Description

These mirrors of guaranteed flatness are suitable for interferometry and other demanding applications. Low-expansion glass (LEBG, see optical materials) is used for the λ/10 series to reduce thermal distortions. Coatings offered are as follows.

Dielectric coatings
Dielectric mirror coatings are very hard and durable and, having negligible absorption, are suitable for high powers. Our coatings, being broad-band, are much more versatile than ordinary laser mirror coatings; Visible-99 has about 99% reflectance over 450-700nm, 0° to 45°. IR-98 covers 700-1064nm with average reflectance of about 98.5% at 0° (97% at 45°); in particular, the reflectance at 1064nm is designed to be high for normal incidence.  

Metal coatings
Metal coatings cover wider ranges than dielectrics and are lower in cost. Ion-plated silver surpasses both aluminium and gold for reflectance over the range 420-1000nm,and is useful throughout the IR. The usual drawbacks of silver (softness and tarnishing) have been much improved by a hard dielectric coating applied by new technology, giving enhanced chemical and mechanical protection.  Silver is not recommended for long term applications in high humidity environments Enhanced aluminium is a good general purpose coating for the visible. The reflectance is considerably increased by the dielectric overcoat and peaks at about 94%.  Protected aluminium (Al + SiOx), used on our elliptical and concave mirrors, is a versatile coating with 85-90% reflectance in the visible and also useful in the IR and UV.  UV aluminium is used for the UV (down to below 180nm) and Protected gold for the IR. Both these coatings are very delicate; to clean use an air-duster (see 110 QC 400) or, if necessary, cotton-wool with acetone or other solvent.