What is a “blazed angled” diffraction grating?

The various light orders of a diffraction grating result in dispersion of the energy and a reduction in light utilization efficiency. However, the diffracted light energy from a diffraction grating with a fine sawtooth profile is concentrated in the direction of the specular reflection, as shown at left. This wavelength is known as the "blaze wavelength." The diffraction grating in a spectrophotometer is normally used near the blaze wavelength. However, multiple diffraction gratings can be used separately to increase the efficiency over a wide range of wavelength.

A different way of viewing the phenomenon of higher-order light is to say that, if d, i, and θ are fixed, a different value of m results in a different λ. This indicates that light of multiple wavelengths θ diffracts in diffraction angles λ, as shown on right. Therefore, a higher-order light cutout filter (short-wavelength cutout filter) is positioned after the monochromator exit slit to extract light at a specific wavelength (normally ±1st-order light).