Dead Horses - Discussion

Theemile wrote:Conversation Topic: Long ranged Energy Weapons/Oversized Energy Weapons

I don’t dispute this is a dead horse, but the reasons it comes ip as viable are different than you state.

The elements that govern beam divergence in lasers (Gaussian beams)are the wavelength and the beam waist diameter. When the wavelength is gamma rays and the diameter is in meters the beam maintains coherency at light hours range.

And while it is difficult to predict where a warship will be in an bour, predicting where say a 200km long orbital platform is a whole different animal. You can look it ip and probably get it to plus or minus a millimeter.

So why doesn’t it work? Reasons. Next topic.

kzt wrote:

Theemile wrote:Conversation Topic: Long ranged Energy Weapons/Oversized Energy Weapons

I don’t dispute this is a dead horse, but the reasons it comes ip as viable are different than you state.

The elements that govern beam divergence in lasers (Gaussian beams)are the wavelength and the beam waist diameter. When the wavelength is gamma rays and the diameter is in meters the beam maintains coherency at light hours range.

And while it is difficult to predict where a warship will be in an bour, predicting where say a 200km long orbital platform is a whole different animal. You can look it ip and probably get it to plus or minus a millimeter.

So why doesn’t it work? Reasons. Next topic.

The inverse square law says that you lose energy at a non-linear rate with increasing range. Double the range, you only get a quarter of the energy delivered. Regardless of frequency/wavelength or beam diameter.

Fox2! wrote:
The inverse square law says that you lose energy at a non-linear rate with increasing range. Double the range, you only get a quarter of the energy delivered. Regardless of frequency/wavelength or beam diameter.

Not lasers.

Look up gaussian beam in Wikipedia. It’s not a bad article. Though as I’m largely taking what they say on trust, as the theory is well past where my physics stopped.

@ kzt. Coherent beams don't diverge, so you are correct.

Daryl wrote:@ kzt. Coherent beams don't diverge, so you are correct.

Yeah, I purposely stayed away from that subtopic, other than glancing on it in the early paragraph about beam control. If you know where your target is, what it is doing, and you can pump enough power, and colliminate the beam properly, theoretically, you should be able to hit anything. One could argue about mount jitter, imperfect lens collimination, and variable dust/gas/debris in the beam path make collimination difficult at long distances, but that could be overcome by power/duration.

However, I have never seen David address this subtopic specifically, and authorial fiat would probably go with "stations use countergrav to do constant course corrections", making precision targeting information hours or days old inaccurate because space is big, OR nobody builds ships specifically to target system infrastructure because it has no peacetime applications or is a screaming EE violation, or some other handwavium.

I agree, it should work in Honorverse physics, but no one does it.

How should we address?

I’d go with “reasons”. Unless Duckk can find someone who wants to build some at least vaguly logical justification. So far the best we’ve come up with is “that isn’t how it works”, which is basically “reasons”.

It’s dead, it won’t work, but why is unknown to us. I suspect the real reason is David didn’t realize what he was creating with gamma ray lasers, but whatever, it doesn’t work.

Coherent beams do diverge as a result of diffraction limitations. However; the divergence angle and beam width at long range is directly proportional to the beam wavelength.

The rule of thumb is:

Beam Divergence Angle = 2.44 x wavelength / aperture diameter.

The prospect of building phased array graser assemblies with multiple emitter elements that are optically linked enables correcting for any imperfections in the individual array elements.

Even the lowest frequency Gamma Rays have wavelengths of less than 1eex-10 meters. An Honorverse battlecruiser could have an emitter array with an effective optical diameter of 100 meters.

Divergence angle would then be:

2.44 x 1eex-10 / 1eex2 = 2.44eex-12

At a range of ten astronomical units (80 lightminutes), the beam diameter would be 1500eex9 meters x 2.44eex-12 = 3.6 meters.

Assuming that you are pumping multiple megaton energy through this beam, that is going to leave a scar.

TFLYTSNBN wrote:Coherent beams do diverge as a result of diffraction limitations. However; the divergence angle and beam width at long range is directly proportional to the beam wavelength.

