Monochromator Reciprocal linear dispersion

A giatfng monochromator wiih a reciprocal linear dispersion of 1.2 nm/mm i.s to be used to separalc the sodium lines at 5SS.9950 nni and. 89.5924 nni. In the ory. what slit width would be required ... 

By the same token, an important criterion of monochromator performance is reciprocal linear dispersion, commonly expressed in Ang-stroms/millimeter. If the reciprocal linear dispersion of a given monochromator is, say, lOA./mm., then at a slit width of 1 mm., the resolution of the unit is lOA. For best energy, the reciprocal linear dispersion... 

Dispersion of a Grating Monochromator. The resolution of a monochromator measures its ability to separate adjacent wavelengths from each other. Resolution is related to a useful quantity called the reciprocal dispersion, or reciprocal linear dispersion,... 

The reciprocal linear dispersion dX/dx) is the function of the geometric slit width S) and spectral bandpass (AA ,) of the monochromator ... 

AAS measurements are almost exclusively carried out in the first order, and a good grating has 2000 to 3000 grooves mm. The reciprocal linear dispersion of 1 nm mm or less can easily be obtained with the usual focal lengths employed. Comparable reciprocal linear dispersions are achieved with a conventional prism monochromator only in the far UV region, while in the near UV and visible regions grating monochromators are superior. 

The effective bandwidth (also called the spectral bandpass or spectral slit width, which is one half the bandwidth when the two slit widths arc identical, is seen to be the range of wavelengths that exit the monochromator at a given wavelength setting. The effective bandwidth can be related to the reciprocal linear dispersion by writing Equation 7-9 in the form... 

By substituting Equation 7-7 into Equation 7-9 we have the reciprocal linear dispersion for a grating monochromator ... 

Quimby et al used a prototype version of the Spectraspan III echelle grating monochromator (Spectrametrics, Inc., Andover, Mass.) with a reciprocal linear dispersion of 0.122 nm/mm at 400 nm. The entrance slit width was 50 m slit height, 500 m exit slit width,... 

The focal length and groove density determine the reciprocal linear dispersion of the monochromator, or how much of the spectrum is spread across a specific distance in the output plane of the monochromator. Thus, short focal length monochromators with coarsely ruled diffraction gratings can produce relatively high scan rates. 

Commercially packaged atomic absorption instrumentation commonly includes a monochromator of about j m focal length with a linear reciprocal dispersion in the range 16-35 A/mm. 

---