Search

A detailed study of thermo-optic properties of 1.5 at.% Yb:Lu2O3 single crystal is performed. Thermo-optic dispersion formulas are derived for dn/dT coefficient and thermal coefficient of the optical path. At the wavelength of 1.03 μm, dn/dT = 5.8 × 10−6 K−1. High-precision temperature-dependent measurements of the thermal expansion coefficient α are performed. At the room temperature (RT), α = 5.880 ± 0.014 × 10−6 K−1. Temperature dependence of the bandgap is analyzed, yielding RT value of E g = 5.15 eV and dE g/dT = –3.7 × 10−4 eV/K. Sensitivity factor of the thermal lens is calculated for a diode-pumped Yb:Lu2O3 crystal versus the pump spot radius and crystal temperature.

We investigate Kerr lens mode locking of Yb:Lu

Ultrafast laser sources are opening new industrial and scientific applications. In particular, SESAM-modelocked thin-disk laser (TDL) oscillators are promising candidates to replace complex amplifier systems by compact high-power oscillators combining high pulse energy and MHz repetition rate. Record-high average powers up to 275 W and peak powers up to 66 MW have been achieved with SESAM-modelocked Yb:YAG TDLs [1]. However, reducing the pulse duration to sub 200 fs while simultaneously increasing the peak power of SESAM-modelocked TDLs remains an ongoing challenge. The sesquioxide Yb:Lu 2 O 3 (Yb:LuO) is a potentially ideal candidate material as it combines a broad emission bandwidth and a high thermal conductivity [2]. Earlier Yb:LuO TDL results include average powers up to 140 W (740 fs) or pulse durations down to 140 fs (7 W), in all cases at moderate peak powers

Ultrafast thin-disk laser (TDL) oscillators generated up to 275 W in pulses with several hundred femtosecond duration [1]. However, the combination of high average output power with short pulse duration is challenging: the power levels of ultrafast TDL oscillators operating in sub-100-fs pulses are currently limited to the sub-10 W regime. In the last years Kerr-Lens Modelocking (KLM) has been established as a successful alternative to SESAM-modelocking of TDLs. The KLM technique has shown to be advantageous for achieving shorter pulse durations at high power levels [2]. So far, nearly all KLM TDLs use Yb:YAG, which is the best developed gain material for the thin-disk configuration but limited in its emission bandwidth. For achieving shorter pulse durations, it is highly attractive to study KLM TDLs based on gain materials with broader emission bandwidth. Yb:LuO exhibits a more than twice broader emission bandwidth than Yb:YAG [3]. Using SESAM-modelocking, Yb:LuO TDLs achieved 141 W in 740-fs pulses [4] and 7 W in 142 fs [5]. Recently, the first Yb:LuO KLM TDL has been demonstrated, generating 165-fs pulses with an output power of 5.9 W [6]. However, the full emission bandwidth of Yb:LuO was so far never exploited in a TDL.

We evaluate limitations in pulse duration for Kerr-lens mode-locked Yb-based thin-disk lasers. The most critical factor is appropriate intracavity dispersion engineering, which enabled operation at 30-fs. Substantially shorter durations are within reach using new designs.

Many experiments aiming at recording the “molecular movie”, i.e., the imaging of the structural dynamics of chemical processes, rely on molecules fixed-in-space.1 One of the most promising approaches to capture such processes is time-resolved x-ray-diffractive imaging.2 Modern x-ray light sources,3 such as the upcoming free-electron lasers with very large photon fluxes such as the European XFEL, LCLS II, or synchrotrons, operate at high repetition rates with ten-thousands to millions of pulses per second, sometimes in burst modes. To allow for efficient measurements, the aligned molecules should be available for all of these pulses. However, the necessary electric field strengths for strong adiabatic alignment of gas-phase ensembles of molecules exceeds 1010 W/cm2 and this field strength must be applied over durations comparable to the rotation periods of the molecules of hundreds of picoseconds to even nanoseconds.4 So far, these intensities are only available from pulsed amplifier systems with repetition rates in the few-Hz to low-kHz range,5 which does not allow for providing aligned molecules for all pulses of the x-ray probe sources. Thus, it prohibits efficient use of these sources.

We propose a novel approach for strong alignment of gas-phase molecules for experiments at arbitrary repetition rates. A high-intracavity-power continuous-wave laser will provide the necessary ac electric field of $\!10^{10}$- $10^{11}~\text{W}/\text{cm}^2$. We demonstrate thin-disk lasers based on Yb:YAG and Yb:Lu$_2$O$_3$ in a linear high-finesse resonator providing intracavity power levels in excess of 100~kW at pump power levels on the order of 50~W. The multi-longitudinal-mode operation of this laser avoids spatial-hole burning even in a linear standing-wave resonator. The system will be scaled up as in-vacuum system to allow for the generation of fields of $10^{11}~\text{W}/\text{cm}^2$. This system will be directly applicable for experiments at modern X-ray light sources, such as synchrotrons or free-electron lasers, which operate at various very high repetition rates. This would allow to record molecular movies through temporally resolved diffractive imaging of fixed-in-space molecules, as well as the spectroscopic investigation of combined X-ray-NIR strong-field effects of atomic and molecular systems.

