The 39-654 is a high-quality dielectric mirror, rectangular in shape with dimensions of 19.1mm in width and 12.7mm in height. This mirror is designed to work specifically with Nd:YAG lasers, optimized for a wavelength of 1064nm. The mirror's coating is a dielectric type, specifically 'edm diel 1064 45 aoi', which is applied to the front surface. This coating is designed to provide high reflectivity at the specified laser wavelength. The mirror has a thickness of 6.35mm and is made from fused silica, identified as 'fused sil mal-1965' in the material ID. The mirror's shape is classified as a 'Thin Lens', suggesting it may have some focusing properties, although this is not explicitly stated in the provided data. According to the vendor, Edmund Optics, the mirror is currently in stock and available for immediate purchase.