A 420 MHz Cr:forsterite femtosecond ring laser and its use for continuum generation in the 1-2 micron range

We present a Cr:forsterite ring laser producing 30 fs pulses at a 420 MHz repetition rate. The output is broadened in highly nonlinear fiber yielding spectra covering 1050-2200 nm. 02000 Optical Society of America OCIS codes: (060.45 10) Optical communications, (140.7090) Ultrafast lasers, (120.3940) Metrology We have developed a chromium-doped forsterite femtosecond ring laser that generates 30 fs pulses at a 420 ME-Iz repetition rate with -500 mW of average power. To our knowledge, this is the first ring configuration as well as the highest repetition rate yet reported for a femtosecond Cr:forsterite laser. The compact solid-state design and broad spectral output make this laser attractive for applications in the important 1.3-1.6 pm regime. Additional spectral broadening of the laser output in highly nonlinear optical fibers leads to supercontinuum generation, with the broadest spectra extending across an octave. The underlying optical frequency comb can be linked to existing optical frequency standards, thereby establishing a broad array of precisely known frequencies across the near infrared spectrum. Because of its importance for fiber-based communications [l], the 1.3-1.6 pm regime is a natural direction in whch to spread the new tools of femtosecond-laser-based frequency metrology [2-41. Towards this end, we have developed a high repetition rate, broadband Cr:forsterite femtosecond laser. Our laser consists of a compact, prismless 6-mirror ring cavity similar to earlier work with Tksapphire [5]. The repetition rate in this present configuration is 420 MHz, yet we believe it could readily be increased to 1 GHz. The pump is a 10 W Ytterbium fiber laser operating at 1075 nm. Intra-cavity dispersion compensation is provided by a combination of chirped and GTI (Gires-Tournois interferometer) mirrors. For the optimal dispersion compensation, we obtain a FWHM spectral width of 59 nm. This spectrum is shown as curve (iv) in Fig. l(a). External compression with chirped mirrors provides 30 fs pulses. The average power is 480 mW, implying a pulse energy of 1.1 nJ. 100