PHY110 Unit 2: Lasers and Applications - MCQ Practice | B. Tech. CSE

1 $What is the full form of LASER?$

A.

Light Absorption by Stimulated Emission of Radiation

B.

Light Amplification by Spontaneous Emission of Radiation

C.

Light Amplification by Stimulated Emission of Radiation

D.

Light Absorption by Spontaneous Emission of Radiation

2 $In the context of light-matter interaction, what is the process where an atom in the ground state absorbs a photon and moves to an excited state?$

A.

Population Inversion

B.

Stimulated Emission

C.

Spontaneous Emission

D.

Stimulated Absorption

3 $Which process is responsible for the output of a laser beam having high coherence?$

A.

Stimulated Emission

B.

Spontaneous Emission

C.

Stimulated Absorption

D.

Spontaneous Absorption

4 $The average time an atom spends in an excited state before undergoing spontaneous emission is known as:$

A.

Coherence time

B.

Transition time

C.

Lifetime of the state

D.

Pumping time

5 $What is the typical lifetime of an atom in a metastable state ?$

A.

seconds

B.

seconds

C.

seconds

D.

seconds

6 $According to Boltzmann's distribution law, the population ratio of two energy levels at thermal equilibrium is given by:$

A.

B.

C.

D.

7 $What is the condition called where the number of atoms in a higher energy state () exceeds the number of atoms in a lower energy state ()?$

A.

Thermal Equilibrium

B.

Ground State Saturation

C.

Optical Pumping

D.

Population Inversion

8 $The Einstein coefficient represents the probability per unit time of which process?$

A.

Stimulated Absorption

B.

Spontaneous Emission

C.

Stimulated Emission

D.

Non-radiative decay

9 $What is the relationship between the Einstein coefficients for stimulated absorption () and stimulated emission ()?$

A.

B.

C.

D.

10 $The ratio of Spontaneous Emission rate to Stimulated Emission rate () is proportional to:$

A.

B.

C.

D.

11 $Which component of a laser system is responsible for providing the necessary positive feedback to sustain oscillations?$

A.

Pumping Source

B.

Active Medium

C.

Cooling System

D.

Optical Resonator (Cavity)

12 $The process of supplying energy to the active medium to achieve population inversion is called:$

A.

Attenuation

B.

Pumping

C.

Resonance

D.

Emission

13 $Which pumping method is primarily used in the Nd:YAG laser?$

A.

Optical Pumping

B.

Chemical Pumping

C.

Electrical Discharge

D.

Direct Current Injection

14 $Which pumping method is primarily used in the He-Ne laser?$

A.

Optical Pumping

B.

Heat Injection

C.

Inelastic Atom-Atom Collision (Electrical Discharge)

D.

Chemical Reaction

15 $The active medium in an Nd:YAG laser is:$

A.

Garnet crystal lattice

B.

Aluminum atoms

C.

Yttrium atoms

D.

Neodymium ions ()

16 $Nd:YAG laser is an example of a____laser.$

A.

4-level

B.

2-level

C.

5-level

D.

3-level

17 $The characteristic output wavelength of an Nd:YAG laser is:$

A.

1.064

B.

10.6

C.

694.3 nm

D.

632.8 nm

18 $In the He-Ne laser, which element provides the metastable state required for energy transfer?$

A.

Neon

B.

Argon

C.

Helium

D.

Krypton

19 $The visible red light emitted by a He-Ne laser has a wavelength of:$

A.

532 nm

B.

694.3 nm

C.

1064 nm

D.

632.8 nm

20 $In a He-Ne laser, the role of the Neon atoms is to:$

A.

Act as the active centers for lasing

B.

Cool the system

C.

Pump the Helium atoms

D.

Provide the mechanical structure

21 $What is the typical ratio of Helium to Neon in a He-Ne gas laser?$

A.

10:1

B.

100:1

C.

1:10

D.

1:1

22 $Which of the following is a characteristic property of a Semiconductor Diode Laser?$

A.

It requires a flash lamp for pumping

B.

It always emits in the UV range

C.

It is very large and bulky

D.

Active medium is a P-N junction

23 $The pumping mechanism in a Semiconductor Laser is:$

A.

Reverse Biasing

B.

Forward Biasing

C.

Optical Pumping

D.

Heating

24 $In a semiconductor laser, photon emission occurs due to:$

A.

Atomic collisions

B.

Recombination of electrons and holes

C.

Vibrational transitions

D.

Rotational transitions

25 $Which material is commonly used for fabricating semiconductor lasers emitting in the infrared region?$

A.

Cadmium Sulfide (CdS)

B.

Gallium Arsenide (GaAs)

C.

Germanium (Ge)

D.

