Basic Design Elements and Configurations in Luminescence Spectrometers

There are four distinct modules to consider in most optical emission spectrometer systems the excitation module, the sample module, the emission module, and the instrument control/data acquisition module. The elements comprising each module (and variations therein) are captured in Fig. 2.7 and described in greater detail in the ensuing section. 

Note that some instrument configurations do not require each element in the module. For example, if a laser excitation source with an intrinsically narrow-bandwidth monochromatic output is employed, then an excitation monochromator is not required and the exciting light is typically coupled directly into the sample compartment via an optical fibre or light pipe. Some of the more elaborate commercial instrument systems also explicitly incorporate 

Xenon flashlamps are the simplest and most readily wavelength tunable pulsed hght sources. These lamps typically have sufficient output radiance from —250 to —800nm for excitation applications. The pulse width depends on a number of factors including output power, but pulse widths of 1 —2 ms are common. Pulse repetition rates of —100 Hz are also fairly common for these sources. 

A variety of other pulsed laser light sources have been incorporated into optical emission spectrometer systems. The two most common ones are based on either a pulsed nitrogen laser or a frequency-upconverted pulsed Nd YAG laser as either a single line source (337 nm for the nitrogen laser, 266,355, or 532 nm for the Nd YAG laser) or used as a pump laser for a tunable secondary laser device such as a dye laser or an optical parametric oscillator (OPO). The ultimate wavelength tunabUity in such systems depends on the characteristics of the secondary laser and can be substantial in the case of the OPO, but at a substantial price in both cost and complexity of operation and maintenance. Nonetheless, these sources can have excellent temporal characteristics (sub-nanosecond pulse durations) and high per pulse energies. 

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