One intriguing idea to control the light emission of a QCL is to use the light emitted by the laser itself. By reflecting it back to the lasing cavity, interferometric effects can be achieved; this peculiar technique takes the name of external optical feedback or self-mixing.
The strong diverging nature of light emitted by THz waveguides makes it difficult to implement such a scheme for QCLs using standard, macroscopic technology. Recently, micro- and nano-mirrors have been realized on a suspended silicon nitride membrane. By carefully placing the membrane in front of the QCL facet, we aim at realizing static and dynamic control of the light within the cavity. By increasing the lasing power we could change the membrane resting position due to radiation pressure and therefore changing the back-reflected light interference. That would make a laser which emitting wavelength changes with emitted power. On the other hand, by dynamically controlling the emitted light to make it resonant with the membrane normal modes we could achieve a frequency-oscillating laser, with frequency sweeps repetition rates of hundreds of kHz, making it a fascinating candidate for broadband THz source.
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