Answer:
The frequency of the emitted EM wave by He-Ne laser is 
Given:
Power emitted by He-Ne laser, P = 1.5 mW = 
Wavelength, 
Solution:
Now, to calculate the frequency,
of the EM wave emitted:
Energy associated with 1 photon = Power of one photon per sec = 
Therefore, power associated with 'N' no. of photons, P = 
where
= Planck's constant
Now,

N = 
Also, we know that:

Thus

