The laser cavity is formed by two mirrors separated by 15 cm. One of the mirrors has an ultra-high reflectivity and the output mirror has the much lower reflectivity of 99.5 %. How many photons are there in the cavity?[/B]
The power of the laser is 1mW and the wavelength is 600nm
E= hc/λ and N=P/E Hence N = Pλ/hc
Power out = Power in x (1 - reflectivity) ........... Not sure about this formula
The Attempt at a Solution
I have different views to what is happening as I think the question is vague. So I only have worked out certain elements.
At full power N = Pλ/hc ...... N=3.01x1015
We could work out the time inside the cavity t = 30x10-2 /3x108 which gives 1 nano second....... Not sure if this is relevant to the question.
Using the formula Power out = Power in x (1 - reflectivity) gives a power of 1x10-3 x(1 -0.05)
Using this new power N = Pλ/hc......... N= 2.86x1015 photons/s
Would I then do 3.01x1015 - 2.86x1015 = 1.6x1014 ??
Not sure if this is correct. Is the time element I tried supposed to be used?