Standard Operating Procedure
Using the Ocean Optics Spectrometer

Introduction

The Ocean Optics spectrometer is a small analysis tool used to capture the spectrum of optical emission sources such as gas discharges. Emitted light from the source is carried via a fiber optic cable to the unit which then samples the spectrum and displays the spectrum in real-time on the PC display.

The OOI spectrometer can use one of two software utilities as outlined below: either the legacy OOIBASE32 or the newer Oceanview utility.

OOIBASE32 Legacy Utility

Spectrometer Output
Figure 1. Spectrometer Interface

USAGE

Begin by reading the manual for the spectrometer, available via the link below.

The spectrometer is activated via an icon on the lab computer. After initialization a display similar to that seen in figure 1 will be seen. The spectrometer is real-time and displays the spectrum as it is analyzed.

Two controls of importance are the Integration Time and Average parameters. Integration Time is used as a light control. By increasing this parameter the spectrometer collects more light and so peaks become larger. If this parameter is set to '1' and peaks are still too large to display the spectrometer is saturated and an attenuating filter must be placed between the source and the fiber probe. The Average parameter allows the spectrometer to average the reading shown over many samples. Setting this to a larger number like '10' stabilizes the display which would otherwise fluctuate rapidly due the the flickering of the spectrum tube driven by an AC source (which turns the tube off 120 times per second).

To save an image of the spectral output use the Copy Graphical Data option from the Edit menu. The image may then be pasted into any word processing (e.g. Word) or Paint-type package (e.g. Paint) and saved to disk as a file for later use in writing a lab report.

Oceanview Utility

Start the utility from the QuickView screen which will start the utility and display a spectrum in real-time immediately. Select the "Acquisition Group" of controls from the far left side of the screen and adjust the integration time so that the spectrometer is unsaturated (and so the peaks are not "flat-topped").

For optimal data, turn off the emission source and store a "dark spectrum" which can then be subtracted from acquired spectra to produce one void of optical and electrical noise.

Oceanview Software Screen

Use In Analysis Of Gas Discharges

Consider the following spectral output of a gas discharge tube filled with helium gas:

From the Hyperphysics web site the known helium lines are listed as:

Where s=strong, m=med, and w=weak

Indeed, as expected, we find peaks at all of these wavelengths ... and a few more to boot! The question begs "Where in $%#& did the line around 545nm come from?". It certainly did not come from helium so it must be from some contaminant. We begin by using the NIST webbook to search the persistent spectral lines for common contaminants in a vacuum system, namely Nitrogen (from a leak), Oxygen (liberated when electrodes heat) and Hydrogen (from water vapour). A quick check reveals that none of these elements exhibit a line near 545nm. What about mercury?? That sounds odd, since it isn't found commonly in our atmosphere (let's hope not, at least :), but suppose the prototype tube (there are several in the lab) was previously used with mercury?

Sure enough, the NIST webbook shows that mercury has a strong line at 546.0nm. Let's NOT take this at face value though ... PROVE it is mercury. This is done by checking that mercury also has a strong line at 615nm ... which also shows as a peak on the output. One would then systematically identify all unknown peaks as to the impurity that caused them. Be forewarned that there may well be more than one impurity in the tube ... anything from traces of the last lab group's experiment to whatever was in the air that day. To identify a weak peak, one may well want to increase the integration time so that while larger peaks are saturated (with flat tops) weaker lines are clearly exhibited for analysis. Save both traces as 'strong' lines and 'weak' lines for later analysis. It may also be required to save a dark spectrum (with NO optical emission source in) and subtract that from any observed spectra to give a "clean" spectrum free of optical and electronic noise.

For precise wavelength determination (required for all experiments), the spectrometer utility can save raw spectral data to a file for later analysis ... NEVER read wavelengths from a graph by approximating them.

In OOIBASE32, Save spectral data using the Copy Spectral Data option from the Edit menu. Copy All Spectral Channels then open an editor such as Notepad in Windows and Paste to get a list like this ...

Master WL	Master Data	
339.10	0.000	
339.49	0.000	
339.87	0.000	
340.26	0.000	
340.64	0.000	
341.02	0.000	
341.41	0.000	
341.79	0.000	
....
1029.35	0.000	
1029.63	0.000	
1029.91	0.000	
1030.19	0.000
Note that the wavelengths (left column) are in nanometers and feature a resolution of better than 0.5nm. Now, simply SAVE this file as something like "HeliumData.txt". The data can be later opened with a text editor or pasted into an Excel spreadsheet for graphing or analysis.

In Oceanview, you can simply SAVE data which will appear in a text file in C:\DocumentsandSettings\operator\oceanview. The resulting text file will have only two columns for wavelength and intensity (a number ranging from zero to 16383) as follows:

480.454	84
480.921	95
481.388	117
481.856	141
482.323	170
482.791	202

Links


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