Diffraction grating order

Diffraction gratings may be made by a holographic process, but blaze characteristics cannot be controlled and their efficiency is low in the infrared. They are mostly used for low-order work in the visible and near-ultraviolet. 

Serious attempts to use LB films in commercial appHcations include the use of lead stearate as a diffraction grating for soft x-rays (64). Detailed discussion on appHcations of LB films are available (4,65). From the materials point of view, the abiHty to build noncentro symmetric films having a precise control on film thickness, suggests that one of the first appHcations of LB films may be in the area of second-order nonlinear optics. Whereas a waveguide based on LB films of fatty acid salts was reported in 1977, a waveguide based on polymeric LB films has not yet been commercialized. 

Prisms have the advantage that, unlike the diffraction gratings described below, they only produce a single-order spectrum. 

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). 

Thus, dispersion of the grating increases as d decreases (i.e., as the grating contains more lines per cm). Also, dispersion is not a function of k, and the linear dispersion is therefore a constant, unlike in the case of a prism. The resolving power of a diffraction grating is proportional to the size of the grating and the order of the diffraction used. 

Sometimes the spectrometer completely obliterates the information at all Fourier frequencies co beyond some finite cutoff Q. This is specifically true of dispersive optical spectrometers, where the aperture determines 1. The cutoff Q may be extended to high Fourier frequencies by multipassing the dispersive element or employing the high orders from a diffraction grating. 

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