Question

A helium neon laser emits red light of wavelength 632.8 nm, which is obtained when neon atoms move from level 5s to level 3p. Given is a tube that contains 0.25 moles of a helium-neon mix, of which 15% are neon atoms. Also given is that while the laser is active, around 2% of the neon atoms are located at one of the two given energy levels at any time.

a) what is the difference in energy between levels 5s and 3p of the neon atom in electron Volt? Show your calculations.

b) which of the following CAN BE the number of Neon atoms that are located at level 3p while the laser is active? Show calculations and reason your answer.

1) 1.92 x 10²⁰

2) 3.93 x 10²⁰

3) 4.51 x 10²⁰

4) 1.92 x 10²⁴

5) 3.93 x 10²⁴

6) 4.51 x 10²⁴

c) The laser emits radiations at a power of 10 milliWatt. Calculate how many stimulated emissions occur in one minute.

THANK YOU

Answer 1

a) Difference in energyin J= (hc)/(wavelength in meters)

where h is Planck's constant and c is speed of light. From this,

E in J=3.143x10-19

E in eV=( E in J)/(1.6x10-19)

            =1.96 eV

b)The tube contains 15% neon in 0.25 mole of He-Ne mixture=(.15)x(.25)x(6.02x1023)

                                                                                                    =2.2575x1022 number of Ne atoms

    According to the question, the number of atoms that can be there in level 3p is 2% of total number of neon atoms=(0.02)x(2.2575x1022)

                       =4.51x1020

c)The number of stimulated emissions=(Energy of laser in watt)/(Energy of photons)

                                                               =(10x10-3)/(hc/632.8nm)

                                                               =3.18x1016 photons/min