Abstract
Telecentric beam scanning using f-θ lenses offers nearly uniform spot size, linear beam displacement, and normal incidence angle over a planar surface. These unique properties allow for the minimization of imaging distortion over a wide field-of-view. In this article, we present a numerical method for designing custom f-θ lenses in the THz regime. We fabricated three lenses made from different commonly used polymer materials in the THz optics. We demonstrated their optical performance metrics compared to a conventional plano-convex lens over the broadband 0.3 THz–1 THz range. We find that the f-θ lens designed using the optical properties of high-density polyethylene achieved superior performance by maintaining a constant phase over a wide field of view of about 34°. We demonstrate this isophase property by measuring a constant time of arrival of the THz time-domain pulses over a reference mirror with a standard deviation of ∼19 fs, in excellent agreement with simulation predictions. This work will pave the way for the design and implementation of highly precise and fast telecentric imaging systems in the THz frequencies.
Highlights
F-θ lenses have found many diverse applications in highly accurate laser beam scanning over the entire electromagnetic spectrum
The final criterion for which the lenses were evaluated is the consistency of the time of arrival (TOA) as a function of the deflection angle
In comparison to the drift measurements, the TPX and high-density polyethylene (HDPE) f-θ lenses show a close to theoretically ideal isophase performance up to 10○ and 17○, respectively
Summary
F-θ lenses have found many diverse applications in highly accurate laser beam scanning over the entire electromagnetic spectrum. Using conventional spherical lenses results in significant image distortions from a planar target Alternative scanning optics, such as flat-field lenses, have been used to address this problem.. F-θ lenses are designed to provide a linear beam displacement as a function of the deflection angle (θ; see Fig. 1), resulting in a constant scan rate on a planar surface. When used in a telecentric system, f-θ lenses produce constant spot size and imaging resolution as a function of the deflection angle, eliminating distortions at the edges of the fieldof-view.. When used in a telecentric system, f-θ lenses produce constant spot size and imaging resolution as a function of the deflection angle, eliminating distortions at the edges of the fieldof-view.9 These properties ensure a broadband THz constant phase over the scanning plane, i.e., the planar focal surface is an isophase. We find that the HDPE f-θ scanning lens can achieve isophase behavior over a wide 34○ field of view, as measured by a constant sub-cycle time of arrival (TOA) ∼1/4 of the pulse duration of the femtosecond probe beam
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