External-cavity diode laser based spectrometer for absolute determination of iodine lines around 633 nm

We have developed and characterized a new iodine spectrometer for absolute frequency measurements of I 2 transitions at the 633-nm region. This region is important especially in length metrology. To obtain good frequency accuracy, the various sources of frequency shifts in the used saturation spectroscopy configuration have been minimized by optimizing the laser beams for spatial and spectral quality. This is done by injection locking a microlens-coupled diode laser with nearly Gaussian output beam to a stable external-cavity diode laser. The use of the injection-locking scheme also reduces the detrimental effects of optical feedback, as well as residual amplitude modulation related to laser frequency modulation via injection current.