Did you ever get the laser adequately stabilized? Your last posts on that topic seemed to suggest that wavelength drift was larger than the current drift. If that is true, then there is something else causing drift, possibly laser temperature.
As for your timing questions, it would help to see the code you are using. Generally you can use Wait (ms) or the timing of a data acquistion process to set the loop time.
Two methods to write to file at slower rates than the loop rate are:
1. Put the file write inside a case structure. Only call that case when the desired write time has elapsed, the desired amount of data has accumulated, or the specified number of iterations between saves has occurred.
2. Use a Producer/Consumer architecture to allow largely independent timing of acqusitions and saves.
Lynn