Rigo Peters

Femtosecond thin-disk laser with 141 W of average power

We present a semiconductor saturable absorber mirror mode-locked thin disk laser based on Yb:Lu(2)O(3) with an average power of 141 W and an optical-to-optical efficiency of more than 40%. The ideal soliton pulses have an FWHM duration of 738 fs, an energy of 2.4 microJ, and a corresponding peak power of 2.8 MW. The repetition rate was 60 MHz and the beam was close to the diffraction limit with a measured M(2) below 1.2.

Broadly tunable high-power Yb:Lu 2 O 3 thin disk laser with 80% slope efficiency

We report on efficient laser operation of high quality crystalline Yb(3+):Lu(2)O(3) in thin disk configuration. Using doping concentrations between 1 at.% to 3 at.% and disk thicknesses between 0.08mm and 0.45mm the optimum crystal parameters have been determined. Pumped at 976 nm the laser operates at 1034 nm and 1080 nm. With a 0.25mm thick 3 at.% Yb:Lu(2)O(3) disk 32.6W of output power at 45.3W incident pump power with a slope efficiency of 80% and a resulting optical-to-optical efficiency of 72% have been realized. These are the highest values in terms of slope efficiency as well as optical-to-optical efficiency for an Yb-doped thin disk laser reported so far. Using an 1mm birefringent filter continuous tuning from 987 nm to 1127 nm with more than 10Wof output power over a tuning range of 90 nm has been achieved.

Thermal and laser properties of Yb:LuAG for kW thin disk lasers

Thin disk laser experiments with Yb:LuAG (Yb:Lu(3)Al(5)O(12)) were performed leading to 5 kW of output power and an optical-to-optical efficiency exceeding 60%. Comparative analyses of the laser relevant parameters of Yb:LuAG and Yb:YAG were carried out. While the spectroscopic properties were found to be nearly identical, investigations of the thermal conductivities revealed a 20% higher value for Yb:LuAG at Yb(3+)-doping concentrations of about 10%. Due to the superior thermal conductivity with respect to Yb:YAG, Yb:LuAG offers thus the potential of improved performance in high power thin disk laser applications.

Model for the calculation of radiation trapping and description of the pinhole method

Radiation trapping is a well-known process that results in the lengthening of observed fluorescence lifetimes in laser materials with significant overlap in their emission and absorption spectra. The pinhole method is a measurement technique that allows the intrinsic fluorescence lifetime of an excited state to be determined in a nondestructive manner. A theoretical description of this method is proposed. A model is developed that identifies the lifetime extrapolated to a zero radius pinhole as the intrinsic fluorescence lifetime. The application of this method to bulk materials and thin discs is discussed.

Efficient femtosecond high power Yb:Lu2O3 thin disk laser

We demonstrate the first passively mode-locked thin disk laser based on Yb:Lu(2)O(3). The laser generates 370-fs pulses with 20.5 W of average power in a diffraction-limited beam (M(2) < 1.1). The nearly transform-limited pulses have a spectral bandwidth of 3.4 nm centered near 1034 nm. With slightly longer pulses (523 fs) we obtained 24 W of average power at a pump power of 56 W, resulting in an optical-to-optical efficiency of 43%, which is higher than for any previously mode-locked thin disk laser.

Femtosecond Yb:Lu(2)O(3) thin disk laser with 63 W of average power.

We present successful power-scaling of an Yb:Lu(2)O(3) thin disk laser to record high-power levels both in cw and mode-locked operation. In a simple multimode resonator we achieved 149 W of output power in cw operation with 73% optical-to-optical efficiency (eta(opt)). Building an 81 MHz fundamental transverse mode resonator with dispersion compensation and a semiconductor saturable absorber mirror (SESAM) for passive mode locking we achieved 63 W of average power in 535 fs pulses (eta(opt)=35%). The output beam is nearly diffraction limited (M(2)<1.2). The 0.78 microJ pulses with a peak power of 1.28 MW had a central wavelength of 1034 nm and were close to the Fourier transform limit. With an SESAM with a larger modulation depth we obtained pulses as short as 329 fs at 40 W average power corresponding to a pulse energy of 0.49 microJ and a peak power of 1.32 MW.

Diode-pumped mode-locked Yb:LuScO(3) single crystal laser with 74 fs pulse duration.

The mode locking of the mixed sesquioxide single crystal Yb:LuScO(3) is demonstrated. This crystal is locally disordered and has the broadest emission spectrum of all sesquioxides known so far. Pulse durations as short as 111 and 74 fs were obtained using the semiconductor saturable absorber mirror and Kerr-lens mode locking, respectively. The latter regime was reached using a two-section distributed Bragg-reflector tapered diode laser as a pump source.

227-fs pulses from a mode-locked Yb:LuScO 3 thin disk laser

The highest average output power and pulse energy from mode-locked laser oscillators are currently achieved using semiconductor saturable absorber mirror (SESAM) [1] mode-locked thin disk lasers (TDL) [2]. Up to now the shortest pulses of 240 fs at 22 W average output power in this configuration were demonstrated with the monoclinic Yb:KYW [3], which suffers from strong anisotropy in its thermal properties, which prevents further power scaling. Using the cubic sesquioxide Yb:Lu2O3 as gain medium, pulses as short as 370 fs could be obtained with a pump power limited output power of 20.5 W at 1034 nm [4]. The new mixed sesquioxide Yb:LuScO3 [5] provides a nearly doubled gain bandwidth compared to Yb:Lu2O3 of more than 20 nm and supports the generation of significantly shorter pulses.

Efficient continuous-wave thin disk laser operation of Yb:Ca 4 YO(BO 3 ) 3 in E∥Z and E∥X orientations with 26 W output power

We report continuous-wave laser operation with Yb(15 at. %):Ca4YO(BO3)3 (Yb:YCOB) reaching 26 W of output power in the thin disk laser setup at an optical-to-optical efficiency of 58% and a slope efficiency of 67% in the E∥Z polarization. In the E∥X polarization the efficiency of the laser was slightly lower, but a large tuning range of 95 nm with several watts of output power could be obtained here. Furthermore, applying the pinhole method, the fluorescence lifetime was determined to be 2.2 ms. The obtained results reveal that Yb:YCOB is a promising candidate for the generation of very short pulses at high pulse energies in the thin disk laser setup.

Ultrashort pulse Yb:LaSc 3 (BO 3 ) 4 mode-locked oscillator

Passive mode-locked laser operation based on an Yb-doped lanthanum scandium borate crystal is demonstrated. Pulse durations as short as 58 fs and 67 fs were achieved applying a Ti:sapphire- and a diode-laser pump source, respectively. The average output powers were 73 mW and 39 mW at a repetition rate of 90 MHz. The laser was broadly tunable from 1028 to 1057 nm in the sub-200 fs pulse regime.