“We installed a 15-kilowatt class solid state laser on the Navy’s Self-Defense Test Ship, the former USS Paul Foster, and defeated small boats under contract to ONR. We set the engines on fire aboard an unmanned RHIB that was the target. It was done from a ship in a maritime environment up to Sea State 3. We couldn’t test beyond Sea State 3, not because the laser couldn’t fire from the ship, but because there was concern about the small unmanned boats that we were shooting at,” said Hixson.

With solid state lasers, diodes are turned on with electricity, and the light from these diodes, in turn, pumps the solid state gain medium.

A laser works by placing mirrors around a gain medium that creates an optical oscillator. Chemical lasers have the chemical reaction as the gain medium. With solid state lasers, diodes are turned on with electricity, and the light from these diodes, in turn, pumps the solid state gain medium.

“With solid state lasers, we’re not necessarily getting more efficient, but we’re scaling to higher powers. The fundamental physics of the gain medium is going to dictate what the efficiency is,” Hixson said. “It’s now an engineering problem and not a physics problem to scale to higher powers.”

Hixson said you can think about a laser weapon system in sub-systems. There’s the laser, which is the light generator or light source. Then there’s the beam control, the element that takes the light from the light generator and focuses it on the target appropriately. The fire control is the user interface on the ship.

“We’re also involved in the robust electric laser initiative – RELI – in fiber laser technology development. The total ‘wall-plug’ efficiency is something like 20 percent. So if you’re looking at a 100-kilowatt laser, you need to pump 500 kilowatts, and you have to dissipate something like 400 kilowatts. With fiber – and different people will quote different efficiencies – power in and power out electrical-to-optical efficiency is about 30 percent. With a 100-kilowatt fiber laser, you pump with 300 kilowatts and you only have to dissipate about 200 kilowatts of heat,” Hixson said. “So those things become important as you’re thinking about integration onto a ship or another platform.”

Unlike bullets, missiles or torpedoes, there’s no ordnance that has to be safely and securely stored on the ship, eliminating weight and space.

Another way to look at efficiency is the duty cycle, Hixson said. “When you’re at sea, and you are firing these lasers, you are not firing them all the time. You are firing them for relatively short periods of time. Which means you don’t need to accommodate 500 megawatts of excess generating power 100 percent of the time to power your slab laser. You can actually have an energy storage scheme where you charge a bank of batteries and you fire the laser for however many targets you might have, and then you have opportunity to recharge when you’re not firing. So the duty cycle is an important parameter to keep in mind as we think about accommodation on specific platforms.”

Laser technology offers speed of light defense, Hixson said. “With kinetic weapons, you have to wait and do battle damage assessment (BDA), whereas with a laser, you’re doing BDA through the very same optics you’re firing a laser. And I think that would be a very attractive feature for surface combatants fighting with lasers.”

Unlike bullets, missiles, or torpedoes, there’s no ordnance that has to be safely and securely stored on the ship, eliminating weight and space. Lasers can engage multiple small targets at a very attractive cost exchange ratio. “You’re using a gallon of diesel fuel to defeat a cheap UAV or a small boat rather than an expensive gun round or missile,” said Hixson. “You don’t have to use your expensive kinetic energy interceptors going after ‘trash targets.’”