How do I write a formula for a laser power curve that repeats 4 times per 360° rotation?

[SimonHollas]

Dear All,

I have an apparatus that produces a graph of results that looks to me like a sine wave (a half wave plate affecting the power throughput of a laser; it goes from maximum to minimum 4x throughout its 360º rotation). My problem is that I need to define this line as a formula but have no idea where to start. Any ideas, anyone?

 

[quasar987]

You look at the amplitude A (maximum height) of the wave. You also find the period T on the x-axis and if the wave is out of phase, you find the distance d from the origin of how much it is out of phase in the direction of positive x. Then the equation is

$$y(x) = Asin \left(\frac{2\pi (x-d)}{T}\right)$$

 

[SimonHollas]

Thanks, Quasar987!