Metastable states are excited energy states of atoms or molecules with a relatively long lifetime (~10-3 sec), where electrons remain longer than in typical excited states .
Why do two-level laser systems not exist? Give one reason.
Two-level laser systems cannot sustain lasing because achieving population inversion is impossible. In a two-level system, the rates of absorption and stimulated emission are equal, so at most, the populations of the two levels can become equal, preventing the necessary condition for lasing where more atoms are in the excited state.
Differentiate spontaneous and stimulated emission of radiation.
- Spontaneous Emission: An excited atom or molecule emits a photon randomly without external influence, resulting in incoherent light (e.g., in a fluorescent lamp).
- Stimulated Emission: An incoming photon triggers an excited atom to emit a second photon with the same phase, frequency, and direction, producing coherent light (basis of laser action).
Mention any two applications of LASERs.
- Medical surgery (e.g., laser eye surgery for vision correction).
- Optical communication (e.g., fiber optic networks for high-speed data transfer).
What are the conditions required for a lasing medium?
- Population Inversion: More atoms must be in the excited state than in the ground state.
- Metastable State: The excited state should have a long lifetime to allow accumulation of atoms.
- Optical Cavity: A resonant cavity with mirrors to provide feedback and amplify the light.
LASER is a short form of
a) Light Amplification by Spontaneous Emission Radiation
b) Light Amplification by Stimulated Emission of Radiation
c) Light Absorption of Stimulated Emission of Radiation
d) Light Absorption by Spontaneous Emission of Radiation
Answer b) Light Amplification by Stimulated Emission of Radiation
What is the significance of a metastable condition for laser transition?
The metastable state allows atoms to remain in an excited state longer, enabling population inversion. This accumulation of excited atoms ensures that stimulated emission dominates over spontaneous emission, a key requirement for sustained laser action.
In ruby laser _______ ions give rise to the laser action.
In ruby laser, chromium (Cr³⁺) ions give rise to the laser action. These ions in the ruby crystal (Al₂O₃ doped with Cr) are responsible for the energy transitions producing the laser light.
What are the prerequisites for laser action?
- Active Medium: A material capable of achieving population inversion (e.g., ruby, gas).
- Pumping Mechanism: A method to excite atoms to higher energy states (e.g., optical pumping).
- Population Inversion: More atoms in the excited state than the ground state.
- Optical Resonator: A cavity with mirrors to amplify light via feedback.