Friday, April 13, 2018

Ultra-Tech: New Laser Options

A while ago a user of the GURPS Discord server by the name of Jose asked me for help designing a TL10 laser that could be used underwater, punch through DR300 and had to be at lest somewhat man portable but at lest he was ok with it being disposable. Sounded like a fun challenge so I gave it go and came up with a bit of an house rule that let him have a laser with a 3 armor divisor at the cost of a major reduction in range, slapped it on a disposable laser and made it out of advanced material to get the weight down to a semi-reasonable level.

Well, he was happy with it and I figured that I had my next blog post.... and then life happened.

But now I'm back! Follow me after the jump for more musings and options to get more millage out of your laser weapons.

While this post took me a while it did give me time to think over a few things I found odd about how Ultra-Tech handles lasers that I came across when building Jose's laser.

You see since he wanted an underwater laser, that meant he was going to need a laser that was either in the green or blue wavelengths. Sure enough Ultra-Tech has rules for blue/green lasers on pg. 114 and the idea that it would double the lasers range is spot on but what I found odd two things.

First was that David seemed to think the only was to get a laser up to being blue is by a technique called frequency doubling (also known as second-harmonics generation) in which the beam is passed through a non-liner crystal which cases the beam to half its intensity but double it frequency. Now this is true for modern lasers as well as probably true for early TL9 lasers but there are already developments in laser optics that will allow lasers of any frequency up to blue to made without having to loose efficiency.

The second thing was something that wasn't just an an issue with the rules for blue/green lase, the assumption that lasers (an other energy weapons) would just outright stop after a certain range in water (or in some cases air). Now once again, there is some truth here. If you were just to shine normal light of a given wavelength, after a given distance it will be totally absorbed by the medium its passing through and stop at a predictable distance. Lasers on the other hand, especially weapons grade ones, are far more coherent and intense then normal light. Water will still start to absorb the laser beam but do to the higher energy per given area this will start to rapidly heat up the water, reducing its density and letting the laser propagate father and farther until all the lasers energy is used up. It's still super inefficient to try and fire a normal laser underwater.

So I figured since I'm going to be working on this for a while, might as well cover these issues and provide some optional rules to address them below.

Lasers and the Amazing Technicolor Wavelengths
The rule that blue/green lasers half you number of shots and halves ROF should only be used for TL8 and early TL9 lasers do to need to use frequency doubling to shorten the wavelength.

For mature TL9 lasers, advancements in optics (such as phased plasmonic nano-antenna arrays being made practical and yes this is a real thing) allows for a laser to be made in any wavelength from 1.5 μm infrared to blue. You can change a laser wavelength but have to have its beam generator replaced with one of a difference color. This costs 1/3rd the base cost of the laser and is a favorable task that takes 10min and gives a +1 to Armory (Beam Weapons) roll to swap the parts.

At TL10 and higher lasers can be assumed to be free electron lasers. As a ready action an free electron lasers can switch from any wavelength from 1.5 μm infrared to violet. At TL11 and higher it can reach up to ultra-violet.

Of course Blue/Green is not the only wavelength option, it just gives the best range option that can be reached, violet is best once free election lasers are available (unless you have to shoot under water). Wavelengths in the ultra-violet and shorter range have even better ranges but are very inefficient in an atmosphere so I will save covering them for another post (that and the two-photon absorption caused by UV lasers is... funky and I still need to think about how to best handle it).

Other wavelengths are between the assumed 1.06 μm  IR  and blue/green are of course available. They are not as useful in most cases but I have included them on the below chart because it's never bad to have more options open. 

 The range modifier is just that, multiply a lasers range by the range modifier of the given wavelength. Note that lasers in the 1.5 μm wavelength are eye safe and more then likely all civilian legal lasers will require to be restricted to this wavelength.

