Grating frequency

The experimental curves showing dependence of diffraction efficiency on exposure dose for different grating frequences can be seen in Fig. 14. The maximum values of diffraction efficiency are approximately equal for all grating frequences and reach 55-65% in exposures in the range 0.8-1.1 J/cm. ... 

Fig. 14. Dependence of diffraction efficiency of image-matrix hologram on exposure dose at different grating frequencies.

The first requirement is a source of infrared radiation that emits all frequencies of the spectral range being studied. This polychromatic beam is analyzed by a monochromator, formerly a system of prisms, today diffraction gratings. The movement of the monochromator causes the spectrum from the source to scan across an exit slit onto the detector. This kind of spectrometer in which the range of wavelengths is swept as a function of time and monochromator movement is called the dispersive type. 

Step size is critical in all sim tilation s. fh is is th c iricrcm en t for in tc-grating th c equation s of motion. It uitim atcly deterrn in cs the accuracy of the numerical integration. For rn olecu les with high frequency motion, such as bond vibrations that involve hydrogens, use a small step size. 

Fluorometry and Phosphorimetry. Modem spectrofluorometers can record both fluorescence and excitation spectra. Excitation is furnished by a broad-band xenon arc lamp foUowed by a grating monochromator. The selected excitation frequency, is focused on the sample the emission is coUected at usuaUy 90° from the probe beam and passed through a second monochromator to a photomultiplier detector. Scan control of both monochromators yields either the fluorescence spectmm, ie, emission intensity as a function of wavelength X for a fixed X, or the excitation spectmm, ie, emission intensity at a fixed X as a function of X. Fluorescence and phosphorescence can be distinguished from the temporal decay of the emission. 

In a simple flame (emission) photometer an interference filter (Section 17.7) can be used. In more sophisticated flame emission spectrophotometers which require better isolation of the emitted frequency, a prism or a grating monochromator is employed. 

The capillary wave frequency is detected by an optical heterodyne technique. The laser beam, quasi-elastically scattered by the capillary wave at the liquid-liquid interface, is accompanied by a Doppler shift. The scattered beam is optically mixed with the diffracted beam from the diffraction grating to generate an optical beat in the mixed light. The beat frequency obtained here is the same as the Doppler shift, i.e., the capillary wave frequency. By selecting the order of the mixed diffracted beam, we can change the wavelength of the observed capillary wave according to Eq. (11). 

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