Scary Lasers

Posted: June 2, 2012 at 10:17 am

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June 1, 2012: Editor Note: The U.S. military is backing off from efforts to deploy combat lasers because none of the development efforts has produced a practical weapon. The following is a personal account of how the search for a combat laser began half a century ago because of an unexpected early success, followed by bizarre complications.


This is how the U.S. Army developed the first combat laser in the 1960s and 70s, but refused to deploy it because it was considered too cruel. It all started with the Advanced Propulsion Technology Branch of the Propulsion Directorate in the Army Missile Command at Redstone Arsenal in the 1960's. Their mission was the development of advanced propulsion concepts such as liquid monopropellants, bipropellants, hybrids, air breathing, etc. for application to Army missiles.

One morning, after a staff meeting with the army generals Dr. Walter Wharton, our supervisor, announced, "Men I've got a new and unusual project for you. It's not propulsion but needs all the technology and skills of propulsion. Here's the pitch: Over the past two years one of our army contractors has failed to demonstrate chemical lasing in a hardware device. The general asked us to take over the effort. And, if we achieved a satisfactory demonstration of the chemical laser, we would be the nucleus of a new laboratory and weapons effort. I told the general the problem was a natural fit to our skills. With the chemists, physicists, engineers, and technicians on our staff and our background in hardware development and testing we could do the job expeditiously."

The basic problem with using a laser as a weapon is power. A laser is focused light energy, being sent from the laser to the target in a short burst. Using batteries or generators and capacitors are too heavy for this to be practical. But the right combination of chemicals can provide the needed energy, at least in theory. The solution is a bit more complex.

Dr. Wharton led us in the analysis and evaluation of the contractor's effort and data. Their device used gaseous hydrogen and gaseous fluorine. The attempt at lasing was through the kinetic reaction states in the laser cavity to form the end product HF. Dr. Wharton, a skilled chemist, immediately determined the critical issue. To allow the intermediate activated molecules the time and space to lase to ground states in the laser cavity, would require supersonic injection by the mixing nozzles and very low cavity pressure. That environment would slow down the kinetics and stretch out the reaction zone allowing the species to lase.

Wharton designated me (Joe Connaughton, a chemical engineer) as team leader for chemist Tony Duncan, laser device operator, physicist Bill Friday, cavity optics and power, and mechanical engineer, Ben Wilson, facility design and development. We had top priority in obtaining hardware, shop, and other support services. In a matter of weeks we had the device set up and ready for operation. The big day came when we were ready to test. Dr. Wharton said, "Get that machine cranked up and don't stop till you get it to lasing. I'll be in the office, so call me if you have any problems or when it starts lasing."

We spent most of the day adjusting the flow of the gases and setting our liquid nitrogen trap and pumping speed. But near the end of the day, Bill Friday held a piece of strip recorder paper three feet from the cavity optics and yelled, "Hey! Look guys at me burn holes in this paper by that invisible laser beam!" We probably didn't project more than a hundred watts of power but it worked. We had an operating HF chemical laser, and we were in business. The next day was show time, which included all day demonstrations to various levels of management including the Commanding General.

We were off and running to build a ten kilowatt HF laser that would define the operating parameters for scale up to weapon grade hardware. It was a large modular boilerplate device designed for research studies. Calorimetric cavity mirrors for precise power measurements and ports for optical flow field visualization were included. The modular design allowed the evaluation and development of laser components to advance the technology of high-energy lasers.

The group quickly expanded to include PhD level scientists, who began to study all aspects of the chemical laser and extrapolate data to weapon system needs. Dr. Barry Allen, with contractor support, researched solid sources for the reactants. He found hydrides and fluorides that had reactant densities greater than the cryogenics were appropriate. He also worked on the successful development of chemical pumps that would replace the huge vacuum blow down system required to pump the boilerplate laser.

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Scary Lasers

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June 2nd, 2012 at 10:17 am