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Unit 2 - Practice Quiz

PHY110 50 Questions
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1 What does the acronym LASER stand for?

A. Light Amplification by Stimulated Emission of Radiation
B. Light Absorption by Stimulated Emission of Radiation
C. Light Amplification by Spontaneous Emission of Radiation
D. Light Absorption by Spontaneous Emission of Radiation

2 In the process of stimulated emission, an incoming photon interacts with an atom in an excited state. How many photons are emitted as a result?

A. Zero
B. One
C. Two
D. Three

3 Which of the following conditions is necessary for laser action to occur?

A. Thermal equilibrium
B. Population inversion
C. Spontaneous absorption
D. Blackbody radiation

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

A. seconds
B. seconds
C. seconds
D. seconds

5 According to Einstein's theory of radiation, which coefficient represents stimulated absorption?

A.
B.
C.
D.

6 What is the relationship between the Einstein coefficients for induced absorption () and stimulated emission ()?

A.
B.
C.
D.

7 The ratio of the rate of spontaneous emission to the rate of stimulated emission (Einstein coefficients ratio ) is proportional to:

A.
B.
C.
D.

8 Which property of laser light refers to the waves having a constant phase difference?

A. Monochromaticity
B. Coherence
C. Directionality
D. Intensity

9 What is the function of the optical resonator (resonant cavity) in a laser?

A. To pump atoms to excited states
B. To cool the system
C. To provide positive feedback and selective amplification
D. To convert electrical energy to light

10 In a He-Ne laser, the active medium is:

A. Helium
B. Neon
C. A mixture of Helium and Neon where Helium is the active center
D. A mixture of Helium and Neon where Neon is the active center

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

A. 1:1
B. 1:10
C. 10:1
D. 100:1

12 What is the primary pumping mechanism used in a He-Ne laser?

A. Optical pumping
B. Electrical discharge
C. Chemical reaction
D. Direct conversion

13 What is the output wavelength of a standard He-Ne laser?

A.
B.
C.
D.

14 The Nd:YAG laser is classified as a:

A. Gas laser
B. Liquid laser
C. Semiconductor laser
D. Solid-state laser

15 Which ion is responsible for the lasing action in an Nd:YAG laser?

A.
B.
C.
D.

16 What is the typical emission wavelength of an Nd:YAG laser?

A.
B.
C.
D.

17 Which pumping method is commonly used for Nd:YAG lasers?

A. Electrical discharge
B. Optical pumping
C. Inelastic atom-atom collisions
D. Forward bias injection

18 How many energy levels are primarily involved in the lasing action of an Nd:YAG laser?

A. Two
B. Three
C. Four
D. Five

19 A Semiconductor laser is also known as a:

A. Gas laser
B. Injection laser diode
C. Dye laser
D. Glass laser

20 Which material is commonly used for fabricating semiconductor lasers?

A. Silicon (Si)
B. Germanium (Ge)
C. Gallium Arsenide (GaAs)
D. Cadmium Sulfide (CdS)

21 What type of semiconductor is required for a laser diode?

A. Indirect band gap
B. Direct band gap
C. Insulator
D. Intrinsic semiconductor

22 The pumping mechanism in a Semiconductor laser is:

A. Optical pumping
B. Heating
C. Forward biasing of p-n junction
D. Reverse biasing of p-n junction

23 What acts as the resonant cavity mirrors in a typical semiconductor laser?

A. External silvered mirrors
B. Polished cleaved faces of the crystal
C. Prisms
D. Diffraction gratings

24 The property of laser light where the beam has very little spread is called:

A. Monochromaticity
B. Directionality
C. Coherence
D. Brightness

25 The process of raising atoms from a lower energy state to a higher energy state is called:

A. Emission
B. Pumping
C. Recombination
D. Scattering

26 According to Boltzmann's distribution law, at thermal equilibrium, the population of the ground state () and excited state () are related as ():

A.
B.
C.
D.

27 The emitted photons in spontaneous emission are:

A. Coherent and in phase
B. Incoherent and random in direction
C. Monochromatic and parallel
D. Polarized in the same direction

28 Holography is a technique of recording and reproducing:

A. 2D images
B. 3D images
C. Sound waves
D. X-ray shadows

29 Which principle is the basis of Holography?

A. Refraction
B. Dispersion
C. Interference
D. Polarization

30 Unlike standard photography which records only intensity, a hologram records:

A. Only phase
B. Only amplitude
C. Both amplitude and phase
D. Only wavelength

31 What type of light source is essential for recording a hologram?

A. Polychromatic light
B. Incoherent light
C. Highly coherent laser light
D. Sunlight

32 In the reconstruction process of a hologram, the hologram is illuminated by:

A. The object beam
B. The reference beam
C. White light
D. UV light

33 Who was awarded the Nobel Prize for the invention of Holography?

A. Albert Einstein
B. Theodore Maiman
C. Dennis Gabor
D. Arthur Schawlow

34 If and are ground and excited states, the frequency of the emitted photon is given by:

A.
B.
C.
D.

35 In a 3-level laser system (like Ruby), population inversion is achieved between:

A. Ground state and Pump state
B. Pump state and Metastable state
C. Metastable state and Ground state
D. It is impossible to achieve

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

A. It requires less pumping energy to achieve population inversion
B. It uses a gas medium
C. It has no metastable state
D. It operates at higher temperatures

37 The role of Helium in a He-Ne laser is to:

A. Emit the laser light
B. Absorb the laser light
C. Transfer energy to Neon atoms via resonant collisions
D. Act as a coolant

38 Which of the following is an application of lasers in industry?

A. CT Scanning
B. Photosynthesis
C. Precision drilling and cutting
D. Generating electricity

39 Which of the following describes the spectral width of a laser beam?

A. Broadband
B. Very narrow
C. Continuous spectrum
D. Variable

40 What is the physical meaning of the Einstein A coefficient ()?

A. Rate of absorption per unit energy density
B. Probability of spontaneous emission per unit time
C. Rate of stimulated emission per unit energy density
D. Lifetime of the atom

41 In an optical resonator, if one mirror is 100% reflective, the other mirror is typically:

A. 100% reflective
B. 0% reflective (transparent)
C. Partially reflective
D. Absorbing

42 The coherence length () is related to the coherence time () by the formula ( is speed of light):

A.
B.
C.
D.

43 Which type of laser is most commonly used in barcode scanners and laser pointers?

A. CO2 Laser
B. Nd:YAG Laser
C. He-Ne or Diode Laser
D. Excimer Laser

44 In the Nd:YAG laser, the transition producing the output is from:

A. Metastable state to Ground state
B. Metastable state to an intermediate level
C. Pump band to Metastable state
D. Ground state to Pump band

45 The extremely high intensity of a laser beam is primarily due to:

A. High power consumption
B. Large aperture size
C. Concentration of energy in a small spatial and spectral region
D. Using a gas medium

46 What is the main disadvantage of a homojunction semiconductor laser compared to a heterojunction one?

A. High threshold current density
B. Low output power
C. Complex fabrication
D. Large size

47 Stimulated emission produces light that amplifies the incident wave. This means the emitted wave has the same:

A. Frequency only
B. Phase only
C. Frequency, Phase, and Direction
D. Amplitude only

48 For a system in thermal equilibrium at temperature , the ratio of populations is given by:

A.
B.
C.
D.

49 Which characteristic makes laser light ideal for fiber optic communication?

A. High divergence
B. Polychromatic nature
C. High frequency (Monochromaticity) and Directionality
D. Incoherence

50 In Holography, the interference pattern is recorded on:

A. A convex lens
B. A mirror
C. A photographic plate/film
D. A prism
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