Windows are used to create a physical barrier between environments such air to water, vacuum to air, or one gas to another. the ideal windows allows an optical beam to pass from one medium to the next without making any change to the beam.
  
  Windows need high transmittance, low wavefront distortion and low scatter. At  the same time they need to be durable and strong. Surface are polished to 40-20 and help parallel to 5arcsec or 3arcmin. Flatness of λ/10 is recommended but some less expensive λ/4 glass windows are offered for situations where flatness is not so critical. 
  
  We provide three types of windows:
       Sapphire windows, Fused Silica Windows and Glass windows