Wavelength    Range Modifier        Water Attenuation Range
1.5 μm IR           ×2/3rd                     0 yrds
1.06 μm  IR        ×1                           0 yrds
Red                   ×4/3rds                    5 yrds
Orange              ×1.67                       11 yrds
Yellow               ×1.67                       22 yrds
Blue/Green        ×2                            55 yrds
Viloet                ×2.67                        44 yrds

Greedy Water
The water attenuation range is that range at which water eats enough away at a lasers energy to half its damage. Half the damage again for each multiple of this range the beam reaches. If the water is murky then it acts just like rain, fog, smoke or snow using the rules found on pg. 114 of Ultra-Tech.

For lasers in the IR range, water is opaque as as a brick wall is to us, treat each yard of water as having a cover DR 37 that ignores any type of lasers armor divisor. This stacks with any additional cover DR granted by the water being murky. 

Technically air also has an attenuation range but it is great enough not to matter in most cases.

Oh and I just noticed that Ultra-Tech mentions nothing on how to handle being potentially blinded by non-eye safe laser frequencies! Well, might as well tackle that while I'm at it heh.

Lasers and Eye Safety
Any laser with a wavelength shorter then 1.5 μm is an eye safety hazard! Anyone without eye protection who looks at the point of incidence (where a laser hits) of a beam with a wavelength less then 1.5 μm must make a HT roll. You get a modifier to this roll based on how far you are from the point, look up how far away you are from the point of incidence on SS/R Table (Basic Set pg. 550). Look over to the size column, the modifier listed there is equal to the size modifier. `If your torso is the point of incidence (ouch!) then your SM to hit modifier is used, if your face is hit (not my face! It's how I make my livins'!) then it is your SM-5. If there is something that partially obscures the point of incidence then you revive a bonus to your HT roll equal to cover penalty the measurement would provide.

If you make your roll, congratulations you have eyes of lead. If you do not make your roll then treat both of your eyes as crippled as under Effects of Crippling Injury (Basic Set pg. 421), treat how much you failed you roll by as how many HP you lost. Any direct laser hit to the eye that is strong enough to cripple it automatically permanently cripples that eye.

Example: Ok let's say you step out of your house one day only to find out a massive laser battle is going on. After taking a moment for this to all to think in and letting the sense of, "Holy crap, this is the most awesome thing EVAR!" clear you quickly realize they are firing blue wavelength lasers and you forgot to bring flash googles to protect your peepers. Just then beam fired from a TL9 Assault Laser strikes a car about 18 yards away  doing 10 points of damage. Now let's say you're in decent health and have a HT of 10. Since the beam hit 18 yards away, which is close to 20 yards, and if we look over to the size column gives you +6 to your HT but since the laser did 10 points of damage which if we treat as 10 yards gives -4, the laser flash reduces your bonus to +2 for a total effective HT of 12. You make your roll and get a 13 and fail by 2... bummer.... Afterwards you will make another HT. If you succeed you are only temporarily blind until you heal an amount of HP worth of damage equal to how much you failed you roll by, in this case 2. If you fail your roll you will take 2 months to heal(!) and if you critically fail.... you're kinda blind permanently. 

And with all that out of the way, time to get into the thing this post was originally about! 

Yeah, getting hit by a pulse laser sucks.
Jose wanted a laser with a little more ump, so my idea was to use a pulse laser. Of course Ultra-Tech already has something called a "pulse-laser" but this is actually describing a concept known as pulsed impulsive kill laser (which totally sounds like a kind of laser that should be on some kinda meds, I'm just saying). A pulse laser in the sense I'm talking about means a laser that rather then firing a coherent beam of photons at the target, it fires its energy in a series of densely focused nano-second pulses. Do to how tightly the pulse is focused the small pulse, despite having only the energy on par with a firecracker, is able to strip some of the electrons off of the matter the pulse comes into contact with. This area then flashes into plasma blasting out a small crater when the next pulse arrives just as the plasma flash fades and then hits the same area unimpeded and blasts a little deeper then the first pulse and so on effectively explosively drilling its way into the target!

