We investigate a regime of parametric amplification in which the pump and signal waves are spectrally separated by only a few hundreds of GHz frequency - therefore resulting in a sub-THz frequency idler wave. Operating in this regime we find an optical parametric amplifier (OPA) behavior which is highly dissimilar to conventional OPAs. In this regime, we observe multiple three-wave mixing processes occurring simultaneously which results in spectral cascading around the pump and signal wave. Via numerical simulations, we elucidate the processes at work and show that cascaded optical parametric amplification offers a pathway toward THz-wave generation beyond the Manly-Rowe limit and toward the generation of high-energy, sparse frequency-combs.

We demonstrate cascaded optical parametric amplification (COPA) as a promising pathway for efficient generation of THz-waves beyond the Manley-Rowe limit. The spectro-temporal characterization of this novel regime of parametric amplification is reported.

A cryogenically cooled, bulk Yb:YAG, four-pass amplifier delivering up to 250 W average power at 100 kHz repetition rate is reported. The 2.5 mJ amplified optical pulses show a sub-20 ps duration before temporal compression and a spectrum supporting a transform-limited duration of 3.6 ps. The power instabilities were measured to be <0.5% rms over 30 min at full power, and the spatial intensity profile showed a flat-top distribution and near diffraction-limited beam quality. This compact amplifier is an ideal source for pumping either near-IR or mid-IR optical parametric chirped pulse amplifiers.

We report on the theoretical and experimental spectro-temporal characterization of cascaded optical parametric amplification as a promising novel method for efficient THz wave generation.

We present a compact and robust cryogenically cooled Yb:YAG chirped pulse amplifier with 250W of average power at a repetition rate of 100 kHz with a near-diffraction limited beam quality.

Our ultrafast amplifiers have produced 250-Watt at 100-kHz and 100-mJ at 250-Hz based on liquid nitrogen cooled Yb:YAG in rod and composite-disk geometries. Clear scaling towards 1-kW average power at 100 kHz and one-Joule pulse energy has emerged.

A cryogenically cooled Yb:YAG amplifier with 4.7-ps laser pulses is employed to generate 100-GHz pulses in lithium niobate via optical rectification. We obtained a high efficiency ~0.05% at 300 K, close to the theoretical prediction.

A family of approaches employing sequences of optical pump pulses, yielding energy conversion efficiencies in the 5-10% range, is introduced. A method to generate these sequences by cascaded optical parametric amplification of narrowband pulses is discussed.

We demonstrate experimentally the onset of cascaded optical parametric amplification (COPA) in periodically-poled lithium niobate. This technique permits narrowband terahertz wave generation beyond the Manley-Rowe limit.

X-ray crystallography is one of the main methods to determine atomic-resolution 3D images of the whole spectrum of molecules ranging from small inorganic clusters to large protein complexes consisting of hundred-thousands of atoms that constitute the macromolecular machinery of life. Life is not static, and unravelling the structure and dynamics of the most important reactions in chemistry and biology is essential to uncover their mechanism. Many of these reactions, including photosynthesis which drives our biosphere, are light induced and occur on ultrafast timescales. These have been studied with high time resolution primarily by optical spectroscopy, enabled by ultrafast laser technology, but they reduce the vast complexity of the process to a few reaction coordinates. In the AXSIS project at CFEL in Hamburg, funded by the European Research Council, we develop the new method of attosecond serial X-ray crystallography and spectroscopy, to give a full description of ultrafast processes atomically resolved in real space and on the electronic energy landscape, from co-measurement of X-ray and optical spectra, and X-ray diffraction. This technique will revolutionize our understanding of structure and function at the atomic and molecular level and thereby unravel fundamental processes in chemistry and biology like energy conversion processes. For that purpose, we develop a compact, fully coherent, THz-driven atto-second X-ray source based on coherent inverse Compton scattering off a free-electron crystal, to outrun radiation damage effects due to the necessary high X-ray irradiance required to acquire diffraction signals. This highly synergistic project starts from a completely clean slate rather than conforming to the specifications of a large free-electron laser (FEL) user facility, to optimize the entire instrumentation towards fundamental measurements of the mechanism of light absorption and excitation energy transfer. A multidisciplinary team formed by laser-, accelerator,- X-ray scientists as well as spectroscopists and biochemists optimizes X-ray pulse parameters, in tandem with sample delivery, crystal size, and advanced X-ray detectors. Ultimately, the new capability, attosecond serial X-ray crystallography and spectroscopy, will be applied to one of the most important problems in structural biology, which is to elucidate the dynamics of light reactions, electron transfer and protein structure in photosynthesis.

