Dr Drullinger of the US National Institute of Standards and Technology (NIST) using an infrared detector to 'see' the beam of an infrared laser. The laser is part of a new caesium atomic clock, NIST-7, which promises to be the world's most accurate. The infrared laser is one of several lasers used in the clock. Other, visible light, lasers are used to 'pump' the caesium atoms to high energies. The timing of resonant oscillations between energy levels is the key to precise time measurement, allowing an accuracy of one part in ten thousand billion (ten to the power 14). The NIST-7 clock is expected to enter service in 1993.