What is the Difference Between Spontaneous and Stimulated Emission

Both spontaneous and stimulated emission are processes that involve excited atoms or molecules losing energy and emitting a photon. Understanding the difference between spontaneous and stimulated emission is important in various fields of science and technology, especially in the study and application of light and lasers.

What is the difference between spontaneous and stimulated emission? Spontaneous emission is a natural process, whereas stimulated emission requires a specific external trigger.

Key Areas Covered

1. What is Spontaneous Emission
      – Definition, Features 
2. What is Stimulated Emission
      – Definition, Features 
3. Similarities Between Spontaneous and Stimulated Emission
      – Outline of Common Features
4. Difference Between Spontaneous and Stimulated Emission
      – Comparison of Key Differences
5. FAQ: Spontaneous and Stimulated Emission
      – Answers to Frequently Asked Questions

Key Terms

Spontaneous Emission, Stimulated Emission

What is Spontaneous Emission

Spontaneous emission is a fundamental quantum mechanical process where an excited atom or molecule releases energy in the form of a photon (light particle) without any external influence. Spontaneous emission happens on its own. The excited atom or molecule does not need any external interaction to emit the photon. The direction, polarization (orientation of the light wave), and even the exact timing of the photon emission are all random. Since the photons are not emitted according to a certain order, they are not in step with each other. This results in light sources like LEDs and fluorescent lights that appear bright but don’t have a very sharp directionality.

Spontaneous emissions can be seen naturally happening in the environment around us. Light in the fireflies emitted at night and colors emitted by atoms in gas discharge lamps and fluorescent lights are good examples of spontaneous emission of light.

What is Stimulated Emission

Stimulated emission is the process where an excited atom or molecule interacts with an incoming photon of a specific energy and gets “stimulated” to release another photon. The key difference here is that the emitted photon has the same energy, phase, and direction as the incoming photon. This feature is used in creating LASER (Light Amplification by Stimulated Emission of Radiation).

Laser is used in cutting and welding materials. Precisely focused laser beams can cut through various materials like metal, plastic, and even diamonds due to their intense heat. They are used in manufacturing, robotics, and surgery. Laser is also used to drill microscopic holes, which is essential for micromachining in electronics and medical devices. Some 3D printers use lasers to selectively sinter or melt materials, building objects layer by layer.

Similarities Between Spontaneous and Stimulated Emission

1. Both processes involve an excited atom or molecule losing energy and dropping down to a lower energy state. 
2. Both processes obey the principle of energy conservation.
3. These processes contribute to the production of light

Difference Between Spontaneous and Stimulated Emission

Definition

• Spontaneous emission is a fundamental quantum mechanical process where an excited atom or molecule releases energy in the form of a photon without any external influence. On the other hand, stimulated emission is the process where an excited atom or molecule interacts with an incoming photon of a specific energy and gets “stimulated” to release another photon.

Nature

• Spontaneous emission happens on its own naturally, whereas stimulated emission happens with an external trigger.

Emission

• In spontaneous emission, the direction, polarization, and the exact timing of the photon emission are all random. In stimulated emission, the emitted photon has the same energy, phase, and direction as the incoming photon.

Coherency

• Spontaneous emission is incoherent, while stimulated emission is coherent.

Conclusion

Spontaneous emission occurs naturally and randomly without external influence, leading to incoherent light, as seen in fireflies and fluorescent lights. In contrast, stimulated emission requires an external trigger, producing coherent light with photons that have the same energy, phase, and direction as the incoming photon, which is the principle behind lasers. This is the main difference between spontaneous and stimulated emission.

FAQ: Spontaneous and Stimulated Emission

1. What is an example of spontaneous emission?

An example of spontaneous emission is the luminescence produced by fireflies. This natural phenomenon occurs when excited atoms within the firefly’s body release energy in the form of light without any external stimulation.

2. What causes stimulated emission?

Stimulated emission occurs when an incoming photon of a specific frequency interacts with an excited atomic electron, causing it to drop to a lower energy level. This interaction triggers the emission of a second photon that is identical in frequency, phase, and direction to the incoming photon.

3. What light is produced by spontaneous emission?

The light produced by spontaneous emission is called luminescence. It encompasses various natural processes where atoms or molecules emit photons without external excitation, such as bioluminescence in fireflies or the glow of certain minerals.

4. What are the characteristics of stimulated emission?

Stimulated emission is an important process for lasers. It produces light that is both monochromatic, meaning it has a single color or wavelength, and coherent, meaning the light waves are synchronized.

5. What are the applications of stimulated emission?

Stimulated emission has various applications, and one of the most important applications is laser (Light Amplification by Stimulated Emission of Radiation). Lasers produce a coherent and monochromatic beam of electromagnetic radiation through stimulated emission. This technology has applications in various fields, including telecommunications, medical procedures like surgery and therapy, manufacturing processes such as cutting and welding, scientific research, and even entertainment, like laser light shows.

Reference:

1. “Stimulated Emission.” Wikipedia. Wikipedia Foundation.
2. “Spontaneous Emission.” Encyclopedia Britannica.

Image Courtesy:

1. “Spontaneous emission” By Spontaneousemission.png: Ilmari Karonenderivative work: Tnorth (talk) (CC BY-SA 3.0) via Commons Wikimedia
2. “Lasers” By 彭嘉傑 – Own work (CC BY 2.5) via Commons Wikimedia