Chapter 16: Q. 67 (page 453)

LASIK eye surgery uses pulses of laser light to shave off tissue
from the cornea, reshaping it. A typical LASIK laser emits a
1.0-mm-diameter laser beam with a wavelength of 193 nm. Each
laser pulse lasts 15 ns and contains 1.0 mJ of light energy.
a. What is the power of one laser pulse?
b. During the very brief time of the pulse, what is the intensity
of the light wave?

Expert verified

a. The power of one laser pulse is $6.67 \times 10^{4} W .$

b. During the very brief time of the pulse, the intensity

of the light wave is $8.5 \times 10^{10} W / m^{2}$ .

Step by step solution

The energy of laser pulse $U = 1 m J = 1 \times 10^{- 3} J$

The laser pulse lasts for a time period of $t = 15 n s = (15 \times 10^{- 9}) s$

Diameter of laser beam,role="math" localid="1649825424330" $d = 1 m m$

The power of laser beam can be determined by,

$P = \frac{U}{t} P = \frac{1 \times 10^{- 4} J}{15 \times 10^{- 9} s} P = 6.67 \times 10^{4} W$

Diameter of laser beam, $d = 1 m m$

Therefore, the radius of the laser beam is,

$r = \frac{1}{2} m m r = 0.5 m m r = 5 \times 10^{- 4} m$

During a very short time of the pulse, the intensity

of the light wave can be determined by, $I = \frac{P}{A}$ , where $A$ is the cross-sectional area of the light beam.

Therefore, the intensity,

role="math" localid="1649826456280" $I = \frac{P}{A} I = \frac{6.67 \times 10^{4} W}{π {(5 \times 10^{- 4} m)}^{2}} I = 8.5 \times 10^{10} W / m^{2}$

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