This make pulse lasers far more penetrating then normal but does come at a price. As I explained here, the more tightly you focus a laser the more your range drops and boy does it get hit hard, with range dropping by a factor of almost 40! So unless you use gravity lenses in your setting or field jacketed UV lasers or combat in your future is really, really close quarters, this option is only really good for adding an close range anti-armor mode to an existing laser rifle or as an dedicated short ranged heavy DEW.

Now back when I designed that laser for Jose I just a quick bit of number checking and spat out a design for him that got the job done and he seemed to be happy with it and I went on my merry way starting to the early version of this blog post showing how to add pulse laser to the list of options you can make with the Blaster and laser Design System and then three more people quit my job, the holidays hit, I was lucky to get a day off a month do to lack of workers and my blog started collecting dust.

It sucked, hard. I hated basically dropping of the GURPS map for so long but it did give me time to think. At first it downed on me the odd way Ultra-Tech handles blue/green lasers, attenuation, and the lack of eye safety rules prompting me to slowly update the scope of this post. Then as did a little more research into pulse lasers to refresh my memory it dawned on me that by just slapping a (3) armor divisor on it I was greatly understating how powerful pulse lasers are. You see, lasers are still just light. This means based on a materials albedo, some of the lasers light would be reflected wasting some of the beams energy. Now in real life this can very by quite a good margin but an approximation of roughly 50% of the energy being radiated away is a good average and given that lasers have an E of 3 in the Laser and Blaster Design System it seems that David came to the same conclusion. Pulse lasers however work a little bit differently. Because they focus their energy so tightly that they can start to ionize the area of incidence, the normal laws of optics starts to break down and far less of the energy is going to be radiated away bringing pulse lasers closer to having a 100% rate of efficiency, much like plasma guns (which is way they have an E of 6). 

But wait! There's more! If you take a look at the above pic showing how the concept behind a pulse laser works, you might notice that each flash of plasma sends shock waves that compress the material being hit causing it to fracture and crack and if that was an more elastic material (such as meat) then the drilling action would cause the it expand, forming a temporary cavity.... just like what happens when a bullet smashes its way through an object. To this end pulse laser do not cause tight beam burning damage but rather a category of piecing damage depending on the beams damage (more power the beam the bigger the wound channel it's going to blast out!) with the incendiary modifier.

Sooo, yeah. That's quite a few things that kinda got glossed over in my original design.

But enough explaining, lets get into how to design one of these bad boys!

Oh... right... since Ultra-Tech already has a pulse laser option I should rename this option, shouldn't I? So instead I shall dub this design option:

High-Output Pulse Laser (TL10+)
The following shows how to design a high-output pulse laser using the Blaster and Laser Design System from Pyramid 3/37 Tech and Toys II.

When designing a high output pulse laser, build it as a normal TL10+ laser with the following changes.

Unlike normal lasers, high output pulse lasers do piercing damage with a size based on how powerful the beam is (see below) with the incendiary modifier and a (3) armor divisor.

To figure the high output pulse lasers type of piercing damage, find which of the below ranges the weapons damage falls under:

  • 3d or less, damage is small piercing (Pi-). 
  • If over 3d through 6d+2, damage is piercing (Pi). 
  • If at lest 7d-1 through 10d-1, damage is large piercing (PI+). 
  • If 10d or greater then damage is huge piercing (Pi++)

Empty Weight
When figuring the lasers empty weight a high output pulse lasers E is 5.

When figuring the lasers half damage range Rb is 0.4.

Shots Table 
Weapon                                  TL9 Cell    TL 10 Cell   TL11 Cell     TL12 Cell
TL10+  High Output Laser    2,083         8,333            33,333           133,333   

Alternatively you can convert existing lasers to being a high output pulse laser by multiplying is damage by 1.67, giving it the (3) AD changing its damage type as shown above and then dividing its range by 36. 