We report on, to the best of our knowledge, the first fs-laser-written waveguide laser in Yb3+:CaGdAlO4 (Yb:CALGO). With Yb:CALGO crystals grown in our labs, we obtained a slope efficiency of 69% and up to 2.4 W of continuous wave (cw) output power in a waveguide-laser configuration. Moreover, bulk laser experiments with Yb:CALGO were performed, and slope efficiencies up to 73%, optical-to-optical efficiencies of 65%, and maximum cw output powers of 3.3 W were reached. These are the highest efficiencies in the laser configuration with Yb:CALGO.

We investigate Kerr lens mode locking of Yb:Lu2O3 thin-disk laser oscillators operating in the sub-100-fs regime. Pulses as short as 35 fs were generated at an average output power of 1.6 W. These are the shortest pulses directly emitted from a thin-disk laser oscillator. The optical spectrum of the 35-fs pulses is almost 3 times broader than the corresponding emission band of the gain crystal. At slightly longer pulse duration of 49 fs, we achieve an average power of 4.5 W. In addition, 10.7 W are obtained in 88-fs pulses, which is twice higher than the previous power record for ultrafast thin-disk lasers generating pulses shorter than 100 fs. Our results prove that Kerr lens mode-locked Yb:Lu2O3 thin-disk lasers are a promising technology for further average power and pulse energy scaling of ultrafast high-power oscillators operating in the sub-100-fs regime.

In the last decades high power ultrafast lasers have attracted considerable attention for many applications. The most promising approach to get high power ultrashort pulses directly from an oscillator is a modelocked thin disk laser (TDL) using a broadband gain material. For this purpose, Yb-doped materials are very suitable since their simple energy-level scheme allows for highly efficient laser operation and the strong electron-phonon coupling results in broad spectra. In addition, to maintain efficient cooling a high thermal conductivity is required which often stands in contradiction to a very broad spectrum. This paper reports on improved crystal growth and highly efficient thin disk laser operation of Yb:CALGO, using a 5.9% Yb-doped CALGO in a TDL setup with 24 pump passes through the gain medium and a pump spot diameter of 1.2 mm. A slope efficiency of 70% and 57% of optical-to-optical efficiency with respect to the incident pump power could be obtained with an output coupler transmission of 1.6%, representing the highest efficiency obtained with this material so far. The laser output power of 30 W was limited by the available pump power from the 50 W fiber coupled pump diode laser.

We obtained 90 nm wavelength tuning with >20 W between 1022 nm and 1072 nm with an Yb:CALGO thin disk laser. This is the widest tuning range of any Yb-doped material at this power level.

We report on, to the best of our knowledge, the first fs-laser-written waveguide laser in Yb3+:CaGdAlO4 (Yb:CALGO). With Yb:CALGO crystals grown in our labs, we obtained a slope efficiency of 69% and up to 2.4 W of continuous wave (cw) output power in a waveguide-laser configuration. Moreover, bulk laser experiments with Yb:CALGO were performed, and slope efficiencies up to 73%, optical-to-optical efficiencies of 65%, and maximum cw output powers of 3.3 W were reached. These are the highest efficiencies in the laser configuration with Yb:CALGO.

Thin-disk laser experiments with Yb:CaGdAlO(4) (Yb:CALGO) have been performed. A slope efficiency of 70% and an optical-to-optical efficiency of 57% could be achieved with a maximum output power of 30.7 W. These are so far the highest efficiencies obtained with this material. Furthermore, tuning experiments were carried out leading to a tuning range of 90 nm in total and 50 nm with more than 20 W of output power. This is to the best of our knowledge the widest wavelength tuning range of any material demonstrated at this power level. For all experiments the thermal evolution of the crystal surface temperature during laser operation was investigated.

Ultrafast thin-disk lasers (TDLs) are often thought to deliver longer pulses than bulk lasers (Fig. 1a). Here we prove that this assumption is wrong and demonstrate the shortest pulses from any Yb:Lu2O 3 and Yb:CaGdAlO 4 (Yb:CALGO) laser (cf. Tab. 1). Our Kerr lens mode-locked (KLM) Yb:Lu 2 O 3 TDL generates 4.5 W in 49-fs pulses and 1.7 W in 40-fs pulses (being 40 % shorter than Yb:Lu 2 O 3 bulk lasers [1]). In addition, we demonstrate the first KLM Yb:CALGO TDL. It generates 30-fs pulses, which is the shortest duration ever obtained from ultrafast TDLs [2,3] and equal to the shortest pulses obtained from Yb-bulk oscillators [4].