A villain is wreaking havok in town. He can become intangible at will, making him invulnerable to all conventional weapons and the hero team's powers.

However one of the heroes notes that since he's not invisible (only slightly translucent*) he must interact with light somewhat normally. That hero then suggests building a laser gun to try and kill him (capturing or containing him is now off the table). But a laser isn't the best choice, is it? Any harmful electromagnetic wave will do.

Assuming the villain interacts with light like a normal human being, what wavelength should our heroes go for?

As far as I know, you would need a huge installation to kill a human with a laser. Gamma rays are much more dangerous but possibly hard to produce.


Assuming current technology. The ideal size of the weapon would be between a handgun and something than can be mounted on an military LUV. The heroes can work with the army to build the weapon.

The only two things to take into account are:

  • Harmfulness of the wavelength for a human being
  • Practicality to produce that wavelength in a lethal amount

(*)The villain is only slightly translucent, in a way you can tell if he's currently intangible or not. Only a small portion of light goes through, about 95% of visible light interacts with him normally. You can assume the same for other wavelengths.

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    $\begingroup$ The question lacks research. Please visit Wikipedia's directed-energy weapon page. If that doesn't answer your question, tell us why and explain the issues you encountered. Thanks. $\endgroup$ – JBH Jul 22 '20 at 14:23
  • $\begingroup$ Your hero team seems to be locking themselves into a difficult and dangerous course of action to confront the villain this way. There may be other clever, safer courses of action to rid the town of their Intangible Menace. $\endgroup$ – user535733 Jul 22 '20 at 14:29
  • $\begingroup$ @JBH Most weapons presented in the article are non-lethal, designed for non-human targets (aircraft or missiles), or we don't know anything about them. It also doesn't say why some wavelengths are preferred over others, although they seem to focus on lasers and microwaves. Why not x-rays or gamma rays? $\endgroup$ – Teleporting Goat Jul 23 '20 at 9:03
  • $\begingroup$ @TeleportingGoat If a laser can destroy a missile or aircraft, you better believe that it'll fry a human. It's just disallowed to test or use the weapon in that way (Geneva convention, etc). The fins of a cruise missile are tougher than human flesh, and metal is more tolerant of heat than meat is. $\endgroup$ – John O Jul 23 '20 at 15:19
  • $\begingroup$ @JohnO missiles are filled with highly volatile explosives and precision engineered to move as fast as possible without detonating themselves. They also don't jump out of the way as soon as they notice thier skin slowly being heated up by a laser; so, missiles are not necessarily harder to kill than a human. $\endgroup$ – Nosajimiki Jul 23 '20 at 17:03

But a laser isn't the best choice, is it? Any harmful electromagnetic wave will do

A blue laser should do. The villain appears to be able to become transparent to most wavelengths except visible light; and the only reasons visible light is innocuous is that its frequency is too low and its energy density is too small.

But concentrate enough a small amount of energy and you get a lot of power. A 7 watt blue light laser can ignite paper (and render instantly, permanently blind).

Concentrate enough such lasers using an appropriate crystal or mirror matrix, and you can literally burn the villain to death.


(Frame challenges removed due to clarifications in the question)

According to some calculations done by PH.D. Rebecca Thompson of the American Physical Society, a headshot from a grid of regular laser pointers as weak as 1 kw in total would probably kill a person faster than they could get out of the way. The HELLADS program is a DARPA project that developed a 75 kW laser that weighs only about 375kg. This means that a 1-2kw weapon based on the same technology would be hand portable.

The exact wavelength of this laser is not public knowledge, but we do know that it is a solid-state laser. The older generations of military grade solid-state lasers they were based off of emitted at a wavelength of about 1 micrometer making them near infrared beams; so, if I had to guess, I'd assume it is likely in the same approximate wavelength.

The HEL beam is about 10 times lighter than previous generations of lasers for its stopping power; so, it's safe to say your heros will care more about replicating the engineering behind it than what exact wavelength it is operating at.

  • $\begingroup$ I'm wondering if the shortest wavelengths are viable. Gamma is undeniably dangerous, but mostly long term. If you shine a 1w blue light on someone, they'll reflect some but absorb the rest on the skin. But a gamma might just pass through, or at best give 1w of power spread out over the targeted area and many layers deeper. The spreading of this energy is detrimental if you want to cause harm. $\endgroup$ – Trioxidane Jul 22 '20 at 21:04
  • $\begingroup$ Gamma rays and X-rays are hard to direct the way you would a laser because they pass through solid matter so easily. If you want to just look at pure weapon potential, you would want to use a near X-ray UV based laser. $\endgroup$ – Nosajimiki Jul 22 '20 at 22:11
  • $\begingroup$ Gamma ray lasers are indeed pretty nifty, but where will the heroes get their macroscopic amounts of halfnium? Though, the x-ray laser is probably overkill no need to focus them with the lasing rods when the kiloton-yield nuke goes off... $\endgroup$ – John O Jul 23 '20 at 15:24

