared QCL technology, continuous-wave devices with customer-specified emission range are nowadays commercially available Their output power is at the best a few hundred mW and several orders of magnitude smaller than that of CO2 lasers, this drawback is mitigated by the possibility of resonant pumping and the strong dipole transitions of molecules such as ammonia. We report QCL-pumped lasing for rotational transitions of 15NH3 at much higher frequencies around 4.5 THz, based on an alternative resonator approach and by exploiting the molecular symmetry to avoid low-frequency laser transitions. A potentially important application of a QCL-pumped molecular laser is heterodyne detection of atomic oxygen, which has its ground state transition at 4.7 THz [16,17]
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