2-16
IM AQ6376-01EN
High-Order Diffracted Light
In principle, the monochromator emits high order diffraction light that is integer multiples
of the input light. The AQ6376 is equipped with an optical filter inside the monochromator
that suppresses incident rays that are less than 1150 nm (only on the standard model
(SUFFIX-10)). However, the optical filter cannot completely eliminate high order
diffraction light. Therefore, it is important to know how the high order diffraction light will
appear.
The following figure is a graph of the wavelengths that appear on the screen versus
the actual wavelengths. The horizontal axis is the wavelengths displayed on the
screen, and the vertical axis is the actual wavelengths. In addition, the solid lines on
the graph indicate the correspondence between the displayed wavelengths and actual
wavelengths. The thick solid line displays the correct optical spectral correspondence
(obviously the displayed wavelengths match the actual wavelengths), and the thin solid
line displays the correspondence with the ghost caused by high order diffraction light.
The numbers written next to the thin solid line indicate the level of suppression of the
ghost caused by high order diffraction light relative to the correct optical spectrum.
However, the values are rough estimates; they are not guaranteed.
For example, if a 1060 nm light, which is shorter than the measurement wavelength
range of the AQ6376, is applied, draw a horizontal line from 1060 nm on the vertical
axis, and the intersections with the lines on the graph correspond to the displayed
wavelengths.
As a result, we can see that in addition to 1060 nm, a ghost appears at the 2120 nm
position. We also see that the level of the ghost is suppressed by more than 40 dB
relative to the correct optical spectrum. Near the 2400 nm measurement wave length
region, the suppression characteristics of the optical filter are low, and the measurement
is greatly affected by high order diffraction light. If the input light contains light less than
1150 nm or greater than 1200 nm, reduce such light using an optical filter in advance
before making measurements.
2.4 Important Points During Measurement
