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The block diagram below shows a general spectrofluorophotometer.
(1) The excitation source is a light source for providing excitation light to irradiate a specimen, and a xenon lamp is usually used.
White light (light composed of various wavelengths) emitted from the light source enters an excitation side spectroscope (2). While measuring an excitation spectrum, this excitation side spectroscope (2) is moved to successively change the wavelength used to irradiate the specimen (this is called scanning or wavelength scanning). In contrast, when measuring a fluorescence spectrum, a specific wavelength is selected and fixed in the excitation side spectroscope.
The light emitted from the excitation side spectroscope travels towards the specimen to excite it. Along the way, a half-mirror is used to split the light beam (diagonal line in the figure above) so that a portion also travels to the monitor detector (3). The monitor detector monitors the intensity of the excitation light irradiating the specimen. Generally, a photoelectric tube (phototube), a photodiode, a photomultiplier tube (also called a photomultiplier or photomul), etc are used.
When the excitation light reaches the specimen, the specimen is excited to emit fluorescent light. The emitted fluorescent light enters a fluorescent light side spectroscope (4) (although omitted in the diagram, this light is condensed by a lens).
When measuring the excitation spectrum, a specific wavelength is selected and fixed in the fluorescent light side spectroscope (4). When measuring a fluorescence spectrum, the fluorescent light side spectroscope is moved to measure the wavelengths of the emitted fluorescent light.
The fluorescent light leaving the fluorescent light side spectroscope enters the fluorescence detector (5). Generally, a photomultiplier tube is used. A fluorescent light detector converts the fluorescent light into an analog electric signal which is converted into a digital signal by an A/D conversion circuit (6).
A computer (7) controls wavelength scanning and digital signal processing.
The following is an optical system diagram of a spectrofluorophotometer.
Although detailed descriptions are omitted here, it is constituted of many optical devices like this.
Performance specifications of a system are described in the last page of its catalog. Meanings of terms used here and how to read numbers are explained.