# Lasers vs. Mirrors

**URL:** <https://boards.straightdope.com/t/lasers-vs-mirrors/110675>\
**Category:** Factual Questions\
**Created:** [May 24, 2002, 5:18pm UTC](https://boards.straightdope.com/t/lasers-vs-mirrors/110675 "2002-05-24T17:18:19Z")\
**Posts on this page:** 2\
**Page:** 2

<div class="post-metadata">

**Author:** ![kanicbird](https://avatars.discourse-cdn.com/v4/letter/k/5f8ce5/32.png) [@kanicbird](https://boards.straightdope.com/u/kanicbird)\
**Post date:** [May 27, 2002, 3:26pm UTC](https://boards.straightdope.com/t/lasers-vs-mirrors/110675/21 "2002-05-27T15:26:56Z")

</div>

WOW another K2 is born - I didn’t see that one comming.

Anyway going back years ago (80’s era), I remember some show that critisized SDI and pointed out how lasers could be defeated. They went by % effectivness decrease. The 3 main things the Ruskies could do to defeat laser based SDI was - 1 put a reflective coat on their missles, 2 rotate their missles during flight, and 3 launch decoys. This obvioulsy biased show took a hit ratio of about (IIRC) 50% and after all 3 were done reduced it to 1%.

---

<div class="post-metadata">

**Author:** ![CalMeacham](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/calmeacham/32/35_2.png) [@CalMeacham](https://boards.straightdope.com/u/CalMeacham)\
**Post date:** [May 27, 2002, 8:34pm UTC](https://boards.straightdope.com/t/lasers-vs-mirrors/110675/22 "2002-05-27T20:34:05Z")

</div>

> [@](#):
>
> A shiny missile would do no good.
> 
> A chemical laser is steered by first spreading out the beam (perhaps a meter across) and directing it with a concave mirror. The beam then gradually focuses down as it traverses the atmosphere to a micrscopic point where it contacts the missile hull. The heat developed instantly sears a hole and damages the delicate innards.
> 
> lather, rinse, repeat.

It’s a complex situation. You want to correct for distortions due to the air if you can (using a seed beam and using a “rubber mirror” to compensate for atmospherc distortion), and if your beam gets too small the energy density causes the air to heat up and act like a negative lens, dispersing the beam (a process called “Thermal Blooming”). You better have the focal length calculatedc properly, or else the beam will start to disperse before it gts to your target. How long a range this will work over I do not know. The MIRACL laser fired at a target only about a kilometer away in the late 80s. All in all, I’d say that usng a mirrored or ablative coating on your missile is by no means futile. If your laser-wielding opponent slips up at all it could save your booster.

[Previous page](https://boards.straightdope.com/t/lasers-vs-mirrors/110675.md?page=1)