Tellurite And Fluorotellurite Glasses For Active And Passive

6. Optical properties; MDO 169
quartz / glass prism. As refractive index increases with frequency, high frequency
radiation is deflected to a higher degree as it passes though the prism [3]. Problems
associated with passing the beam through a material (such as absorption) can be avoided
by using a diffraction grating. This device consists of a glass or ceramic plate with fine
parallel grooves of the order of the wavelength of light (≈ 1 µm). The grating is covered
in a reflective coating (aluminium). Reflection from the grating results in interference,
which is constructive at certain angles, depending on the wavelength of the light. The
intensity of the diffracted beam is enhanced by shaping the grating in a certain way,
resulting in blazing [3].
Fourier transform (FT)
The spectrometer used in this study operated by a Fourier transform (FT) method. The
Fourier transform infrared (FTIR) spectrometer used a Michelson inferometer to analyse
the individual frequencies present in a composite signal. The Michelson inferometer
operated by splitting the beam from the sample into two, then introduced a path
difference, δ, into one of them, which was varied. The two beams were then recombined,
and interfered constructively or destructively, depending on δ. The intensity of the signal
from the sample, I, varied according to equation (6.4) [3].
~ ~
I ( δ ) = I(
f )( 1+
cos 2πfδ
)
(6.4)