How Chemistry Affects Scan Time for a Raman Analyzer

To get good results from your Handheld Raman analyzers, you need a good scan. Since these analyzers are used for rapid, precise identification of explosives and potentially hazardous materials, a good scan is critical in helping military and civilian first responders to quickly identify unknown solid and liquid chemicals. (Read more about Explosives Identification Using Raman Technology.)

The key to getting a good scan is to accurately position the laser focal point on the substance that you are scanning. The focal point is the spot in the laser beam that produces the greatest amount of Raman signal. Regions in the beam before and after this point may not produce enough signal for identification.

The focal point is usually permanently positioned at about 3/4 inch (~16 mm) from the laser aperture. When using a nose cone, you need to make sure that the nose cone is installed straight and that the laser aperture is fully inserted into the nose cone. Your user manual usually contains information on how to position the focal point for the most common scanning situations. In most Raman instruments, the nose cone does not change the position of the focal point. Its only purpose is to help you manually position the instrument so that the focal point is in the correct place when you perform a scan.

You should expect your Raman instruments to display results within approximately 30 seconds. However, be aware that scan time may be prolonged if the substance:

Emits no or very low levels of Raman signal

Some chemicals do not have a strong signal response to a Raman laser and therefore cannot be positively identified.
Examples include dilute solutions and elemental substances. The instrument may be unable to collect enough data from a scan of such substances.

Emits fluorescent light

Fluorescence is a naturally occurring chemical property that causes some molecules to emit light.
Examples of highly fluorescent substances include organic compounds, biological substances, and strongly colored materials. High levels of fluorescence obscure the Raman signal that a substance emits, in the same way that glaring light obscures the image in a photograph.

If a point-and-shoot scan does not finish after a few minutes, scan a sample of the substance in a vial. But be aware:

Amber, brown, green, and blue glass or plastic bottles can be highly fluorescent.

Common examples include wine bottles, chemical bottles, and beer bottles. You may need to extract a sample from the bottle and scan it in a vial.

Of course, always follow safe scanning best practices which include:

Do not use a handheld Raman instrument if you have not undergone training by the manufacturer/supplier or an authorized representative.
If the instrument uses a Class 3B laser, follow recommended safety procedures. Failing to do so can cause damage to the eyes, hazard of fire, and/or hazard of detonation or explosion.
CAUTION: Do not scan gunpowder, any dark-colored powders, or match tips.