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RF spectrum showing the repetition frequency and the carrier-envelope offset frequency of the comb of a free-running FemtoFiber laser
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Mode-locked lasers generate broad spectra – so-called frequency combs – with myriads of equidistant lines. The lines of the comb are separated by the repetition frequency of the pulsed laser. With the FFS-SYNC-PLL option, the repetition frequency of the scientific fiber lasers can be synchronized to a highly-stable oscillator, thus generating a comb which can be used as an optical ruler. The optical ruler can be used for measuring optical frequency differences with high accuracy or for phase-locking two or more CW lasers to make them mutually coherent.
The lines of the comb are generally not exact harmonics of the repetition rate, but they are displaced by the carrier-envelope offset frequency, vCEO, which is the rate at which the optical phase of the pulse shifts from one pulse to the next. It is possible to stabilize vCEO by controlling the pump power of the FemtoFiber oscillator.
Recent tests have shown that the precision of a frequency measurement carried out with a scientific fiber laser is solely limited by currently available frequency standards, see E. Benkler et al., Optics Express 13, 5662 (2005). In contrast to previous technology, the portable and push-button scientific fiber lasers allow continuous measurements for days and weeks. TOPTICA's highest peak power and proprietary technique to control the spectral shape of the supercontinuum provides highest output power at virtually any wavelength in the infrared and visible spectral range. The result is exceptionally high signal to noise ratios in the optical heterodyne experiments.
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