Baryshev A., Hovenier J.N., Adam A.J.L., Kašalynas I., Gao J.R., Klaassen T.O., et al. Phase locking and spectral linewidth of a two-mode terahertz quantum cascade laser. Physics Letters. 2006;89.
Abstract: We have studied the phase locking and spectral linewidth of an ~ 2.7 THz quantum cascade laser by mixing its two lateral lasing modes. The beat signal at about 8 GHz is compared with a microwave eference by applying conventional phase lock loop circuitry with feedback to the laser bias current. Phase locking has been demonstrated, resulting in a narrow beat linewidth of less than 10 Hz. Under requency stabilization we find that the terahertz line profile is essentially Lorentzian with a minimum linewidth of ~ 6.3 kHz. Power dependent measurements suggest that this linewidth does not approach the Schawlow-Townes limit.
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