Monochromatic light/monochromator

When recording excitation and fluorescence spectra it must be ensured that monochromatic light falls on the detector This can best be verified in instruments built up on the kit principle or in those equipped with two monochromators (spectrofluonmeters) The majority of scanners commercially available at the moment do not allow of such an optical train, which was realized in the KM3 chromatogram spectrometer (Zeiss) So such units are not able to generate direct absorption or fluorescence spectra for the charactenzation of fluorescent components... 

To identify a certain pigment, monochromatic light is required, but the assessment of food quality by a human inspector or by a device requires normal daylight. The evaluation procedure, however, to be discussed in the next section, also involves decomposition into monochromatic (red, green, and blue) regions. Monochromatic dissection of a continuous spectrum by monochromators can be achieved in three ways ... 

Monochromatic light consists of one color" (one wavelength). The better the monochromator, the narrower is the range of wavelengths in the emerging beam. 

The linear dispersion. This is the spectral width in nm transmitted through the exit slit of the monochromator. It is given in units of nm/mm. For example 5 nm/mm would mean that the nominal bandwidth of the monochromatic light is 5 nm if the slit width is 1 mm. This defines the purity of the monochromatic light. 

Double and Multiple Monochromators. If monochromatic light of very high purity is required, it is often necessary to use two or several monochromators in series, such that the exit light of the first one becomes the entrance light of the second. The reasons for using such complex optical arrangements are two-fold. 

Two methods of obtaining monochromatic light are used. The first involves color filters and the second either prism or grating monochromators. Color filters may be used to advantage with a mercury arc since the lines are well separated. However, no color filter system is really adequate for modern photochemistry. 

Irradiation. The thick sheets were irradiated with monochromatic light according to ref. [2] using an Applied Photophysics Model 5350 photo-irradiator equipped with a 900 W short arc high pressure xenon lamp, a f/3.4 monochromator and an exit lens of quartz providing illumination over an area of 1.3 by 2.4 cm at a distance of 16 cm from the lens. The illumination was uniform over the central area (0.8 by 1.7 cm) which was analyzed. The entrance slit of die monochromator was kept at 5 nm and the exit slit at 10 nm to secure enough output energy. Irradiations were performed at ambient temperatures (ca. 23°Q in air. 

After an investigation of several years with the same type of algae and approximately the same intensity of monochromatic light as used by Warburg we are forced to conclude that the photosynthetic process is considerably less efficient than the 0.2 or 0.3 which is now accepted.63 With the monochromator already described and with direct, microchemical analysis of the gas or by titration for oxygen we find a quantum yield of about 0.05 changing somewhat with the conditions. Under our conditions ten to twenty quanta instead of the classical four seem to be necessary to convert one molecule of carbon dioxide into plant material. 

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