Robert Hall and the Solid-State Laser

The debt we all owe must be paid someday, and for inventor Robert N. Hall, that debt came due in 2016 at the ripe age of 96. Robert Hall’s passing went all but unnoticed by everyone but his family and a few close colleagues at General Electric’s Schenectady, New York research lab, where Hall spent his remarkable career.

That someone who lives for 96% of a century would outlive most of the people he had ever known is not surprising, but what’s more surprising is that more notice of his life and legacy wasn’t taken. Without his efforts, so many of the tools of modern life that we take for granted would not have come to pass, or would have been delayed. His main contribution started with a simple but seemingly outrageous idea — making a solid-state laser. But he ended up making so many more contributions that it’s worth a look at what he accomplished over his long career.

Merry Christmas

Robert N. Hall in his lab. Source: General Electric

Robert Hall, given the middle name Noel in honor of his arrival on Christmas Day in 1919, was an inquisitive lad from the start. It seemed that inventing ran in the family, with his uncle Sydney being an aircraft engine designer and self-described career inventor. At a young age, his uncle took him to a sort of industrial fair in his hometown of New Haven, Connecticut, where Robert got to see all sorts of demonstrations and displays of the latest electrical innovations. His uncle explained how everything worked, which inspired young Robert to read and study as much as he could.

By the time high school rolled around, he was experimenting in a lab he built in his bedroom. He also discovered astronomy and build his own telescopes from scratch. An obviously promising student, Robert was recruited by Caltech and won a scholarship just before the start of World War II. When his funds ran out, he worked at Lockheed Aircraft, gaining valuable experience in industry and making contacts that would serve him well later.

He finally finished his physics degree in 1942 and was recruited by General Electric for their Schenectady Research Lab. As a test engineer in an industrial R&D facility during a time of war and complete national mobilization, Hall had a chance to make an impact, which he took full advantage of. Working with a team focused on using magnetrons to jam German radar, Hall’s team designed and built the first continuous-wave (CW) magnetrons. These devices would be employed during the war, but would also go on to become the heart of every microwave oven in use today. It’s even said that the possibly apocryphal story of the Raytheon engineer who was inspired to build the first microwave oven by a melting chocolate bar had his pocket zapped by one of Hall’s CW magnetrons.

Hall was encouraged to leave GE and seek his Ph.D. in physics, again from Caltech. He returned to Schenectady in 1948, ready to head up a lab of his own in the relatively new field of semiconductors. In a perfect lesson in exquisite timing, Bell Labs announced the transistor shortly after he arrived, and the whole semiconductor field exploded. GE being GE, they were mainly interested in the uses of semiconductors in power electronics, so Hall worked on high-power transistors and germanium power rectifiers. He contributed greatly to the field with innovations in purifying germanium by fractional crystallization, achieving purities that no other group was capable of. He also worked on silicon transistors, inventing two ways to dope the silicon: alloying and impurity diffusion. Pretty much every transistor ever made can trace its lineage back to those two methods.

Challenge Accepted

Hall’s innovations made GE a leader in silicon transistors by the early 1960s, and secured Hall’s place as the leading expert on semiconductors. Word came to the physics world of the invention of the laser in May of 1960, and Hall and his team devoured all the information they could get on the new field that showed so much promise. But the early lasers were complicated and fussy devices, and the need for a simpler laser was clear.

Good-natured and well-liked by his peers, Hall was teased that since he had already invented so many things, he should take a stab at a solid-state laser. Even though he thought it would be impossible, he accepted the challenge and hit the books. He knew that gallium arsenide diodes could emit enormous amounts of infrared light, so he crunched the numbers and found that he might be able to make a laser from the stuff. He put together a small team and got to work, and within just a few days, they had built a working device from a crystal only 1/3 of a millimeter on a side. It needed liquid nitrogen cooling and only worked in pulse mode, but the world finally had a laser that didn’t need pumping by an outside source of energy. The solid-state laser had arrived.

US Patent 3,245,002, for a “Stimulated Emission Semiconductor”

The GE team wrote up their results quickly and submitted a paper to the Physical Review Letters. Sadly, some chicanery resulted when the paper was sent out for peer review. Two of the reviewers were from two different competing corporate labs working on solid-state lasers, and when they read of Hall’s success, they short-circuited the process and held a press conference to announce that they had “invented” the solid-state laser. Luckily, Hall’s patent was granted along with the others; in any event, his team was the first to publish, so there’s little doubt as to the fatherhood of the solid-state laser.

Hall continued working at GE until his retirement, racking up 43 patents and 81 publications. His other work impacted the fields of nuclear physics, where his high-purity semiconductors are used for sensitive gamma-ray detectors. And while GE never developed Hall’s laser into a commercial product — the work of building a continuous-wave room-temperature solid-state laser was left to others — every single point-of-sale barcode scanner, CD player, laser pointer, and perhaps most importantly, every fiber optic connection that would eventually stitch together the backbone of the Internet, all trace back to that tiny crystal on Robert Hall’s lab bench in 1962.

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