32-fs Kerr-lens mode-locked Yb:CaGdAlO 4 oscillator optically pumped by a bright fiber laser

In this study, we report on a pure Kerr-lens mode-locked Yb:CaGdAlO 4 oscillator optically pumped by a diffraction-limited fiber laser. At the repetition rate of 96 MHz, several configurations have been studied to achieve either pulse duration of 40 fs with average powers up to the watt level or shorter pulse duration down to 32 fs. To the best of our knowledge, this represents the shortest pulse duration ever achieved with an Yb-doped bulk material and the highest average power for sub-40-fs Kerr-lens mode-locked Yb-bulk oscillator. OCIS codes: (140.4050) Mode-locked lasers; (140.3615) Lasers, ytterbium; (140.7090) Ultrafast lasers. http://dx.doi.org/10.1364/OL.39.006001 During the past decade, Yb-doped crystals have raised a great interest for the generation of high average power ultra-short pulses due to their excellent spectroscopic and thermal properties [1]. Among them, Yb:CaGdAlO 4 (Yb:CALGO) crystal is one of the most promising candidates for sub-50-fs oscillator thanks to its broad and flat emission band [2]. Recent works reported pulse generation as short as 40 fs in this material [3], which is very close to the shortest (35 fs) pulse duration ever obtained from an Yb-doped bulk material-based oscillator [4,5]. However, these ultra-short pulse oscillators generate average powers never exceeding a few tens of milliwatts. This power limitation results from the unavailability of bright powerful (diffraction limited) pump sources as well as the typical response time of saturable absorbers. The thin-disk technology provides an efficient alternative to significantly increase the average power [6]. Although very impressive powers are demonstrated, the shortest pulse duration reported in Yb:CALGO thin-disk oscillator is limited to 62 fs [7]. Improving the average power while maintaining the pulse duration as short as possible is a challenging goal we aim at achieving making use of pure Kerr-lens mode-locking (KLM) technique combined with high-brightness pumping. By this way, recent works on Yb:CaF 2 reported significant improvements in average power of bulk oscillators with the generation of sub-70 fs with several watts [8]. In this Letter, we report on a pure Kerr-lens mode-locked Yb:CALGO oscillator delivering pulse duration of 40 fs at the watt level by means of a powerful single mode, polarized Yb-doped fiber pump emitting around 979.5 nm. After optimization of the output coupler transmission, the oscillator can provide the shortest pulse ever produced in Yb-doped bulk material with pulses as short as 32 fs. To the best of our knowledge, it is the first realization of a pure Kerr-lens mode-locking in Yb:CALGO crystal. For this, we use a high-brightness optical pumping with a single-mode fiber laser source [9]. After describing the experimental setup, we present the performance of the KLM Yb:CALGO os-cillator and discuss the optimization to provide the shortest pulse durations. The experimental setup of the laser cavity and pumping geometry is sketched in Fig. 1. We use a 5-mm-long, 2 mm × 4 mm Brewster-angle cut, Yb:CALGO crystal doped at 5 at. %. It is mounted in a water-cooled copper holder. We have chosen the c-cut orientation to avoid the anisotropy of temperature-dependent refractive index that could appear at high average pump power [10] and to eliminate the polarization state sensitivity in cross-section emission [2]. The Yb:CALGO crystal is positioned between two concave mirrors (M 1 , M 2 , 100-mm-radius-of-curvature) in a standard X-fold cavity configuration. To compensate astigmatism due to the Brewster-angle incidence, these mirrors are tilted with an angle of 8°. On one side, the cavity ends by a high-reflection (HR) mirror and closed on the other side by a 35% output-coupler (OC). A pair of SF10 prisms separated by a distance of 450 mm is used for fine intra-cavity dispersion control. The net intracavity group delay dispersion (GDD) is calculated to be close to −2200 f

Sub-50 fs, Kerr-lens mode-locked Yb:CaF 2 laser oscillator delivering up to 2.7 W (orale)

By means of a high-brightness optical pumping scheme with a fiber laser, we demonstrate Kerr-lens mode locking (KLM) with an Yb:CaF 2 laser crystal. Stable 48 fs pulses are produced at an average power of 2.7 W

Pumping Yb-doped bulk materials with 976 nm fiber lasers (orale)

Advanced Solid State Lasers (ASSL) © OSA 2014 Fig. 1: Rayleigh range for Optical pumping with low brightness (left) and High brightness (right) Abstract: The exceptional brightness of an Yb fiber pump laser allows to measure unexpectedly high gain in Yb amplifiers, achieve pure Kerr-lens mode-locking and demonstrate the shortest fs pulse ever generated with an Yb oscillator

Efficient OPSL-pumped mode-locked Yb:Lu2O3 laser with 67% optical-to-optical efficiency

We present a mode-locked Yb:Lu(2)O(3) laser with up to 67% of optical-to-optical efficiency. By utilizing a high brightness optically pumped semiconductor laser (OPSL) as a pump source and using a semiconductor saturable absorber mirror (SESAM) we obtained self-starting mode locking. A pulse duration of 571 fs at 4.73 W of average output power with an optical-to-optical efficiency of 67% was achieved. In a slightly different cavity configuration the pulse duration was reduced to 313 fs at 2.16 W of average output power. In both cases the pulse duration was longer than the Fourier limit and the spectrum supports significantly shorter pulse durations. The laser wavelength is centered at 1034 nm and the repetition rate is 100.76 MHz in both cases. In continuous wave fundamental mode operation the optical-to-optical efficiency was as high as 78% with output powers exceeding 5 W