Question

In LASIK surgery, a laser is used to reshape the cornea of the eye to improve vision. The laser produces extremely short pulses of light, each containing 1.0 mJ of energy. Part A In each pulse there are 9.7×1014 photons. What is the wavelength of the laser?

Answer 1

To solve this problem it is necessary to apply the related concepts laser pulse energy.

By definition the energy of a laser pulse in terms of number of photons is

$E = N \frac{hc}{\lambda}$

Where,

$\lambda =$ Wavelength

N = Number of photons in each laser pulse

h = Planck constant

c = Speed of light

We need to find the wavelength, then re-arrange the equation we have

$\lambda = \frac{Nhc}{E}$

Converting the unit the energy from J to eV, we have

$E= 1*10^{-3}J(\frac{1eV}{1.6*10^{-19}J})$

$E = 6.25*10^{15}eV$

Replacing,

$\lambda = \frac{Nhc}{E}$

$\lambda = \frac{(9.7*10^{14})(4.136*10^{-15})(3*10^8)}{6.25*10^{15}}$

$\lambda = 192.4nm$

Therefore the wavelength of the laser is 182.4nm

Note: The Planck constant used is in units of eV.