Optical path length measurement of spherical dielectric shells with axicon-generated Bessel beams; applications to corneal sensing

Baggio, Mariangela; Tamminen, Aleksi; Zarrinkhat, Faezeh; Nefedova, Irina; Aspelin, Arthur; Ala‐Laurinaho, Juha; Wallace, Vincent P.; Brown, E. R.; Taylor, Zachary D.

doi:10.1109/irmmw-thz50926.2021.9567440

Cited by 2 publications

(2 citation statements)

References 4 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Previously, we extracted the water content of corneal phantoms [12] and quartz permittivity [13], by using the GBT. In [14] quartz permittivity was extracted with an axicon hyperbolic lens, but we did not correct the phase velocity as we do in this paper.…”

Section: Introductionmentioning

confidence: 99%

Submillimeter-Wave Cornea Phantom Sensing Over an Extended Depth of Field With an Axicon-Generated Bessel Beam

Baggio

Tamminen

Lamberg

et al. 2023

IEEE Trans. THz Sci. Technol.

View full text Add to dashboard Cite

The feasibility of a 220 -330 GHz zero order axicon generated Bessel beam for corneal water content was explored. Simulation and experimental data from the 25-degree cone angle hyperbolic-axicon lens illuminating metallic spherical targets demonstrate a monotonically decreasing, band integrated, backscatter intensity for increasing radius of curvature from 7 -11 mm, when lens reflector and optical axis are aligned. Further, for radii >= 9.5 mm, maximum signal was obtained with a 1 mm transverse displacement between lens and reflector optical axes arising from spatial correlation between main lobe and out of phase side lobes. Thickness and permittivity parameter estimation experiments were performed on an 8 mm radius of curvature, 1 mm thick fused quartz dome over a 10 mm axial span. Extracted thickness and permittivity varied by less than ~ 25 μm and 0.2 respectively after correction for superluminal velocity. Estimated water permittivity and thickness of water backed gelatin phantoms showed significantly more variation due to a time varying radius of curvature. To the best of our knowledge, this is the first work that describes axicon generated Bessel beam measurements of layered spheres with varying radii of curvature, in the submillimeter range.

show abstract

Section: Introductionmentioning

confidence: 99%

Submillimeter-Wave Cornea Phantom Sensing Over an Extended Depth of Field With an Axicon-Generated Bessel Beam

Baggio

Tamminen

Lamberg

et al. 2023

IEEE Trans. THz Sci. Technol.

View full text Add to dashboard Cite

show abstract

“…Most commercial THz lenses (i.e., plano-convex lenses, such as TPX50, Menlo Systems, Newton, NJ) suffer from spherical aberrations at the focal plane and yield a small FOV because they are not designed for imaging applications via beam-steering. Axicon lenses have been proposed for extracting corneal parameters in the THz regime by extending the depth of focus using a Bessel beam, however the beam's first-order sidelobes are sensitive to variations in the target's radius of curvature, making hydration mapping challenging [39][40][41]. In this paper, we design a hyperbolic-elliptical aspheric lens to image the cornea with normal incidence angle over the entire span of the FOV.…”

Section: Introductionmentioning

confidence: 99%

Design and characterization of a hyperbolic-elliptical lens pair in a rapid beam steering system for THz spectral imaging of the cornea

Virk¹,

Harris²,

Arbab³

2023

Preprint

View full text Add to dashboard Cite

Terahertz (THz) time-domain spectroscopy has been investigated for assessment of the hydration levels in the cornea, and changes in corneal topography and the intraocular pressure. Previous efforts at THz imaging of the cornea have employed off-axis parabolic mirrors to achieve normal incidence along the spherical surface. However, this comes at the cost of an asymmetric field-of-view (FOV) and a long scan time because it requires raster-scanning the collimated beam across the large mirror diameter. In this paper, we propose a solution by designing a pair of aspheric lenses that can provide a larger symmetric spherical FOV (9.6 mm) and reduce the scan time by two orders of magnitude using a novel beam-steering approach. Using Nelder-Mead optimization, a hyperbolic-elliptical lens was designed to achieve normal incidence and phase-front matching between the focused THz beam and the target curvature. The lenses were machined from a slab of high-density polyethylene and characterized in comparison to ray-tracing simulations by imaging several targets of similar sizes to the cornea. Our experimental results showed excellent agreement in the increased symmetric FOV and confirmed the reduction in scan time to about 3-4 seconds. In the future, this lens design process can be extended for imaging the sclera of the eye and other curved biological surfaces, such as nose and fingers.

show abstract

Optical path length measurement of spherical dielectric shells with axicon-generated Bessel beams; applications to corneal sensing

Cited by 2 publications

References 4 publications

Submillimeter-Wave Cornea Phantom Sensing Over an Extended Depth of Field With an Axicon-Generated Bessel Beam

Submillimeter-Wave Cornea Phantom Sensing Over an Extended Depth of Field With an Axicon-Generated Bessel Beam

Design and characterization of a hyperbolic-elliptical lens pair in a rapid beam steering system for THz spectral imaging of the cornea

Contact Info

Product

Resources

About