Diode-pumped 60-fs Yb:phosphate glass laser

cently this technique has been extended to mode-locked Nd:WO,? N d K F 3 and Cr:YAG4 lasers, showing a great potential of the SESAM. Cr:forsterite lasers operate at 1.13-1.37-pm range and a Kerr-lens mode-locked forsterite laser has produced as short as 25-fs pulses.' Development of a stable ultrashort pulse source in this wavelength range has practical importance in communications, fiber sensing or ranging, and other applications. In this paper, we demonstrate a semiconductor saturable absorber started mode-locked forsterite laser. To the best of our knowledge, this is the first mode-locked forsterite laser using SESAM. The saturable absorber is a 10-nm-thick In,,,,Ga,,,,As quantum well grown by molecular beam epitaxy (MBE) at a temperature of 500°C. The bottom reflector is a 16 pair of GaAsiAlAs semiconductor layers. To release the strain in the quantum well due to the lattice mismatch, a 100-nm Ino,3~Alo,6zAs buffer layer is grown between the quantum well and the bottom Bragg reflector. The structure is shown in Fig. 1. This structure is in contrast to the SESAM in Ref. 3 where a 80-nm-thick InGaAs absorber was grown at low temperature as a saturable absorption layer at 1300 nm. The layout of the laser is shown in Fig. 2. The pumping is the fundamental wave of a diodepumped NdWO, OEM model (SpectraPhysics T40-Z-106C). The forsterite crystal (Mitsui Mining & Smelting Co.) is 7 mm long with the Cr-doping density of 1.2 X 1019 cmP3. A 20-cm concave mirror at one end of the cavity focuses on the SESAM. A pair of SF6 Brewster prisms separated by 17 cm are placed in the other end to provide the dispersion compensation. A 2% output coupler is located in the dispersive end of the cavity. The modelocking starts at 3.2 W absorbed pumping power and the output power at 5 W absorbed pumping power is 60 mW. Figure 3(a) shows a fringe-resolved autocorrelation trace and Fig. 3(b) is the power spectrum centered at 1285 nm. The pulse width and the spectrum bandwidth are 40 fs and 50 nm respectively. The time-bandwidth product is 0.37, 1.2 times of transform limited. Both the pulse width and the spectrum bandwidth are comparable to those obtained solely by Kerr lens modelocking in this laser. In conclusion, we have demonstrated a selfstart femtosecond mode-locking in forsterite laser. We will further discuss the SESAM design and the dispersion compensation technique for mode-locked forsterite lasers based on our measured group delay of forsterite crystal. This work was supported by a ProposalBased Advanced Industrial Technology R&D I