Monitoring and controlling source stability

摘要

PCT No. PCT/GB87/00049 Sec. 371 Date Sep. 11, 1987 Sec. 102(e) Date Sep. 11, 1987 PCT Filed Jan. 27, 1987 PCT Pub. No. WO87/04572 PCT Pub. Date Jul. 30, 1987.A method and apparatus for monitoring and/or controlling the frequency of a beam of coherent radiation. The apparatus comprises a reference source (1) which is controlled to generate reference radiation beam with a frequency which is repeatedly swept through a range of operating frequencies. This reference beam is combined with a beam of coherent radiation from a test source and the combined beams are fed to a photodiode (9). The output of the photodiode (9) can be displayed so that the upper and lower beat frequencies can be determined enabling the variation of the average of the upper and lower beat frequencies with time to be monitored. Alternatively, the average beat frequency can be fed back as a control signal to control the test beam source (8). In this latter case, the frequency of the test beam will be locked.