We describe cascaded difference-frequency generation (DFG) between multiple laser-lines generating terahertz pulses at >10% energy-conversion efficiency. DFG initiated by a laser-line and weak laser-seed rapidly cascades to self-generate multiple laser-lines and produce exponential terahertz growth.

We report on a compact, high-energy, cryogenically-cooled Yb:YAG bulk-amplifier delivering energies > 100 mJ at 200 Hz repetition rate with excellent beam quality and spectrum supporting 5-ps pulses.

We report on a cryogenic composite thin-disk amplifier featuring ASE mitigation and 8-dB gain per bounce delivering up to 160 mJ energy diffraction-limited pulses with 5 ps transform-limited pulse duration at 100 Hz repetition rate.

We report the fabrication and visible laser operation of Pr,Mg:SrAl12O19 waveguides. Waveguiding structures were created by focusing the radiation of a femtosecond Ti:sapphire laser into bulk material. Guiding losses were determined to be as low as 0.12 dB cm(-1) at 632.8 nm. By employing a frequency-doubled optically pumped semiconductor laser, waveguide laser operation was realized at wavelengths of 525.3, 644.0, and 724.9 nm with output powers as high as 36, 1065, and 504 mW, respectively. To the best of our knowledge this is the first demonstration of green laser operation in a Pr(3+)-doped crystalline waveguide laser.

We report to the best of our knowledge on the first green laser operation of a Pr3+-doped crystalline waveguide laser. Furthermore red and deep red laser operation with output powers of > 1 W and >500 mW was achieved. The optical-to-optical efficiency was as high as 31% and 19%, respectively.

We report on laser operation in the visible spectral region of Pr,Mg:CaAl12O19. Output powers and slope efficiencies in excess of 300 mW and 25 % were achieved, respectively. In addition spectroscopic investigations will be presented.

In this Letter, we report on laser operation of Pr3+,Mg2+:SrAl12O19 pumped by a frequency-doubled optically pumped semiconductor laser. By employing a V-type cavity, we demonstrate cw laser operation at room temperature in the green spectral range in a doped oxide host for the first time to the best of our knowledge. Furthermore, efficient laser operation was realized in the orange, red, and deep red spectral range with output powers exceeding 1.1 W at emission wavelengths of 643.6 and 724.4 nm.

We present the first demonstration of laser oscillation of Ho3+:LiLuF4 in the visible spectral range. Furthermore, we investigated the spectroscopic properties with regard to its potential as an active medium for diode pumped solid state lasers.

We report on the first results of diode pumped laser operation of Pr3+:LaF3 in a quasi continuous wave (qcw) mode with average output powers of up to 80.0 mW (≈ 161.3 mW qcw) and a maximum slope efficiency of 37% at 719.8 nm. Furthermore it was possible to operate the laser at 537.1 nm and 635.4 nm and to tune the emission wavelength from 609 nm to 623 nm. The pump source was an InGaN laser diode with a maximum output power of 1 W at a central emission wavelength of 442 nm.

Polarization dependent ground state absorption, excited state absorption and emission cross sections of Pr, Mg:SrAl12O19 are determined in the visible and ultraviolet spectral region. It is shown that excited state absorption to the 4f5d configuration does neither occur on the pump wavelength in the blue region nor on any of the visible laser transitions. Efficient laser action at 643.5 nm is demonstrated with slope efficiencies of up to 47% with respect to the absorbed pump power. Output powers up to 75 mW are achieved by pumping with an InGaN laser diode at 444 nm.