Details for AlGaAs coatings order

• Coating structure can be found in http://nodus.ligo.caltech.edu:8080/PSL_Lab/1340, 55 layers, T = 197ppm.
• Coatings for 4 mirrors plane/concave, 1” diameter, 1/4” thick, with radius of curvature = 1.0m.
• AlGaAs coatings will be applied on the concave side of the mirror.
• Flat side is already AR coated
• absorption loss 6-10ppm / scattered loss 3-4ppm
• Spot radius (1/e^2 power) will be 215 um.
• The mirrors have an annulus on the rim for optical contact with thickness ~ 3mm. This area should be kept clean.
• The coating wafer should be inside the mirror sagitta to make sure that it will not obstruct the optical bond area. By calculation, the wafer with 8mm diameter, 4.5um thick should be ok. The maximum diameter that makes the coating to be above the sagitta is about 16mm, for 4 um thickness.

• Required coating diameter = 5-8mm, Power loss due to clipping is less than 0.1 ppm, see below figure.

Above, plot of ratio of power due to finite size mirror P(r) / P0,  P(r) is the power of the beam at radius r from the center. G Cole said that the wafer can be made to 8mm diameter. diameter between 5-8 mm should be good for us.