5
Section 4
Introduction
UV/Visible Spectroscopy is based on the absorption of light as a function of wavelength.
All spectrophotometers have a light source that generates light of specific wavelengths. The
SmartSpec 3000 uses a xenon flash lamp as its light source. Xenon flash lamps have several
advantages over the conventional light sources in that they reduce warm up time, do not heat
up the instrument and have a lamp life of 10 to 15 years. Additionally, xenon flash lamps
emit both UV and visible wavelengths, in contrast to deuterium lamps which emit only UV
wavelengths. In the SmartSpec 3000, the xenon flash lamp pulses light only when measuring
absorbance of a sample.
Fig. 5. A symbolic representation of the SmartSpec 3000 optics module.
The path of light in the SmartSpec 3000 is as follows:
Light from the xenon flash lamp
Lens
Sample
Slit
Concave mirror
Grating
Concave mirror
Photodiode array detector
The advantages of using a grating as a dispersion device are that:
1. They eliminate nonlinear dispersion.
2. Are not temperature sensitive.
Photodiode arrays have several advantages:
1. They acquire spectral data simultaneously without mechanically moving parts;
2. Have excellent wavelength reproducibility and,
3. A wide dynamic range.
It is also important to note here that in an array, several photodiode detectors are arranged
on a silicon crystal. The added benefit of an array is the ability to do side-by-side readings, thus
increasing speed.
Source
Lens
Sample
Slit
Grating
Detector
Concave
Mirror
Concave
Mirror
