Terahertz waves have unique propagation and penetration ability, and these reasons have been widely used in nondestructive testing. Compared with other terahertz imaging approaches, terahertz digital holography can retrieve both quantitative amplitude and phase information about an object wavefront in real time. A continuous-wave terahertz reflective digital holographic method is proposed for measuring the profile of covered objects. Subpixel image registration and image fusion algorithms are presented to expand the field-of-view (FOV) of the system. The validity of the proposed method is verified by the experiment using an optical pumped far-IR gas laser and a pyroelectric array detector. The profile of a metallic bookmark covered by a polytetrafluoroethylene plate is obtained. The FOV is expanded by a factor of 1.75 compared with that of a reconstruction performed employing single hologram.
Terahertz imaging technology has been widely used in various fields. In continuous-wave terahertz imaging system, when the large size object is located at the unfocused position, Bessel beam with non-diffractive properties show its large depth of focus advantage over Gaussian beam. Bessel beam can be generated by the axicon, which has high conversion efficiency. The non-diffraction distance and the main lobe size of the Bessel beam depend on the parameters of the axicon and incident light wavelength. We analyzed that the influence on the axial two-dimensional intensity distribution of a zero-order Bessel beam by changing the axicon parameters and the incident Gaussian beam size. Experimentally, the axicon with different parameters were fabricated using different materials. Then the two-dimensional intensity distribution of the Bessel beam in the axial and transverse direction were recorded and analyzed. The experimental results is basically consistent with the theoretical ones.
Terahertz nondestructive testing is an increasingly important technology in recent years. Compared with visible and infrared bands, terahertz wave can easily penetrate common nonpolar and nonmetal materials without ironize the sample because of low energy. Digital holography can reconstruct the quantitative amplitude and phase distributions of the object wavefront. We proposed a continuous-wave terahertz reflective off-axis digital holography to measure the morphology of encapsulated object. An experimental system was built using a 2.52 THz (118.83 μm) far-infrared gas laser 295-FIR and a pyroelectric array detector. The morphology of the metallic bookmark hidden behind the optically opaque materials such as polytetrafluoroethylene and Polypropylene plates were obtained by angular spectrum integral and phase unwrapping algorithm. It proves that THz digital holography is an effective nondestructive testing method.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.