Concept drawing of a Northrop Grumman-designed 'sixth-generation' fighter jet. Northrop Grumman.
According to Northrop engineers, it is tailless, stealthy, and packs a laser cannon. It conspicuously resembles a scaled-down version of Northrop’s most notable feat of aerospace engineering, the B-2 stealth bomber.
Planners want greater weapons capacity, greater stealth, and higher survivability—jets.
 Key to achieving that self-sufficiency: directed-energy weapons, more colloquially known as lasers.
The idea: The jets could use a rechargeable solid-state laser to shoot down enemy missiles or aircraft that come within a certain range, essentially creating a no-fly zone around each aircraft.
The major challenge, Northrop acknowledges, isn’t so much in airframe design but in conquering the constraints of fundamental physics.
High-powered lasers are famously inefficient, converting only about a third of the energy they expend into target-incinerating laser beam power. So for every megawatt of energy from a laser weapon, twice that is wasted as heat. For a stealth jet trying to hide from sophisticated radar and infrared sensors, venting huge amounts of heat is roughly equivalent to firing off signal flares.

1. According to Fortune, a laser is only 1/3 efficient. To achieve a one megawatt laser output, you need three megawatts of power input!

2. To focus a megawatt laser (like the Boeing ABL), need two sets of huge optics. Need a tracking laser and a second firing laser. An additional problem is the constant fluctuation of air density. This makes it difficult to keep a beam focused on a target. This means wasted energy.

3. A laser weapon would require a big aircraft. This is bad for stealth. A large airplane means a larger RCS.

4. In the thin upper atmosphere, the Boeing ABL could only achieve a 50 to 100 mile range. In the mid-atmosphere, probably looking at 50 miles maximum. Modern BVR missiles have greater range than 50 miles. This means a BVR missile has longer range than a laser.

5. No practical defense (aside from electronic countermeasure) can be placed on an aircraft to stop a kinetic kill by a missile. On the other hand, lots of defenses can be employed to defeat a laser. Countermeasures against a laser include spinning, mirror-like finish, heat tiles, ablative armor, etc.

As the Fortune article mentions, a laser weapon creates a new heat problem of infrared detection.
In conclusion, I don't think a laser weapon is practical. The downsides far outweigh the benefit. Sure, a solid-state laser is reloadable. However, there are too many problems and I still think a salvo of BVR missiles is more effective. Martian2

Remember Dale Brown's books on lasers on bombers.



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