AMSTERDAM, Netherlands, May 7 -- ASM Lithography said that a US government committee has approved its plan to buy the Silicon Valley Group Inc., including a unit that develops optical technology applicable in missiles and spy planes. The Committee on Foreign Investment, a unit of the Treasury Department, which considers national security issues when foreign companies buy US firms, gave the go-ahead to the $1.6 billion buyout of the California-based company after an agreement was reached about its subsidiary, Tinsley Laboratories, ASML said. The acquisition was expected to be completed by May 21, ASML chief executive Doug Dunn, told a conference call for journalists and investors. Dunn said the Dutch firm will "do its best" to sell Tinsley, which employs about 120 people, to a US company in the next half year. If a buyer isn't found, he said, ASML will be subjected to "strict" conditions set out by the US government.