From a practical engineering POV, near infrared lasers have the greatest range in atmosphere, which allows you some latitude in targeting the bad guy. This is important since lasers are notorious power hogs, and the conversion efficiency from generator or chemical reaction to light is very poor. You will need a large installation, waste heat rejection, the optical train and a high quality mirror. A US Army experimental anti aircraft laser installation requires a tactical transport truck, since the power generator is a 300Kw turbine engine from a scout helicopter.

enter image description here

Dynetics and Lockheed design for a laser weapon

Longer wavelengths are possible, including microwaves, but the size of the mirror becomes correspondingly larger. The microwave Active Denial System fires a beam which causes pain, but only non lethal amounts of energy is delivered to the target. Obviously a more powerful microwave generator could be installed, but the size of the vehicle could be adversely affected

enter image description here

Vehicle mounted ADS

For the best results, you may need to go for a laser weapon mounted on an aircraft. This provides elevated sightlines for sensors and the laser beam, the ability to rapidly reposition the weapon, and the ability to tap into a large and powerful turbine engine for energy

enter image description here

F-35 laser mount for the F-35A and C models. Marines are out of luck

Super science is pretty expensive these days.....


Simply scan through the frequencies. When the baddy flinches, turn up to 11 and fry him.


Close to visible light seems best

Visible light is chosen by the eyes for a reason. They are fast, abundant and have a lot of energy. That means you don't need incredibly sensitive eyes. Maybe ultraviolet is better, someone might know this better, but visible light packs a punch. If you go higher in wavelength you get into trouble with passing through the body, like x-rays. So lots of energy is lost.

But your guy is transparent, which means visible light passes through, not imparting it's energy. So you need to have something around that spectrum that imparts it's energy and doesn't pass through him. But is he transparent in those spectrums? We don't know.

But there is the problem. A beam of light from a handheld flashlight doesn't do much, unless you can focus it on a tiny point for a little while. Maybe he's translucent because he's allergic, so a focused beam would do more damage, but unlikely. So expecting more than focussing the beam and burning him would be difficult.

Maybe he's overly sensitive to radiation? Humans are pretty good with it as creatures.

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    $\begingroup$ Visible light isn't any faster than other EM radiation, nor does it carry the most energy. The sun's energy output is indeed highest in the visible light range, but I don't see why the natural abundance of visible light from the sun should dictate that those wavelengths are best for this purpose. As you point out, most visible light barely interacts with the antagonist, so it seems like a poor first choice. High-energy wavelengths like X-rays and gamma rays are dangerous because they pass through the body, damaging anything they hit along the way. $\endgroup$ – Nuclear Hoagie Jul 22 '20 at 17:07
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    $\begingroup$ JUst to remphasize what @NuclearWang said : All photons travel at the same speed - the speed of light and that's the same everywhere in the universe. You want more energy then you raise the frequency (decrease the wavelength). $\endgroup$ – StephenG Jul 22 '20 at 17:43
  • $\begingroup$ @stephenG Gamma is shorter. Gamma flows through the body for a large part. Imparting it's energy not just over a surface area, but 3 dimensional. And not all energy at that. It is a mistake quickly made. Alpha radiation is more dangerous when you can put it inside the body, as it won't move through you. It just hits with incredible force at the immediate surrounding. I would prefer ultraviolet then, as more will be absorbed by the skin directly. But I'm curious. Is a flashlight of gamma short term more dangerous than a focused ultraviolet flashlight? Maybe you're right. I don't know. $\endgroup$ – Trioxidane Jul 22 '20 at 20:50
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    $\begingroup$ "Your guy is transparent" "visible light barely interacts with the antagonist" I think you misunderstood. I said "slightly translucent", he's not transparent. Only a small portion of light goes through, about 95% of visible light interacts with him normally. $\endgroup$ – Teleporting Goat Jul 23 '20 at 9:36
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    $\begingroup$ @Trioxidane I'm not sure how I could do more than "only slightly transluscent". I added a note to avoid further confusion, I hope it's clear too. $\endgroup$ – Teleporting Goat Jul 23 '20 at 12:46

You don't need a ray gun. Just shoot him with a normal gun, and when your Menace becomes intangible, watch him fall through the ground to the center of the Earth.

Once there, he can either become tangible and die from heat and pressure, or remain intangible for as long as his air supply lasts before suffocating.

Problem solved!

  • $\begingroup$ That's not an answer to my question. There's already another one about how to beat an intangible villain. My question is: the heroes decided to try out this method. What would they then chose that makes the most sense? $\endgroup$ – Teleporting Goat Jul 24 '20 at 17:27

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