Nightmarish michelson interferometer question

[sachi]

We have to "closely spaced" frequencies f1 and f2. "The moving mirror moves at a constant speed v. Explain how the Doppler effect on the light reflected from the moving mirror affects the recorded signal as a function of time. Estimate the value of v required to resolve the freq. difference of 500 MHz between two modes of a laswe within a time of 0.1s."

I'm very confused about this. Under normal circumstances I'm pretty sure there is no moving mirror! I can only assume that the "closely" spaced frequencies are so closely spaced that they can't be resolved by the instrument, therefore we have to artificially introduce a doppler freq. shift in one of the components.
I'm using the doppler shift formula from spec. rel. that shift in freq. = (v/c) * original frequency. Therefore surely v = 500MHz *c/f1
or we could have used f2, as they are almost equal. I can't see how the time 0.1s comes into it. Thanks very much

 

[Andrew Mason]

We have to "closely spaced" frequencies f1 and f2. "The moving mirror moves at a constant speed v. Explain how the Doppler effect on the light reflected from the moving mirror affects the recorded signal as a function of time. Estimate the value of v required to resolve the freq. difference of 500 MHz between two modes of a laswe within a time of 0.1s."

I'm very confused about this. Under normal circumstances I'm pretty sure there is no moving mirror! I can only assume that the "closely" spaced frequencies are so closely spaced that they can't be resolved by the instrument, therefore we have to artificially introduce a doppler freq. shift in one of the components.
I'm using the doppler shift formula from spec. rel. that shift in freq. = (v/c) * original frequency. Therefore surely v = 500MHz *c/f1
or we could have used f2, as they are almost equal. I can't see how the time 0.1s comes into it. Thanks very much

Can you give us the whole problem? You are assuming we know what you are talking about here.

There is a doppler shift only if the mirror is moving relative to the source of the light. How do you get such motion in a Michelson interferometer? You need to clearly explain what it is you are talking about.

AM