# Homework Help: Intensity after Laser Round Trip

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1. May 14, 2017

### cake-jake1

1. The problem statement, all variables and given/known data
Im having trouble understanding where the value of 0.95 came from which takes into account mirror losses.

1 Flat mirror, So no given reflection coefficients as system has no curved mirrors.
Given that the distributed cavity Loss coefficient is 10^-4 and the signal gain coefficient Is 10^-3.
Evaluate the intensity of the light beam after a round trip through the cavity of length 20cm.

Both coefficients are per cm.

Starting intensity is 1pW.

3. The attempt at a solution
Our lecturer actually gave us a sort of run through of this question,
And has Pout = Pin ( 1 + (20*gain - 20*loss)) *(losses on the mirror)
Losses on the mirror is given as 0.95. However I have no idea how this is calculated, and given a similar question is likely to come up in my final exam I am here asking for help!

Similarly I know there are scenarios where curved mirrors can be brought into the question and the reflection coefficient needs to be bought into play, how would this be done?

Many Thanks if anyone can help :)

2. May 17, 2017

### andrevdh

That value is not calculated it is just how the mirror is constructed, although I would think that the loss is 5% and 95% is reflected.

3. May 17, 2017

### scottdave

I agree with @andrevdh . Usually laser mirrors are constructed to transmit a small portion (say 5%) through and reflect the rest (95% in my example). Perhaps it said something about transmission factor. It has been awhile since I have worked with lasers.