The 488 nm line from an argon ion laser is doppler broadened to 2.7×109 hz. given that the laser’s mirrors are 1 m apart, determine the number of longitudinal modes within the gain bandwidth of the 488 nm line. assume that the index of refraction of the gas is 1

The number of longitudinal modes within the gain bandwidth is 18.

Explanation:

Given that,

Wavelength = 488 nm

Frequency

Distance = 1 m

Index of refraction of the gas = 1

We need to calculate the number of longitudinal modes within the gain bandwidth

Using formula of number of longitudinal modes

Where, f = Doppler frequency

c = speed of light

l= separation

Put the value into the formula

Hence, The number of longitudinal modes within the gain bandwidth is 18.

scattering of light by tiny particles in air to produce the colors we see on sky, is dependent on the following factors:

(i) wavelength of light

(ii) size of the scattering particle  

(iii) distance traveled by light through the atmosphere.

according to rayleigh's law of scattering, the amount of scattering is inversely proportional to the fourth power of its wavelength. shorter the wavelength, greater is its scattering. hence violet/blue light is scattered more than red.

sun's light is a composite light ( visible light) with wavelengths in the range 400 nm (violet) to 700 nm (red). as sunlight passes through our atmosphere, the molecules of air scatter light according to their wavelengths. during sunrise and sunset, the sun's position is below the horizon. hence light from the sun travels a greater distance in the atmosphere when compared to its position a noon.

as sunlight enters the earth's atmosphere, blue light is scattered away and at the end of its journey in the sky, only red and orange wavelengths remain in the beam.

hence at sunrise and sunset, the sky appears reddish orange.