Waveguide engineering is essential for terahertz (THz) Quantum Cascade Lasers (QCLs) to achieve high power output at approximately1 THz, due in part to confinement of the lowest order Transverse Magnetic (TM) mode. In this work, we report on waveguide engineering of approximately 1 THz QCLs to achieve lower gain threshold by increasing the confinement factor and decreasing the total waveguide loss. Gain threshold is modeled for the common types of THz QCL waveguides, i.e., Semi-Insulating Single Plasmon (SISP) and Metal-Metal (MM) waveguides at approximately 1 THz. A SISP-MM hybrid waveguide design is introduced for the first time, resulting in a lower gain threshold than SISP and MM waveguide designs alone. A SISP-MM hybrid design is presented with over 87% confinement factor and 26.55 cm-1 optical loss.
Broadband laser ranging (BLR) is essentially a spectral interferometer used to infer distance to a moving target. The light source is a mode-locked fiber laser, and chromatic dispersion maps the spectral interference pattern into the time domain, yielding chirped beat signals at the detector. A BLR record is a sequence of these chirped signals, representing consecutive target positions. To infer distance to a target, each underlying pulse envelope must be consistently registered and subtracted despite environmentally-induced variability. Then, nonlinear transformation of the phase is applied to remove the chirp, an FFT is performed to determine the peak frequency of the de-chirped signal, and a calibration factor relating de-chirped frequency to distance results in target position. Here, these analysis steps are discussed in detail.
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