On Sun, 2009-12-20 at 10:54 -0500, Kenneth Lerman wrote: > Yes, I have an Agilent 5517D which is a frequency stabilized two > frequency laser that I got on Ebay. > > How fast can the counters on the 5I20 count? I would need a pair of > perhaps 32 bit counters that can count at more than 4 MHz and can be > read out "simultaneously". (Actually, copied into another set of > registers at the same time and then transferred to the host before the > next copy time). > > Ken > > Anders Wallin wrote: > >> A laser interferometer is on my todo list. I've acquired all of the > >> optics on ebay for a total of a few hundred dollars. I've built a power > >> supply. The major part I'm missing is the counting and interpolating > >> electronics with a computer interface. > >> > > > > Hi Ken, > > > > the heterodyne interferometers I have found described mostly use a > > two-frequency laser which emits two orthogonal polarizations with > > slightly (500kHz? or in your case 4 MHz) different frequency. Did you > > find a Zeeman-stabilized two-frequency laser on ebay? Or are you > > planning to DIY and put magnets around a normal HeNe tube? Sams Laser > > FAQ has a description: > > http://www.repairfaq.org/sam/laserchn.htm#chndzees > > > > The other method is to use an acousto-optic modulator to shift the > > frequency of the light. But the papers I've found use two modulators, > > and I only have one to spare right now... > > > > If I can either find a two-frequency HeNe or DIY with magnets then I'd > > be interested in testing this, possibly with the m5i20 (already has > > fpga code for fast encoder counters) for data acquisition. > > > > Anders > > The datasheet for the 5i20 mentions 8 counter channels at 100 MHz. Fast enough? ;-)
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