I remember as a five-year-old cowering as I watched a rerun of H.G. Wells' War of the Worlds on TV. Those evil Martians could even destroy the vaunted weapons that had won World War II with their deadly heat ray. Flash forward about seven years and I marveled at the power and accuracy of phasers used by the starship Enterprise. Klingons never stood a chance against Captain Kirk (unless they were cloaked). Later still, the Star Wars franchise made liberal use of beam weapons. The Death Star could obliterate whole planets with a single strike.
Beam weapons have been standard fare in Science Fiction my entire life. Imagine my surprise when I googled "beam weapons" recently to discover the US military has actually been testing and deploying laser-based systems. The future has arrived.
What is a Laser? In very broad terms, a laser is a device that converts a form of energy (it can be either photons or electrons) into a directed beam of light of a single wavelength (coherent light). Coherent light possesses some interesting properties. The waves are oriented perpendicular to the photon's direction of travel, and the wave amplitudes self-align. These attributes allow a laser to pack quite a punch, maintaining a highly focused beam of radiant energy over much longer distances than non-coherent light.
In principle a laser is a simple device. There are four different technologies in use today, but the most likely used by the military is a solid-state laser, so I'll describe that.
A solid-state laser consists of an energy pumping source(a bright light emitter), and a laser medium (a solid cylinder of transparent glass-like material doped with specific rare earth elements). The flat ends of the cylindrical laser medium are mirror coated. One end is fully reflective, the opposite face is partially mirrored.
Quantum magic occurs inside the laser medium. The pump irradiates the medium, exciting electrons within its matrix. These electrons jump to higher but unstable orbitals which then cascade down lower energy states to return to the original base energy level. Some intermediate energy levels are meta stable, meaning the electrons can persist there until bumped by a photon. When this disturbed electron falls to the base energy state, it can emit two or more photons of a specific wavelength. These photons bounce back and forth between the mirrors, often colliding with other metastable electrons, generating a cascading effect. Eventually, a percentage of these coherent photons escape through the partially reflective mirror, creating the laser beam. The resultant beam of light can be guided and directed by passing it through an optical fiber not unlike the fibers that carry your cable and internet signals.
The power output of a laser is measured in Watts. Consider a 100W incandescent light bulb, its light radiating in all directions. If you hold your hand near an illuminated 100W bulb, it can get uncomfortably hot in a pretty short time. Imagine if all that energy were concentrated into a narrow beam the width of a pencil lead. Ouch. Now imagine a beam of one kilo Watt(kW), ten times as powerful.
Now let's talk beam weapons.
US Navy Of the military service branches, the US Navy is the farthest along in laser deployment. A system called HELIOS (High Energy Laser and Integrated Optical-dazzler and Surveillance), has been installed aboard a DDG
Arleigh Burke class guided missile destroyer since 2016. This 60kWbeam weapon system is designed to defend against inexpensive non-self-guided weapons such as drones or small watercraft (like the small boat that bombed the USS Cole in 2000).
The Navy is deploying lasers because after the initial development and installation, they are cheaper to use than anti-aircraft missiles or .50 caliber bullets.
Last year a 150kW system was deployed aboard the USS Portland, a San Antonio-class amphibious transport dock ship to protect landing craft and amphibious assault vehicles carrying Marines, their equipment and their supporting helicopters and Ospreys.
US Army The Army has announced the deployment of four Stryker battalions mounted with 50kW lasers early this year for short range air defense against drones, rockets, artillery and mortars. Like the Navy, the Army is using beam weapons to defend against non-self-guided weapons at close range.
Last October, the Army awarded a contract to develop a300kW solid state truck-mounted laser by 2024 powerful enough to destroy a continuum of objects, from cruise missiles, manned and unmanned aircraft, to drones.
US Air Force That same month the U.S. Air Force took delivery of the Airborne High Energy Laser (AHEL) weapon to begin testing aboard AC-130JGhostrider gunships within the next year. The Air Force seems especially enamored with the stealth capabilities of this 60kW beam weapon. With no sound and no visible beam, the AHEL can engage targets from
miles away, burning through materials, starting fires, and even detonating munitions, all with the enemy unable to trace the source of the attack. Unlike the Navy's and Army's laser deployments, the Air Force is deploying their system as an offensive weapon. Given the incredible sophistication of the tracking systems utilized by military lasers, they could be extremely accurate and effective weapons.
Final Thoughts Today's laser-based weapons are bulky, due to their power requirements. Ship- or aircraft-based systems are wired directly into the carrier vehicle's power system. Truck-mounted systems must use a very large battery pack (the most powerful civilian electric vehicle battery packs are roughly100kWh), or a generator.
In the near-term, I expect to see two trends. Vehicle-based or fixed systems will become more powerful, allowing destruction of ever larger targets at ever greater distances, or of greater numbers of small targets at close range (think a cloud of bomb-carrying drones). I foresee the eventual replacement of the Star Wars missile-based missile defense with a laser-based system, assuming no new antiballistic missile treaties preclude it. As a child of the Cold War, I personally welcome the day when nuclear missiles, including hyper missiles, will be rendered obsolete.
The other trend will be miniaturization, toward deployment of hand-held weapons. Ten or fifteen years from now I foresee a backpack version of the Stryker-mounted system used by remote foot patrols when they come under mortar attack. Another portable system could employ laser rifles tethered to a backpack power source. Not exactly hand-held Star Trek phasers, but a step in that direction.
For Further Readinghttps://www.physics-and-radio-electronics.com/physics/laser/differenttypesoflasers.htmlhttps://www.zmescience.com/science/u-s-army-tests-its-first-high-energy-laser-weapon/#:~:text=According%20to%20Task%20%26%20Purpose%2C%20the,truck%2Dmounted%20laser%20by%202024https://www.popsci.com/technology/us-navy-laser-weapon-test/https://www.popsci.com/technology/military-defensive-laser-weapon/https://www.sandboxx.us/blog/air-force-takes-delivery-of-stealthy-laser-weapon-for-ghostrider-gunships/ 
