First principle DFT-based microscopic many-body models are used to investigate inter- and intra-valley carrier dynamics in the monolayer transition-metal dichalcogenide MoTe2. Electron-electron and electron-phonon scatterings are calculated for transitions within the full Brillouin zone to determine overall carrier relaxation timescales as well as intra- and inter-valley transition rates. For excitation above the barriers separating bandstructure valleys carriers are found to relax on a ten femtosecond timescale into hot quasi-Fermi distributions at the band minima. Subsequently, the hot carrier plasma is cooled down on a picosecond timescale predominantly through emission of optical phonons. Local carrier occupations lead to strong energy renormalizations in momentum space. However, for the material investigated here, the global energy minimum remains at the K-points once carriers relax into global quasi-Fermi distributions. No transition from a direct to an indirect bandgap is observed.

A systematic microscopic approach combining ab-initio density functional theory with the Dirac-Bloch equations is applied to investigate the intra-excitonic transitions of magneto-excitons in transition metal dichalcogenide monolayers. For the example of hBN-encapsulated $\mathrm{Mo}{\mathrm{S}}_{2}$, the linear optical response and mid-infrared spectra of the pre-excited system are numerically evaluated. It is shown that the transition probability between a subset of the magneto-excitons can be inverted under suitable conditions to display negative absorption, i.e., gain. With the help of an applied magnetic field, the absorption and gain spectra can be tuned over a wide spectral range. Evaluating the Zeeman shift of the excitonic states, effective $g$ factors are deduced that depend on the dielectric environment of the sample under consideration.

The dynamics of band-gap renormalization and gain build-up in monolayer MoTe$_2$ is investigated by evaluating the non-equilibrium Dirac-Bloch equations with the incoherent carrier-carrier and carrier-phonon scattering treated via quantum-Boltzmann type scattering equations. For the case where an approximately $300$ fs-long high intensity optical pulse generates charge-carrier densities in the gain regime, the strong Coulomb coupling leads to a relaxation of excited carriers on a few fs time scale. The pump-pulse generation of excited carriers induces a large band-gap renormalization during the time scale of the pulse. Efficient phonon coupling leads to a subsequent carrier thermalization within a few ps, which defines the time scale for the optical gain build-up energetically close to the low-density exciton resonance.

The quasi-two dimensional Coulomb interaction potential in transition metal dichalcogenides is determined using the Kohn-Sham wave functions obtained from ab initio calculations. An effective form factor is derived that accounts for the finite extension of the wave functions in the direction perpendicular to the material layer. The resulting Coulomb matrix elements are used in microscopic calculations based on the Dirac Bloch equations yielding an efficient method to calculate the band gap and the opto-electronic material properties in different environments and under various excitation conditions.

It is shown that the three-fold rotational symmetry in transition metal dichalcogenides leads to a Coulomb induced renormalization of the effective electron and hole masses near the $K$-points of the Brillouin zone. The magnitude of the renormalization depends on the dielectric configuration. The effective exciton mass $m=0.4 m_0$ of a freely suspended MoS$_2$ monolayer changes to $m= 0.35 m_0$ with hBN encapsulation. The mass renormalization increases the excitonic binding energy and reduces the exciton diamagnetic shift and cyclotron frequency. Detailed comparisons with high field measurements of the excitonic diamagnetic shift show excellent agreement.

Demonstration of a regenerative amplifier with “mixed pulse trains” for micromachining: femtosecond pulses for effective ablation directly followed by nanosecond pulses for smoothening of the surface amplified within one single thin disk resonator. © 2019 The Author(s)

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.

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.

Get PDF Email Share Share with Facebook Tweet This Post on reddit Share with LinkedIn Add to CiteULike Add to Mendeley Add to BibSonomy Get Citation Copy Citation Text M. Larionov and J. Neuhaus, "Regenerative thin disk amplifier with a pulse energy of 120 mJ at 1 kHz," in Advanced Solid State Lasers, OSA Technical Digest (online) (Optica Publishing Group, 2014), paper ATh2A.51. Export Citation BibTex Endnote (RIS) HTML Plain Text Citation alert Save article

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.

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.

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.

This study investigates a mode-locked Yb:YAG thin-disk laser oscillator with self-imaging active multipass cell and large output coupling rates for a suppression of nonlinear optical effects.The experimentally generated pulse energies of more than 25 muJ at sub-picosecond pulse length of 928 fs are believed to be the highest ever obtained directly from an ultrafast laser oscillator without further amplification stages. Stable single pulse operation in ambient atmosphere is obtained with this system, with average output powers above 76 W at a repetition rate of 2.93 MHz.

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.

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 laser's 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.

Here we first report the first demonstration of passive mode locking in a Ti-sapphire laser end-pumped Tm3+,Ho3+:YAG laser utilizing ISBTs in InGaAs/AlAsSb quantum wells grown on an InP substrate. The experimental setup is schematically shown in Fig. 1. The pump source is a tunable Ti-sapphire laser with a maximum output power of 2.2 W at 785 nm, corresponding to the peak absorption of the Tm3+, Ho3+:YAG crystal. A 4.9 mm-long 5at.%- Tm3+,0.4at.%-Ho3+:YAG crystal is employed and water-cooled to 15AcircdegC. The n-doped InGaAs/AlAsSb QWs are inserted in the cavity under Brewster angle in order to achieve an electric field component along the growth direction of the QWs. The whole cavity length is 53.3 cm. The output coupler has a transmission of 0.5% at 2 Icircfrac14m. A maximum output power of 40 mW is obtained at a center wavelength of 2.09 Icircfrac14m.

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 laser's 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.

We demonstrate the generation of pulses with twenty-five microjoules of energy generated from a thin-disk oscillator at repetition rates below three megahertz with the potential to drive high field experiments. First micromachining experiments are presented.