Laser Diode Questions

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Very Short Answers Questions [1 Mark Questions]

Ques. Which of the following is a unique property of a laser?

1. Wavelength
2. Coherence
3. Speed
4. Directional

Ans. The correct answer is b. Coherence

Explanation: Coherence is an important feature of laser beams because wave trains of the same frequency are in phase in laser beams. High coherence leads to exceptionally high power.

Ques. What is the need to achieve population inversion?

1. To bring most of the atoms to the ground state
2. To achieve a stable condition
3. To reduce the time of production of laser
4. To excite most of the atoms

Ans. The correct answer is d. To excite most of the atoms

Explanation: When population inversion occurs, the majority of atoms are excited. This causes the incident beam to be amplified through stimulated emission. As a result, the laser beam is produced.

Ques. What is the full form of LASER?

1. Light Amplification by Stimulated Emission of Radiation
2. Light Absorbing Solar Energy Resource
3. Light Absorbent and Stimulated Emission of Radiation
4. Light Amplification of Singular Emission of Radiations

Ans. The correct answer is a. Light Amplification by Stimulated Emission of Radiation

Explanation: The acronym LASER stands for Light Amplification by Stimulated Emission of Radiations. Stimulated Emission is the mechanism through which radiations are amplified.

Ques. Phonons are

1. Quanta of light waves
2. Quanta of heat
3. Quanta of energy
4. Quanta of sound waves

Ans. The correct answer is d. Quanta of sound waves

Explanation: Phonons are the quanta of sound waves. When energy is applied to the lattice, it absorbs it and is stimulated to a higher state. When it returns to its ground state, it emits radiation in the sound-wave region known as phonons.

Ques. In Stimulated Absorption, what is the lifetime of an atom's ground state?

1. 1 hour
2. 1 second
3. Infinity
4. None of the above

Ans. The correct answer is c. Infinity

Explanation: Atoms are totally stable in their ground state. They are not subjected to any extreme force that may cause them to become unstable. All of the forces are in equilibrium. As a result, because the atom is stable in its ground state, its lifetime is infinite.

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Short Answers Questions [2 Marks Questions]

Ques. What is meant by laser diodes?

Ans. A laser diode is a semiconductor device that uses a p-n junction to produce coherent light with the same phase and frequency. It either belongs to the infrared or visible spectrum. It is sometimes referred to as an injection laser diode. This technology is comparable to standard LED technology.

Ques. What is meant by laser?

Ans. A laser is a device that produces light using an optical amplification process that is based on the stimulated emission of electromagnetic radiation. The term LASER is an abbreviation that stands for Light Amplification by Stimulated Emission of Radiation.

Ques. What is meant by coherence?

Ans. The characteristics of the interrelationship between the physical parameters of a single wave or between several waves are described by coherence. When two waves have the same frequency and have a constant relative phase difference, they are said to be coherent.

Ques. What is a semiconductor diode?

Ans. A semiconductor diode is a p-n junction diode with metallic contacts at both ends that allow external voltage to be applied. It is only capable of conducting electricity in one direction.

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Long Answers Questions [3 Marks Questions]

Ques. What are the disadvantages of laser diodes?

Ans. The following are the disadvantages of laser diodes

• When compared to other light-emitting devices, it is expensive.
• Lasers are dangerous to the eyes.
• A laser diode is a temperature-sensitive device, and its functioning is influenced by rising temperatures.
• High-power laser diodes are not suitable for indoor use.

Ques. What are the main characteristics of laser diodes?

Ans. The following are the characteristics of laser diodes

• Laser diodes generally emit a narrow beam of light that contains only one color. That is, it is monochromatic.
• Lasers have the same frequency and wavelength for the most part.
• Most of the emitted light is focused on a narrow path that can be easily driven using optical fiber.
• Laser diodes are often coherent and have the ability to traverse long distances.
• The approach or threshold of the laser diode is an essential feature. It will turn on once the threshold value is reached.

Ques. What are the applications of laser diodes?

Ans. The following are the applications of laser diodes

• CDs and other associated devices contain laser diodes.
• Laser diodes are commonly utilized in barcode readers.
• It also provides connectivity services, similar to Optical Fibre Communication.
• Laser diodes can also be used for laser screening and printing.
• Other equipment that uses laser diodes, such as rangefinders and spectrometers, is available.

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Very Long Answers Questions [5 Marks Questions]

Ques. What are the different types of laser diodes?

Ans. The different types of laser diodes are

• Double Heterostructure Laser Diode: It is also called a double heterojunction semiconductor laser. Heterostructure is a substance that is often crushed between two p-type and n-type materials. This diode's active and potential regions are used for greater optical amplification, which is an extra benefit of using it.
• Quantum Well laser Diode: The quantum well is essentially a thin layer in the center of a diode. In a nutshell, quantum energy is often used to convert electrons from greater energy to lower energy.
• Separate Confinement Heterostructure Laser Diode: In general, these layers have a lower refractive index, which increases light emission even more.
• Vertical Cavity Surface Emitting Laser Diode: This laser diode helps the emitted light in exiting the device perpendicular to the chip. Obviously, the optical cavity is normally oriented perpendicular to the axis of the current flow.
• External Cavity Diode Laser: A tunable diode laser is an external cavity diode laser. These lasers may be tuned for wavelength and have a narrow emission spectral line width.
• Fabry Perot Laser: The most popular form of laser diode is a Fabry Perot laser diode (FP laser diode), which has a laser resonator that is a Fabry Perot interferometer. As a result, there are significant light reflections at both ends, but not within the gain medium.

Ques. What are the main principles behind the working of a laser?

Ans. The laser diodes work on the principle of stimulated emission and so emissions occur in three types:

• Stimulated absorption: The laser diode is made up of a p-n junction with holes and electrons. (A hole is the lack of an electron). At the p-n junction, electrons absorb energy and transfer to a higher energy level when a specified voltage is applied. Holes are generated in the initial position of the energized electron. For a short period of time, electrons remain in this exciting condition without merging with holes, which is referred to as "recombination time" or "upper-state life." Most laser diodes have a recombination time of about a millisecond.
• Stimulated emission: Excited electrons in the higher state recombine with holes. The energy difference created as electrons fall from a higher energy level to a lower energy level is converted into photons or electromagnetic radiation. The same process is used to create light in LEDs. The frequency of the released photon is determined by the difference between the two energy levels.
• Spontaneous emission: Photons strike electrons at a higher energy level in stimulated emission, and these photons are produced by an external light source. When these photons reach the electrons, they absorb energy, recombine with the holes, and produce an additional photon. As a result, one incident photon triggers the emission of another photon. As a result, it is known as stimulated emission.

Ques. Write about the construction of a laser diode.

Ans. A laser diode is composed of two semiconductor layers: P-type and N-type. These semiconductors are composed of gallium arsenide and doped with selenium, aluminum, or silicon.

• A depletion layer exists between the two semiconductors because the electron-hole combination occurs when a voltage is applied to the diode.
• The front view is totally polished, acting as a reflecting surface or mirror, while the side view is partially polished, acting as a partially reflecting surface.
• Metal contacts connect the front face to the semiconductor, allowing biasing. Biasing is the process of providing power to a diode.
• Laser diodes emit light with the same frequency.

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