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THz Transmission Spectrometer:
Transmission
measurement is the best method for characterization of highly
transparent materials. In particular, transmission spectra of plane
parallel plates exhibit a periodic transmission pattern caused by
interference (Fabry-Perot etalon fringes). Real and imaginary parts of
the dielectric constant can be determined from these measurements, as
the period and amplitude of the etalon fringes depend on the material
refractive index and absorption, respectively.
Characterization
of semi-transparent materials requires a THz Mach-Zehnder
interferometer (shown below), since no etalon fringes can be observed in
the transmission spectra of such materials. The Mach-Zehnder setup
enables measurements of a phase shift induced by the sample as a
function of frequency. Combining this data with transmission spectrum,
real and imaginary parts of the dielectric constant can be calculated.
THz Mach-Zehnder Spectrometer:
Characterization
of semi-transparent materials requires a THz Mach-Zehnder inferometer
(shown below), since no etalon fringes can be observed in the
transmission spectra of such materials. The Mach-Zehnder setup enables
measurements of a phase shift induced by the sample as a function of
frequency. Combining this data with transmission spectrum, real and
imaginary parts of the dielectric constant can be calculated.
Highly absorptive materials can only be characterized in a reflection geometry, illustrated below.
THz Reflection Spectrometer:
Opaque
materials characterization requires the reflection spectrometer (shown
above). Because the transmitted signal is too small for
characterization, a system using 6-axis control is employed to measure
the reflected signal. As with the transmission and phase spectrometers
the index of refraction, extinction coefficient and the real and
imaginary parts of the dielectic function can be quickly calculated from
the software's theoretical fitting capacity.
The transmission, Mach-Zehnder and reflection spectrometers are supported by TScan software, enabling automated data acquisition and analysis. One spectral scan takes 1 - 5 minutes for each of the BWOs employed in the system.
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