The growth, spectroscopic properties, and laser performance of Yb:YVO4 crystal with laser diode pumping are reported. A peak absorption cross section of 7.4 x 10(-20) cm2 at 985 nm, a radiative lifetime of 0.25 ms, and a stimulated-emission cross section of 1.25 x 10(-20) cm2 at 1008 nm for pi polarization were determined for the Yb3+ ions in YVO4. Continuous-wave laser action of Yb:YVO4 at 1020-1027 nm was demonstrated with an output power of 610 mW and a slope efficiency of 49%.

We report the first demonstration, to our knowledge, of soft-aperture Kerr-lens mode locking in a diodepumped femtosecond Yb 3+ : YVO 4 laser. Near-transform-limited pulses as short as 61 fs are generated around a center wavelength of 1050 nm with an output power of 54 mW and a pulse repetition frequency of 104.5 MHz. This is, to our knowledge, the shortest pulse generated directly from an Yb laser having a crystalline host material. The femtosecond operation has a mode-locking threshold at an absorbed pump power of 190 mW. 3 From the point of view of the development of new Yb-doped crystals for reliable and efficient femtosecond lasers, materials are preferred that possess high cross sections (in particular, the emission cross section) 4 together with broad gain spectra 5-7 and good physical and mechanical properties. 8 In this context, given the strong and broad absorption peak (FWHM of ϳ8 nm) at around 985 nm, which is compatible with optical pumping by well-developed InGaAs laser diodes, the extremely low quantum defect ͑ϳ3.5% ͒, and a relatively broad and smooth 5 (glasslike) emission spectrum, the Yb: YVO 4 crystal is a good candidate gain medium for incorporation into diode-pumped femtosecond lasers for the 1-m spectral region. Indeed, 120-fs pulses with an average power of 300 mW were generated from a diode-pumped Yb: YVO 4 laser that was passively mode locked by using a semiconductor saturable absorber mirror (SESAM). 9In fact, most of the work in the field of ultrashort Yb lasers has concentrated on the employment of SESAMs 10 for passive mode locking. Kerr-lens mode locking 11 (KLM) is another well-developed technique for the generation of ultrashort pulses from lasers that are efficient, compact, and have reduced cavity component counts. 12 Reducing the intracavity losses by excluding a SESAM (nonsaturable losses) can lead to a substantial enhancement in the optical efficiency of such a femtosecond laser. In addition, the shortest pulse generated directly from a laser was produced using the KLM technique. 13 One of the critical parameters for reliable Kerr-lens mode locking is a high value of the nonlinear refractive index n 2 of a laser medium. Although, Major et al. have shown that a number of Yb-doped crystals are characterized by relatively high n 2 and are promising for KLM operation, 14,15 only the Yb:KYW laser has been mode locked successfully by using the optical Kerr effect under the conditions of direct diode pumping. 16,17 In this Letter we describe the parameters of a new Yb-doped YVO 4 crystal, which was selected for possible exploitation in KLM solid-state lasers. Impressively, our KLM Yb: YVO 4 laser produced pulses as short as 61 fs at a center wavelength of 1050 nm with an average output power of 54 mW for an absorbed pump power of just 400 mW. The nonlinear refractive indices were measured for the Yb: YVO 4 crystal by using the z-scan technique and were found to be 19 ϫ 10 −16 cm 2 / W and 15ϫ 10 −16 cm 2 / W for and polarizations, respectively, at 1080 nm.A schematic of the laser c...

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