Efficient nonlinear compression of a thin-disk oscillator to 8.5 fs at 55 W average power.

We demonstrate an efficient hybrid-scheme for nonlinear pulse compression of high-power thin-disk oscillator pulses to the sub-10 fs regime. The output of a home-built, 16 MHz, 84 W, 220 fs Yb:YAG thin-disk oscillator at 1030 nm is first compressed to 17 fs in two nonlinear multipass cells. In a third stage, based on multiple thin sapphire plates, further compression to 8.5 fs with 55 W output power and an overall optical efficiency of 65% is achieved. Ultrabroadband mid-infrared pulses covering the spectral range 2.4-8µm were generated from these compressed pulses by intra-pulse difference frequency generation.

Multi-octave, CEP-stable source for high-energy field synthesis.

The development of high-energy, high-power, multi-octave light transients is currently the subject of intense research driven by emerging applications in attosecond spectroscopy and coherent control. We report on a phase-stable, multi-octave source based on a Yb:YAG amplifier for light transient generation. We demonstrate the amplification of a two-octave spectrum to 25 µJ of energy in two broadband amplification channels and their temporal compression to 6 and 18 fs at 1 and 2 µm, respectively. In this scheme, due to the intrinsic temporal synchronization between the pump and seed pulses, the temporal jitter is restricted to long-term drift. We show that the intrinsic stability of the synthesizer allows subcycle detection of an electric field at 0.15 PHz. The complex electric field of the 0.15-PHz pulses and their free induction decay after interaction with water molecules are resolved by electro-optic sampling over 2 ps. The scheme is scalable in peak and average power.

Carrier-envelope phase stable, 5.4 µJ, broadband, mid-infrared pulse generation from a 1-ps, Yb:YAG thin-disk laser.

We report on a simple scheme to generate broadband, µJ pulses centered at 2.1 µm with an intrinsic carrier-envelope phase (CEP) stability from the output of a Yb:YAG regenerative amplifier delivering 1-ps pulses with randomly varying CEP. To the best of our knowledge, the reported system has the highest optical-to-optical efficiency for converting 1-ps, 1 µm pulses to CEP stable, broadband, 2.1 µm pulses. The generated coherent light carries an energy of 5.4 µJ, at 5 kHz repetition rate, that can be scaled to higher energy or power by using a suitable front end, if required. The system is ideally suited for seeding broadband parametric amplifiers and multichannel synthesizers pumped by picosecond Yb-doped amplifiers, obviating the need for active timing synchronization. Alternatively, this scheme can be combined with high-power oscillators with tens of µJ energy to generate CEP stable, multioctave supercontinua, suitable for field-resolved and time-resolved spectroscopy.

Cross-polarized, multi-octave supercontinuum generation.

The generation of superoctave spectra from the interaction of intense ultrashort optical pulses and cubic nonlinearity is the result of interplay between the dispersion and nonlinearity of a material and various propagation effects. The cubic nonlinearity can be enhanced when it is combined with a quadratic-cascaded nonlinearity, relaxing the requirement on the laser's peak intensity for supercontinuum (SC) generation. In this Letter, we demonstrate and compare the generation of an SC driven from cubic and cascaded quadratic nonlinearities at an anomalous and zero dispersion wavelength (ZDW). We show the filament-free SC generation of femtosecond mid-infrared pulses by harvesting cascaded quadratic nonlinearity and, at ZDW, requires a lower threshold peak intensity and results in a higher power spectral density for the newly generated spectral components. The presented method is a suitable approach for generating multi-octave spectra from low peak-power, high average-power oscillators or a suitable seed for optical parametric amplifiers and multi-octave field synthesizers.

20 mJ, 1 ps Yb:YAG Thin-disk Regenerative Amplifier.

