Lecture Notes: Energy States of an Atom

Overview

• Three energy states of an atom: E1 (Ground State), E2, and E3.
• Ground state (E1) is the stable state where atoms or electrons prefer to stay.

Energy States and Transitions

Stimulated Absorption

• Energy difference given: E3 - E1.
• Atoms jump from E1 to E3 due to external energy input.
• This process is called Stimulated Absorption.

Spontaneous Emission

• E3 state has a lifetime of 10^-8 seconds, making it unstable.
• Atoms spontaneously jump from E3 to E2 after their lifetime.
• This is known as Spontaneous Emission.

Meta-Stable State (E2)

• Lifetime of E2 is 10^-3 seconds, making it meta-stable.
• Atoms accumulate in E2 because they quickly leave E3 but stay longer in E2.
• Population Inversion occurs when there are more atoms in the excited state (E2) than in the ground state (E1).

Definition

• Population Inversion: More atoms in excited state than in the ground state.
• Typically, atoms are more in the ground state than in excited states.

Stimulated Emission

• External energy provided: E2 - E1.
• Atoms jump from E2 to E1, producing coherent and in-phase photons.
• This process is Stimulated Emission, leading to a laser emission.

Laser Characteristics

• Coherent Light: Light waves are in phase, leading to constructive interference.
• High Intensity: Laser intensity can be higher than the sun's intensity.
• Highly Directional: Laser light propagates in a focused beam rather than dispersing like a bulb.

Technical Details

• During Stimulated Emission, atoms can't move from E1 to E2 due to Population Inversion and energy-level restrictions (Pauli Exclusion Principle).

Example: Ruby Laser

• Material: Al2O3 (Aluminum trioxide)
• Some Aluminum atoms replaced by Cr+3 (Chromium plus 3) atoms.
• Ruby consists of Aluminum Oxide where some Al atoms are replaced by Cr atoms.
• Chromium atoms have meta-stable states facilitating laser emissions.

Key Points

• Understanding energy states and transitions is crucial for creating lasers.
• Characteristics of laser light make it unique and useful for various applications.

Final Remarks

• For further clarity, refer to the textbook on Ruby lasers and the principles of chromium atoms.
• Questions and confusions are welcome for discussion.