Question

A  green laser operates at 488.0 nm with an output power of 2.5 mW. Calculate the average output in photons/s (“photon flux”). What would the output power be for the same flux of 244.0 nm photons? What would the photon flux be for a 488.0 nm laser operating at 5.0 mW?

Answer 1

First of all, what is the definition of power?

POWER =

Therefore,

where =

.................................... eq (1)

where P is the power in watts,

n/T gives the photon flux measured in photons per second,

and E is the energy of the photon... that is the laser's energy.

h is the plank"s constant equal to h = 6.62606957 x 10^-34 and c is the speed of the photon = 3x10⁸ ms^-1.

is the wavelength of the photonscalculated in meters.. commonly in nanometers (nm)

Lets calculate...

CONDITION 1

; ; n/T = ?

substituting all values in eq (1),

2.5 x 10^-3W = (n/T) x hc/(488 x 10^-9m)

photon flux n/T or   6.137 x 10¹⁵ photons per second.

CONDITION 2

P = ? ; same flux, 6.137 x 10¹⁵ photons per second;

substitute in eq (1)

P = 6.137x 10¹⁵ x hc / (244 x 10^-9m)

P = 5 x 10^-3 W or.... 5mW

CONDITION 3

? ; ; P = 5 mW = 5 x 10^-3 W

again the same equation,

5 x 10^-3 W = (n/T) hc / (488 x 10^-9m)

n/T or 1.227 x 10¹⁶ photons per second.

h = 6.62606957 x 10^-34

c = 3x10⁸ ms^-1.