Calculate the electric field amplitude

In summary, To calculate the average irradiance for a given laser beam with a wavelength of 645nm, power of 3mW, and a diameter of 1mm, you can use the formula S_avg = (1/2) * c * n * ε0 * E0^2. However, to find the field amplitude E_0, you need to know the constant of proportionality, which is not provided in the given information. You can find the photon flux by calculating the energy per photon and dividing it by the intensity (P/A). However, without the constant of proportionality, you cannot find the electric field amplitude E_0.
  • #1
dmriser
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Homework Statement



Calculate the average irradiance for the given laser beam.

λ=645nm, P=3mW, d=1mm.

Homework Equations



S=[E X H]
S_avg = (1/2) * c * n * ε0 * E0^2

The Attempt at a Solution



I understand the Poynting vector and I can derive the average irradiance formula. I cannot however find the field amplitude E_0 with the information I have.

I know that the field amplitude is proportional to photon flux, but I can't find anywhere what the constant of proportionality is.

First, I calculated the energy per photon.. 3 * 10^-19 J, then I find the photon flux by finding intensity (P/A). From this information I arrive at the photon flux.. From here I don't know what to do.

To be clear, I have something like this for photon flux: 1x1019 photons/m2*s
 
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  • #2
I need to find the electric field amplitude E_0, but I don't know how to do that. Help would be appreciated. Thank you.
 

FAQ: Calculate the electric field amplitude

What is the formula for calculating the electric field amplitude?

The formula for calculating the electric field amplitude is E = kq/r^2, where E represents the electric field amplitude, k is the Coulomb's constant (9 x 10^9 Nm^2/C^2), q is the magnitude of the charge, and r is the distance between the charge and the point where the electric field is being measured.

How do you determine the direction of the electric field amplitude?

The direction of the electric field amplitude is determined by the direction of the electric force that would be exerted on a positive test charge placed at that point. The electric field lines point away from positive charges and towards negative charges.

Can the electric field amplitude be negative?

Yes, the electric field amplitude can be negative. This indicates that the direction of the electric field is opposite to the direction of the force that would be exerted on a positive test charge at that point. This can occur when there are multiple charges present in the system.

What is the unit of measurement for electric field amplitude?

The unit of measurement for electric field amplitude is newtons per coulomb (N/C) or volts per meter (V/m).

How does distance affect the electric field amplitude?

As distance increases, the electric field amplitude decreases. This is because the electric field is spread out over a larger area as distance increases, resulting in a weaker field strength. The relationship between distance and electric field amplitude is inversely proportional to the square of the distance (E ∝ 1/r^2).

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