Another interesting question: Is the solid lasing element fiber optic,
or something else?
On 10/24/2020 12:57 AM, ken mason wrote:
"Not clear if the coolant actually takes part in the lasing, or simply doesn't interfere with it, though the latter seems implied."
If it were the former then it may be analogous to a dye laser so double your pleasure, nothing wasted, sounds almost too good to be true.
I still need a diagram to see the configurations of all the components and coolant paths.
K
On Fri, Oct 23, 2020 at 12:10 PM Henry Vanderbilt <hvanderbilt@xxxxxxxxxxxxxx <mailto:hvanderbilt@xxxxxxxxxxxxxx>> wrote:
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 thathave
*did*
real military value.) The recent hypersonics hype smells much theI guess the difference now is the "enemy/ies" are all on the same
same to
me...
Henry
hypersonic
bandwagon.
Troy