# Would this laser rifle really work? **URL:** \ **Category:** Factual Questions\ **Created:** [April 2, 2003, 7:11pm UTC](https://boards.straightdope.com/t/would-this-laser-rifle-really-work/166025 "2003-04-02T19:11:59Z")\ **Posts on this page:** 4\ **Page:** 2
**Author:** ![Happy\_Fun\_Ball](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/happy_fun_ball/32/17664_2.png) [@Happy\_Fun\_Ball](https://boards.straightdope.com/u/Happy_Fun_Ball)\ **Post date:** [April 5, 2003, 7:57am UTC](https://boards.straightdope.com/t/would-this-laser-rifle-really-work/166025/21 "2003-04-05T07:57:05Z")
> [@](#): > > \*Originally posted by Q.E.D. \* > \*\*Neglecting collimation optics, of course, which the link doesn’t discuss. \*\* A gaussian beam expands as 2w(z)= 2w[sub]o/sub[sup]1/2[/sup], where 2w[sub]o[/sub] is the beam waist (i.e. minimum diameter). The constant z[sub]o[/sub] designates the Raleigh range and is proportional to w[sub]o[/sub][sup]2[/sup]. If you want to collimate the beam you expand it, thus increasing z[sub]o[/sub]. In the pdf file it says > [@](#): > > **Effective range of the TIS-1 is dependent upon dispersion of the 1.3mm diameter laser beam over distance and is estimated at excess of 1500 meters.** To me this says that they have not expanded and collimated the beam. It also says that this rifle is crap and has no basis in reality. > [@](#): > > _Originally posted by Bill H._ > **It’s a proposal for something that technology may enable in 20 years.** Could be, but it seems more likely (to me) that this is an April fools day joke. My grasp of thermal physics and chemistry is atrocious: is there anybody out there that can speak to the veracity of these numbers? > [@](#): > > **Initially contained at a state of thermal equilibrium at a high temperature (2173K) and pressure (272 atm) within a gas reservoir heated by a Polonium-210 power cell offering a high energy density of 141 W/g, the gas mixture is permitted, upon release of the weapon trigger, to enter a restrictive nozzle throat annulus whereby the gas will achieve local sonic velocity (Mach 1.0). Exiting the annulus, the gas is permitted to enter a supersonic expansion nozzle, consisting of an inverted aerospike configuration. Within the expansion nozzle, the gas temperature and pressure will be significantly reduced (to 288.1 K and O.1122 atm respectively) resulting in the onset of a hypersonic gas velocity of 1998 m/s (Mach 5.98).** Po-210 has a density of 9.4 grams/c[sup]3[/sup]. How big would the power pack have to be to keep the gas at 2173 K assuming that they are 100% efficient at capturing the 141 W/g? What the hell is an inverted aerospike configuration? How hard is it to accelerate a gas to 2000 m/s in 1 meter long space? One thing I can do is verify that Po-210 has a “high energy density of 141 W/g”. Po-210 has a half life of 138 days and decays by emitting an alpha particle with 5.3 MeV. In 1 second that means a gram of pure (un-decayed) Po-210 would only emit roughly 100 J of energy in the alpha particles. So the 141 is of the right order of magnitude, but the fact that it is off by 25% adds more inconsistency to this “potential design”. It must be crap! ---
**Author:** ![Urban\_Ranger](https://avatars.discourse-cdn.com/v4/letter/u/e9c0ed/32.png) [@Urban\_Ranger](https://boards.straightdope.com/u/Urban_Ranger)\ **Post date:** [April 5, 2003, 8:22am UTC](https://boards.straightdope.com/t/would-this-laser-rifle-really-work/166025/22 "2003-04-05T08:22:31Z")
> [@](#): > > \*Originally posted by scr4 \* > There are a few minor advantages. It’ll be easier to aim because a laser beam will not be affected by wind and gravity, and will have essentially infinite speed. Yet a laser beam loses coherence quickly, and coherence is what makes a laser beam different from a normal light beam. ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [April 5, 2003, 9:00am UTC](https://boards.straightdope.com/t/would-this-laser-rifle-really-work/166025/23 "2003-04-05T09:00:35Z")
> [@](#): > > \*Originally posted by Urban Ranger \* > \*\*Yet a laser beam loses coherence quickly, and coherence is what makes a laser beam different from a normal light beam. \*\* Are you talking about atmospheric refraction and scattering? Scattering is usually negligible (unless you’re in a cloud or fog), and adaptive optics can compensate for refraction. Or are there other ways for laser beams to lose coherence? ---
**Author:** ![Tuckerfan](https://avatars.discourse-cdn.com/v4/letter/t/eada6e/32.png) [@Tuckerfan](https://boards.straightdope.com/u/Tuckerfan)\ **Post date:** [April 5, 2003, 1:22pm UTC](https://boards.straightdope.com/t/would-this-laser-rifle-really-work/166025/24 "2003-04-05T13:22:54Z")
> [@](#): > > \*Originally posted by Jumping Bean \* > \*\*Apart form the fact that they have a certain “gee-whiz” sci-fi mystique to them reinforced by countless films I’ve never understood what the appeal of a laser weapon would be. If you were able to pack that much energy into portable package couldn’t you find a more lethal way to deliver it than by punching small fully cauterized holes into people? Seems like even an immensely powerful laser weapon wouldn’t be able to inflict the kind of nasty sucking chest wounds that a present day machine-gun round could. I would be curious to hear if anyone thinks that, even leaving power consumption aside, one could make a laser weapon that could compete with good ole fashioned kinetic force. \*\* There’s also the advantage that, in theory, one weapon could do multiple jobs. So, if you had a really high-powered laser rifle, an infantry man could not only take on other foot soldiers, but also armored vehicles as well, using the same weapon. You no longer _need_ to equip the foot soldiers in your army with a wide variety of weapons, such as rockets, rifles, or heavy machine guns. One weapon does it all. (Though I can see a few reasons to keep missiles.) Of course, armored vehicles like tanks can carry much more powerful lasers. . . [Previous page](https://boards.straightdope.com/t/would-this-laser-rifle-really-work/166025.md?page=1)