Engineering Physics Multiple Choice Questions on “Helium Neon Laser”.
1. Which of the following is a four-level laser?
a) ND: YAG
b) Ruby
c) He-Ne
d) Argon laser
Answer: c
Clarification: He-Ne laser is a four-level laser. Whenever an electric discharge is passed through the gas, the helium atoms gets to higher energy states, as the concentration of helium atoms is higher. It was one of the first successfully operated laser.
2. The difference between He-Ne Laser is __________
a) It gives pulsed output
b) It gives a non-continuous laser beam
c) It gives a continuous laser beam
d) No difference
Answer: c
Clarification: As we know, the ruby laser beam is discontinuous and pulsed. However, the He-Ne laser beam is a continuous laser beam. Also, it is a four-level laser while ruby laser is a three-level laser.
3. He-Ne laser is a type of ____________
a) Solid laser
b) Liquid laser
c) Gas laser
d) Diode laser
Answer: c
Clarification: He-Ne laser is the most widely used laser. It was the first continuous laser generated. Gas lasers are less prone to damage by overheating, as compared to solid laser.
4. Which pumping method is used in He-Ne laser?
a) Optical Pumping
b) Electrical Excitation
c) Chemical Pumping
d) Direct Conversion
Answer: b
Clarification: Generally, in He-Ne laser, an electric discharge is used to excite the atoms of the active medium. This process is known as Electrical Excitation and is normally used in gas lasers.
5. The He-Ne laser operates at a wavelength of ____________
a) 540 nm
b) 632 nm
c) 690 nm
d) 717 nm
Answer: b
Clarification: The helium-neon laser operates at a wavelength of 632.8 nanometers (nm), in the red portion of the visible spectrum. It is the most widely used gas laser.
6. The number of photons emitted for a 2.5 mW He-Ne laser is __________
a) 4.9 X 1015
b) 5.9 X 1015
c) 6.9 X 1015
d) 7.9 X 1015
Answer: b
Clarification: We know, for a He-Ne laser, λ = 6328 Å = 6.328 X 10-7 m
Power = 2.5 mW = 2.5 X 10-3 E
Energy = Power X Time = 0.0025 X 1
= 0.0025
Number of photons in each pulse = Energy X λ / hc
= 0.0025 X 6.6 X 10-7/6.6 X 10-34 X 3 X 108
= 7.9 X 1015.
7. The output of a He-Ne laser has pulse duration of 15 ms and average output power of 1 W per pulse. How much energy is released per pulse?
a) 5 mJ
b) 10 mJ
c) 15 mJ
d) 20 mJ
Answer: c
Clarification: As we know, Energy = Power X Time
= 1 W X 15 X 10-3 s
= 15 mJ.
8. When the transition takes place from En6 -> En5, what is the wavelength of produced beam?
a) 6328 Å
b) 33913 Å
c) 11523 Å
d) 7550 Å
Answer: b
Clarification: When the lasing transition is from En6 -> En5, it produces a beam of 33913 Å. The opper level is same in this case and in the 6328 Å transition.
9. He-Ne laser is used in Holography.
a) True
b) False
Answer: a
Clarification: He-Ne laser is highly coherent and monochromatic. Due to this, it is used in holography, spectrometers, prints, scanners, etc. It is widely used in Laboratories.
10. Which of the following shows the laser transition in Neon in He-Ne laser?
a) 
b) 
c) 
d) 
Answer: b
Clarification: The transition shown in the following figure is the correct transition that takes place in the Ne atoms. Between two or more layer, as soon as population inversion is achieved, the lasing action starts.