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

1 $What is the full form of LASER?$

A.

Light Amplification by Spontaneous Emission of Radiation

B.

Light Absorption by Spontaneous Emission of Radiation

C.

Light Amplification by Stimulated Emission of Radiation

D.

Light Absorption by Stimulated 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.

Stimulated Absorption

B.

Population Inversion

C.

Stimulated Emission

D.

Spontaneous Emission

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

A.

Spontaneous Absorption

B.

Stimulated Emission

C.

Spontaneous Emission

D.

Stimulated Absorption

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

A.

Coherence time

B.

Lifetime of the state

C.

Transition time

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.

Optical Pumping

B.

Population Inversion

C.

Ground State Saturation

D.

Thermal Equilibrium

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

A.

Stimulated Emission

B.

Spontaneous Emission

C.

Stimulated Absorption

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.

Optical Resonator (Cavity)

C.

Cooling System

D.

Active Medium

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

A.

Resonance

B.

Emission

C.

Attenuation

D.

Pumping

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

A.

Electrical Discharge

B.

Direct Current Injection

C.

Chemical Pumping

D.

Optical Pumping

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

A.

Inelastic Atom-Atom Collision (Electrical Discharge)

B.

Chemical Reaction

C.

Optical Pumping

D.

Heat Injection

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

A.

Neodymium ions ()

B.

Yttrium atoms

C.

Aluminum atoms

D.

Garnet crystal lattice

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

A.

2-level

B.

3-level

C.

4-level

D.

5-level

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

A.

694.3 nm

B.

10.6

C.

632.8 nm

D.

1.064

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

A.

Helium

B.

Krypton

C.

Argon

D.

Neon

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.

Provide the mechanical structure

B.

Pump the Helium atoms

C.

Cool the system

D.

Act as the active centers for lasing

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

A.

1:1

B.

100:1

C.

10:1

D.

1:10

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.

Active medium is a P-N junction

D.

It is very large and bulky

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

A.

Forward Biasing

B.

Heating

C.

Optical Pumping

D.

Reverse Biasing

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

A.

Recombination of electrons and holes

B.

Atomic collisions

C.

Rotational transitions

D.

Vibrational transitions

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

A.

Gallium Arsenide (GaAs)

B.

Cadmium Sulfide (CdS)

C.

Silicon (Si)

D.

Germanium (Ge)

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

A.

The voltage applied

B.

The length of the cavity

C.

The doping concentration only

D.

The bandgap energy of the material

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

A.

Intensity

B.

Directionality (low divergence)

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.

Temporal Coherence

B.

Polarization

C.

Intensity

D.

Spatial Coherence

29 $What is Holography?$

A.

A technique of 2D photography

B.

A method of X-ray imaging

C.

A technique of lensless 3D photography

D.

A method to measure light intensity

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

A.

Phase; Amplitude

B.

Amplitude; Phase and Amplitude

C.

Wavelength; Intensity

D.

Frequency; Phase

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

A.

Interference

B.

Refraction

C.

Polarization

D.

Diffraction

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

A.

Polychromatic light

B.

Incoherent light

C.

Highly Coherent light (Laser)

D.

White light

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

A.

Concave Lens

B.

Prism

C.

Diffraction Grating

D.

Mirror

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.

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

B.

It requires no pumping

C.

It uses less expensive mirrors

D.

It operates at lower frequencies

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

A.

High Coherence

B.

High Intensity

C.

High Divergence

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.

Stopping the laser

D.

Extracting the laser output

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

A.

The length of the laser tube

B.

The energy difference between the lasing levels

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.

Ruby Laser

B.

All lasers are pulsed

C.

He-Ne Laser

D.

Nitrogen Laser

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

A.

Barcode scanning

B.

CD players

C.

Fiber optic communication (at 1550nm)

D.

Material processing (cutting, welding)

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

A.

Ideally infinite

B.

Variable depending on time

C.

Extremely narrow

D.

Very broad

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

A.

Very thin ()

B.

External to the diode

C.

Made of gas

D.

Very thick ()

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

A.

Works only in vacuum

B.

Too small

C.

High threshold current density

D.

Low power consumption

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

A.

Temporal Coherence

B.

Amplitude Stability

C.

Frequency Stability

D.

Spatial 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.

Spontaneous emission dominates, making lasing difficult

C.

Spontaneous emission is negligible

D.

Stimulated emission is not required

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.

Laser cutting

C.

Tattoo removal

D.

Hair removal

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

A.

The image disappears

B.

Each piece contains the whole image (with reduced resolution)

C.

The image becomes inverted

D.

Only part of the image is seen

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

A.

Stefan-Boltzmann Law

B.

Rayleigh-Jeans Law

C.

Wien's Displacement Law

D.

Planck's Radiation Law

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

A.

Zero

B.

Equal

C.

Infinite

D.

Unrelated

Unit 2: Lasers and Applications - Practice Quiz

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