Yb^3+-doped YVO_4 crystal for efficient Kerr-lens mode locking in solid-state lasers

Abstract

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...

High-power ultrafast thin disk laser oscillators and their potential for sub-100-femtosecond pulse generation

“…As can be seen in Table 2, Yb-doped vanadate crystals also enabled the generation of very short femtosecond pulses [76,77]. Some of these materials such as Yb:LuVO and Yb:YVO have been used in a CW thin disk laser but the output power has not exceeded 15 W [55].…”

47-fs diode-pumped Yb^3+:CaGdAlO_4 laser

“…Nevertheless, with their high thermal conductivity and atypical ultraflat and relatively high emission cross section, we believe that Yb-doped CaGdAlO 4 crystals are particularly suitable for the generation of unprecedented ultrashort pulses from Yb-doped bulk material based oscillators with high average power and thus could be a good alternative to present-day industrial femtosecond oscillators based on Yb: KGd͑WO 4 ͒ 2 crystals. Furthermore, in contrast to the method used recently to achieve extremely short pulse durations with Yb: KY͑WO 4 …”

58 fs pulses from a mode-locked Yb:LuVO4 laser

“…The broad emission spectra of Yb-doped vanadates are attractive not only for tunable laser operation in the 1 µm spectral range but also for reliable and efficient diode-pumped femtosecond lasers. Both mode-locking with a semiconductor saturable absorber mirror (SESAM) and Kerr-lens mode-locking have been demonstrated for Yb:YVO 4 [6,7]. The pulses obtained were as short as 120 fs and 61 fs for SESAM and Kerr-lens mode-locked operation, respectively.…”