Question

A person's vision may be improved significantly by having the cornea reshaped with a laser beam, in a procedure known as photorefractive keratectomy. The excimer laser used in these treatments produces ultraviolet light with a wavelength of 170 nm .

Part A What is the difference in energy between the two levels that participate in stimulated emission in the excimer laser?

Part B How many photons from this laser are required to deliver an energy of 1.50×10?13 J to the cornea?

Answer 1

1.

Energy produced by given ultralight wavelength will be

E = hc/lambda

lambda = wavelength = 170 nm

c = speed of light

So,

E = 6.626*10^-34*3*10^8/(170*10^-9)

E = 1.17*10^-18 J = 1.17*10^-18/(1.6*10^-19) eV

E = 7.31 eV

Part B.

No of photon required to deliver given energy will be

n*E = E1

E = energy of single photon = 1.17*10^-18 J

E1 = total energy = 1.50*10^-13 J

So,

n = E1/E

n = 1.50*10^-13/(1.17*10^-18)

n = 128205 photons = 1.28*10^5 photons

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