Lasers are classified according to the eye-damage danger they pose. Class 2 lasers, including many laser pointers, produce visible light with no greater than 1.0 mW total power. They're relatively safe because the eye's blink reflex limits exposure time to 250 ms. Requried:
a. Find the intensity of a 1-mW class 2 laser with beam diameter 2.0 mm .
b. Find the total energy delivered before the blink reflex shuts the eye.
c. Find the peak electric field in the laser beam.

(a)  The intensity of laser beam is  .

(b)  The total energy delivered before the blink reflex shuts the eye is .

(c)  The required value of peak electric field in the laser beam is .

Given data:

The power of laser is, .

The exposure time is, .

The beam diameter is, .

a)

The standard expression for the intensity of beam is given as,

I = P/A

Here, P is the power of the laser  and A is the cross-sectional area of the beam. And its value is,

Then intensity is,

Thus, the intensity of laser beam is .

(b)

The expression for the total energy delivered is given as,

E = Pt

Solving as,

Thus, the total energy delivered before the blink reflex shuts the eye is .

(c)

The expression for the peak electric field is given as,

Solving as,

Thus, the required value of peak electric field in the laser beam is .

Learn more about the laser intensity here:

link

a) 318.2 W/m^2

b) 2.5 x 10^-4 J

c) 1.55 x 10^-8 v/m

Explanation:

Power of laser P = 1 mW = 1 x 10^-3 W

exposure time t = 250 ms = 250 x 10^-3 s

If beam diameter = 2 mm = 2 x 10^-3 m

then

cross-sectional area of beam A = = (3.142 x )/4

A = 3.142 x 10^-6 m^2

a) Intensity I = P/A

where P is the power of the laser

A is the cros-sectional area of the beam

I = ( 1 x 10^-3)/(3.142 x 10^-6) = 318.2 W/m^2

b) Total energy delivered E = Pt

where P is the power of the beam

t is the exposure time

E = 1 x 10^-3 x 250 x 10^-3 = 2.5 x 10^-4 J

c) The peak electric field is given as

E =

where I is the intensity of the beam

E is the electric field

c is the speed of light = 3 x 10^8 m/s

= 8.85 x 10^9 m kg s^-2 A^-2

E =  = 1.55 x 10^-8 v/m