Optical thickness measurement with multi-wavelength THz interferometry

We report unambiguous thickness measurement with an all-optical THz source. The optical thickness variation of a test target was measured in a Mach–Zehnder interferometer to approximately 0.5% of the illumination wavelength using an optical parametric THz laser. The frequency of the laser was contin...

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Bibliographic Details
Published in:Optics and lasers in engineering 2014-10, Vol.61, p.19-22
Main Authors: Nguyen, T.D., Valera, J.D.R., Moore, A.J.
Format: Article
Language:English
Subjects:
Electronics
Illumination
Interferometry
Lasers
Mach-Zehnder interferometers
Metrology
Optical thickness
Optoelectronics
Phase-step
Synthetic wavelength
Thickness measurements
THz
Wavelengths
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Summary:We report unambiguous thickness measurement with an all-optical THz source. The optical thickness variation of a test target was measured in a Mach–Zehnder interferometer to approximately 0.5% of the illumination wavelength using an optical parametric THz laser. The frequency of the laser was continuously tuneable, enabling a synthetic wavelength to be produced by sequential illumination at discrete frequencies, thus extending the unambiguous measurement range to half the synthetic wavelength. The all-optical source provides some advantages with respect to opto-electronic and electronic sources, particularly measurement speed and resolution. •Optical thickness measured with an optical parametric THz laser.•A synthetic wavelength produced by sequential illumination at discrete frequencies.•First unambiguous thickness measurement with an all-optical THz source.•Show source suitable for interferometric measurements with direct detection.
ISSN:0143-8166
1873-0302
DOI:10.1016/j.optlaseng.2014.04.007