Stimulated Emission

Definition

Stimulated emission is the process by which an incoming photon causes an excited atom or molecule to release its energy in the form of a photon, resulting in two photons that are coherent and have the same phase, frequency, and direction. This phenomenon is essential for understanding the operation of lasers and has significant implications in quantum mechanics, particularly in relation to transition probabilities and the interaction between matter and electromagnetic fields.

5 Must Know Facts For Your Next Test

1. Stimulated emission is a key concept in laser technology, enabling the amplification of light by creating coherent photons.
2. The probability of stimulated emission occurring can be calculated using Fermi's Golden Rule, which helps determine transition rates between energy states.
3. For stimulated emission to dominate over spontaneous emission, certain conditions must be met, including achieving population inversion in the system.
4. The emitted photons during stimulated emission are identical to the incoming photon in terms of energy, phase, and direction, leading to the coherent light characteristic of lasers.
5. Understanding stimulated emission is crucial for exploring the quantization of the electromagnetic field and its interaction with matter in quantum mechanics.

Review Questions

• How does stimulated emission differ from spontaneous emission, and what role does this difference play in laser operation?
  • Stimulated emission occurs when an incoming photon prompts an excited atom or molecule to emit a second photon that is coherent with it, while spontaneous emission happens randomly without external prompting. This difference is vital for laser operation because lasers rely on stimulated emission to produce a coherent beam of light. By ensuring that more stimulated emissions occur than spontaneous emissions, lasers can maintain their powerful and focused light output.
• In what way does Fermi's Golden Rule relate to stimulated emission and transition probabilities in quantum systems?
  • Fermi's Golden Rule provides a framework to calculate the transition probabilities between energy states in quantum systems, including the transition from an excited state to a lower energy state during stimulated emission. This rule takes into account factors such as the density of final states available for the emitted photon and the interaction strength between the light field and the atom. Consequently, it helps predict how efficiently stimulated emission can occur under various conditions.
• Evaluate how the concept of population inversion is crucial for achieving effective stimulated emission in laser systems.
  • Population inversion is essential for effective stimulated emission because it ensures that more atoms are in an excited state than in lower energy states. When this condition is met, stimulated emission becomes more probable than spontaneous emission, allowing for a chain reaction where one emitted photon stimulates further emissions from other excited atoms. This leads to a significant amplification of light intensity, which is fundamental to laser operation. Without population inversion, lasers cannot produce coherent beams efficiently.

Related terms

Spontaneous Emission: The process by which an excited atom or molecule randomly emits a photon without external influence, leading to a loss of energy.

Photon: A quantum of electromagnetic radiation, which carries energy and momentum, and exhibits both wave-like and particle-like properties.

Laser: A device that produces a coherent beam of light through the process of stimulated emission, where photons amplify the light as they stimulate further emissions.