This is a report on a 100 W, 20 mJ, 1 ps Yb:YAG thin-disk regenerative amplifier. A homemade Yb:YAG thin-disk, Kerr-lens mode-locked oscillator with turn-key performance and microjoule-level pulse energy is used to seed the regenerative chirped-pulse amplifier. The amplifier is placed in airtight housing. It operates at room temperature and exhibits stable operation at a 5 kHz repetition rate, with a pulse-to-pulse stability less than 1%. By employing a 1.5 mm-thick beta barium borate crystal, the frequency of the laser output is doubled to 515 nm, with an average power of 70 W, which corresponds to an optical-to-optical efficiency of 70%. This superior performance makes the system an attractive pump source for optical parametric chirped-pulse amplifiers in the near-infrared and mid-infrared spectral range. Combining the turn-key performance and the superior stability of the regenerative amplifier, the system facilitates the generation of a broadband, CEP-stable seed. Providing the seed and pump of the optical parametric chirped-pulse amplification (OPCPA) from one laser source eliminates the demand of active temporal synchronization between these pulses. This work presents a detailed guide to set up and operate a Yb:YAG thin-disk regenerative amplifier, based on chirped-pulse amplification (CPA), as a pump source for an optical parametric chirped-pulse amplifier.

1 kW, 200 mJ picosecond thin-disk laser system.

We report on a laser system based on thin-disk technology and chirped pulse amplification, providing output pulse energies of 200 mJ at a 5 kHz repetition rate. The amplifier contains a ring-type cavity and two thin Yb:YAG disks, each pumped by diode laser systems providing up to 3.5 kW power at a 969 nm wavelength. The average output power of more than 1 kW is delivered in an excellent output beam characterized by M2=1.1. The output pulses are compressed to 1.1 ps at full power with a pair of dielectric gratings.

Near-PHz-bandwidth, phase-stable continua generated from a Yb:YAG thin-disk amplifier.

We report on the generation of a multi-octave, phase-stable continuum from the output of a Yb:YAG regenerative amplifier delivering 1-ps pulses with randomly varying carrier-envelope phase (CEP). The intrinsically CEP-stable spectral continuum spans from 450 nm to beyond 2500 nm, covering a spectral range of about 0.6 PHz. The generated coherent broadband light carries an energy of 4 µJ, which can be scaled to higher values if required. The system has been designed and is ideally suited for seeding broadband parametric amplifiers and multichannel synthesizers pumped by picosecond Yb:YAG amplifiers, obviating the need for active timing synchronization required in previous approaches. The presented concept paves the way to cost-effective, reliable all-Yb:YAG single-cycle sources with terawatt peak-power and tens-of-Watts average power.

Self-compressed, spectral broadening of a Yb:YAG thin-disk amplifier.

We demonstrate pulse shortening of 1-ps Yb:YAG thin-disk regenerative amplifier to 500 fs by cross-polarized wave generation (XPW) in a 6 mm BaF2 crystal. The process is self-compressed and has 8.5% conversion efficiency corresponding to 18 µJ energy. Our theoretical and experimental investigation shows that the factor of 3 spectral broadening and pulse shortening in ps-XPW-generation only happens in unsaturated regime. We demonstrate that the initial spectral chirp affects the spectral broadening and pulse shortening of XPW pulses.

Broadband beamsplitter for high intensity laser applications in the infra-red spectral range.

We report on design, production and characterization of an extremely broadband multilayer beamsplitter, covering wavelength range from 0.67 - 2.6 µm. The group delay dispersion has small oscillations in the above mentioned working range. We used a new algorithm with floating constants allowing us to obtain a smooth and near constant GDD. The optical element based on the beamsplitter is used for dividing a low-energy super-octave spectrum into several sub-spectral regions which are later amplified and coherently combined.

High-power, 1-ps, all-Yb:YAG thin-disk regenerative amplifier.

