Laser Principles - Optical Physics - Physics Previous Year Questions

1

2007 · Physics · Optical Physics · Laser Principles

Physics (PH) 2007

In a He-Ne laser, the laser transition takes place in

A

He only.

B

Ne only.

C

Ne first, then in He.

D

He first, then in Ne.

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2

2008 · Physics · Optical Physics · Laser Principles

Physics (PH) 2008

The coherence length of laser light is

A

directly proportional to the length of the active lasing medium.

B

directly proportional to the width of the spectral line.

C

inversely proportional to the width of the spectral line.

D

inversely proportional to the length of the active lasing medium.

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3

2008 · Physics · Optical Physics · Laser Principles

Physics (PH) 2008

When the refractive index \(\mu\) of the active medium changes by \(\Delta\mu\) in a laser resonator of length \(L\), the change in the spectral spacing between the longitudinal modes of the laser is (c is the speed of light in free space)

A

\(\dfrac{c}{2(\mu + \Delta\mu)L}\)

B

\(\dfrac{c}{2\Delta\mu L}\)

C

\(\dfrac{c}{2L}\dfrac{\Delta\mu}{\mu(\mu + \Delta\mu)}\)

D

zero

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4

2009 · Physics · Optical Physics · Laser Principles

Physics (PH) 2009

Five energy levels of a system including the ground state are shown below. Their lifetimes and the allowed electric dipole transitions are also marked.

Which one of the following transitions is the most suitable for a continuous wave (CW) laser ?

A

1 → 0

B

2 → 0

C

4 → 2

D

4 → 3

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5

2011 · Physics · Optical Physics · Laser Principles

Physics (PH) 2011

The population inversion in a two level laser material CANNOT be achieved by optical pumping because

A

the rate of upward transitions is equal to the rate of downward transitions

B

the upward transitions are forbidden but downward transitions are allowed

C

the upward transitions are allowed but downward transitions are forbidden

D

the spontaneous decay rate of the higher level is very low

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6

2021 · Physics · Optical Physics · Laser Principles

Physics (PH) 2021

To sustain lasing action in a three-level laser as shown in the figure, necessary condition(s) is(are)

A

lifetime of the energy level 1 should be greater than that of energy level 2

B

population of the particles in level 1 should be greater than that of level 0

C

lifetime of the energy level 2 should be greater than that of energy level 0

D

population of the particles in level 2 should be greater than that of level 1

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7

2022 · Physics · Optical Physics · Laser Principles

Physics (PH) 2022

Frequency bandwidth $\Delta\nu$ of a gas laser of frequency $\nu$ Hz is
\(\Delta\nu = \frac{2\nu}{c}\sqrt{\frac{\alpha}{A}}\) where $\alpha = 3.44 \times 10^6$ m$^2$ s$^{-2}$ at room temperature and $A$ is the atomic mass of the lasing atom. For $^4$He - $^{20}$Ne laser (wavelength = 633 nm), $\Delta\nu = n \times 10^6$ Hz. The value of $n$ is __________ (Round off to one decimal place)

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