Imagine a monochromatic laser beam of radius 1 mm made up of a sinusoidal plane
ID: 2134975 • Letter: I
Question
Imagine a monochromatic laser beam of radius 1 mm made up of a sinusoidal plane wave propicating in the -x(hat) direction with wavelength 700nm, emitted from a laser with power 1mW. For such a laser beam, calculate the amplitudes E_0 and B_0 of the electric and magnetic fields.
If the laser beam is perpendicularly incident on a piece of thin foil that completely absorbs the light, what is the radiation pressure on the foil? express your anser in N/m^2
If the foil has mass/area of 1.6*10^-3 kg/m^2 and both the laser beam and the foil have the same size then what will the acceleration of the foil be?
Most points for full explanations please and thank you for your time!
Explanation / Answer
intensity I = power/area = Emax^2/2uoC
Emax^2 = 1*10^-3 * 2*4pi*10^-7 * 3*10^8/pi *(10^-3)^2
Emax = 489.89 N/C
Erms = Emaxc/1.414 = 346.46 N/C
Bmax = Emax/c = 489.89/3*10^8 = 1.632 *10^-6 T
Brms = Bmax/1.414 = 2.45*10^-6 T
b. radiation pressure Pr = I/c = 10^-3/3*10^8 = 3.33*10^-12 N/m^2
c. force F= ma = IA/c
a = I A/mc = 3.33*10^-12/1.6*10^-3 = 2.08*10^-9 m/s^2