In this post, some conceptual and numerical questions are asked to make your concept clear about the LASER.

MCQ LASER PArt-2

Q 1      The output of the He-Ne laser lies in

a.)   IR spectrum

b.) visible spectrum

c.) UV spectrum

d.) X-ray spectrum

Q2        The first step to getting output from a laser is to excite an active medium. What is this process called?

a.) Exciting

b.) pumping

c.) raising

d.) resonating

Q3        Which laser is produced due to the excitation of molecules?

1. He-Ne laser
2. CO₂ laser
3. semiconductor laser
4. ruby laser

Q4       In He-Ne laser,neon atoms obtain energy

a.)On collision from He atom

b.) from a chemical reaction

c.) from electrical pumping

d.) optical pumping

Q5        In He-Ne laser the lasing action is produced by

1. He-Ne both
2. Ne only
3. Electrons of He
4. none of above

Q6         Once the active medium is excited, the first photons of light are produced by which physical process?

1. Black body radiation
2. Spontaneous emission
3. Stimulated emission
4. Plank’s oscillation

Q7    Ruby laser is

1. two level laser
2. four-level laser
3. three level laser
4. none of the above

Q8        CO₂ laser is

1. Two level laser
2. four-level laser
3. three level laser
4. none of the above

Q9        The population inversion process is observed due to the existence of

1. Ground state
2. Metastable state
3. Excited state
4. none of the above

Q10      What is the process responsible for producing photons in a diode laser?

1. Fermi level shift
2. Majority carrier injection
3. Carrier freeze out
4. Electron hole recombination

ANSWER KEYS of above 10 MCQs

1 Correct: b

2Correct : b

3Correct : b

4Correct : a

5 Correct: b

6 Correct: b

7Correct : c

8Correct : b

9  Correct: b

10Correct : d

Numerical-based LASER questions

1. The laser lights emitted in the ruby laser have a wavelength of 7000 Å and the total number of Cr³⁺ ions is 2.5 ×10¹⁹. The total energy available per laser pulse is

1. 5 J
2. 5 J
3. 1 J
4.  8 J

2. The CO₂ laser is having an energy difference of 0.12 eV between the two states involved in lasing actions. What is the wavelength of emitted radiation?

1.    9.35 μm
2.    10.35 μm
3.     8.17 μm
4.    10.95 μm

3. A certain ruby laser emits 1.14 J pulses of light. There are 3.8 × 10¹⁸ ions of Cr³⁺ in the ruby. The wavelength of the ruby laser is

1. 6524 A⁰
2. 6925 A⁰
3. 6625 A⁰
4. 6823 A⁰

4. A laser pulse is focused on the target to a very small spot of radius 1.5×10^-5 What is the power per unit area delivered by a laser pulse of energy 8.0×10^-3 joule given the pulse length in time as 10^-9 sec.

1. 13x 10¹⁶ W/m²
2. 69 x 10¹¹ W/m²
3. 13x 10¹¹W/m²
4. 69×10¹⁶ W/m²

5. What is the population inversion ratio of the two states in a He-Ne laser that produces a light of wavelength 6000A⁰ at 270C?

1. 54 x 10^-22
2. 08 x10^-30
3. 54 x 10^-12
4. 77 x 10^-35

6Q. A certain laser emits light of a wavelength of 15 μ The energy of the upper lasing level is 18.7 eV. What is the energy of the lower lasing level?

1. 665 eV
2. 718 eV
3. 617 eV
4. 534 eV

7Q.

1. In the He-Ne laser, the He atom while colliding with the Ne atom excites them. This produces population inversion which allows stimulated emission. Which energy level diagram correctly shows the excitation of Ne atoms by He atoms, the spontaneous IR emission from the Ne, and the stimulated emission of red color

8Q. The diagram shows some of the energy levels of He – Ne. The energies of the levels are given in eV. The elements are the major constituents of the laser that emits red light.

Which transition between the labeled levels gives rise to the emission of the laser

light?

1. E₃ to E₂
2. E₆ to E₅
3. E₂  to  E₁
4. E₅ to  E₄

9Q.

1. The electron de-excite to the ground state in a random process and produce a photon of energy E₁
2. The incident electron of energy E₁ induces the atom to de-excite and emit an electron of energy E₁. The incident electron is absorbed by the atom.
3. ) An incident photon of energy E₁ induces the atom to de-excite and emit a photon of energy E₁ which moves with the incident photon in the same phase.
4. An incident photon of energy less than E₁ induces the atom to de-excite and emit a photon of energy E₁ which moves with the incident photon in the same phase.

10Q. Which of the following statements regarding the creation of a laser is incorrect

1. A laser medium enclosed in a tube with a fully reflective mirror at one end and a partially reflective mirror at the other.
2. )An inverted population of atoms, a meta-stable excited state induced by an external energy source.
3. The process commences when an excited atom spontaneously emits a photon parallel to the axis of the tube.
4. A small aperture in one mirror allows some of the photons to emerge from the tube to form a coherent laser beam.

11Q.

The value of wavelength λ  is

1. 6390 A⁰
2. 6903 A⁰
3. 5935 A⁰
4. 6300 A⁰

12 Q. Which of the following statements best explains why laser light is monochromatic?

1. The excited electrons are in a metastable state.
2. The system is in a state of population inversion.
3. The system has only one excited state
4. The emitted photons have the same energy as an incident.

13Q. Which of the following is not a necessary condition for population inversion?

1. The laser medium has an excited state that is metastable.
2. The energy source to induce population inversion in the laser medium.
3.  An incident electron triggers the laser action.
4. The emitted photons are confined in the laser medium long enough to produce amplification.

14Q. Match the different types of laser with the corresponding atom/ion/molecules used to achieve population inversion.

(A) He- Ne laser                 (1)  N2 molecules

(B) Co2 laser                     (2)  Cr³⁺  ions

(C) Ruby laser                   (3)  He atom

A         B           C

1. (1)      (3)        (2)
2. (3)      (1)        (2)
3. (3)      (2)        (1)
4. (2)      (1)        (3)

Answer Keys:

This master quiz is to make concepts more clear about the LASER

1 Correct: c

2Correct: b

3Correct: c

4Correct: a

5Correct : d

6Correct : c

7Correct: b

8Correct: b

9Correct: c

10Correct:  b

11Correct :  d

12Correct:  a

13Correct:  c

14Correct: b

READ ALSO:

Semiconductor diode LASER

Ruby Laser Construction and Working

Semiconductor LASER Construction and Working

Six Major Misconceptions in LASER what Student Thinks

How to Find LASER Wavelength Using a Diffraction Grating in the Lab

He-Ne gas Laser: Its Principle, Construction and Working

Carbon dioxide (CO2) gas Laser