Ok, now with all this, here's how I should of stated Jose's weapon:

With the advent of 22nd century technologies even the poorest navies could afford to cover their ships hulls in active cell systems that would literally cover this ships "skin"  in advanced sensors and effectively let the ship sense the world around it. This of course made it very difficult for special forces to sabotage the ships of small navies that decided to act up. No longer could you send in a team to place explosives against the hull, the ship would feel the bomb, alert security teams and often had anti-frogmen countermeasures built in. Close ranged guided torpedo strikes were also less useful since the active cell sensors would detect the launch and often have counters for this line of attack as well.

So what was needed was a weapon system that could fire almost silently and could hit the ships hull before it could react. There was one such weapon system who also had benefited from the fruits of the 22nd century, the directed energy laser.  Lasers were almost totally silent and hit the target effectively instantaneously.

However there were some drawbacks to over come.

Even though developments in free electron lasers meant that is was trivial to make a laser in the blue wavelength which would give it the best range underwater, that range would still not be that great. Given how quickly water absorbed even blue light, it would limit effective range to around 40 meters before the water would start to greatly degrade the beam.

Another hurdle was the required power of the beam. In order to be effective against the widest range of navel targets it was figured that the weapons would need to be able to reliably defeat roughly 10.5cm of RHA equivalent. This meant a very big laser, too big to portable by special forces. The decision was then made to make this a high-energy pulse laser since it was going to be used at fairly close range. This did knock quite a few pounds off of the weapon but it still clocked in at 195lbs.

So finally it was decided to make the weapon a once shot disposable laser. Since the cooling, beam generator and power supply only needed to be survive one firing and then burn out they could get away with using incredibly lightweight and under regulation parts which brought the weight (and cost of the unit down to something manageable.

With its self contained and sealed unit, the actual laser its self was called a Laser Emitter-Disposable (or LED). The LED houses both the full laser assembly and a power pack made up of 15 nonrechargeable B power cells which powered it and ended weighing only 19.5lbs.

To be man-usable the LED was fitted to a 4.4lbs non-disposable shoulder mounted assembly that houses a duel-model 16×/8× hyperspectral optical sight (can operate in a 8× binocular vision mode with +3 to aim or a narrow mode 16× with +4 to aim but gives No Peripheral Vision, see Basic Set pg. 151. See Ultra-Tech pg. 61 for more on how hyperspectral passive visual sensors work. Runs off a C cell for 100hrs) and a integrated IFF system (See Ultra-Tech pg. 151. Can be manually switch off when not needed). The LED plus the mount was called the Directed Energy Disposable Ordnance Weapon-Laser (pronounced Dead-Owl).

The only downside to this system was due to its disposable nature, the LED was desired to discharge its melted internals out both ends to help blast the heat build up away from the firer. To this end the weapon was designed to vent its melted parts through non-melted parts to held blunt the blow but it also had to be vented out both ends to keep the weapons from being thrown off target do to the reconciles nature of laser weapons though to keep the discharge from interfering with the beam, its vented around and slightly off angle from the lens.

This discharge also meant that once it was fired the attacked ship, along with any other in the area, would know the exact location of the firer. This would do little for the target ship but it would also greatly reduce the life expectancy of the firer. To counter this, the DEL was also designed to be fitted to remote operated, disposable, underwater drones that would let the special forces team stand off from a safe distance and then guide in the drone to the target giving them time they needed to get away after the target was taken out. In this mode the weapon has ST 12M.

A single LED costs $9,800. Fore and backblast: 2d+1 cr.

GUNNER (BEAMS) (DX-4, or other Gunner-4)
TL   Weapon            Damage                 Acc        Range        Weight   ROF   Shot    ST     Bulk   Rcl   Cost           LC  Notes 
10   DECDOW-L     7d×4(3) pi++ inc    15 +4    650/2,000   24/15B  1        1[10]    9†    -7          1      $16,400/$45 1     [1]
[1]Hazardous fore and backblast (see entry).


  1. Thank You for another informative post.

    I do have a couple of questions.

