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A diffraction grating is a periodic optical component that separates light into many beams that go in different directions. It's an alternative to using a prism to study spectra. When light strikes the grating, the split light will often have maxima at an angle ?.

Resolvance of Grating In practice, the resolvance is stated in the form R=? /?? for applications like the observation of the sodium doublet. We know the wavelength difference to be ?? = . 59 nm, so the resolvance can help us to anticipate whether a particular diffraction grating could resolve that difference.

Dsin ? = n ? The number of slits per metre on the grating, N = 1/ d where d is the grating spacing. For a given order and wavelength, the smaller the value of d, the greater the angle of diffraction.

The resolving power of a grating is the product of the diffracted order in which it is used and the number of grooves illuminated by the incident radiation. It can also be expressed in terms of grating width, groove spacing, and diffracted angles.

Typical gratings used in Raman spectrometers vary from about 300 gr/mm (low resolution) up to 1800 gr/mm (high resolution); more specialized gratings, such as 2400 gr/ mm and 3600 gr/mm can also be used, but they have certain physical and practical limitations (to be discussed, following).

And so, the general equation for the points of zero intensity in the diffraction pattern of a single slit is: a sin T = ml m = 1,2,3, ... But usually we are just interested in the location of the first minimum, when m = 1, because most of the light enery is located in the central diffraction maximum.

Spectral Resolution It is usually expressed as the Full Width Half Maximum (FWHM). The resolution can be theoretically determined by multiplying the reciprocal dispersion of the grating by the slit width. The bandpass with a 1200 lines/mm grating is half that of the same arrangement with a 600 lines/mm grating.

The spectral resolution or spectral resolving power, R, of a spectrograph is defined as the ability to distinguish between two wavelengths separated by a small amount ??. Spectral resolution is usually quoted either in terms of ?? (usually in units of nm or Å) or in terms of the dimensionless quantity: R = ? / ??.

What are Diffraction Gratings. A diffraction grating is an optical element that divides(disperses) light composed of lots of different wavelengths(e.g., white light) into light components by wavelength. The simplest type of grating is one with a large number of evenly spaced parallel slits.

A wavelength resolution far better than 1 nm is easily possible with a grating monochromator. Typical achievable wavelength resolutions of such monochromators are about 0.01 nm to 0.1 nm.