Ocean Optics USB2000 - Manual (Page 36)

Appendix A
USB2000 Operating Instructions 31
Appendix A: Calibrating the Wavelength of the
USB2000
This Appendix describes how to calibrate the wavelength of your spectrometer. Though each spectrometer is
calibrated before it leaves Ocean Optics, the wavelength for all spectrometers will drift slightly as a function of
time and environmental conditions. Ocean Optics recommends periodically recalibrating the USB2000.
About Wavelength Calibration
You are going to be solving the following equation, which shows that the relationship between pixel number and
wavelength is a third-order polynomial…
λ
p
= I + C
1
p + C
2
p
2
+ C
3
p
3
...where
λ
is the wavelength of pixel p, I is the wavelength of pixel 0, C
1
is the first coefficient (nm/pixel), C
2
is the
second coefficient (nm/pixel
2
), and C
3
is the third coefficient (nm/pixel
3
). You will be calculating the value for I and
the three Cs.
Calibrating the Spectrometer
Preparing for Calibration
To re-calibrate the wavelength of your spectrometer, you will need the following:
• A light source capable of producing spectral lines
Note: Ocean Optics’ HG-1 Mercury-Argon lamp is ideal for recalibration. If you do not have an HG-1, you
will need a light source that produces several (at least 4-6) spectral lines in the wavelength region of
your spectrometer.
• A USB2000 spectrometer
• An optical fiber (for spectrometers without a built-in slit, a 50-
µ m fiber works best)
• A spreadsheet program (Excel or Quattro Pro, for example) or a calculator that performs third-order linear
regressions
Note: If you are using Microsoft Excel, choose Tools | Add-Ins and check AnalysisToolPak and
AnalysisTookPak-VBA.