Hey Lynn,
Thanks for the input. It seems like the lock-in method will be difficult to implement mainly because it will be difficult to define a reference frequency. However, are you sure we have to worry a lot about the 192 measurement per second because I think we can consider those seperate measurements. There will be no correlation between each of those 192 measurements/second actually and we can think of those as a seperate 260Hz+280 KHz mixed signal waves (or whatever mixed signal we choose to measure with the lock-in) which have somewhat random phases and amplitudes (they are random except for the fact that they are defined spatially by the structure we are measuring). For the the lock-in method the 192 measurements per second happens at a much slower rate than the signal we want to actually measure. Is this is more an issue with the IQ approach you are suggesting? I still need to get up to speed with the IQ approach.
I have been reading up on IQ modulation. It seems to avoid the need to use filters to select the upper or lower sidebands and it looks like this is a method for generating single sideband modulated signals directly. Do you think this could be used to generate the reference frequency for the lock-in amplifier?
-Eric