Figure 2: Electrical inter-mode beat note analysis for the 6-mm long terahertz QCL.
From: Homogeneous spectral spanning of terahertz semiconductor lasers with radio frequency modulation
(a) Electrical inter-mode beat note mapping. A 10-mA current step and 300-kHz resolution bandwidth (RBW) are used in this measurement. Each curve was recorded 20, and the results were averaged. The right y-axis shows the L-I curve for reference. (b–e) are the single-shot beat note spectra measured at 800, 900, 1000, and 1100 mA, respectively. The smallest RBW used for the linewidth measurement is 1 kHz. For clarity, the frequency of each spectrum is subtracted by the individual central frequency. (f) Beat note spectrum measured with the “Max Hold” function of the spectrum analyser at 900 mA. The time duration used for the “Max Hold” measurement is 3 minutes. For all the inter-mode beat note measurements, the QCL is running in cw mode, and the heat sink temperature is stabilized at 15 K.
