MOGlabs MWM, Manual, Page: 45 / 96

6. Calibration
Recalibration of the
MWM
can be required due to drift and metal creep,
accidental mechanical shock, or to change the operating wavelength. Usu-
ally it is a very simple process of measuring a known laser wavelength and
clicking one button. Multi-point calibration across the operating wave-
length range will improve the accuracy.
Calibration consists of measuring a tunable light source using the
MWM
.
The location of the diffracted spot on the imaging sensor is recorded, along
with an independent wavelength measurement of the light source. A best-
fit polynomial fit is calculated, translating imaging pixel location to wave-
length.
6.1 Existing wavelength range
Here we describe recalibration, if the operating wavelength is unchanged.
From the
mogwave
application, select the
Spectrum
menu, then
Calibrate
,
to start the calibration application. The normal wavelength measurement
program will continue to run, so that you can see the measured wavelength
using the current calibration data.
The calibration process requires measuring the wavelength of a light source,
and entering the known wavelength for that source. Before entering data,
please make sure that the units are the same in both the normal and Cal-
ibrate windows, typically
(nm, vac)
. Avoid using
(nm, air)
because the
measurements are subject to arbitrary variations in pressure and temper-
ature.
The Calibration window shows two graphs. The upper graph shows the en-
tered (known) wavelength against spectrum channel or bin which is effec-
tively the uncalibrated wavelength. The lower graph shows the difference
between the entered (known) wavelength and the calculated wavelength
using the old calibration.
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