Frequency noise investigation of Terahertz QCLs
Authors: Bartalini S., Vitiello M. S.,Consolino L., Borri S., Eramo R., Tredicucci A., Inguscio M., De Natale P.
Autors Affiliation: Istituto Nazionale di Ottica (INO) – CNR
More Information: In this work we report on the measurement of the frequency noise power spectral density of THz QCLs operating in the 2.5-3.2 THz range, addressed to the extraction of the intrinsic linewidth of QCL emitters working in the far infrared. The frequency noise measurements have been performed by using the side of a molecular transition of CH3OH as a frequency discriminator. This is a well-established method for a low-noise conversion of the laser frequency fluctuations into detectable intensity variations. The laser frequency is locked to the half height position of the absorption line, so that the spectrum of the intensity transmitted by this discriminator reproduces the spectrum of the laser frequency fluctuations amplified by the slope of the absorption profile. The signal detection has been preliminary performed by employing far infrared pyroelectric detector and furthermore extended on a larger frequency bandwidth by using a hot electron bolometer working at low temperature. Figure 1(a) shows the absorption profile measured by driving a 2.5 THz QCL in continuous wave while the input current has been swept from 360 mA and 390 mA. In figure 1(b) the comparison between the frequency and amplitude noise measured in a 10 kHz bandwidth is reported and used to estimate the emission linewidth of the investigated THz QCLs.KeyWords: QCL; THz; Frequency noise