Instead, as a physicist, he created a company based on new technology, lasers delivering high-powered beams of light through hair-thin optical fibers. His company, founded in 1991 and now known as IPG Photonics Corp., soon won a contract in Germany to supply lasers for use in obstacle-warning systems for helicopters.

Seeking access to U.S. financial markets, Dr. Gapontsev moved IPG’s base to Oxford, Mass., in 1998. IPG’s sales of devices to telecom companies boomed, and the company raised about $100 million from investors led by TA Associates in 2000. Then a crash in the telecom market slashed IPG’s sales and raised questions about its ability to recover.

Dr. Gapontsev invested heavily in other applications for fiber lasers. IPG now focuses on industrial applications, such as metal cutting, welding, engraving and 3-D printing. Lasers also are used in cosmetic or medical applications, including hair removal and treatment of kidney stones.

In May, Dr. Gapontsev stepped down as chief executive officer but remained executive chairman. He died Oct. 22 at the age of 82. The company hasn’t disclosed a cause of death. Colleagues said he was still reporting for work a week before he died.

Dr. Gapontsev was known for demanding rapid action. “We were never quite running fast enough for him inside the company,” said Timothy Mammen, the company’s chief financial officer.

Valentin Pavlovich Gapontsev was born Feb. 23, 1939, in Moscow. His father was a Russian artillery captain during World War II, and his mother worked in the legal profession.

In 1946, the family moved to Lviv in western Ukraine. Dr. Gapontsev studied at the Lviv Polytechnic Institute and the Moscow Institute of Physics and Technology, where he earned a Ph.D. He worked at the Soviet Academy of Sciences, specializing in laser material physics, from 1967 until the early 1990s.

One of Dr. Gapontsev’s early fans in the U.S. was Michael C. Child, an executive at TA Associates, a private-equity firm. Mr. Child has served as a director of IPG for more than two decades.

IPG registered for an initial public offering in early 2001 but canceled it a few months later as the market for telecom applications imploded. Dr. Gapontsev accelerated development of industrial applications for fiber lasers to make up for the loss of telecom business.

One problem was that IPG had been relying on other companies to make the diodes used to emit light waves. Those diodes were too costly to allow IPG to offer competitive cutting and welding tools. So Dr. Gapontsev led a crash program to produce diodes in house at a much lower cost.

Heavy investment in diodes and industrial applications strained IPG’s balance sheet. By mid-2003, the company was running out of cash. IPG finally obtained a short-term credit line from banks and soon began benefiting from an upturn in sales.

In 2006, IPG made a successful initial public offering of shares. On Tuesday, IPG reported third quarter revenue of $379 million, up 19% from a year earlier. Its market value currently is around $9 billion. Forbes this year estimated Dr. Gapontsev’s net worth at $2.8 billion.

Dr. Gapontsev, a naturalized U.S. citizen, was surprised several years ago to find that his name had been included on a list of 96 wealthy Russians compiled for Congress by the U.S. Treasury. IPG feared that his inclusion with these so-called oligarchs might lead to sanctions. That didn’t happen, however, and IPG eventually persuaded the Treasury to write a letter stating that Dr. Gapontsev wouldn’t be listed as an oligarch if the department were to produce another such list.

Dr. Gapontsev is survived by his wife, Vera Sapeluk, as well as a son and a grandson. He lived primarily in Worcester, Mass., but also had an apartment in Boston and a weekend home on Cape Cod. He pursued a hobby of ocean fishing with the same intensity he brought to business. “It was not relaxed fishing,” Mr. Child said.