Page 232 - Photodetection and Measurement - Maximizing Performance in Optical Systems

Measurand Modulation

Measurand Modulation 225

Tungsten point
electrode
0-6kV 4 x1M Resistors
HT PSU
Corona wind
e
e
Dimpled
water surface
Sample
To diode array
spectrometer:
Deuterium Silica Decreasing
lamp cuvette Ground absorption
Absorbance
wire

Wavelength
Figure 10.12 Corona-wind modulation spectroscopy. Charged particle injection
from a high-voltage corona can be used to degrade and modify a wide variety
of organic samples. The system is easily installed within the measurement
spectrometer.

0.02
0ppm
0
0.5ppm

-0.02 1ppm
Absorbance Difference -0.04

-0.06

-0.08 2ppm

-0.1

-0.12
200 220 240 260 280 300 320 340
Wavelength (nm)
Figure 10.13 Corona-wind modulation spectroscopy of benzene in water at concentrations of 0, 0.5,
1, 2ppm.

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