In soft tissue laser surgery, a highly focused beam of light is used to vaporize

Question

In soft tissue laser surgery, a highly focused beam of light is used to vaporize tissues with the high water content. Typical values for the beam diameter in such applications is 0.4 mm, while the intensity of the beam is 20 W/ cm^2.

1. How much energy is transmitted by believer in a time of .3 ms?

2. After the laser is used to make a small incisions, the beam can be defocused to increase the beam diameter and then be used to cauterize the surrounding tissues to decrease post operative swelling. For cauterization an intensity of 50 mW/cm^2 is used. Assuming that the power of the laser remains the same as in part one, what beam diameter should be used for cauterization?

Explanation / Answer

I = 20 W/cm^2, d = 0.4 mm, t = 0.3 ms

I = P/A = Q/At

A = pi*r^2

20 = Q/(3.14*0.02^2*0.3*10^-3)

Q = 7.56*10^-6 W/s

2) I = P/A

I1/I2 = d2^2/d1^2

20/0.05 = (d2/0.4)^2

d2 = 8 mm

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