Abstract
The phenomenon of self-pulsation (SP) in terahertz (THz) quantum cascade lasers (QCLs) due to optical feedback was reported recently. In this Letter, we propose a THz imaging modality using the SP phenomenon in a THz QCL. We explore the theoretical oscillation properties of the SP scheme and demonstrate its suitability to perform imaging experimentally. The SP imaging scheme operates in self-detection mode, eliminating the need for an external detector. Moreover, the scheme requires only a fixed current, meaning that one can avoid many of the pitfalls associated with high temperature operation of THz QCLs, including frequency chirp and mode hops caused by sweeping the laser current. This also means that one is free to locate the operating point at the maximum power, to produce the desired beam profile or for highest spectral purity, depending on the application. The SP imaging modality proposed in this work can be translated directly to high operating temperature THz QCLs.
Highlights
High temperature operation of THz quantum cascade lasers (QCLs) in pulsed mode at ∼250 K has been demonstrated recently by Khalatpour et al.,6 which scitation.org/journal/app is contrary to the long-held belief that THz QCLs are associated with cryogenic cooling and efficient operation at ultra-low temperatures
In this SP scheme, the THz QCL is driven by a square current pulse—a fixed current—that is effective in producing THz images at high frame-rate and can be translated directly to forthcoming room temperature devices
A number of issues with high temperature operation, including that the lasers’ dynamic working range reduces with increasing operation temperature and the light–current curves peak sharply at a single current at higher temperatures, have been pointed out in Refs. 6 and 21; most of them are common to all QCLs, and none of them would prevent the successful usage of our sensing and imaging scheme
Summary
Emission frequency sweeping through driving current modulation is widely used in THz QCL based SM imaging systems with a static target.10,16,17 This imposes a demanding requirement for the current range at which the laser operates, i.e., the lasers’ dynamic working range, especially for high temperature operation of THz QCLs. High temperature operation of THz QCLs in pulsed mode at ∼250 K has been demonstrated recently by Khalatpour et al.,6 which scitation.org/journal/app is contrary to the long-held belief that THz QCLs are associated with cryogenic cooling and efficient operation at ultra-low temperatures.
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