4137 / Length (Meter): Laser-Wellenlaengennormal at the PTB in Braunschweig: EUROPA, DEUTSCHLAND, NIEDERSACHSEN, BRAUNSCHWEIG (BRAUNSCHWEIG, GERMANY), 17.04.2007: Laser wavelength standard with a stabilized, frequency doubled Neodym:YAG-Laser which provides light of a specific frequency for interferometric length measurement. Realization of SI base unit of length, the meter, in a lab at Physikalisch-Technische Bundesanstalt PTB in Braunschweig, Germany. The three glass cylinders contain gaseous iodine which provides the reference frequency to which the laser is tuned. In back: Dr. Harald Schnatz. - Marc Steinmetz / VISUM - Keywords: Germany, Physikalisch, Technische, Bundesanstalt, PTB, science, technology, physics, metrology, base, unit, international, system, of, units, SI, measure, measurement, standard, accurate, accuracy, lab, experiment, frequency, optics, optical, scientist, scientists, people, laser, beam, beams, meter, metre, interferometric, length, light, green, metrical