Joerg Neuhaus

Subpicosecond thin-disk laser oscillator with pulse energies of up to 25.9 microjoules by use of an active multipass geometry

The pulse shaping dynamics of a diode-pumped laser oscillator with active multipass cell was studied experimentally and numerically. We demonstrate the generation of high energy subpicosecond pulses with a pulse energy of up to 25.9 microJ at a pulse duration of 928 fs directly from a thin-disk laser oscillator. These results are achieved by employing a selfimaging active multipass geometry operated in ambient atmosphere. Stable single pulse operation has been obtained with an average output power in excess of 76 W and at a repetition rate of 2.93 MHz. Self starting passive mode locking was accomplished using a semiconductor saturable absorber mirror. The experimental results are compared with numerical simulations, showing good agreement including the appearance of Kelly sidebands. Furthermore, a modified soliton-area theorem for approximating the pulse duration is presented.

Passively mode-locked Yb:YAG thin-disk laser with pulse energies exceeding 13 μJ by use of an active multipass geometry

We demonstrate the generation of high-energy picosecond pulses directly from a thin-disk laser oscillator by employing a self-imaging active multipass geometry. Stable single-pulse operation has been obtained with an average output power in excess of 50 W, excluding a cw background of 8%, at a repetition rate of 3.8 MHz. Self-starting passive mode locking was accomplished using a semiconductor saturable absorber mirror. The maximum pulse energy was 13.4 microJ at a pulse duration of 1.36 ps with a time-bandwidth product of 0.34. Single-pass external frequency doubling with a conversion efficiency of 60% yielded >28 W of average power at 515 nm.

Passively mode-locked Tm,Ho:YAG laser at 2 µm based on saturable absorption of intersubband transitions in quantum wells

We report the first demonstration of a solid state laser passively mode-locked through the saturable absorption of short-wavelength intersubband transitions in doped quantum wells: a continuous wave Ti:sapphire laser end-pumped Tm,Ho:YAG laser at the center wavelength of 2.091 mum utilizing intersubband transitions in narrow In(0.53)Ga(0.47)As/Al(0.53)As(0.47)Sb quantum wells. Stable passive mode-locking operation with maximum average output power of up to 160 mW for 2.9 W of the absorbed pump power could last for hours without external interruption and a mode-locked pulse with duration of 60 ps at repetition rate of 106.5 MHz was generated.

Numerical analysis of a sub-picosecond thin-disk laser oscillator with active multipass geometry showing a variation of pulse duration within one round trip

The mode locking dynamics of a diode-pumped thin-disk laser oscillator with an active multipass cell operated in ambient atmosphere was studied numerically. The numerical results are compared to experimental results of a passively mode-locked thin-disk Yb:YAG laser with several megahertz repetition rate, sub-picosecond pulse duration, and >10 μJ pulse energy. The numerical simulations prove that the soliton area theorem predicts a correct pulse duration when considering an average pulse energy inside the oscillator. Furthermore, they show a variation in the full width at half-maximum pulse length for the pulse that propagates within the oscillator. This oscillation shows a behavior that is contrary to a change in the pulse length given by the soliton area theorem when considering the real pulse energies at respective points in the resonator. The “breathing” is caused by the strong influence of the self-phase modulation of the ambient atmosphere and large amounts of dispersion resulting in a deviation from the sech2 pulse shape and a chirped pulse.

High-energy ultrafast thin-disk oscillators

We have studied experimentally and numerically the pulse shaping dynamics of a diode-pumped thin-disk laser oscillator with active multipass cell and large output coupling rates. We demonstrate the generation of high energy subpicosecond pulses with energies of up to 25.9 μJ and durations of 928 fs directly from a thin-disk laser oscillator without further amplification. We have achieved these results by employing a selfimaging active multipass geometry in order to increase the output coupling rate for a suppression of nonlinear optical effects. With this system we have obtained stable single pulse operation in ambient atmosphere with average output powers above 76W at a repetition rate of 2.93 MHz. A semiconductor saturable absorber mirror was used to start and stabilize passive soliton mode locking. The experimentally studied laser pulses show good agreement with numerical simulations including the appearance of Kelly sidebands. We present a modification to the soliton area theorem that is applicable for such a laser oscillator with active multiple pass cell and large output coupling rate. While numerically simulating the laser, we also investigated the intracavity pulse dynamics within one round-trip and limitations for power scaling. Furthermore, we demonstrate the lasers potential for micro machining applications by showing first examples of material processing, such as the determination of ablation thresholds and ablation rates for various materials.

Yb:YAG regenerative thin-disk amplifiers as an ideal pump and seed source for OPCPA

We present experimental and theoretical results for parallel amplification of 350 fs and 2.7 ps in the same Yb:YAG regenerative thin-disk amplifier for high energy OPCPA pumping and stable supercontinuum generation for OPCPA seeding.

Pulse Energies Exceeding 20 µJ Directly from a Subpicosecond Yb:YAG Oscillator by Use of Active Angular Multiplexing

We demonstrate the generation of pulses with twenty-five microjoules of energy generated from a thin-disk oscillator at a repetition rate of 2.94MHz, corresponding to an average output power of seventy-six watts.

Generation of high-energy femtosecond pulses by use of spectral broadening effects in Yb:YAG thin-disk regenerative amplifiers

As a result of experimentally verified simulations of Yb:YAG regenerative amplifiers utilizing spectral broadening effects due to self-phase modulation, we provide a map for the optimized choice of initial chirp and internal group-delay dispersion (GDD) within the amplifier. We show that the shortest pulse durations can be obtained with negative internal GDD, being, however, limited by the damage threshold of the optical components due to increased peak powers and by a breakup of pulses comparable to the propagation of higher-order solitons. We propose that by usage of increasing amounts of positive internal GDD, along with a corresponding amount of negative initial GDD, the obtainable peak powers after compression can be scaled far beyond the usual gain-bandwidth limitation.

Ultrafast Yb:YAG thin-disk oscillator with pulse energies exceeding 25 μJ suitable for efficient ablation with negligible heat affects

We have studied experimentally and numerically the pulse shaping dynamics of a diode-pumped thin-disk laser oscillator with active multipass cell and large output coupling rates. We demonstrate the generation of high energy subpicosecond pulses with energies of up to 25.9 μJ and durations of 928 fs directly from a thin-disk laser oscillator without further amplification. We have achieved these results by employing a selfimaging active multipass geometry in order to increase the output coupling rate for a suppression of nonlinear optical effects. With this system we have obtained stable single pulse operation in ambient atmosphere with average output powers above 76W at a repetition rate of 2.93 MHz. A semiconductor saturable absorber mirror was used to start and stabilize passive soliton mode locking. The experimentally studied laser pulses show good agreement with numerical simulations including the appearance of Kelly sidebands. We also present a modification to the soliton area theorem that is applicable for such a laser oscillator with active multiple pass cell and large output coupling rate. Furthermore, we demonstrate the lasers potential for micro machining applications by showing first examples of material processing, such as the determination of ablation thresholds and ablation rates for various materials.

Pulse energies exceeding 20 μJ directly from a femtosecond Yb:YAG oscillator

We demonstrate the generation of the highest pulse energies ever reported directly from a mode-locked oscillator: Twenty-five microjoules from a thin-disk oscillator operating in air, corresponding to an average output power of seventy-three watts.