The tools for precise optical frequency metrology

Femtosecond lasers with a repetition rate of approximately I GHz are commonly used frequency comb generators for precise optical frequency metrology. They are conveniently compact, yield unambiguous frequency readings with the help of a commercial wavemeter, and can yield greater heterodyne beat signals against a cw laser than systems with lower repetition rates. This chapter reviews the technology of oscillators based on Tisapphire and Cr:forsterite that operate at repetition rates of up to 3.5 GHz. Aside from a discussion of these "standard" lasers with a typical full-width-at-halfmaximum (FWHM) bandwidth of 30 nm, one section is dedicated to the generation of a broadband continuum with a I GHz oscillator. This laser allows frequency measurements without additional spectral broadening and can be phase locked to a reference oscillator for uninterrupted periods