Re: [ATM] plop

[Jeff Anderson-Lee <jonah@eecs.berkeley.edu>]

Jerry B. Hillman wrote:

>The mirror is F4.5 so would six still be enough?
>
Sure.  Below are some numbers from Plop for a six point cell for your 
mirror (d=15in, t=1.5in, f-4.5, pyrex), at various radii.  If you throw 
them in a .csv file and load them into Excel you can graph the results.  
Even without the graph you can see some trends.

The RMS is minimal at around r=0.57, but is acceptable over pretty much 
the whole range (0.51<=r<=0.68).  The P-V is not as smooth, but is also 
within reason over most of the range but is best over the range 
0.50<=r<=0.62.  The focus tolerance (sharpest focus range) for this 
optic at 500nm wavelength is about 0.020 mm or 0.0005 in, so if we want 
to moderate the need for refocusing due to support we might choose 
r>=0.62.  (However flex in the mount and thermal changes are likely to 
exceed this amount anyway.) 

Considering all three factors, I might choose the pad support radius to 
be between 0.6R and 0.625R just for the ease of working with the 
numbers.  That works out to a radius between 4.5 inches and  4.6875 (or 
4+11/16) inches for a 15 inch mirror (about 114 mm to 120 mm). 

If you make the bars with about 4+5/8 inches between the support points, 
you could make them 5+5/8 inches long to give added space for a pad 
centered 1/2 inch in at either end.  These three bars should be mounted 
with their centers at a 4 inch radius. 

Or, if you are comfortable with metric, make the bars 14 cm long with 
the center of the pads in 12 mm from each end and support the bar 
centers at a 10 cm radius.

Jeff

r, rms, pv, refocus
0.50, 4.353e-06, 1.744e-5, -0.0591
0.51, 3.909e-06, 1.608e-5, -0.0561
0.52, 3.502e-06, 1.625e-5, -0.0531
0.53, 3.146e-06, 1.643e-5, -0.0502
0.54, 2.837e-06, 1.519e-5, -0.0471
0.55, 2.588e-06, 1.395e-5, -0.0440
0.56, 2.416e-06, 1.368e-5, -0.0409
0.57, 2.340e-06, 1.492e-5, -0.0378
0.58, 2.360e-06, 1.697e-5, -0.0347
0.59, 2.405e-06, 1.690e-5, -0.0315
0.60, 2.520e-06, 1.682e-5, -0.0283
0.61, 2.694e-06, 1.748e-5, -0.0251
0.62, 2.918e-06, 1.964e-5, -0.0219
0.63, 3.181e-06, 2.178e-5, -0.0187
0.64, 3.394e-06, 2.193e-5, -0.0155
0.65, 3.613e-06, 2.168e-5, -0.0122
0.66, 3.849e-06, 2.168e-5, -0.0090
0.67, 4.100e-06, 2.356e-5, -0.0057
0.68, 4.362e-06, 2.544e-5, -0.0025
0.69, 4.584e-06, 2.600e-5, -0.0008
0.70, 4.777e-06, 2.561e-5,  0.0041

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