We report a 100 W, 20 mJ, 1-ps, all-Yb:YAG thin-disk regenerative amplifier seeded by a microjoule-level Yb:YAG thin-disk Kerr-lens mode-locked oscillator. The regenerative amplifier is implemented in a chirped pulse amplification system and operates at an ambient temperature in air, delivering ultrastable output pulses at a 5 kHz repetition rate and with a root mean square power noise value of less than 0.5%. Second harmonic generation of the amplifier's output in a 1.5 mm-thick BBO crystal results in more than 70 W at 515 nm, making the system an attractive source for pumping optical parametric chirped pulse amplifiers in the visible and near-infrared spectral ranges.

Decoupling chaotic amplification and nonlinear phase in high-energy thin-disk amplifiers for stable OPCPA pumping.

The dynamics of chirped pulse amplification in thin-disk regenerative amplifiers relevant to the pumping of optical parametric chirp pulse amplification systems are described. It is shown that the suitability for reproducible pumping of subsequent nonlinear processes requires a balance between the demands of avoiding chaotic pulse train dynamics and providing a reproducible spectral phase. We describe measures that may be taken to ensure that a laser system operates in the desired stable regime.

Efficient, octave-spanning difference-frequency generation using few-cycle pulses in simple collinear geometry.

We present experimental observations and corresponding numerical simulations illustrating the difference-frequency generation of mid-infrared radiation using few-cycle near-infrared-to-visible pulses, which yields conversion efficiencies above 12% in beta-barium borate crystal. Type I and type II phase-matching are shown to yield qualitatively different intensity-scaling behavior, with the former showing higher overall efficiency, especially with the addition of a zero-order wave plate for modifying the polarization state of the pulse, and the latter having a better stability of the spectrum versus input intensity.

Carrier-envelope-phase-stable, 1.2 mJ, 1.5 cycle laser pulses at 2.1 µm.

We produce 1.5 cycle (10.5 fs), 1.2 mJ, 3 kHz carrier-envelope-phase-stable pulses at 2.1 µm carrier wavelength, from a three-stage optical parametric chirped-pulse amplifier system, pumped by an optically synchronized 1.6 ps Yb:YAG thin disk laser. A chirped periodically poled lithium niobate crystal is used to generate the ultrabroad spectrum needed for a 1.5 cycle pulse through difference frequency mixing of spectrally broadened pulse from a Ti:sapphire amplifier. It will be an ideal tool for producing isolated attosecond pulses with high photon energies.

Pump-seed synchronization for MHz repetition rate, high-power optical parametric chirped pulse amplification.

We report on an active synchronization between two independent mode-locked lasers using a combined electronic-optical feedback. With this scheme, seed pulses at MHz repetition rate were amplified in a non-collinear optical parametric chirped pulse amplifier (OPCPA). The amplifier was seeded with stretched 1.5 nJ pulses from a femtosecond Ti:Sapphire oscillator, while pumped with the 1 ps, 2.9 µJ frequency-doubled output of an Yb:YAG thin-disk oscillator. The residual timing jitter between the two oscillators was suppressed to 120 fs (RMS), allowing for an efficient and broadband amplification at 11.5 MHz to a pulse energy of 700 nJ and an average power of 8 W. First compression experiment with 240 nJ amplified pulse energy resulted in a pulse duration of ~10 fs.

Active stabilization for optically synchronized optical parametric chirped pulse amplification.

The development of new high power laser sources tends toward optical parametric chirped pulse amplification (OPCPA) in recent years. One of the difficulties in OPCPA is the the temporal overlap between pump and seed pulses. In this work we characterize our timing jitter on a single-shot basis using spectrally resolved cross-correlation in combination with a position sensitive detector. A commercial beam stabilization is adapted to actively enhance temporal overlap. This delay-stabilizer reduces the RMS jitter from σ = 127 fs down to σ = 24 fs. The enhanced temporal overlap is demonstrated in our frontend and we propose the scheme to be applicable in many optically synchronized high-repetition-rate OPCPA systems.