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As I know, lasers can be use to drill holes on diamonds or shape diamonds, I was imaging we can use a very wide laser source to drill holes through rocky bodies, and hence use it to replace machines to build underground tunnels, dig underground for mining, or other usages that need to drill holes through rocky bodes.

Is the idea that drilling holes with lasers possible in engineering and physical view? If possible, how to explaination that nowadays we still use machines to drill tunnels physically? It it just because the cost of lasers are higher or just technically impossible?

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    $\begingroup$ @downvoter If you downvote I suggest you at least comment why. Otherwise it's bullying and you're not improving the community or the post. $\endgroup$ – AER Aug 22 '16 at 7:19
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Correct, lasers can drill holes but there are a couple of important things to know:

  1. Lasers work by using the strongly directed "in-phase" light to heat the substance and effectively burn it off. Rock has one of the highest melting temperatures let alone boiling temperature. So it would use an enormous amount of energy to generate this heat;
  2. I suspect that having a laser that wide would be less effective than a ring of lasers and then remove the internal rock. The amount of gaseous rock that would be generated would obfuscate the lasers light and cause a huge jet of silicon based gas (silica has a boiling temperature of 2,950 °C) which would set when cold enough and cause all sorts of other technical issues.

Technically possible but there are better ways. In response to why it's not used now, the energy would be too high and we don't have the technology to produce that much power (energy per time) in a laser (and probably not even in the circuitry or power generation either).

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  • $\begingroup$ Actually, pulse lasers will explode material without melting it, and look at lasers used for tissue which are tuned to disrupt the atomic bonds and don't heat surrounding tissue. $\endgroup$ – JDługosz Aug 22 '16 at 6:45
  • $\begingroup$ @JDługosz Good point. Using differential thermal expansion I presume? Similar to the ring of lasers mass removal would be required. $\endgroup$ – AER Aug 22 '16 at 6:49
  • $\begingroup$ I think it causes spalling by actually vaporizing a cery tiny spot, so the resulting explosion cracks the surrounding material especially if beneith the surface. Also metals have their own strange effects. I expanded that into an Answer. Wikipedia doesn’t cover pulsed laser ablation/spalling it seems. $\endgroup$ – JDługosz Aug 22 '16 at 7:12
  • $\begingroup$ @JDługosz Yes, exactly. Very cool. Thanks for sharing $\endgroup$ – AER Aug 22 '16 at 7:18
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I can suggest a few gee-wiz ideas to make a plusible laser excavator.

First, there are lasers designed for blasting holes in material and they work by using intense and ultra-short pulses. This shocks the material and makes it explode like a warm glass that's dropped in cold water. You can search for pulsed laser ablation for more information.

Second, consider the magical way that lasers can cut skin and other tissue so it just melts away without heating the surrounding tissue at all. This works by exciting the molecular bonds with just the right push to break them.

Lasers are also used to determine the chemical composition. And look at the third word in the name Laser-induced breakdown spectroscopy. The ChemCam does indeed leave holes behind!

ChemCam

So, imagine a system that uses laser spectroscopy to determine the exact mineral bonds present in a particular spot, and then blasts it with tuned pulses to disintegrate those bonds.

The final alternative is simply raw power. The Stanford LCLS is an X-Ray laser a trillion times brighter than “traditional” synchrotron light sources, which are themselves many orders of magnitude brighter than normal sources. When it hits a sample, the electrons are simply blown away faster than the heavier nulculi can react, and the following explosion of positivly charged atoms follows at a much slower time scale.

However, raw power is very inefficient. Using energy to break up the material, even using pressure like conventional tunnel boring machines, is far cheaper.

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