XPost: sci.electronics.design   
   From: jappel@linux01.gwdg.de   
      
   Phil Hobbs wrote:   
      
   >> It would be interesting to see how fast an edge you could create with   
   >> a mechanical chopper. Nanoseconds would be tough.   
      
   For my Ph.D-thesis work I needed a fast, but lossless shutter (to create   
   pulses of squeezed light) and used a 25µm slit glued onto the rim of 3.5"   
   hard disk drive overdriven to up to 300 rpm.   
      
   That gave pulses < 0.5 µs. The big advantage compared with the polygon   
   mirror approach which we tried before was that during the pulse duration the   
   phase fronts of the beam stayed surprisingly nice -- the squeezed light was   
   measured with a homodyne detector and therefore had to interfere with a   
   reference beam. The interference visibility was still very good, even though   
   the spinning disk moved quite a lot of air inside its case and was not   
   exactly noiseless.   
      
   > Mechanical streak cameras are surprisingly fast--you spin a polygon on   
   > an air bearing (or a magnetic bearing in a vacuum) and look at the   
   > scanned beam from some distance.  You can do 12 facets x 100k rpm x 10m   
   > ~ 2500 km/s. (*) Nanoseconds are _easy_.  They did stuff like that back   
   > in the 40s and 50s for bomb development.   
      
   That's very impressive and quite a bit faster than the slit. Balancing a   
   polygon mirror for 100 000 rpms probably is no simple engineering task   
   either...   
      
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