Answer:
a) U = 0.375 mJ
b) p_rad = 4.08 mPa
c) λ_med = 604 nm ; f_med = 3.7 * 10^14 Hz
d) E_o = 3.04 * 10^4 V / m , B _o = 1.013 *10^-4 Nm/Amp
Explanation:
Given:
λ_air : wavelength = 810 * 10^(-9) m
P: Power delivered = 0.25 W
d : Diameter of circular spot = 0.00051 m
c : speed of light vacuum = 3 * 10^8 m/s
n_air : refraction Index of light in air = 1
n_med : refraction Index of light in medium = 1.34
ε_o : permittivity of free space = 8.85 * 10^-12 C / Vm
part a
The Energy delivered to retina per pulse given that laser pulses are 1.50 ms long:
U = P*t
U = (0.25 ) * (0.0015 )
U = 0.375 mJ
Answer : U = 0.375 mJ
part b
What average pressure would the pulse of the laser beam exert at normal incidence on a surface in air if the beam is fully absorbed?
p_rad = I / c
Where I : Intensity = P / A
p_rad = P / A*c
Where A : Area of circular spot = pi*d^2 / 4
p_rad = 4P / pi*d^2*c
p_rad = 4(0.25) / pi*0.00051^2*(3.0 * 10^8)
p_rad = 0.00408 Pa
Answer : p_rad = 4.08 mPa
part c
What are the wavelength and frequency of the laser light inside the vitreous humor of the eye?
λ_med = n_air*λ_air / n_med
λ_med = (1) * (810 nm) / 1.34
λ_med = 604 nm
f_med = f_air
f_med = c / λ_air
f_med = (3*10^8) / (810 * 10^-9)
f_med = 3.7 * 10^14 Hz
Answer : λ_med = 604 nm ; f_med = 3.7 * 10^14 Hz
d)
What is the electric and magnetic field amplitude in the laser beam?
I = P / A
I = 0.5*ε_o*c*E_o ^2
I = 4P / pi*d^2
Hence, E_o = ( 8 P / ε_o*c*pi*d^2 ) ^ 0.5
E_o = ( 8 * 0.25 / (8.85*10^-12) * (3*10^8) * π * (0.00051)^2) ^ 0.5
E_o = 3.04 * 10^4 V / m
For maximum magnetic field strength:
B_o = E_o / c
B_o = 3.04 * 10^4 / (3*10^8)
B _o = 1.013 *10^-4 Nm/Amp
Answer: E_o = 3.04 * 10^4 V / m , B _o = 1.013 *10^-4 Nm/Amp
