Optical sideband technique

Fig. 5.59a,b. Optical sideband technique for precise tuning of the laser wavelength X (a) experimental setup (b) stabilization of the sideband vr onto the transmission peak of the FPI... 

Beside the purely spectroscopic part there has also been important development of active optical components such as electro-optic and acousto-optic modulators. Such components allowed the use of modulation schemes earlier used in the microwave region to be used in optical spectroscopy. In the early 80 s the FM-sideband technique both for stabilisation to molecular lines as well as to passive cavities were demonstrated [45,46]. The developing field of non-linear optics and the wave-mixing picture established a framework in which line shapes of different modulation schemes in saturation spectroscopy could be understood [47, 45, 46, 48,49]. 

Hall and co-workers investigated line profiles of hyperfine structure components in I2 with a refined optical phase modulation/radiofrequency sideband technique using a saturating and a probe laser beam. 

An examination of the above equations shows that the intermodulated DFM technique realizes an FM Differential Interferometer which produces a locking signal similar to conventional FM laser locking, but in which the optical tuning parameter A=(0Q-2tr n c/2L is replaced by the radio frequency (differential) tuning parameter 5=(0j-2tr c/2L. The DFM sideband structure creates an optical subtraction in the photodiode of the (n+l)-th cavity resonance curve from the (n-l)-th curve and thus permits accurate, low noise measurements of the cavity mode spacing. 

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