Using laser to overcome conservation of etendue

In summary, the conversation discusses the possibility of using mirrors and lenses to focus energy from a star to boil a planet on the other side of the galaxy. While this idea seems plausible, it is not feasible due to the limitations of optics. However, it is suggested that using solar panels and a laser could potentially work, although diffraction may limit its effective range. The conversation also raises questions about the laws of thermodynamics and the need for cooling in a laser system.
  • #1
SlowThinker
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I was watching a video where the author (Isaac Arthur) says it's possible to use mirrors and lens around a star to focus the energy to boil a planet on the other side of the galaxy.
At first it sounds reasonable, surely you have enough energy, but I have doubts that mirrors would be able to do that. On the other hand, solar panels and a laser should be.
I was wondering if it would be possible to use mirrors to charge the laser directly? It seems the laser would violate the law of conservation of etendue, and thus violate the 2nd law of thermodynamics, i.e. heat its target higher than the temperature of the source star.
Where is the flaw in such a design? Does a laser need cooling to operate? Or would it actually work?
 
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  • #2
SlowThinker said:
At first it sounds reasonable, surely you have enough energy, but I have doubts that mirrors would be able to do that.

You're right, you cannot do it with the setup shown/implied in the video. Your lens/mirror would need to be placed closer to the planet than to the original star. This is because the image of the star would need to be much smaller than the size of the star itself, something that can only be accomplished if you place your optical system closer to the planet than to the star.

SlowThinker said:
On the other hand, solar panels and a laser should be.

I think diffraction would limit the effective range of a laser to much less than the multi-kiloparsec range.
 

FAQ: Using laser to overcome conservation of etendue

1. What is conservation of etendue?

The conservation of etendue is a fundamental principle in optics that states the product of the area and the solid angle of light cannot be changed by any optical system. In simpler terms, it means that the size of a light source cannot be made smaller or the direction of light cannot be changed without affecting the brightness of the light.

2. How can laser be used to overcome conservation of etendue?

Laser light is highly directional and can be focused to a very small spot, allowing for efficient use of light. By using a laser, the light can be concentrated and directed to a smaller area, effectively overcoming the limitations of conservation of etendue.

3. What are some practical applications of using laser to overcome conservation of etendue?

One example is in laser scanning technology, where a laser beam is used to scan a large area and produce a high-resolution image. Another application is in laser cutting, where a focused laser beam is used to cut through materials with high precision.

4. Are there any limitations to using laser to overcome conservation of etendue?

While laser light can be focused to a very small spot, it still follows the laws of physics and cannot be focused to a point with zero size. Additionally, the use of laser can be expensive and may not be suitable for all applications.

5. How does using laser to overcome conservation of etendue impact the efficiency of an optical system?

Using laser can greatly increase the efficiency of an optical system by allowing for the concentration and direction of light to a specific area. This can lead to better performance and reduced energy consumption in various applications.

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