https://spectrum.ieee.org/tech-talk/aerospace/military/fiber-lasers-face-a-challenger-in-laser-weapons
And now a new contender for high-power defense apps - "liquid lasers".
General Atomics is working on them. Per this article, these are
apparently solid-state lasers with liquid cooling passages through the
lasing medium. Coolant is carefully matched for refractive index with
the solid medium, and coolant flow is managed to avoid turbulence. Not
clear if the coolant actually takes part in the lasing, or simply
doesn't interfere with it, though the latter seems implied.
Also mentioned that they're shooting for a ballpark couple hundred
kilowatts output for useful weapon applications, at lasing-device mass
on the order of 5 kg/kw output. (A DARPA goal of 150kw output at 750kg
mass is mentioned for "a fighter jet", presumably a F-35.)
Also mentioned that apparently they can usefully combine the output of
multiple individual devices, which implies very good phase control.
Also implied that the same is true of fiber optic lasers. With limits
(in both cases?) on how many devices can be usefully combined. Mike
Griffin Congressional testimony is mentioned in this regard.
They also mention "a high-density modular high-power lithium-ion battery
system able to store three megajoules of energy", presumably to allow
periods of high-power laser operation in between longer periods of
charging from lower-power continuous sources. These might actually have
rocketry applications, for running pumps, depending.
Henry
On 10/15/2020 3:38 PM, Henry Vanderbilt wrote:
Bill,
I'm sure they're electrically-powered continuous-wave lasers that are being reported on as in field-test in the tens of kilowatts power range. If I was sure they were diode lasers however, I wouldn't have phrased that part "I presume". It's been a while since I followed the technology closely.
I suspect Ken/Roxanna has it right; the technology involved is likely fiber optic lasers. Which on hasty reading-up, can be pumped with diode emitters, so at least I'm not totally off base.
My understanding is that Free Electron Lasers are pulsed, not continuous output. And my impression is that while they're still being looked at for defense apps, they're not the frontrunner these days. To the extent one can trust an impression of an inherently sensitive subject gained purely from reports in the open press, of course.
Henry
On 10/15/2020 3:06 PM, William Claybaugh wrote:
Henry:
You sure those are diodes? All the one’s I’ve seen were FEL’s.
Bill
On Thu, Oct 15, 2020 at 2:59 PM Henry Vanderbilt <hvanderbilt@xxxxxxxxxxxxxx <mailto:hvanderbilt@xxxxxxxxxxxxxx>> wrote:
Apply a potential difference to a conductive material, and you'll
get a net migration of electrons along the potential direction.
"electric".
Oh, you wanted something more specific than that? :-) Current
public reports of tests and prototypes seem to cluster around
what I presume are diode lasers with continuous outputs in the
tens of kilowatts range, mounted with appropriate pointing and
beam-forming on ships, aircraft, and large ground vehicles. Some
stories give the impression that the customers think another
order of magnitude of reliable power output (in the hundreds of
kilowatts) will give them a useful area defense against targets
heavier than the small rockets/shells and small drones commonly
mentioned as current test targets.
Henry
On 10/15/2020 1:48 PM, roxanna Mason wrote:
electric lasers these days.
Elaborate on "electric"
Ken
On Thu, Oct 15, 2020 at 1:41 PM Henry Vanderbilt
<hvanderbilt@xxxxxxxxxxxxxx <mailto:hvanderbilt@xxxxxxxxxxxxxx>>
wrote:
Utility in evading missile defenses aside, one thing to keep
in mind is, for certain targets - among them ships - payload
fraction is less important. A hypersonic impact delivers
TNT-equivalent energy for the entire vehicle mass involved
even with no actual warhead on board at around Mach 9, and
the equivalent energy of a 25%-of-vehicle mass TNT warhead
at Mach ~4.5.
Given that the main penetrating-defenses advantages seem to
be maneuvering beyond an interceptor's ability to follow,
and operating in atmosphere bands where the interceptor
loses effectiveness, effective anti-missile beam weapons
will likely negate much of those advantages and largely
obsolete expensive hypersonics. Which may well explain why
USN (and USAF) seems very interested in electric lasers
these days.
Henry
On 10/15/2020 2:23 AM, George Herbert wrote:
OT...
It’s not much of a secret I do missiles and nuclear proliferation
research and analysis including threat systems analysis as a side job.
There are a few things you can do with hypersonic weapons. You can
approach targets in the inconvenient altitude and speed band where there’s too
little lift for normal fins and too much for unstreamlined exoatmospheric
interceptors. Midcourse defense gets very difficult... You can change
direction in hypersonic flight, allowing flightpaths avoiding defenses or
attacking simultaneously from different directions, complicating defenses.
Under some circumstances they can use trajectory changes in target approach to
maneuver out of interceptor engagement envelopes after interceptor burnout.
Against rapidly maneuvering targets there is a better target volume capability.
Under some circumstances the range is longer than a smaller ballistic
trajectory Maneuvering Reentry Vehicle can do.
They are much more expensive and harder to do than maneuvering
ballistic RVs. They can’t carry effective decoys, IR sensors see them
thousands of kilometers away, and avoiding defenses has to be done essentially
blind because they can’t credibly detect incoming interceptors with onboard
sensors.
The payload fraction of ballistic RVs is about 0.5, of maneuvering RVs
0.3-0.4, of hypersonic glide weapons 0.2 or less and Hypersonic cruise weapons
0.1 or so. For the same payload they’re tremendously larger missiles to start
with, with corresponding ship, aircraft, submarine, truck, or silo capacity
issues.
They make better sense as Chinese antiship Missiles than as US prompt
conventional strike missiles. The countries don’t have analogous needs.
-george
Sent from my iPhone
On Oct 14, 2020, at 10:19 PM, Troy Prideaux<troy@xxxxxxxxxxxxxxxxxxxxx>
<mailto:troy@xxxxxxxxxxxxxxxxxxxxx> wrote:
attracted a lot of attention and hype but had no military valuewhatsoever.
(For the sponsoring nation, that is -- it had considerable value toenemies,
their
since it pulled desperately-scarce resources away from things that *did*have
real military value.) The recent hypersonics hype smells much the sameI guess the difference now is the "enemy/ies" are all on the same
to
me...
Henry
hypersonic
bandwagon.
Troy