A diffraction grating is an optical element that diffracts energy into its constituent wavelengths. The groove density, depth and profile dictate the spectral range, efficiency, resolution and performance of the diffraction grating.
There are typically two different types of diffraction grating – the ruled grating and the holographic grating. A ruled grating is produced by a ruling engine that cuts grooves into the coating on the grating substrate (typically glass coated with a thin reflective layer) using a diamond tipped tool. A holographic grating is produced using a photolithographic technique and can have either a sinusoidal or blazed profile.
Sinusoidal groove profiles are the most common groove shape for holographic gratings where the grooves are symmetrical and therefore have no blaze direction. A sinusoidal grating offers a wider spectral coverage compared to a blazed grating but usually has lower efficiency.
A blazed holographic grating has had the sinusoidal profile transformed into a ‘saw tooth’ profile. This saw tooth profile increases the efficiency of the diffraction grating over the wavelength region of interest without increasing the stray light. Spectrum Scientific uses a proprietary blazing technique which creates a blazed grating that demonstrates considerably lower stray light with equivalent or better efficiency when compared to ion-etched gratings. Currently this technique is limited to a blaze region of 200-300mm.
In addition to plane gratings, Spectrum Scientific is one of the few companies that designs and manufactures blazed aberration corrected, flat field imaging gratings optimized for the UV and visible wavelengths.