Fully automated wavelength calibration method optimizes0 pages

Technical Note
SPECTROSCOPY GROUP

Fully automated wavelength
calibration method optimizes
data accuracy
An intelligent new routine

The
recent
launch
of
Princeton
Instruments’
™
powerful LightField 64-bit data acquisition software
also heralded the arrival of a brand new, fully
automated wavelength calibration method developed
to achieve unprecedented accuracy for spectroscopy
applications (see Figures 1–4). Currently offered as a
LightField package option, patent-pending IntelliCal™
technology from Princeton Instruments enables fast,
reliable wavelength calibration with minimal user input
(see Appendix).
In essence, IntelliCal is a full-spectrum calibration routine
that refines a theoretical spectrograph model based on the
physical properties of the actual instrument being utilized.
This technical note will first provide a review of critical
problems inherent to traditional calibration techniques and
then present basic IntelliCal theory, comparative data, and
key implications of the new method.

Motivation

The development of IntelliCal was fueled by the desire to
surmount several shortcomings associated with traditional
wavelength calibration methods, especially overreliance on
user input for accuracy. By and large, the post-calibration
wavelength accuracy is not known by the software programs
utilized in these traditional routines, so its determination is
left up to the user.

1

Figure 1. IntelliCal source installed on an Acton Series SP2300
spectrograph from Princeton Instruments.

Using a source with multiple known emission lines to
illuminate the entrance slit of the spectrograph, it is
possible to determine a direct wavelength-to-detector pixel
coordinate correlation. There are two common types of
wavelength space calibration: (1) a polynomial fit where
only two or three emission lines are used and (2) a fit to the
Czerny-Turner model.
Some routines utilize a polynomial fit to define the spectral
dispersion across the focal plane and thus obtain calibration
results at the pixel level. This technique, in which a polynomial
is fit to a plurality of known emission lines, is both the more
accurate and more tedious of the aforementioned methods.
The user must not only determine which emission lines are
seen by the detector, but must redo the calibration each
time the grating is moved. Furthermore, the accuracy of this

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