An optical radiation source has been developed by coupling a dye laser to a small integrating sphere with an optical fiber. The radiant power from this source, which is monochromatic and spectrally tunable, has been stabilized to ±0.02%. Nonuniformities in the emitted optical radiation field caused by speckle have been overcome by vibrating the fiber at ultrasonic frequencies. The source has been successfully used in a spectrophotometer to measure the transmittance of a large lens with an uncertainty of ±0.01%, and the spectral responsivity of a filter radiometer with an uncertainty of ±0.04%.
Valerie E. Anderson, Nigel P. Fox, and David H. Nettleton, "Highly stable, monochromatic and tunable optical radiation source and its application to high accuracy spectrophotometry," Appl. Opt. 31, 536-545 (1992)