lasers for eye surgery nm

How do I solve this problem involving a laser, energy, and wavelength?

(a) In the stimulated emission for a certain laser, the photons arise from a transition between energy levels 2.24 eV apart. What is the wavelength of light emitted by this laser?

HELP: By now you should know that the energy of a photon is E = h*f. Given the energy of a photon, you can determine its frequency and therefore its wavelength. Be careful of the units!

(b) Lasers are now used in eye surgery. Given that the wavelength of a certain laser is 514 nm and the power of the laser is 1.8 W, how many photons are released if the laser is used for 0.052 s during the surgery?

# of photons =

HELP: You know the energy released per second (the power) and the time the laser is on – from this you can calculate the total energy released.

HELP: You also know the wavelength of each photon and can therefore calculate the energy of each photon. Knowing the total energy and the energy of each individual photon leads you to the number of photons!

a) the energy between the levels is 2.24eV * 1.60×10^-19J/eV = 3.584×10^-19J

Now we have E = h*f so f = E/h = 3.584×10-19/6.63×10^-34 = 5.4057×10^14Hz

So ? = c/f = 3.00×10^8m/s/5.4057×10^14Hz = 5.550×10^-7m = 555.0nm

b) If ? = 514nm then f = c/? = 3.00×10^8/514×10^-9 = 5.8366×10^14Hz

So E = P*t = n*h*f

So n = P*t/(h*f) = 1.8W*0.052s/(6.63×10^-34*5.8366×10^14) = 2.42×10^17 photons

Tell others about this site!