# Engineering Physics Questions and Answers – Carbon Dioxide Laser and Semiconductor Laser

This set of Engineering Physics Puzzles focuses on “Carbon Dioxide Laser and Semiconductor Laser”.

1. What is the wavelength of the emitted laser by a carbon dioxide?
a) 9.4 μm
b) 10.6 μm
c) 11.4 μm
d) 12.5 μm

Explanation: The radiations emitted in a CO2 laser has a wavelength of 10.6 μm. It is a four-level laser. The transition takes place between the different vibrational states of the molecule.

2. Which of the following is a characteristic of semiconductor lasers?
a) Output in Visible region
b) High Efficiency
c) Output in UV region
d) Pulsed output

Explanation: Semiconductor lasers such as GaAs, InP, InSb etc. are used extensively because of their high efficiency. Also, they can be employed in optical communications with ease.

3. In the CO2 molecular gas laser, transition takes place between the ______________
a) Molecular states
b) Atomic states
c) Vibrational states
d) Energy states

Explanation: In the CO2 molecular gas laser, transition takes place between the vibrational states of Carbon dioxide molecules. It is a very efficient laser.

4. Which of the following is a four-level laser?
a) ND: YAG
b) Ruby
c) Argon laser
d) CO2 laser

Explanation: The CO2 laser is a very efficient laser. It is a four-level laser and it operates at 10.6 μm in the far IR region. The active medium is a gas mixture of CO2, N2 and He.

5. Which of the following gas is not a part of the active medium in a CO2 laser?
a) CO2
b) N2
c) He
d) O2

Explanation: The active medium of a CO2 laser consists of a mixture of CO2, N2 and He. It is the vibrational transition in the CO2 that results in the lasing action.

6. The highest powered CO2 laser had a power of _________
a) 1 W
b) 10 W
c) 1000 W
d) 10000 W

Explanation: Light from a CO2 laser is powerful enough to cut many materials, including cloth, wood and paper; the most powerful CO2 lasers are used for machining steel and other metals. The highest-powered CO2 lasers run over 1,000 W.

7. The active medium of a semiconductor diode is the junction of the forward biased P-N diode.
a) True
b) False

Explanation: When the p-side of a semiconductor diode is connected to the positive terminal of the battery and the n-side to the negative terminal, the diode is said to be forward biased. A semiconductor laser is essentially a semiconductor diode, where the active medium is the forward biased p-n junction.

8. Semiconductors lasers do not need mirrors to form optical cavity.
a) True
b) False

Explanation: Semiconductor lasers do not require two external mirrors to form an optical cavity. Reflection from the cleaved ends of the semiconductor is enough to produce lasing.

9. The following figure shows the laser spectrum for ________

a) CO2 Laser
b) Fabry-Pot Semiconductor Laser
c) DFB semiconductor laser
d) FBG semiconductor laser

Explanation: Fabry-Pot semiconductor laser is a type of semiconductor laser which is characterized by the use of the cleavage plane of a laser crystal for reflection of the light emitted in the active layer. It’s lasing spectrum observed is as shown in the figure.

10. Where is ND: YAG most commonly used?
a) Cosmetic Surgery
b) Welding
c) Photography
d) Optical Communications

Explanation: ND: YAG is most commonly used for cosmetic energy because it has the property of maximum energy absorption by the target (hair or lesion) with minimum absorption by the surrounding skin structures.

11. In which region of the electromagnetic spectrum, does the semiconductor laser lies?
a) Visible Region
b) UV Region
c) Microwave Region
d) Infrared Region

Explanation: In the gallium arsenide laser, the wavelength of the emitted laser is around 845 nm to 905 nm, which lies in the infrared region of the electromagnetic spectrum.

12. The following graph shows the physical gain for which kind of laser?

a) CO2 Laser
b) Semiconductor Laser
c) Helium Laser
d) Ruby Laser

Explanation: The given figure shows the physical gain for a semiconductor laser. The upper band is the conduction band while the lower one is the valence band. The lasing action is taking place between the two bands.

Sanfoundry Global Education & Learning Series – Engineering Physics.

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