Tina Clausnitzer

High-power femtosecond Yb-doped fiber amplifier.

We report on the generation of linearly chirped parabolic pulses with 17-W average power at 75 MHz repetition rate and diffraction-limited beam quality in a large-mode-area ytterbium-doped fiber amplifier. Highly efficient transmission gratings in fused silica are applied to recompress these pulses down to 80-fs with an efficiency of 60%, resulting in a peak power of 1.7 MW. Power scaling limitations given by the amplifier bandwidth are discussed.

An intelligible explanation of highly-efficient diffraction in deep dielectric rectangular transmission gratings.

This paper describes in a very easy and intelligible way, how the diffraction efficiencies of binary dielectric transmission gratings depend on the geometrical groove parameters and how a high efficiency can be obtained. The phenomenological explanation is based on the modal method. The mechanism of excitation of modes by the incident wave, their propagation constants and how they couple into the diffraction orders helps to understand the diffraction process of such gratings and enables a grating design without complicated numerical calculations.

Highly efficient transmission gratings in fused silica for chirped-pulse amplification systems

We report on highly efficient transmission gratings in fused silica with a grating period of 800 nm generated by electron-beam lithography. At a wavelength of 1060 nm, 95% diffraction efficiency is achieved under Littrow conditions. The damage threshold, extremely enhanced compared with conventional gold-coated diffraction gratings, makes these gratings the key elements in high average power (>100 W) femtosecond fiber chirped-pulse amplification systems.

Investigation of the polarization-dependent diffraction of deep dielectric rectangular transmission gratings illuminated in Littrow mounting.

Dielectric transmission gratings with a similar period as the wavelength of the incident light can exhibit strong polarization dependence. By optimizing the groove width of a negative first-order Littrow transmission grating it can be achieved that light is transmitted to the zeroth order for one polarization, regardless of the groove depth, while it is efficiently diffracted for the other polarization. An investigation of this remarkable effect, based on a modal field representation inside the grating, as well as experimental results are presented.

High-average-power femtosecond fiber chirped-pulse amplification system.

Efficient generation of 76-W average power of 400-fs pulses at 75-MHz repetition rate by use of a diode-pumped ytterbium-doped double-clad fiber-based chirped-pulse amplification system is demonstrated. The key element in the system is a diffraction grating compressor consisting of highly efficient transmission gratings in fused silica, allowing recompression at this high power level.

Highly-dispersive dielectric transmission gratings with 100% diffraction efficiency.

A new approach for the realization of highly dispersive dielectric transmission gratings is presented, which enables the suppression of any reflection losses and, thus, 100% diffraction efficiency. By applying a simple two-mode-model a comprehensible explanation as well as a theoretical design of such a reflection-free transmission grating is presented.

2 kW incoherent beam combining of four narrow-linewidth photonic crystal fiber amplifiers.

We report on beam combining of four narrow-linewidth fiber amplifier chains, running at different wavelengths and each delivering 500 W optical output power. The main amplifier stage consists of a large mode area photonic crystal fiber. The four output beams of the amplifier chains are spectrally (incoherent) combined using a polarization-independent dielectric reflective diffraction grating to form an output beam of 2 kW continuous-wave optical power with good beam quality (M(2)x = 2.0, M(2)y = 1.8).

Low-loss grating for coupling to a high-finesse cavity

A concept for a low-loss all-reflective cavity coupler is experimentally demonstrated at a wavelength of 1064 nm. A 1450-nm period dielectric reflection grating with a diffraction efficiency of 0.58% in the - 1st order is used in the 2nd-order Littrow configuration as a coupler to form a cavity with a finesse of 400. The application of such reflective low-loss cavity couplers in future generations of gravitational-wave detectors and implementation issues are discussed.

Narrow band resonant grating of 100% reflection under normal incidence

A resonant grating mirror comprising a multilayer submirror and a grating slab waveguide submirror exhibiting constructive mutual reflection is shown experimentally to provide zero transmission. Its reflection line width of less than 1 nm, its polarization selectivity and low overall loss make the device usable as a longitudinal mode filter in a disk laser in the 1000-1100 nm wavelength range.

Short-pulse optical parametric chirped-pulse amplification for the generation of high-power few-cycle pulses

We report ultrabroadband optical parametric chirped-pulse amplification (OPCPA) with an output pulse energy of up to 250 μJ from an OPCPA stage pumped by short pulses of ~100 fs duration at 395 nm wavelength. In order to generate ultrahigh-power pulses in the few-cycle regime, such a short-pulse-pumped OPCPA scheme appears to be a promising route, by virtue of its inherently advantageous features. Firstly, the stretching and compression fidelity as well as the pulse contrast are increased due to the short pump- and seed-pulse durations. Additionally, the higher pump powers allow for using thinner OPA crystals, thereby increasing the amplification bandwidth that will support even shorter pulse durations. We present experimental results where the effective bandwidth of the seed pulses was increased in the OPCPA process resulting in a shortened transform-limited pulse duration in addition to the energy gain. The amplified pulses from OPCPA have been compressed to the sub-10-fs, few-cycle range by using chirped mirrors. Scaling of this short-pulse-pumped OPCPA technique for few-cycle-pulse generation to the highest (TW–PW) power levels is also planned (Petawatt Field Synthesizer project at the Max-Planck-Institut fur Quantenoptik).