The rule of thumb is:

Beam Divergence Angle = 2.44 x wavelength / aperture diameter.

The prospect of building phased array graser assemblies with multiple emitter elements that are optically linked enables correcting for any imperfections in the individual array elements.

Even the lowest frequency Gamma Rays have wavelengths of less than 1eex-10 meters. An Honorverse battlecruiser could have an emitter array with an effective optical diameter of 100 meters.

Divergence angle would then be:

2.44 x 1eex-10 / 1eex2 = 2.44eex-12

At a range of ten astronomical units (80 lightminutes), the beam diameter would be 1500eex9 meters x 2.44eex-12 = 3.6 meters.

Assuming that you are pumping multiple megaton energy through this beam, that is going to leave a scar.

If they can keep all the emitters synchronized to keep the coherence and pump enough energy into them, yes.

I do wonder about the particle density in the medium and how much it would affect the dispersion and coherency at those distances. If I remember correctly, interplanetary medium contains on average 5 million particles per cubic meter.

Also, wouldn't some of those particles be accelerated from the energy transfer to create a "bow shock" that increases in mass the further it travels with the beam and soak up more and more energy up to a point?

Joat42 wrote:

TFLYTSNBN wrote:Coherent beams do diverge as a result of diffraction limitations. However; the divergence angle and beam width at long range is directly proportional to the beam wavelength.

The rule of thumb is:

Beam Divergence Angle = 2.44 x wavelength / aperture diameter.

The prospect of building phased array graser assemblies with multiple emitter elements that are optically linked enables correcting for any imperfections in the individual array elements.

Even the lowest frequency Gamma Rays have wavelengths of less than 1eex-10 meters. An Honorverse battlecruiser could have an emitter array with an effective optical diameter of 100 meters.

Divergence angle would then be:

2.44 x 1eex-10 / 1eex2 = 2.44eex-12

At a range of ten astronomical units (80 lightminutes), the beam diameter would be 1500eex9 meters x 2.44eex-12 = 3.6 meters.

Assuming that you are pumping multiple megaton energy through this beam, that is going to leave a scar.

If they can keep all the emitters synchronized to keep the coherence and pump enough energy into them, yes.

I do wonder about the particle density in the medium and how much it would affect the dispersion and coherency at those distances. If I remember correctly, interplanetary medium contains on average 5 million particles per cubic meter.

Also, wouldn't some of those particles be accelerated from the energy transfer to create a "bow shock" that increases in mass the further it travels with the beam and soak up more and more energy up to a point?

The entire point of phased array technology is that it does keep the emitters synchronized. Phased array radars have been in use on warships and ground installations for decades. The F-22 and F-35 have phased array radars. The proposed F-15X and B1R bombers would have phased array radars.

I had known that phased array lasers were theoretically possible but had been away from the research long enough to be surprised that the technology has been proven. I do not know how much progress has been made in miniturizing the optical phase shifters. The smaller the phase shifters, the more the beam can be aimed off axis. It appears that the Sixth Generation fighter might have a conformal, phased array laser!

TFLYTSNBN wrote:
I had known that phased array lasers were theoretically possible but had been away from the research long enough to be surprised that the technology has been proven. I do not know how much progress has been made in miniturizing the optical phase shifters. The smaller the phase shifters, the more the beam can be aimed off axis. It appears that the Sixth Generation fighter might have a conformal, phased array laser!

Alot of money is going into something similar currently, Fiberoptic lasers. The short of it is you fire lasers into modified fiberoptics which contain more repeater elements than necessary - the result is after the beam comes out of dozens of meters of looped fiber, it is far stronger than the beam that entered it. Every fiber optic cable has these rice grain sized
(or smaller now) photo multipliers embeded in them periodically to keep the beam from fading in strength. But for a laser weapon, you just use more photo multipliers, placed closer together than is required to just keep the output level - and voila - the beam grows in strength with each photo multiplier it hits.

Currently 6 to a dozen of these are arrayed together for the lite AA laser systems the Navy/AF/Army are field testing. Currently all the lasers are in phase, but future plans are to up the # of cables and make the array "active" so it is electronically steerable.

darn, I broke my own rule.