Question

A laser rated at 0.15 J can generate radiation in 2.0 ns pulses with the wavelength of 732 nm. (a)What is the power output per pulse? (b) How many photons are produced in one pulse? Express this quantity in einsteins (mole of photons) (c) If the efficiency of the laser is 10 % and repetition rate, 13 Hz, what electrical power does it use?

Answer 1

a) as P = E /T = 0.15 J/ 2 * 10^-9

=0.075 * 10⁹ watt

b)  E = ħ c / λ

E = energy per photon ,h = plancks constant = 6.626x10^-34 J s
c = speed of light = 3.00x10^8 m/s , λ = wavelength =732 nm = 732 x10^-9 m

E = (6.626x10^-34 J s) x (3.00x10⁸ m/s) / 732x10^-9 m = 0.027 * 10^-17 J



and for 0.15 J

0.15 J x (1 photon / 0.027 * 10^-17 J) = 5.55 *  10¹⁷ photons

`1 einstein = 6.023 * 10²³ no of photons

1 photon = 1/  6.023 * 10²³ einstein

5.55 * 10¹⁷ no of photons= 5.55 * 10¹⁷ /  6.023 * 10²³ E   = 0.92 * 10⁶ einstein