    Firstly: When firing large lasers underwater, is the heating of the water by the beam being attenuated likely to become a hazard, or would this only show up if you're doing something stupid like firing ship-mounted lasers in a swimming pool?

    Secondly: You seem to have done a deeper dive into laser weapon physics, so are there other aspects of either how GURPS handles laser weapons, or the design system specifically that you think could be done better, or did you get all of them with the rules changes above?

    1. Thanks! I try my best.

      For your question, yes the energy absorbed would start to heat up the water. If there is enough energy, it will cause a steam explosion. Now for most handheld lasers, there would be some violent bubbling of the water around the beam at most.

      Just to give you an example, it takes about 4.2kJ to heat a kilogram of water 1°C. Assuming the water starts out at ~20°C, it would talk almost 340kJ to reach the boiling point. It would then a staggering 2.3 megajoule to push that kilogram of water passed its point of vaporization so it would actually boil! A 5d laser only has ~16kj of energy in its beam, even a 20d laser wouldn't even get close to boiling a kilo of water!

      For your second question, GURPS handles energy weapons with far more realism then I have ever seen in anyother major published RPG system. That being said, it's not perfect. However thankfully forum regular Dr. Luke Campbell builds lasers for his day job and has taken a crack at stating up a more realistic system for both lasers and particle beams (he even recently helped out with an episode of a youtube program called Because Science where his laser wizardry was used to explain how star wars blasters work)

      However, around the time I started my blog, Luke, Anthony, David and myself got into a talk about energy weapons and if I remember correctly he was going to incorporate some of that stuff into in to the GURPS Armory book which, yes is still being worked on. It's just even lower on the pecking order then even the VDS and with the Kickstarter and with Kromms personal life issues hitting hard right now... these books are still a long way off sadly.

    2. I thought that might be the case. So only worry about if somebody is using a lot of lasers in a situation where the water can't circulate easily ... aka, the example I gave of 'ship-scale lasers in a swimming pool' ... and to be honest, steam explosions from that will probably be the least of everyone's problems.

      GURPS Armory ... that would be a fun book. I want VDS so very much, but I'm thinking that will show up when it shows up. In the meantime I've been playing with the 3rd ed version to get my fix. :)

    3. Honestly I've got enough of my own personal design systems to hold myself over.On the other hand I would give just about anything just to get eight minutes to look over the Armory manuscript since there are still some factors of how GURPS handles regular and EM guns that I'm still in the dark about.

    4. It looks like you kind if duplicated and then modified Luke Campbell's work at regarding attenuation in water. I wonder why you changed his numbers. His are rather well researched, as is all of the other information on lasers and directed energy weapons on his site.

    5. While Luke was definitely an excellent teacher, helping to fill in my many gaps in knowledge on how lasers actually work; the attenuation ranges are just a well know limit of how far a given wavelength can travel before the material acts as being opaque to it.

      The only reason his and mine numbers are different are 1) I used GURPS standard yards rather then meters and did some rounding ups and 2) for simplicity I used the range at which half the energy would be absorbed by the water where Luke used (if I’m remembering it t right) the point at which either a quarter or a third of the lasers energy would of been absorbed.

  2. The fact that GURPS "pulse" lasers weren't actually pulsed lasers always bothered me and I'd been ruminating how to fix it or add in a more accurate version for a while. Nice to see you beat me to the punch!

    1. Well to be fair, at the time Ultra-tech was coming out pulsed impulsive kill lasers were also just being called pulse lasers (for reason that should be obvious when reading that name lol). These types of lasers are now being called pulsed energy projectiles. The name is still a bit too "pew-pew-pew" sounding to me for a real weapon but eh, better then a laser that sounds like it's bipolar.

      Oh and I came across a PM discussion I had about a year ago with David on lasers that I forgot about and in it he explained a bit about how he worked out lasers for 4th ed. They are technically pulse lasers in how they work, they just favor a more balanced approach being less focused then the ones I stated up for greater range.