Problem 28.61: Removing vascular lesions Part A A pulsed dye laser emits light o

Question

Problem 28.61: Removing vascular lesions Part A A pulsed dye laser emits light of wavelength 600 nm in 430 pulses Because this wavelength is strongly absorbed by the hemoglobin in the blood the method is especially effective for removing various types of blemishes due to blood, such as port-wine-colored birthmarks. To get a reasonable estimate of the power required for such laser surgery. we can model te blood as having the same specific heat and heat of vaporization as water (4190 J/kg.K 2.256 x 106 J/kg). Suppose that each pulse must remove 2.10 of blood by evaporating it, starting at 33.0°C. How much energy must each pulse deliver to the blemish? pulse = m.J Submit My Answers Give Up Part B What must be the power output of this laser? Submit My Answers Give Up Part C How many photons does each pulse deliver to the blemish? photons Submit My Answers Give Up

Explanation / Answer

a) Energy, E, which each pulse delivers to the blemish to remove 2.10 ug of blood
= [(2.10*10^-9)*{4190*(100-33) + 2.256*10^6}] J,

where 2.256 is the latent heat of water in NJ/kg
E = 5.33*10^-3 J = 5.33 mJ

b)Required power output of this laser = (5.3310^-3)/{430*(10^-6)} = 11.395 W

c)We know

Energy of each photon = hc/lambda = [6.62*(10^-34)*3*(10^8)}/{600*(10^-9)} J = 3.31*10^-19 J

Number, N of photons does each pulse deliver to the blemish = {5.33*(10^-3)}/{3.31*(10^-19)};
N = 1.61*10^16

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