Silicon (Si)

26 $The wavelength of light emitted by a semiconductor laser depends primarily on:$

A.

The doping concentration only

B.

The voltage applied

C.

The bandgap energy of the material

D.

The length of the cavity

27 $Which property of laser light implies that the photons travel in a single direction with very little spreading?$

A.

Directionality (low divergence)

B.

Intensity

C.

Coherence

D.

Monochromaticity

28 $The property of a laser beam having a constant phase difference between two points in space at a given time is called:$

A.

Polarization

B.

Temporal Coherence

C.

Intensity

D.

Spatial Coherence

29 $What is Holography?$

A.

A method to measure light intensity

B.

A technique of lensless 3D photography

C.

A technique of 2D photography

D.

A method of X-ray imaging

30 $Ordinary photography records the__of light, while holography records__.$

A.

Wavelength; Intensity

B.

Phase; Amplitude

C.

Amplitude; Phase and Amplitude

D.

Frequency; Phase

31 $The physical principle behind the recording of a hologram is:$

A.

Refraction

B.

Interference

C.

Polarization

D.

Diffraction

32 $What type of light source is strictly required for recording a hologram?$

A.

Incoherent light

B.

White light

C.

Polychromatic light

D.

Highly Coherent light (Laser)

33 $In the reconstruction of a hologram, the hologram acts as a:$

A.

Mirror

B.

Concave Lens

C.

Prism

D.

Diffraction Grating

34 $Which Einstein coefficient is related to the absorption of radiation?$

A.

B.

C.

D.

35 $Why is a 4-level laser generally more efficient than a 3-level laser?$

A.

It operates at lower frequencies

B.

It requires no pumping

C.

The terminal laser level is not the ground state, so it is easier to empty

D.

It uses less expensive mirrors

36 $Which of the following is NOT a property of laser light?$

A.

High Coherence

B.

High Divergence

C.

High Intensity

D.

High Monochromaticity

37 $In an optical resonator, if the reflection coefficient of one mirror is 100% and the other is slightly less (e.g., 98%), the latter is used for:$

A.

Injecting the pump energy

B.

Cooling the cavity

C.

Extracting the laser output

D.

Stopping the laser

38 $The color of the light emitted by a laser is determined by:$

A.

The energy difference between the lasing levels

B.

The length of the laser tube

C.

The intensity of the pumping source

D.

The diameter of the laser tube

39 $Which of the following lasers is capable of continuous wave (CW) operation?$

A.

Nitrogen Laser

B.

All lasers are pulsed

C.

Ruby Laser

D.

He-Ne Laser

40 $A typical application of the Nd:YAG laser is:$

A.

Material processing (cutting, welding)

B.

Fiber optic communication (at 1550nm)

C.

Barcode scanning

D.

CD players

41 $The spectral width (bandwidth) of a laser beam is:$

A.

Very broad

B.

Ideally infinite

C.

Variable depending on time

D.

Extremely narrow

42 $In a homojunction semiconductor laser, the active region is:$

A.

Made of gas

B.

External to the diode

C.

Very thick ()

D.

Very thin ()

43 $What is the primary disadvantage of a homojunction semiconductor laser compared to a heterojunction one?$

A.

Low power consumption

B.

Works only in vacuum

C.

High threshold current density

D.

Too small

44 $Which term describes the constancy of the phase relationship of a wave at a fixed point over a period of time?$

A.

Frequency Stability

B.

Amplitude Stability

C.

Spatial Coherence

D.

Temporal Coherence

45 $In the Einstein relation, what does this imply for UV or X-ray lasers?$

A.

It is very easy to build them

B.

Stimulated emission is not required

C.

Spontaneous emission is negligible

D.

Spontaneous emission dominates, making lasing difficult

46 $The 'Ruby Laser', historically the first laser, is an example of a:$

A.

4-level solid state laser

B.

Gas laser

C.

3-level solid state laser

D.

Semiconductor laser

47 $Which of the following is an application of Holography?$

A.

Data storage (Holographic memory)

B.

Tattoo removal

C.

Laser cutting

D.

Hair removal

48 $When a hologram is cut into pieces, what happens?$

A.

The image becomes inverted

B.

The image disappears

C.

Only part of the image is seen

D.

Each piece contains the whole image (with reduced resolution)

49 $The energy density of radiation in a cavity at thermal equilibrium is given by:$

A.

Planck's Radiation Law

B.

Rayleigh-Jeans Law

C.

Stefan-Boltzmann Law

D.

Wien's Displacement Law

50 $For a system in thermal equilibrium, the rate of upward transitions (absorption) and downward transitions (emission) must be:$

A.

Unrelated

B.

Zero

C.

Infinite

D.

Equal

Unit 2: Lasers and Applications - Practice Quiz

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