Raman Spectroscopy and
the Laser Gas Analyzer at work
In 1928 Indian Physicist C. V. Raman demonstrated that
monochromatic light passing through a substance scatters and
produces a spectrum that is unique to that substance. Raman found
that bands appearing in the spectrum distinctively characterize the
chemical composition of the substance illuminated.
Since the 1960s the precisely monochromatic light emitted by
lasers has enabled numerous scientific and industrial applications
of spectroscopy based on Raman’s work to detect and quantify the
presence of chemical compounds in solids and liquids.
ARI’s Laser Gas Analyzer exploits the phenomenon that gas
molecules struck by laser light absorb it and re-emit light at
frequencies different from the laser. The molecular bonds of each
gas molecule uniquely determine the resulting “Raman Shift”
frequency(ies) of the re-emitted light. The shifts are so discrete
and precise that the intensity of light observed at various shifted
frequencies is directly proportional to the concentrations of
constituent molecules in the atmosphere.
The heart of the Laser Gas Analyzer is a detector module that
shines a safe, low-power laser through a gas sampling chamber. The
chamber has eight ports, each fitted with an optical filter and
light sensor to measure the intensity of light at a specific
When an atmosphere sample is analyzed pumps draw the gas to the
sampling chamber. A media filter at the intake removes particulate
In the chamber the gases pass through the laser beam, and the
molecules emit their characteristic light signatures. Electronics
for each light sensor provide a digital signal quantifying its
particular gas component.
The detector is connected to a specially-built computer that
logs, interprets and displays the sensor data. The computer
typically communicates with the control systems for the equipment
being monitored and controlled.
Custom-fitted piping and a proprietary valve manifold subsystem
connect the detector to the phyiscal environment being measured. The
valve manifold assures
that the gas samples drawn from multiple sources and locations each
are presented uncontaminated to the sampling chamber.
Gas Process Real-Time Control
ARI’s Laser Gas Analyzer and Controller combines the LGA with
existing process gas control valves and safety systems on site.
The system monitors process conditions and adds process gas in
response to reaction needs in real time. This ability results in
tighter control of reactive processes as well as the opportunity to
reduce process gas consumption significantly.
Because the system measures all types of reactive gases in
near-real time, accurate atmosphere control of industrial gas
processes can become easier to understand and control.
For example, when used with non-standard atmosphere mixtures for
heat treating, the sophisticated control enables improvements in
processing speed from 20% to 50%, enhancing heat treating facility
bottom-line profits by 25% and more.
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